/**
 * @license
 * Copyright 2025 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

import { Client } from '@modelcontextprotocol/sdk/client/index.js';

import { AjvJsonSchemaValidator } from '@modelcontextprotocol/sdk/validation/ajv';
import type {
  jsonSchemaValidator,
  JsonSchemaType,
  JsonSchemaValidator,
} from '@modelcontextprotocol/sdk/validation/types.js';
import {
  SSEClientTransport,
  type SSEClientTransportOptions,
} from '@modelcontextprotocol/sdk/client/sse.js';
import { StdioClientTransport } from '@modelcontextprotocol/sdk/client/stdio.js';
import {
  StreamableHTTPClientTransport,
  type StreamableHTTPClientTransportOptions,
} from '@modelcontextprotocol/sdk/client/streamableHttp.js';
import { EnvHttpProxyAgent } from 'undici';
import type { Transport } from '@modelcontextprotocol/sdk/shared/transport.js';
import {
  ListResourcesResultSchema,
  ListRootsRequestSchema,
  ReadResourceResultSchema,
  ResourceListChangedNotificationSchema,
  ToolListChangedNotificationSchema,
  ErrorCode,
  McpError,
  PromptListChangedNotificationSchema,
  ProgressNotificationSchema,
  type GetPromptResult,
  type Prompt,
  type ReadResourceResult,
  type Resource,
  type Tool as McpTool,
} from '@modelcontextprotocol/sdk/types.js';
import { parse } from 'shell-quote';
import {
  AuthProviderType,
  type Config,
  type MCPServerConfig,
  type GeminiCLIExtension,
} from '../config/config.js';
import { GoogleCredentialProvider } from '../mcp/google-auth-provider.js';
import { ServiceAccountImpersonationProvider } from '../mcp/sa-impersonation-provider.js';
import { DiscoveredMCPTool } from './mcp-tool.js';
import { McpComplianceTransport } from './mcp-compliance-transport.js';

import type { CallableTool, FunctionCall, Part, Tool } from '@google/genai';
import { basename } from 'node:path';
import { pathToFileURL } from 'node:url';
import { randomUUID } from 'node:crypto';
import type { McpAuthProvider } from '../mcp/auth-provider.js';
import { MCPOAuthTokenStorage } from '../mcp/oauth-token-storage.js';
import { MCPOAuthProvider } from '../mcp/oauth-provider.js';
import { DynamicStoredOAuthProvider } from '../mcp/stored-token-provider.js';
import { OAuthUtils } from '../mcp/oauth-utils.js';

import type { PromptRegistry } from '../prompts/prompt-registry.js';
import {
  getErrorMessage,
  isAuthenticationError,
  UnauthorizedError,
} from '../utils/errors.js';
import type {
  Unsubscribe,
  WorkspaceContext,
} from '../utils/workspaceContext.js';
import { getToolCallContext } from '../utils/toolCallContext.js';
import type { ToolRegistry } from './tool-registry.js';
import { debugLogger } from '../utils/debugLogger.js';
import { type MessageBus } from '../confirmation-bus/message-bus.js';
import { coreEvents } from '../utils/events.js';
import {
  type ResourceRegistry,
  type MCPResource,
} from '../resources/resource-registry.js';
import { validateMcpPolicyToolNames } from '../policy/toml-loader.js';
import {
  sanitizeEnvironment,
  type EnvironmentSanitizationConfig,
} from '../services/environmentSanitization.js';
import { expandEnvVars } from '../utils/envExpansion.js';

import {
  GEMINI_CLI_IDENTIFICATION_ENV_VAR,
  GEMINI_CLI_IDENTIFICATION_ENV_VAR_VALUE,
} from '../services/shellExecutionService.js';

export const MCP_DEFAULT_TIMEOUT_MSEC = 10 * 60 * 1000; // default to 10 minutes

export type DiscoveredMCPPrompt = Prompt & {
  serverName: string;
  invoke: (params: Record<string, unknown>) => Promise<GetPromptResult>;
};

/**
 * Enum representing the connection status of an MCP server
 */
export enum MCPServerStatus {
  /** Server is disconnected or experiencing errors */
  DISCONNECTED = 'disconnected',
  /** Server is actively disconnecting */
  DISCONNECTING = 'disconnecting',
  /** Server is in the process of connecting */
  CONNECTING = 'connecting',
  /** Server is connected and ready to use */
  CONNECTED = 'connected',
  /** Server is blocked via configuration and cannot be used */
  BLOCKED = 'blocked',
  /** Server is disabled and cannot be used */
  DISABLED = 'disabled',
}

/**
 * Enum representing the overall MCP discovery state
 */
export enum MCPDiscoveryState {
  /** Discovery has not started yet */
  NOT_STARTED = 'not_started',
  /** Discovery is currently in progress */
  IN_PROGRESS = 'in_progress',
  /** Discovery has completed (with or without errors) */
  COMPLETED = 'completed',
}

/**
 * Interface for reporting progress from MCP tool calls.
 */
export interface McpProgressReporter {
  registerProgressToken(token: string | number, callId: string): void;
  unregisterProgressToken(token: string | number): void;
}

export interface RegistrySet {
  toolRegistry: ToolRegistry;
  promptRegistry: PromptRegistry;
  resourceRegistry: ResourceRegistry;
}

/**
 * A client for a single MCP server.
 *
 * This class is responsible for connecting to, discovering tools from, and
 * managing the state of a single MCP server.
 */
export class McpClient implements McpProgressReporter {
  private client: Client | undefined;
  private transport: Transport | undefined;
  private status: MCPServerStatus = MCPServerStatus.DISCONNECTED;
  private isRefreshingTools: boolean = false;
  private pendingToolRefresh: boolean = false;
  private isRefreshingResources: boolean = false;
  private pendingResourceRefresh: boolean = false;
  private isRefreshingPrompts: boolean = false;
  private pendingPromptRefresh: boolean = false;

  private readonly registeredRegistries = new Set<RegistrySet>();

  /**
   * Map of progress tokens to tool call IDs.
   * This allows us to route progress notifications to the correct tool call.
   */
  private readonly progressTokenToCallId = new Map<string | number, string>();

  constructor(
    private readonly serverName: string,
    private readonly serverConfig: MCPServerConfig,
    private readonly workspaceContext: WorkspaceContext,
    private readonly cliConfig: McpContext,
    private readonly debugMode: boolean,
    private readonly clientVersion: string,
    private readonly onContextUpdated?: (signal?: AbortSignal) => Promise<void>,
  ) {}

  getServerName(): string {
    return this.serverName;
  }

  /**
   * Connects to the MCP server.
   */
  async connect(): Promise<void> {
    if (this.status !== MCPServerStatus.DISCONNECTED) {
      throw new Error(
        `Can only connect when the client is disconnected, current state is ${this.status}`,
      );
    }
    this.updateStatus(MCPServerStatus.CONNECTING);
    try {
      this.client = await connectToMcpServer(
        this.clientVersion,
        this.serverName,
        this.serverConfig,
        this.debugMode,
        this.workspaceContext,
        this.cliConfig,
      );

      this.registerNotificationHandlers();

      const originalOnError = this.client.onerror;
      this.client.onerror = (error) => {
        if (this.status !== MCPServerStatus.CONNECTED) {
          return;
        }
        if (originalOnError) originalOnError(error);
        this.cliConfig.emitMcpDiagnostic(
          'error',
          `MCP ERROR (${this.serverName})`,
          error,
          this.serverName,
        );
        this.updateStatus(MCPServerStatus.DISCONNECTED);
      };
      this.updateStatus(MCPServerStatus.CONNECTED);
    } catch (error) {
      this.updateStatus(MCPServerStatus.DISCONNECTED);
      throw error;
    }
  }

  /**
   * Discovers tools and prompts from the MCP server into the specified registries.
   */
  async discoverInto(
    cliConfig: McpContext,
    registries: RegistrySet,
  ): Promise<void> {
    this.assertConnected();
    this.registeredRegistries.add(registries);

    const prompts = await this.fetchPrompts();
    const tools = await this.discoverTools(
      cliConfig,
      registries.toolRegistry.getMessageBus(),
    );
    const resources = await this.discoverResources();
    this.updateResourceRegistry(resources, registries.resourceRegistry);

    if (prompts.length === 0 && tools.length === 0 && resources.length === 0) {
      throw new Error('No prompts, tools, or resources found on the server.');
    }

    for (const prompt of prompts) {
      registries.promptRegistry.registerPrompt(prompt);
    }
    for (const tool of tools) {
      registries.toolRegistry.registerTool(tool);
    }
    registries.toolRegistry.sortTools();

    // Validate MCP tool names in policy rules against discovered tools
    try {
      const discoveredToolNames = tools.map((t) => t.serverToolName);
      const policyRules = cliConfig.getPolicyEngine?.()?.getRules() ?? [];
      const warnings = validateMcpPolicyToolNames(
        this.serverName,
        discoveredToolNames,
        policyRules,
      );
      for (const warning of warnings) {
        coreEvents.emitFeedback('warning', warning);
      }
    } catch {
      // Policy engine may not be available in all contexts (e.g. tests).
      // Validation is best-effort; skip silently if unavailable.
    }
  }

  /**
   * Unregisters registries so this client will no longer update them when it receives
   * list_changed notifications from the server.
   */
  removeRegistries(registries: RegistrySet): void {
    this.registeredRegistries.delete(registries);
  }

  /**
   * Disconnects from the MCP server.
   */
  async disconnect(): Promise<void> {
    if (this.status !== MCPServerStatus.CONNECTED) {
      return;
    }
    for (const registries of this.registeredRegistries) {
      registries.toolRegistry.removeMcpToolsByServer(this.serverName);
      registries.promptRegistry.removePromptsByServer(this.serverName);
      registries.resourceRegistry.removeResourcesByServer(this.serverName);
    }
    this.updateStatus(MCPServerStatus.DISCONNECTING);
    const client = this.client;
    this.client = undefined;
    if (this.transport) {
      await this.transport.close();
    }
    if (client) {
      await client.close();
    }
    this.updateStatus(MCPServerStatus.DISCONNECTED);
  }

  /**
   * Returns the current status of the client.
   */
  getStatus(): MCPServerStatus {
    return this.status;
  }

  private updateStatus(status: MCPServerStatus): void {
    this.status = status;
    updateMCPServerStatus(this.serverName, status);
  }

  private assertConnected(): void {
    if (this.status !== MCPServerStatus.CONNECTED) {
      throw new Error(
        `Client is not connected, must connect before interacting with the server. Current state is ${this.status}`,
      );
    }
  }

  private async discoverTools(
    cliConfig: McpContext,
    messageBus: MessageBus,
    options?: { timeout?: number; signal?: AbortSignal },
  ): Promise<DiscoveredMCPTool[]> {
    this.assertConnected();
    return discoverTools(
      this.serverName,
      this.serverConfig,
      this.client!,
      cliConfig,
      messageBus,
      {
        ...(options ?? {
          timeout: this.serverConfig.timeout ?? MCP_DEFAULT_TIMEOUT_MSEC,
        }),
        progressReporter: this,
      },
    );
  }

  private async fetchPrompts(options?: {
    signal?: AbortSignal;
  }): Promise<DiscoveredMCPPrompt[]> {
    this.assertConnected();
    return discoverPrompts(
      this.serverName,
      this.client!,
      this.cliConfig,
      options,
    );
  }

  private async discoverResources(): Promise<Resource[]> {
    this.assertConnected();
    return discoverResources(this.serverName, this.client!, this.cliConfig);
  }

  private updateResourceRegistry(
    resources: Resource[],
    resourceRegistry: ResourceRegistry,
  ): void {
    resourceRegistry.setResourcesForServer(this.serverName, resources);
  }

  async readResource(
    uri: string,
    options?: { signal?: AbortSignal },
  ): Promise<ReadResourceResult> {
    this.assertConnected();
    return this.client!.request(
      {
        method: 'resources/read',
        params: { uri },
      },
      ReadResourceResultSchema,
      options,
    );
  }

  /**
   * Registers notification handlers for dynamic updates from the MCP server.
   * This includes handlers for tool list changes and resource list changes.
   */
  private registerNotificationHandlers(): void {
    if (!this.client) {
      return;
    }

    const capabilities = this.client.getServerCapabilities();

    debugLogger.log(
      `Registering notification handlers for server '${this.serverName}'. Capabilities:`,
      capabilities,
    );

    if (capabilities?.tools) {
      if (capabilities.tools.listChanged) {
        debugLogger.log(
          `Server '${this.serverName}' supports tool updates. Listening for changes...`,
        );
      } else {
        debugLogger.log(
          `Server '${this.serverName}' has tools but did not declare 'listChanged' capability. Listening anyway for robustness...`,
        );
      }

      this.client.setNotificationHandler(
        ToolListChangedNotificationSchema,
        async () => {
          debugLogger.log(
            `🔔 Received tool update notification from '${this.serverName}'`,
          );
          await this.refreshTools();
        },
      );
    }

    if (capabilities?.resources) {
      if (capabilities.resources.listChanged) {
        debugLogger.log(
          `Server '${this.serverName}' supports resource updates. Listening for changes...`,
        );
      } else {
        debugLogger.log(
          `Server '${this.serverName}' has resources but did not declare 'listChanged' capability. Listening anyway for robustness...`,
        );
      }

      this.client.setNotificationHandler(
        ResourceListChangedNotificationSchema,
        async () => {
          debugLogger.log(
            `🔔 Received resource update notification from '${this.serverName}'`,
          );
          await this.refreshResources();
        },
      );
    }

    if (capabilities?.prompts) {
      if (capabilities.prompts.listChanged) {
        debugLogger.log(
          `Server '${this.serverName}' supports prompt updates. Listening for changes...`,
        );
      } else {
        debugLogger.log(
          `Server '${this.serverName}' has prompts but did not declare 'listChanged' capability. Listening anyway for robustness...`,
        );
      }

      this.client.setNotificationHandler(
        PromptListChangedNotificationSchema,
        async () => {
          debugLogger.log(
            `🔔 Received prompt update notification from '${this.serverName}'`,
          );
          await this.refreshPrompts();
        },
      );
    }

    this.client.setNotificationHandler(
      ProgressNotificationSchema,
      (notification) => {
        const { progressToken, progress, total, message } = notification.params;
        const callId = this.progressTokenToCallId.get(progressToken);

        if (callId) {
          coreEvents.emitMcpProgress({
            serverName: this.serverName,
            callId,
            progressToken,
            progress,
            total,
            message,
          });
        }
      },
    );
  }

  /**
   * Refreshes the resources for this server by re-querying the MCP `resources/list` endpoint.
   *
   * This method implements a **Coalescing Pattern** to handle rapid bursts of notifications
   * (e.g., during server startup or bulk updates) without overwhelming the server or
   * creating race conditions in the ResourceRegistry.
   */
  private async refreshResources(): Promise<void> {
    if (this.isRefreshingResources) {
      debugLogger.log(
        `Resource refresh for '${this.serverName}' is already in progress. Pending update.`,
      );
      this.pendingResourceRefresh = true;
      return;
    }

    this.isRefreshingResources = true;

    try {
      do {
        this.pendingResourceRefresh = false;

        if (this.status !== MCPServerStatus.CONNECTED || !this.client) break;

        const timeoutMs = this.serverConfig.timeout ?? MCP_DEFAULT_TIMEOUT_MSEC;
        const abortController = new AbortController();
        const timeoutId = setTimeout(() => abortController.abort(), timeoutMs);

        let newResources;
        try {
          newResources = await this.discoverResources();

          for (const registries of this.registeredRegistries) {
            // Verification Retry: If no resources are found or resources didn't change,
            // wait briefly and try one more time. Some servers notify before they're fully ready.
            const currentResources =
              registries.resourceRegistry.getResourcesByServer(
                this.serverName,
              ) || [];
            const resourceMatch =
              newResources.length === currentResources.length &&
              newResources.every((nr: Resource) =>
                currentResources.some((cr: MCPResource) => cr.uri === nr.uri),
              );

            if (resourceMatch && !this.pendingResourceRefresh) {
              debugLogger.log(
                `No resource changes detected for '${this.serverName}'. Retrying once in 500ms...`,
              );
              const retryDelay = 500;
              await new Promise((resolve) => setTimeout(resolve, retryDelay));
              newResources = await this.discoverResources();
            }

            this.updateResourceRegistry(
              newResources,
              registries.resourceRegistry,
            );
          }
        } catch (err) {
          debugLogger.error(
            `Resource discovery failed during refresh: ${getErrorMessage(err)}`,
          );
          clearTimeout(timeoutId);
          break;
        }

        if (this.onContextUpdated) {
          await this.onContextUpdated(abortController.signal);
        }

        clearTimeout(timeoutId);

        this.cliConfig.emitMcpDiagnostic(
          'info',
          `Resources updated for server: ${this.serverName}`,
          undefined,
          this.serverName,
        );
      } while (this.pendingResourceRefresh);
    } catch (error) {
      debugLogger.error(
        `Critical error in resource refresh loop for ${this.serverName}: ${getErrorMessage(error)}`,
      );
    } finally {
      this.isRefreshingResources = false;
    }
  }

  /**
   * Registers a progress token for a tool call.
   */
  registerProgressToken(token: string | number, callId: string): void {
    this.progressTokenToCallId.set(token, callId);
  }

  /**
   * Unregisters a progress token.
   */
  unregisterProgressToken(token: string | number): void {
    this.progressTokenToCallId.delete(token);
  }

  /**
   * Refreshes prompts for this server by re-querying the MCP `prompts/list` endpoint.
   */
  private async refreshPrompts(): Promise<void> {
    if (this.isRefreshingPrompts) {
      debugLogger.log(
        `Prompt refresh for '${this.serverName}' is already in progress. Pending update.`,
      );
      this.pendingPromptRefresh = true;
      return;
    }

    this.isRefreshingPrompts = true;

    try {
      do {
        this.pendingPromptRefresh = false;

        if (this.status !== MCPServerStatus.CONNECTED || !this.client) break;

        const timeoutMs = this.serverConfig.timeout ?? MCP_DEFAULT_TIMEOUT_MSEC;
        const abortController = new AbortController();
        const timeoutId = setTimeout(() => abortController.abort(), timeoutMs);

        try {
          let newPrompts = await this.fetchPrompts({
            signal: abortController.signal,
          });

          for (const registries of this.registeredRegistries) {
            // Verification Retry: If no prompts are found or prompts didn't change,
            // wait briefly and try one more time. Some servers notify before they're fully ready.
            const currentPrompts =
              registries.promptRegistry.getPromptsByServer(this.serverName) ||
              [];
            const promptsMatch =
              newPrompts.length === currentPrompts.length &&
              newPrompts.every((np) =>
                currentPrompts.some((cp) => cp.name === np.name),
              );

            if (promptsMatch && !this.pendingPromptRefresh) {
              debugLogger.log(
                `No prompt changes detected for '${this.serverName}'. Retrying once in 500ms...`,
              );
              const retryDelay = 500;
              await new Promise((resolve) => setTimeout(resolve, retryDelay));
              newPrompts = await this.fetchPrompts({
                signal: abortController.signal,
              });
            }

            registries.promptRegistry.removePromptsByServer(this.serverName);
            for (const prompt of newPrompts) {
              registries.promptRegistry.registerPrompt(prompt);
            }
          }
        } catch (err) {
          debugLogger.error(
            `Prompt discovery failed during refresh: ${getErrorMessage(err)}`,
          );
          clearTimeout(timeoutId);
          break;
        }

        if (this.onContextUpdated) {
          await this.onContextUpdated(abortController.signal);
        }

        clearTimeout(timeoutId);

        this.cliConfig.emitMcpDiagnostic(
          'info',
          `Prompts updated for server: ${this.serverName}`,
          undefined,
          this.serverName,
        );
      } while (this.pendingPromptRefresh);
    } catch (error) {
      debugLogger.error(
        `Critical error in prompt refresh loop for ${this.serverName}: ${getErrorMessage(error)}`,
      );
    } finally {
      this.isRefreshingPrompts = false;
    }
  }

  getServerConfig(): MCPServerConfig {
    return this.serverConfig;
  }

  getInstructions(): string | undefined {
    return this.client?.getInstructions();
  }

  /**
   * Refreshes the tools for this server by re-querying the MCP `tools/list` endpoint.
   *
   * This method implements a **Coalescing Pattern** to handle rapid bursts of notifications
   * (e.g., during server startup or bulk updates) without overwhelming the server or
   * creating race conditions in the global ToolRegistry.
   */
  private async refreshTools(): Promise<void> {
    if (this.isRefreshingTools) {
      debugLogger.log(
        `Tool refresh for '${this.serverName}' is already in progress. Pending update.`,
      );
      this.pendingToolRefresh = true;
      return;
    }

    this.isRefreshingTools = true;

    try {
      do {
        this.pendingToolRefresh = false;

        if (this.status !== MCPServerStatus.CONNECTED || !this.client) break;

        const timeoutMs = this.serverConfig.timeout ?? MCP_DEFAULT_TIMEOUT_MSEC;
        const abortController = new AbortController();
        const timeoutId = setTimeout(() => abortController.abort(), timeoutMs);

        try {
          for (const registries of this.registeredRegistries) {
            let newTools = await this.discoverTools(
              this.cliConfig,
              registries.toolRegistry.getMessageBus(),
              {
                signal: abortController.signal,
              },
            );
            debugLogger.log(
              `Refresh for '${this.serverName}' discovered ${newTools.length} tools.`,
            );

            // Verification Retry (Option 3): If no tools are found or tools didn't change,
            // wait briefly and try one more time. Some servers notify before they're fully ready.
            const currentTools =
              registries.toolRegistry.getToolsByServer(this.serverName) || [];
            const toolNamesMatch =
              newTools.length === currentTools.length &&
              newTools.every((nt) =>
                currentTools.some(
                  (ct) =>
                    ct.name === nt.name ||
                    (ct instanceof DiscoveredMCPTool &&
                      ct.serverToolName === nt.serverToolName),
                ),
              );

            if (toolNamesMatch && !this.pendingToolRefresh) {
              debugLogger.log(
                `No tool changes detected for '${this.serverName}'. Retrying once in 500ms...`,
              );
              const retryDelay = 500;
              await new Promise((resolve) => setTimeout(resolve, retryDelay));
              newTools = await this.discoverTools(
                this.cliConfig,
                registries.toolRegistry.getMessageBus(),
                {
                  signal: abortController.signal,
                },
              );
              debugLogger.log(
                `Retry refresh for '${this.serverName}' discovered ${newTools.length} tools.`,
              );
            }

            registries.toolRegistry.removeMcpToolsByServer(this.serverName);

            for (const tool of newTools) {
              registries.toolRegistry.registerTool(tool);
            }
            registries.toolRegistry.sortTools();
          }
        } catch (err) {
          debugLogger.error(
            `Discovery failed during refresh: ${getErrorMessage(err)}`,
          );
          clearTimeout(timeoutId);
          break;
        }

        if (this.onContextUpdated) {
          await this.onContextUpdated(abortController.signal);
        }

        clearTimeout(timeoutId);

        this.cliConfig.emitMcpDiagnostic(
          'info',
          `Tools updated for server: ${this.serverName}`,
          undefined,
          this.serverName,
        );
      } while (this.pendingToolRefresh);
    } catch (error) {
      debugLogger.error(
        `Critical error in refresh loop for ${this.serverName}: ${getErrorMessage(error)}`,
      );
    } finally {
      this.isRefreshingTools = false;
    }
  }
}

/**
 * Map to track the status of each MCP server within the core package
 */
const serverStatuses: Map<string, MCPServerStatus> = new Map();

/**
 * Track the overall MCP discovery state
 */
let mcpDiscoveryState: MCPDiscoveryState = MCPDiscoveryState.NOT_STARTED;

/**
 * Map to track which MCP servers have been discovered to require OAuth
 */
export const mcpServerRequiresOAuth: Map<string, boolean> = new Map();

/**
 * Event listeners for MCP server status changes
 */
type StatusChangeListener = (
  serverName: string,
  status: MCPServerStatus,
) => void;
const statusChangeListeners: Set<StatusChangeListener> = new Set();

/**
 * Add a listener for MCP server status changes
 */
export function addMCPStatusChangeListener(
  listener: StatusChangeListener,
): void {
  statusChangeListeners.add(listener);
}

/**
 * Remove a listener for MCP server status changes
 */
export function removeMCPStatusChangeListener(
  listener: StatusChangeListener,
): void {
  statusChangeListeners.delete(listener);
}

/**
 * Update the status of an MCP server
 */
export function updateMCPServerStatus(
  serverName: string,
  status: MCPServerStatus,
): void {
  serverStatuses.set(serverName, status);
  // Notify all listeners
  for (const listener of statusChangeListeners) {
    listener(serverName, status);
  }
}

/**
 * Get the current status of an MCP server
 */
export function getMCPServerStatus(serverName: string): MCPServerStatus {
  return serverStatuses.get(serverName) || MCPServerStatus.DISCONNECTED;
}

/**
 * Get all MCP server statuses
 */
export function getAllMCPServerStatuses(): Map<string, MCPServerStatus> {
  return new Map(serverStatuses);
}

/**
 * Get the current MCP discovery state
 */
export function getMCPDiscoveryState(): MCPDiscoveryState {
  return mcpDiscoveryState;
}

/**
 * Extract WWW-Authenticate header from error message string.
 * This is a more robust approach than regex matching.
 *
 * @param errorString The error message string
 * @returns The www-authenticate header value if found, null otherwise
 */
function extractWWWAuthenticateHeader(errorString: string): string | null {
  // Try multiple patterns to extract the header
  const patterns = [
    /www-authenticate:\s*([^\n\r]+)/i,
    /WWW-Authenticate:\s*([^\n\r]+)/i,
    /"www-authenticate":\s*"([^"]+)"/i,
    /'www-authenticate':\s*'([^']+)'/i,
  ];

  for (const pattern of patterns) {
    const match = errorString.match(pattern);
    if (match) {
      return match[1].trim();
    }
  }

  return null;
}

/**
 * Handle automatic OAuth discovery and authentication for a server.
 *
 * @param mcpServerName The name of the MCP server
 * @param mcpServerConfig The MCP server configuration
 * @param wwwAuthenticate The www-authenticate header value
 * @returns True if OAuth was successfully configured and authenticated, false otherwise
 */
async function handleAutomaticOAuth(
  mcpServerName: string,
  mcpServerConfig: MCPServerConfig,
  wwwAuthenticate: string,
  cliConfig: McpContext,
): Promise<boolean> {
  try {
    debugLogger.log(`🔐 '${mcpServerName}' requires OAuth authentication`);

    const serverUrl = mcpServerConfig.httpUrl || mcpServerConfig.url;

    // Try to discover OAuth config from the WWW-Authenticate header first
    let oauthConfig = await OAuthUtils.discoverOAuthFromWWWAuthenticate(
      wwwAuthenticate,
      serverUrl,
    );

    if (!oauthConfig && hasNetworkTransport(mcpServerConfig)) {
      // Fallback: try to discover OAuth config from the base URL
      const baseUrl = OAuthUtils.extractBaseUrl(serverUrl!);
      oauthConfig = await OAuthUtils.discoverOAuthConfig(baseUrl);
    }

    if (!oauthConfig) {
      cliConfig.emitMcpDiagnostic(
        'error',
        `Could not configure OAuth for '${mcpServerName}' - please authenticate manually with /mcp auth ${mcpServerName}`,
        undefined,
        mcpServerName,
      );
      return false;
    }

    // OAuth configuration discovered - proceed with authentication

    // Create OAuth configuration for authentication
    const oauthAuthConfig = {
      enabled: true,
      authorizationUrl: oauthConfig.authorizationUrl,
      issuer: oauthConfig.issuer,
      tokenUrl: oauthConfig.tokenUrl,
      scopes: oauthConfig.scopes || [],
    };

    // Perform OAuth authentication
    debugLogger.log(
      `Starting OAuth authentication for server '${mcpServerName}'...`,
    );
    const authProvider = new MCPOAuthProvider(new MCPOAuthTokenStorage());
    await authProvider.authenticate(mcpServerName, oauthAuthConfig, serverUrl);

    debugLogger.log(
      `OAuth authentication successful for server '${mcpServerName}'`,
    );
    return true;
  } catch (error) {
    cliConfig.emitMcpDiagnostic(
      'error',
      `Failed to handle automatic OAuth for server '${mcpServerName}': ${getErrorMessage(error)}`,
      error,
      mcpServerName,
    );
    return false;
  }
}

/**
 * Create RequestInit for TransportOptions.
 *
 * @param mcpServerConfig The MCP server configuration
 * @param headers Additional headers
 * @param sanitizationConfig Configuration for environment sanitization
 */
function createTransportRequestInit(
  mcpServerConfig: MCPServerConfig,
  headers: Record<string, string>,
  sanitizationConfig: EnvironmentSanitizationConfig,
): RequestInit {
  const extensionEnv = getExtensionEnvironment(mcpServerConfig.extension);
  const expansionEnv = { ...process.env, ...extensionEnv };

  const sanitizedEnv = sanitizeEnvironment(expansionEnv, {
    ...sanitizationConfig,
    enableEnvironmentVariableRedaction: true,
  });

  const expandedHeaders: Record<string, string> = {};
  if (mcpServerConfig.headers) {
    for (const [key, value] of Object.entries(mcpServerConfig.headers)) {
      expandedHeaders[key] = expandEnvVars(value, sanitizedEnv);
    }
  }

  return {
    headers: {
      ...expandedHeaders,
      ...headers,
    },
  };
}

/**
 * Create an AuthProvider for the MCP Transport.
 *
 * @param mcpServerConfig The MCP server configuration
 */
function createAuthProvider(
  mcpServerConfig: MCPServerConfig,
): McpAuthProvider | undefined {
  if (
    mcpServerConfig.authProviderType ===
    AuthProviderType.SERVICE_ACCOUNT_IMPERSONATION
  ) {
    return new ServiceAccountImpersonationProvider(mcpServerConfig);
  }
  if (
    mcpServerConfig.authProviderType === AuthProviderType.GOOGLE_CREDENTIALS
  ) {
    return new GoogleCredentialProvider(mcpServerConfig);
  }
  return undefined;
}
/**
 * Creates an OAuth token provider for transports so token lookup/refresh happens
 * at request/auth time instead of freezing a single token at transport creation.
 */
function createDynamicOAuthTokenProvider(
  mcpServerName: string,
  mcpServerConfig: MCPServerConfig,
): McpAuthProvider {
  return new DynamicStoredOAuthProvider(mcpServerName, mcpServerConfig);
}

/**
 * Create a transport with OAuth token for the given server configuration.
 *
 * @param mcpServerName The name of the MCP server
 * @param mcpServerConfig The MCP server configuration
 * @param accessToken The OAuth access token
 * @param cliConfig The CLI configuration providing sanitization and diagnostic reporting
 * @returns The transport with OAuth token, or null if creation fails
 */
async function createTransportWithOAuth(
  mcpServerName: string,
  mcpServerConfig: MCPServerConfig,
  accessToken: string,
  cliConfig: McpContext,
): Promise<Transport | null> {
  try {
    const headers: Record<string, string> = {
      Authorization: `Bearer ${accessToken}`,
    };
    const transportOptions:
      | StreamableHTTPClientTransportOptions
      | SSEClientTransportOptions = {
      requestInit: createTransportRequestInit(
        mcpServerConfig,
        headers,
        cliConfig.sanitizationConfig,
      ),
    };

    const transport = createUrlTransport(
      mcpServerName,
      mcpServerConfig,
      transportOptions,
    );
    return transport ? new McpComplianceTransport(transport) : null;
  } catch (error) {
    cliConfig.emitMcpDiagnostic(
      'error',
      `Failed to create OAuth transport for server '${mcpServerName}': ${getErrorMessage(error)}`,
      error,
      mcpServerName,
    );
    return null;
  }
}

/**
 * Discovers tools from all configured MCP servers and registers them with the tool registry.
 * It orchestrates the connection and discovery process for each server defined in the
 * configuration, as well as any server specified via a command-line argument.
 *
 * @param mcpServers A record of named MCP server configurations.
 * @param mcpServerCommand An optional command string for a dynamically specified MCP server.
 * @param toolRegistry The central registry where discovered tools will be registered.
 * @returns A promise that resolves when the discovery process has been attempted for all servers.
 */

export async function discoverMcpTools(
  clientVersion: string,
  mcpServers: Record<string, MCPServerConfig>,
  mcpServerCommand: string | undefined,
  toolRegistry: ToolRegistry,
  promptRegistry: PromptRegistry,
  debugMode: boolean,
  workspaceContext: WorkspaceContext,
  cliConfig: Config,
): Promise<void> {
  mcpDiscoveryState = MCPDiscoveryState.IN_PROGRESS;
  try {
    mcpServers = populateMcpServerCommand(mcpServers, mcpServerCommand);

    const discoveryPromises = Object.entries(mcpServers).map(
      ([mcpServerName, mcpServerConfig]) =>
        connectAndDiscover(
          clientVersion,
          mcpServerName,
          mcpServerConfig,
          toolRegistry,
          promptRegistry,
          debugMode,
          workspaceContext,
          cliConfig,
        ),
    );
    await Promise.all(discoveryPromises);
  } finally {
    mcpDiscoveryState = MCPDiscoveryState.COMPLETED;
  }
}

/**
 * A tolerant JSON Schema validator for MCP tool output schemas.
 *
 * Some MCP servers (e.g. third‑party extensions) return complex schemas that
 * include `$defs` / `$ref` chains which can occasionally trip AJV's resolver,
 * causing discovery to fail. This wrapper keeps the default AJV validator for
 * normal operation but falls back to a no‑op validator any time schema
 * compilation throws, so we can still list and use the tool while emitting a
 * debug log.
 */
class LenientJsonSchemaValidator implements jsonSchemaValidator {
  private readonly ajvValidator = new AjvJsonSchemaValidator();

  getValidator<T>(schema: JsonSchemaType): JsonSchemaValidator<T> {
    try {
      return this.ajvValidator.getValidator<T>(schema);
    } catch (error) {
      debugLogger.warn(
        `Failed to compile MCP tool output schema (${
          (schema as Record<string, unknown>)?.['$id'] ?? '<no $id>'
        }): ${error instanceof Error ? error.message : String(error)}. ` +
          'Skipping output validation for this tool.',
      );
      return (input: unknown) => ({
        valid: true as const,
        // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
        data: input as T,
        errorMessage: undefined,
      });
    }
  }
}

/** Visible for Testing */
export function populateMcpServerCommand(
  mcpServers: Record<string, MCPServerConfig>,
  mcpServerCommand: string | undefined,
): Record<string, MCPServerConfig> {
  if (mcpServerCommand) {
    const cmd = mcpServerCommand;
    // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
    const args = parse(cmd, process.env) as string[];
    if (args.some((arg) => typeof arg !== 'string')) {
      throw new Error('failed to parse mcpServerCommand: ' + cmd);
    }
    // use generic server name 'mcp'
    mcpServers['mcp'] = {
      command: args[0],
      args: args.slice(1),
    };
  }
  return mcpServers;
}

/**
 * Connects to an MCP server and discovers available tools, registering them with the tool registry.
 * This function handles the complete lifecycle of connecting to a server, discovering tools,
 * and cleaning up resources if no tools are found.
 *
 * @param mcpServerName The name identifier for this MCP server
 * @param mcpServerConfig Configuration object containing connection details
 * @param toolRegistry The registry to register discovered tools with
 * @returns Promise that resolves when discovery is complete
 */
export async function connectAndDiscover(
  clientVersion: string,
  mcpServerName: string,
  mcpServerConfig: MCPServerConfig,
  toolRegistry: ToolRegistry,
  promptRegistry: PromptRegistry,
  debugMode: boolean,
  workspaceContext: WorkspaceContext,
  cliConfig: McpContext,
): Promise<void> {
  updateMCPServerStatus(mcpServerName, MCPServerStatus.CONNECTING);

  let mcpClient: Client | undefined;
  try {
    mcpClient = await connectToMcpServer(
      clientVersion,
      mcpServerName,
      mcpServerConfig,
      debugMode,
      workspaceContext,
      cliConfig,
    );

    mcpClient.onerror = (error) => {
      cliConfig.emitMcpDiagnostic(
        'error',
        `MCP ERROR (${mcpServerName}):`,
        error,
        mcpServerName,
      );
      updateMCPServerStatus(mcpServerName, MCPServerStatus.DISCONNECTED);
    };

    // Attempt to discover both prompts and tools
    const prompts = await discoverPrompts(mcpServerName, mcpClient, cliConfig);
    const tools = await discoverTools(
      mcpServerName,
      mcpServerConfig,
      mcpClient,
      cliConfig,
      toolRegistry.messageBus,
      { timeout: mcpServerConfig.timeout ?? MCP_DEFAULT_TIMEOUT_MSEC },
    );

    // If we have neither prompts nor tools, it's a failed discovery
    if (prompts.length === 0 && tools.length === 0) {
      throw new Error('No prompts or tools found on the server.');
    }

    // If we found anything, the server is connected
    updateMCPServerStatus(mcpServerName, MCPServerStatus.CONNECTED);

    // Register any discovered prompts and tools
    for (const prompt of prompts) {
      promptRegistry.registerPrompt(prompt);
    }
    for (const tool of tools) {
      toolRegistry.registerTool(tool);
    }
    toolRegistry.sortTools();
  } catch (error) {
    if (mcpClient) {
      // eslint-disable-next-line @typescript-eslint/no-floating-promises
      mcpClient.close();
    }
    cliConfig.emitMcpDiagnostic(
      'error',
      `Error connecting to MCP server '${mcpServerName}': ${getErrorMessage(
        error,
      )}`,
      error,
      mcpServerName,
    );
    updateMCPServerStatus(mcpServerName, MCPServerStatus.DISCONNECTED);
  }
}

function isMcpMethodNotFoundError(error: unknown): boolean {
  return error instanceof McpError && error.code === ErrorCode.MethodNotFound;
}

/**
 * Discovers and sanitizes tools from a connected MCP client.
 * It retrieves function declarations from the client, filters out disabled tools,
 * generates valid names for them, and wraps them in `DiscoveredMCPTool` instances.
 *
 * @param mcpServerName The name of the MCP server.
 * @param mcpServerConfig The configuration for the MCP server.
 * @param mcpClient The active MCP client instance.
 * @param cliConfig The CLI configuration object.
 * @param messageBus Optional message bus for policy engine integration.
 * @returns A promise that resolves to an array of discovered and enabled tools.
 * @throws An error if no enabled tools are found or if the server provides invalid function declarations.
 */
export async function discoverTools(
  mcpServerName: string,
  mcpServerConfig: MCPServerConfig,
  mcpClient: Client,
  cliConfig: McpContext,
  messageBus: MessageBus,
  options?: {
    timeout?: number;
    signal?: AbortSignal;
    progressReporter?: McpProgressReporter;
  },
): Promise<DiscoveredMCPTool[]> {
  try {
    // Only request tools if the server supports them.
    if (mcpClient.getServerCapabilities()?.tools == null) return [];

    const response = await mcpClient.listTools({}, options);
    const discoveredTools: DiscoveredMCPTool[] = [];
    for (const toolDef of response.tools) {
      try {
        if (!isEnabled(toolDef, mcpServerName, mcpServerConfig)) {
          continue;
        }

        if (toolDef.inputSchema) {
          try {
            const transform = (obj: unknown): unknown => {
              if (obj === null || typeof obj !== 'object') return obj;
              if (Array.isArray(obj)) return obj.map(transform);

              const res = { ...obj } as Record<string, unknown>;

              if (Array.isArray(res['type']) && res['type'].length === 2) {
                const nIdx = res['type'].indexOf('null');
                if (nIdx !== -1 && typeof res['type'][1 - nIdx] === 'string') {
                  res['type'] = res['type'][1 - nIdx];
                  res['nullable'] = true;
                }
              }

              for (const k in res) {
                if (Object.prototype.hasOwnProperty.call(res, k)) {
                  res[k] = transform(res[k]);
                }
              }
              return res;
            };

            // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
            toolDef.inputSchema = transform(toolDef.inputSchema) as {
              type: 'object';
              properties?: Record<string, object>;
              required?: string[];
            };
          } catch (error) {
            cliConfig.emitMcpDiagnostic(
              'error',
              `Failed to parse adjusted inputSchema for tool '${toolDef.name}' from server '${mcpServerName}'. Using original schema. Error: ${error instanceof Error ? error.message : String(error)}`,
              error,
              mcpServerName,
            );
          }
        }

        const mcpCallableTool = new McpCallableTool(
          mcpClient,
          toolDef,
          mcpServerConfig.timeout ?? MCP_DEFAULT_TIMEOUT_MSEC,
          options?.progressReporter,
        );

        // Extract annotations from the tool definition
        const annotations = toolDef.annotations;
        const isReadOnly = annotations?.readOnlyHint === true;

        const tool = new DiscoveredMCPTool(
          mcpCallableTool,
          mcpServerName,
          toolDef.name,
          toolDef.description ?? '',
          toolDef.inputSchema ?? { type: 'object', properties: {} },
          messageBus,
          mcpServerConfig.trust,
          isReadOnly,
          undefined,
          cliConfig,
          mcpServerConfig.extension?.name,
          mcpServerConfig.extension?.id,
          annotations as Record<string, unknown> | undefined,
        );

        discoveredTools.push(tool);
      } catch (error) {
        cliConfig.emitMcpDiagnostic(
          'error',
          `Error discovering tool: '${
            toolDef.name
            // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
          }' from MCP server '${mcpServerName}': ${(error as Error).message}`,
          error,
          mcpServerName,
        );
      }
    }
    return discoveredTools;
  } catch (error) {
    if (!isMcpMethodNotFoundError(error)) {
      cliConfig.emitMcpDiagnostic(
        'error',
        `Error discovering tools from ${mcpServerName}: ${getErrorMessage(
          error,
        )}`,
        error,
        mcpServerName,
      );
    }
    return [];
  }
}

class McpCallableTool implements CallableTool {
  constructor(
    private readonly client: Client,
    private readonly toolDef: McpTool,
    private readonly timeout: number,
    private readonly progressReporter?: McpProgressReporter,
  ) {}

  async tool(): Promise<Tool> {
    return {
      functionDeclarations: [
        {
          name: this.toolDef.name,
          description: this.toolDef.description,
          parametersJsonSchema: this.toolDef.inputSchema,
        },
      ],
    };
  }

  async callTool(functionCalls: FunctionCall[]): Promise<Part[]> {
    // We only expect one function call at a time for MCP tools in this context
    if (functionCalls.length !== 1) {
      throw new Error('McpCallableTool only supports single function call');
    }
    const call = functionCalls[0];

    const progressToken = randomUUID();
    const context = getToolCallContext();
    if (context && this.progressReporter) {
      this.progressReporter.registerProgressToken(
        progressToken,
        context.callId,
      );
    }

    try {
      const result = await this.client.callTool(
        {
          name: call.name!,
          // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
          arguments: call.args as Record<string, unknown>,
          _meta: { progressToken },
        },
        undefined,
        { timeout: this.timeout },
      );

      return [
        {
          functionResponse: {
            name: call.name,
            response: result,
          },
        },
      ];
    } catch (error) {
      // Return error in the format expected by DiscoveredMCPTool
      return [
        {
          functionResponse: {
            name: call.name,
            response: {
              error: {
                message: error instanceof Error ? error.message : String(error),
                isError: true,
              },
            },
          },
        },
      ];
    } finally {
      if (this.progressReporter) {
        this.progressReporter.unregisterProgressToken(progressToken);
      }
    }
  }
}

/**
 * Discovers and logs prompts from a connected MCP client.
 * It retrieves prompt declarations from the client and logs their names.
 *
 * @param mcpServerName The name of the MCP server.
 * @param mcpClient The active MCP client instance.
 */
export async function discoverPrompts(
  mcpServerName: string,
  mcpClient: Client,
  cliConfig: McpContext,
  options?: { signal?: AbortSignal },
): Promise<DiscoveredMCPPrompt[]> {
  // Only request prompts if the server supports them.
  if (mcpClient.getServerCapabilities()?.prompts == null) return [];

  try {
    const response = await mcpClient.listPrompts({}, options);
    return response.prompts.map((prompt) => ({
      ...prompt,
      serverName: mcpServerName,
      invoke: (params: Record<string, unknown>) =>
        invokeMcpPrompt(
          mcpServerName,
          mcpClient,
          prompt.name,
          params,
          cliConfig,
        ),
    }));
  } catch (error) {
    if (isMcpMethodNotFoundError(error)) {
      return [];
    }
    cliConfig.emitMcpDiagnostic(
      'error',
      `Error discovering prompts from ${mcpServerName}: ${getErrorMessage(
        error,
      )}`,
      error,
      mcpServerName,
    );
    throw error;
  }
}

export async function discoverResources(
  mcpServerName: string,
  mcpClient: Client,
  cliConfig: McpContext,
): Promise<Resource[]> {
  if (mcpClient.getServerCapabilities()?.resources == null) {
    return [];
  }

  const resources = await listResources(mcpServerName, mcpClient, cliConfig);
  return resources;
}

async function listResources(
  mcpServerName: string,
  mcpClient: Client,
  cliConfig: McpContext,
): Promise<Resource[]> {
  const resources: Resource[] = [];
  let cursor: string | undefined;
  try {
    do {
      const response = await mcpClient.request(
        {
          method: 'resources/list',
          params: cursor ? { cursor } : {},
        },
        ListResourcesResultSchema,
      );
      resources.push(...(response.resources ?? []));
      cursor = response.nextCursor ?? undefined;
    } while (cursor);
  } catch (error) {
    if (isMcpMethodNotFoundError(error)) {
      return [];
    }
    cliConfig.emitMcpDiagnostic(
      'error',
      `Error discovering resources from ${mcpServerName}: ${getErrorMessage(
        error,
      )}`,
      error,
      mcpServerName,
    );
    throw error;
  }
  return resources;
}

/**
 * Invokes a prompt on a connected MCP client.
 *
 * @param mcpServerName The name of the MCP server.
 * @param mcpClient The active MCP client instance.
 * @param promptName The name of the prompt to invoke.
 * @param promptParams The parameters to pass to the prompt.
 * @returns A promise that resolves to the result of the prompt invocation.
 */
export async function invokeMcpPrompt(
  mcpServerName: string,
  mcpClient: Client,
  promptName: string,
  promptParams: Record<string, unknown>,
  cliConfig: McpContext,
): Promise<GetPromptResult> {
  cliConfig.setUserInteractedWithMcp?.();
  try {
    const sanitizedParams: Record<string, string> = {};
    for (const [key, value] of Object.entries(promptParams)) {
      if (value !== undefined && value !== null) {
        sanitizedParams[key] = String(value);
      }
    }

    const response = await mcpClient.getPrompt({
      name: promptName,
      arguments: sanitizedParams,
    });

    return response;
  } catch (error) {
    if (
      error instanceof Error &&
      !error.message?.includes('Method not found')
    ) {
      cliConfig.emitMcpDiagnostic(
        'error',
        `Error invoking prompt '${promptName}' from ${mcpServerName} ${promptParams}: ${getErrorMessage(
          error,
        )}`,
        error,
        mcpServerName,
      );
    }
    throw error;
  }
}

/**
 * @visiblefortesting
 * Checks if the MCP server configuration has a network transport URL (SSE or HTTP).
 * @param config The MCP server configuration.
 * @returns True if a `url` or `httpUrl` is present, false otherwise.
 */
export function hasNetworkTransport(config: MCPServerConfig): boolean {
  return !!(config.url || config.httpUrl);
}

/**
 * Helper function to retrieve a stored OAuth token for an MCP server.
 * Handles token validation and refresh automatically.
 *
 * @param serverName The name of the MCP server
 * @returns The valid access token, or null if no token is stored
 */
async function getStoredOAuthToken(serverName: string): Promise<string | null> {
  const tokenStorage = new MCPOAuthTokenStorage();
  const credentials = await tokenStorage.getCredentials(serverName);
  if (!credentials) return null;

  const authProvider = new MCPOAuthProvider(tokenStorage);
  return authProvider.getValidToken(serverName, {
    // Pass client ID if available
    clientId: credentials.clientId,
  });
}

/**
 * Helper function to create an SSE transport with optional OAuth authentication.
 *
 * @param config The MCP server configuration
 * @param accessToken Optional OAuth access token for authentication
 * @returns A configured SSE transport ready for connection
 */
function createSSETransportWithAuth(
  config: MCPServerConfig,
  accessToken?: string | null,
): SSEClientTransport {
  const headers = {
    ...config.headers,
    ...(accessToken ? { Authorization: `Bearer ${accessToken}` } : {}),
  };

  const options: SSEClientTransportOptions = {};
  if (Object.keys(headers).length > 0) {
    options.requestInit = { headers };
  }

  return new SSEClientTransport(new URL(config.url!), options);
}

/**
 * Helper function to connect a client using SSE transport with optional OAuth.
 *
 * @param client The MCP client to connect
 * @param config The MCP server configuration
 * @param accessToken Optional OAuth access token for authentication
 */
async function connectWithSSETransport(
  client: Client,
  config: MCPServerConfig,
  accessToken?: string | null,
): Promise<void> {
  const transport = createSSETransportWithAuth(config, accessToken);
  await client.connect(transport, {
    timeout: config.timeout ?? MCP_DEFAULT_TIMEOUT_MSEC,
  });
}

/**
 * Helper function to show authentication required message and throw error.
 * Checks if there's a stored token that was rejected (requires re-auth).
 *
 * @param serverName The name of the MCP server
 * @throws Always throws an error with authentication instructions
 */
async function showAuthRequiredMessage(
  serverName: string,
  cliConfig: McpContext,
): Promise<never> {
  const hasRejectedToken = !!(await getStoredOAuthToken(serverName));

  const message = hasRejectedToken
    ? `MCP server '${serverName}' rejected stored OAuth token. Please re-authenticate using: /mcp auth ${serverName}`
    : `MCP server '${serverName}' requires authentication using: /mcp auth ${serverName}`;

  cliConfig.emitMcpDiagnostic('info', message, undefined, serverName);
  throw new UnauthorizedError(message);
}

/**
 * Helper function to retry connection with OAuth token after authentication.
 * Handles both HTTP and SSE transports based on what previously failed.
 *
 * @param client The MCP client to connect
 * @param serverName The name of the MCP server
 * @param config The MCP server configuration
 * @param accessToken The OAuth access token to use
 * @param httpReturned404 Whether the HTTP transport returned 404 (indicating SSE-only server)
 * @param cliConfig The CLI configuration providing sanitization and diagnostic reporting
 */
async function retryWithOAuth(
  client: Client,
  serverName: string,
  config: MCPServerConfig,
  accessToken: string,
  httpReturned404: boolean,
  cliConfig: McpContext,
): Promise<void> {
  if (httpReturned404) {
    // HTTP returned 404, only try SSE
    debugLogger.log(
      `Retrying SSE connection to '${serverName}' with OAuth token...`,
    );
    await connectWithSSETransport(client, config, accessToken);
    debugLogger.log(
      `Successfully connected to '${serverName}' using SSE with OAuth.`,
    );
    return;
  }

  // HTTP returned 401, try HTTP with OAuth first
  debugLogger.log(`Retrying connection to '${serverName}' with OAuth token...`);

  const httpTransport = await createTransportWithOAuth(
    serverName,
    config,
    accessToken,
    cliConfig,
  );
  if (!httpTransport) {
    throw new Error(
      `Failed to create OAuth transport for server '${serverName}'`,
    );
  }

  try {
    await client.connect(httpTransport, {
      timeout: config.timeout ?? MCP_DEFAULT_TIMEOUT_MSEC,
    });
    debugLogger.log(
      `Successfully connected to '${serverName}' using HTTP with OAuth.`,
    );
  } catch (httpError) {
    await httpTransport.close();

    // If HTTP+OAuth returns 404 and auto-detection enabled, try SSE+OAuth
    if (
      String(httpError).includes('404') &&
      config.url &&
      !config.type &&
      !config.httpUrl
    ) {
      debugLogger.log(`HTTP with OAuth returned 404, trying SSE with OAuth...`);
      await connectWithSSETransport(client, config, accessToken);
      debugLogger.log(
        `Successfully connected to '${serverName}' using SSE with OAuth.`,
      );
    } else {
      throw httpError;
    }
  }
}

/**
 * Interface for MCP operations that require configuration or diagnostic reporting.
 * This is implemented by the central Config class and can be mocked for testing
 * or used by the non-interactive CLI.
 */
export interface McpContext {
  readonly sanitizationConfig: EnvironmentSanitizationConfig;
  emitMcpDiagnostic(
    severity: 'info' | 'warning' | 'error',
    message: string,
    error?: unknown,
    serverName?: string,
  ): void;
  setUserInteractedWithMcp?(): void;
  isTrustedFolder(): boolean;
  getPolicyEngine?(): {
    getRules(): ReadonlyArray<{
      toolName: string;
      mcpName?: string;
      source?: string;
    }>;
  };
}

/**
 * Creates and connects an MCP client to a server based on the provided configuration.
 * It determines the appropriate transport (Stdio, SSE, or Streamable HTTP) and
 * establishes a connection. It also applies a patch to handle request timeouts.
 *
 * @param mcpServerName The name of the MCP server, used for logging and identification.
 * @param mcpServerConfig The configuration specifying how to connect to the server.
 * @returns A promise that resolves to a connected MCP `Client` instance.
 * @throws An error if the connection fails or the configuration is invalid.
 */
export async function connectToMcpServer(
  clientVersion: string,
  mcpServerName: string,
  mcpServerConfig: MCPServerConfig,
  debugMode: boolean,
  workspaceContext: WorkspaceContext,
  cliConfig: McpContext,
): Promise<Client> {
  const mcpClient = new Client(
    {
      name: 'gemini-cli-mcp-client',
      version: clientVersion,
    },
    {
      // Use a tolerant validator so bad output schemas don't block discovery.
      jsonSchemaValidator: new LenientJsonSchemaValidator(),
    },
  );

  mcpClient.registerCapabilities({
    roots: {
      listChanged: true,
    },
  });

  mcpClient.setRequestHandler(ListRootsRequestSchema, async () => {
    const roots = [];
    for (const dir of workspaceContext.getDirectories()) {
      roots.push({
        uri: pathToFileURL(dir).toString(),
        name: basename(dir),
      });
    }
    return {
      roots,
    };
  });

  let unlistenDirectories: Unsubscribe | undefined =
    workspaceContext.onDirectoriesChanged(async () => {
      try {
        await mcpClient.notification({
          method: 'notifications/roots/list_changed',
        });
      } catch {
        // If this fails, its almost certainly because the connection was closed
        // and we should just stop listening for future directory changes.
        unlistenDirectories?.();
        unlistenDirectories = undefined;
      }
    });

  // Attempt to pro-actively unsubscribe if the mcp client closes. This API is
  // very brittle though so we don't have any guarantees, hence the try/catch
  // above as well.
  //
  // Be a good steward and don't just bash over onclose.
  const oldOnClose = mcpClient.onclose;
  mcpClient.onclose = () => {
    oldOnClose?.();
    unlistenDirectories?.();
    unlistenDirectories = undefined;
  };

  let firstAttemptError: Error | null = null;
  let httpReturned404 = false; // Track if HTTP returned 404 to skip it in OAuth retry
  let sseError: Error | null = null; // Track SSE fallback error

  try {
    const transport = await createTransport(
      mcpServerName,
      mcpServerConfig,
      debugMode,
      cliConfig,
    );
    try {
      await mcpClient.connect(transport, {
        timeout: mcpServerConfig.timeout ?? MCP_DEFAULT_TIMEOUT_MSEC,
      });
      return mcpClient;
    } catch (error) {
      await transport.close();
      // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
      firstAttemptError = error as Error;
      throw error;
    }
  } catch (initialError) {
    let error = initialError;

    // Check if this is a 401 error FIRST (before attempting SSE fallback)
    // This ensures OAuth flow happens before we try SSE
    if (isAuthenticationError(error) && hasNetworkTransport(mcpServerConfig)) {
      // Continue to OAuth handling below (after SSE fallback section)
    } else if (
      // If not 401, and HTTP failed with url without explicit type, try SSE fallback
      firstAttemptError &&
      mcpServerConfig.url &&
      !mcpServerConfig.type &&
      !mcpServerConfig.httpUrl
    ) {
      // Check if HTTP returned 404 - if so, we know it's not an HTTP server
      httpReturned404 = String(firstAttemptError).includes('404');

      const logMessage = httpReturned404
        ? `HTTP returned 404, trying SSE transport...`
        : `HTTP connection failed, attempting SSE fallback...`;
      debugLogger.log(`MCP server '${mcpServerName}': ${logMessage}`);

      try {
        // Try SSE with stored OAuth token if available
        // This ensures that SSE fallback works for authenticated servers
        await connectWithSSETransport(
          mcpClient,
          mcpServerConfig,
          await getStoredOAuthToken(mcpServerName),
        );

        debugLogger.log(
          `MCP server '${mcpServerName}': Successfully connected using SSE transport.`,
        );
        return mcpClient;
      } catch (sseFallbackError) {
        // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
        sseError = sseFallbackError as Error;

        // If SSE also returned 401, handle OAuth below
        if (isAuthenticationError(sseError)) {
          debugLogger.log(
            `MCP server '${mcpServerName}': SSE returned 401, OAuth authentication required.`,
          );
          // Update error to be the SSE error for OAuth handling
          error = sseError;
          // Continue to OAuth handling below
        } else {
          debugLogger.log(
            `MCP server '${mcpServerName}': SSE fallback also failed.`,
          );
          // Both failed without 401, throw the original error
          throw firstAttemptError;
        }
      }
    }

    // Check if this is a 401 error that might indicate OAuth is required
    if (isAuthenticationError(error) && hasNetworkTransport(mcpServerConfig)) {
      mcpServerRequiresOAuth.set(mcpServerName, true);

      // Only trigger automatic OAuth if explicitly enabled in config
      // Otherwise, show error and tell user to run /mcp auth command
      const shouldTriggerOAuth = mcpServerConfig.oauth?.enabled;

      if (!shouldTriggerOAuth) {
        await showAuthRequiredMessage(mcpServerName, cliConfig);
      }

      // Try to extract www-authenticate header from the error
      const errorString = String(error);
      let wwwAuthenticate = extractWWWAuthenticateHeader(errorString);

      // If we didn't get the header from the error string, try to get it from the server
      if (!wwwAuthenticate && hasNetworkTransport(mcpServerConfig)) {
        debugLogger.log(
          `No www-authenticate header in error, trying to fetch it from server...`,
        );
        try {
          const urlToFetch = mcpServerConfig.httpUrl || mcpServerConfig.url!;

          // Determine correct Accept header based on what transport failed
          let acceptHeader: string;
          if (mcpServerConfig.httpUrl) {
            acceptHeader = 'application/json';
          } else if (mcpServerConfig.type === 'http') {
            acceptHeader = 'application/json';
          } else if (mcpServerConfig.type === 'sse') {
            acceptHeader = 'text/event-stream';
          } else if (httpReturned404) {
            // HTTP failed with 404, SSE returned 401 - use SSE header
            acceptHeader = 'text/event-stream';
          } else {
            // HTTP returned 401 - use HTTP header
            acceptHeader = 'application/json';
          }

          const response = await fetch(urlToFetch, {
            method: 'HEAD',
            headers: {
              Accept: acceptHeader,
            },
            signal: AbortSignal.timeout(5000),
          });

          if (response.status === 401) {
            wwwAuthenticate = response.headers.get('www-authenticate');
            if (wwwAuthenticate) {
              debugLogger.log(
                `Found www-authenticate header from server: ${wwwAuthenticate}`,
              );
            }
          }
        } catch (fetchError) {
          debugLogger.debug(
            `Failed to fetch www-authenticate header: ${getErrorMessage(
              fetchError,
            )}`,
          );
        }
      }

      if (wwwAuthenticate) {
        debugLogger.log(
          `Received 401 with www-authenticate header: ${wwwAuthenticate}`,
        );

        // Try automatic OAuth discovery and authentication
        const oauthSuccess = await handleAutomaticOAuth(
          mcpServerName,
          mcpServerConfig,
          wwwAuthenticate,
          cliConfig,
        );
        if (oauthSuccess) {
          // Retry connection with OAuth token
          const accessToken = await getStoredOAuthToken(mcpServerName);
          if (!accessToken) {
            throw new Error(
              `Failed to get OAuth token for server '${mcpServerName}'`,
            );
          }

          await retryWithOAuth(
            mcpClient,
            mcpServerName,
            mcpServerConfig,
            accessToken,
            httpReturned404,
            cliConfig,
          );
          return mcpClient;
        } else {
          throw new Error(
            `Failed to handle automatic OAuth for server '${mcpServerName}'`,
          );
        }
      } else {
        // No www-authenticate header found, but we got a 401
        // Only try OAuth discovery when OAuth is explicitly enabled in config
        const shouldTryDiscovery = mcpServerConfig.oauth?.enabled;

        if (!shouldTryDiscovery) {
          await showAuthRequiredMessage(mcpServerName, cliConfig);
        }

        // For SSE/HTTP servers, try to discover OAuth configuration from the base URL
        debugLogger.log(
          `🔍 Attempting OAuth discovery for '${mcpServerName}'...`,
        );

        if (hasNetworkTransport(mcpServerConfig)) {
          const serverUrl = new URL(
            mcpServerConfig.httpUrl || mcpServerConfig.url!,
          );
          const baseUrl = `${serverUrl.protocol}//${serverUrl.host}`;

          // Try to discover OAuth configuration from the base URL
          const oauthConfig = await OAuthUtils.discoverOAuthConfig(baseUrl);
          if (oauthConfig) {
            debugLogger.log(
              `Discovered OAuth configuration from base URL for server '${mcpServerName}'`,
            );

            // Create OAuth configuration for authentication
            const oauthAuthConfig = {
              enabled: true,
              authorizationUrl: oauthConfig.authorizationUrl,
              issuer: oauthConfig.issuer,
              tokenUrl: oauthConfig.tokenUrl,
              scopes: oauthConfig.scopes || [],
            };

            // Perform OAuth authentication
            // Pass the server URL for proper discovery
            const authServerUrl =
              mcpServerConfig.httpUrl || mcpServerConfig.url;
            debugLogger.log(
              `Starting OAuth authentication for server '${mcpServerName}'...`,
            );
            const authProvider = new MCPOAuthProvider(
              new MCPOAuthTokenStorage(),
            );
            await authProvider.authenticate(
              mcpServerName,
              oauthAuthConfig,
              authServerUrl,
            );

            // Retry connection with OAuth token
            const accessToken = await getStoredOAuthToken(mcpServerName);
            if (!accessToken) {
              throw new Error(
                `Failed to get OAuth token for server '${mcpServerName}'`,
              );
            }

            // Create transport with OAuth token
            const oauthTransport = await createTransportWithOAuth(
              mcpServerName,
              mcpServerConfig,
              accessToken,
              cliConfig,
            );
            if (!oauthTransport) {
              throw new Error(
                `Failed to create OAuth transport for server '${mcpServerName}'`,
              );
            }

            await mcpClient.connect(oauthTransport, {
              timeout: mcpServerConfig.timeout ?? MCP_DEFAULT_TIMEOUT_MSEC,
            });
            // Connection successful with OAuth
            return mcpClient;
          } else {
            throw new Error(
              `OAuth configuration failed for '${mcpServerName}'. Please authenticate manually with /mcp auth ${mcpServerName}`,
            );
          }
        } else {
          throw new Error(
            `MCP server '${mcpServerName}' requires authentication. Please configure OAuth or check server settings.`,
          );
        }
      }
    } else {
      // Handle other connection errors
      // Re-throw the original error to preserve its structure
      throw error;
    }
  }
}

/**
 * Helper function to create the appropriate transport based on config
 * This handles the logic for httpUrl/url/type consistently
 */
function createUrlTransport(
  mcpServerName: string,
  mcpServerConfig: MCPServerConfig,
  transportOptions:
    | StreamableHTTPClientTransportOptions
    | SSEClientTransportOptions,
): StreamableHTTPClientTransport | SSEClientTransport {
  // Create a proxy-aware fetcher that respects NO_PROXY for this MCP server
  // This is especially important for local MCP servers (localhost, 127.0.0.1)
  // when a company proxy is globally configured.
  const noProxy = process.env['NO_PROXY'] || process.env['no_proxy'];
  const agent = new EnvHttpProxyAgent({ noProxy });

  // Wrap fetch to:
  // 1. Use the proxy-aware agent (respecting NO_PROXY)
  // 2. Treat GET 404 as 405 so servers that do not support the
  //    optional SSE GET stream (e.g. n8n native MCP) are handled gracefully.
  // The SDK already silently ignores 405; 404 is semantically equivalent here.
  const baseFetch =
    (transportOptions as StreamableHTTPClientTransportOptions).fetch ??
    globalThis.fetch;

  const httpOptions: StreamableHTTPClientTransportOptions = {
    ...transportOptions,
    fetch: async (url, init) => {
      // If we have an explicit NO_PROXY, we use a proxy-aware dispatcher.
      // We use the global fetch but pass a custom dispatcher in the init options.
      // This avoids manual response reconstruction and dangerous type casts.
      const res = noProxy
        ? await globalThis.fetch(url, {
            ...init,
            dispatcher: agent,
          } as RequestInit)
        : await baseFetch(url, init);

      return init?.method === 'GET' && res.status === 404
        ? new Response(null, { status: 405, statusText: 'Method Not Allowed' })
        : res;
    },
  };

  // Priority 1: httpUrl (deprecated)
  if (mcpServerConfig.httpUrl) {
    if (mcpServerConfig.url) {
      debugLogger.warn(
        `MCP server '${mcpServerName}': Both 'httpUrl' and 'url' are configured. ` +
          `Using deprecated 'httpUrl'. Please migrate to 'url' with 'type: "http"'.`,
      );
    }
    return new StreamableHTTPClientTransport(
      new URL(mcpServerConfig.httpUrl),
      httpOptions,
    );
  }

  // Priority 2 & 3: url with explicit type
  if (mcpServerConfig.url && mcpServerConfig.type) {
    if (mcpServerConfig.type === 'http') {
      return new StreamableHTTPClientTransport(
        new URL(mcpServerConfig.url),
        httpOptions,
      );
    } else if (mcpServerConfig.type === 'sse') {
      return new SSEClientTransport(
        new URL(mcpServerConfig.url),
        transportOptions,
      );
    }
  }

  // Priority 4: url without type (default to HTTP)
  if (mcpServerConfig.url) {
    return new StreamableHTTPClientTransport(
      new URL(mcpServerConfig.url),
      httpOptions,
    );
  }

  throw new Error(`No URL configured for MCP server '${mcpServerName}'`);
}

/** Visible for Testing */
export async function createTransport(
  mcpServerName: string,
  mcpServerConfig: MCPServerConfig,
  debugMode: boolean,
  cliConfig: McpContext,
): Promise<Transport> {
  const noUrl = !mcpServerConfig.url && !mcpServerConfig.httpUrl;
  if (noUrl) {
    if (
      mcpServerConfig.authProviderType === AuthProviderType.GOOGLE_CREDENTIALS
    ) {
      throw new Error(
        `URL must be provided in the config for Google Credentials provider`,
      );
    }
    if (
      mcpServerConfig.authProviderType ===
      AuthProviderType.SERVICE_ACCOUNT_IMPERSONATION
    ) {
      throw new Error(
        `No URL configured for ServiceAccountImpersonation MCP Server`,
      );
    }
  }
  if (mcpServerConfig.httpUrl || mcpServerConfig.url) {
    let authProvider = createAuthProvider(mcpServerConfig);
    const headers: Record<string, string> =
      (await authProvider?.getRequestHeaders?.()) ?? {};

    if (authProvider === undefined) {
      const tokenStorage = new MCPOAuthTokenStorage();
      const credentials = await tokenStorage.getCredentials(mcpServerName);
      const shouldUseDynamicOAuthProvider = !!credentials;

      if (!shouldUseDynamicOAuthProvider && mcpServerConfig.oauth?.enabled) {
        cliConfig.emitMcpDiagnostic(
          'info',
          `MCP server '${mcpServerName}' requires authentication using: /mcp auth ${mcpServerName}`,
          undefined,
          mcpServerName,
        );
      }

      if (shouldUseDynamicOAuthProvider) {
        debugLogger.log(
          `Found stored OAuth token for server '${mcpServerName}'`,
        );
        authProvider = createDynamicOAuthTokenProvider(
          mcpServerName,
          mcpServerConfig,
        );
      }
    }

    const transportOptions:
      | StreamableHTTPClientTransportOptions
      | SSEClientTransportOptions = {
      requestInit: createTransportRequestInit(
        mcpServerConfig,
        headers,
        cliConfig.sanitizationConfig,
      ),
      authProvider,
    };

    return new McpComplianceTransport(
      createUrlTransport(mcpServerName, mcpServerConfig, transportOptions),
    );
  }

  if (mcpServerConfig.command) {
    if (!cliConfig.isTrustedFolder()) {
      throw new Error(
        `MCP server '${mcpServerName}' uses stdio transport but current folder is not trusted. Use 'gemini trust' to enable it.`,
      );
    }
    const extensionEnv = getExtensionEnvironment(mcpServerConfig.extension);
    const expansionEnv = { ...process.env, ...extensionEnv };

    // 1. Sanitize the base process environment to prevent unintended leaks of system-wide secrets.
    const sanitizedEnv = sanitizeEnvironment(expansionEnv, {
      ...cliConfig.sanitizationConfig,
      enableEnvironmentVariableRedaction: true,
    });

    const finalEnv: Record<string, string> = {
      [GEMINI_CLI_IDENTIFICATION_ENV_VAR]:
        GEMINI_CLI_IDENTIFICATION_ENV_VAR_VALUE,
      ...extensionEnv,
    };
    for (const [key, value] of Object.entries(sanitizedEnv)) {
      if (value !== undefined) {
        finalEnv[key] = value;
      }
    }

    // Expand and merge explicit environment variables from the MCP configuration.
    if (mcpServerConfig.env) {
      for (const [key, value] of Object.entries(mcpServerConfig.env)) {
        finalEnv[key] = expandEnvVars(value, expansionEnv);
      }
    }

    const transport: Transport = new McpComplianceTransport(
      new StdioClientTransport({
        command: mcpServerConfig.command,
        args: mcpServerConfig.args || [],
        env: finalEnv,
        cwd: mcpServerConfig.cwd,
        stderr: 'pipe',
      }),
    );

    if (debugMode) {
      // The `McpComplianceTransport` wrapper hides the underlying `StdioClientTransport`,
      // which exposes `stderr` for debug logging. We need to unwrap it to attach the listener.

      const underlyingTransport =
        transport instanceof McpComplianceTransport
          ? transport.transport
          : transport;

      if (
        underlyingTransport instanceof StdioClientTransport &&
        underlyingTransport.stderr
      ) {
        underlyingTransport.stderr.on('data', (data) => {
          // eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
          const stderrStr = data.toString().trim();
          debugLogger.debug(
            `[DEBUG] [MCP STDERR (${mcpServerName})]: `,
            stderrStr,
          );
        });
      }
    }
    return transport;
  }

  throw new Error(
    `Invalid configuration: missing httpUrl (for Streamable HTTP), url (for SSE), and command (for stdio).`,
  );
}
interface NamedTool {
  name?: string;
}

function getExtensionEnvironment(
  extension?: GeminiCLIExtension,
): Record<string, string> {
  const env: Record<string, string> = {};
  if (extension?.resolvedSettings) {
    for (const setting of extension.resolvedSettings) {
      if (setting.value !== undefined) {
        env[setting.envVar] = setting.value;
      }
    }
  }
  return env;
}

/** Visible for testing */
export function isEnabled(
  funcDecl: NamedTool,
  mcpServerName: string,
  mcpServerConfig: MCPServerConfig,
): boolean {
  if (!funcDecl.name) {
    debugLogger.warn(
      `Discovered a function declaration without a name from MCP server '${mcpServerName}'. Skipping.`,
    );
    return false;
  }
  const { includeTools, excludeTools } = mcpServerConfig;

  // excludeTools takes precedence over includeTools
  if (excludeTools && excludeTools.includes(funcDecl.name)) {
    return false;
  }

  return (
    !includeTools ||
    includeTools.some(
      (tool) => tool === funcDecl.name || tool.startsWith(`${funcDecl.name}(`),
    )
  );
}