/**
 * Shared utilities for running MCP servers with Streamable HTTP transport.
 */

import { createMcpExpressApp } from "@modelcontextprotocol/sdk/server/express.js";
import type { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
import cors from "cors";
import type { Request, Response } from "express";

export interface ServerOptions {
  port: number;
  name?: string;
}

/**
 * Starts an MCP server with Streamable HTTP transport in stateless mode.
 *
 * @param createServer - Factory function that creates a new McpServer instance per request.
 * @param options - Server configuration options.
 */
export async function startServer(
  createServer: () => McpServer,
  options: ServerOptions,
): Promise<void> {
  const { port, name = "MCP Server" } = options;

  const app = createMcpExpressApp({ host: "0.0.0.0" });
  app.use(cors());

  app.all("/mcp", async (req: Request, res: Response) => {
    const server = createServer();
    const transport = new StreamableHTTPServerTransport({
      sessionIdGenerator: undefined,
    });

    res.on("close", () => {
      transport.close().catch(() => {});
      server.close().catch(() => {});
    });

    try {
      await server.connect(transport);
      await transport.handleRequest(req, res, req.body);
    } catch (error) {
      console.error("MCP error:", error);
      if (!res.headersSent) {
        res.status(500).json({
          jsonrpc: "2.0",
          error: { code: -32603, message: "Internal server error" },
          id: null,
        });
      }
    }
  });

  const httpServer = app.listen(port, (err) => {
    if (err) {
      console.error("Failed to start server:", err);
      process.exit(1);
    }
    console.log(`${name} listening on http://localhost:${port}/mcp`);
  });

  const shutdown = () => {
    console.log("\nShutting down...");
    httpServer.close(() => process.exit(0));
  };

  process.on("SIGINT", shutdown);
  process.on("SIGTERM", shutdown);
}