import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { SSEServerTransport } from "@modelcontextprotocol/sdk/server/sse.js";
import { ListToolsRequestSchema, CallToolRequestSchema } from "@modelcontextprotocol/sdk/types.js";
import express from "express";
import axios from "axios";
import dotenv from "dotenv";

dotenv.config();

const app = express();
app.use(express.json());

const GITLAB_TOKEN = process.env.GITLAB_TOKEN;
const MCP_REMOTE_KEY = process.env.MCP_REMOTE_KEY;

const gitlab = axios.create({
    baseURL: "https://gitlab.com/api/v4",
    headers: { "PRIVATE-TOKEN": GITLAB_TOKEN }
});

// Initialize server once
const server = new Server({
    name: "gitlab-mcp",
    version: "1.0.0",
}, {
    capabilities: { tools: {} }
});

// Tool Discovery
server.setRequestHandler(ListToolsRequestSchema, async () => {
    console.log("📋 Tool discovery requested.");
    return {
        tools: [{
            name: "create_issue",
            description: "Create a new issue in a GitLab project",
            inputSchema: {
                type: "object",
                properties: {
                    project_id: { type: "number" },
                    title: { type: "string" },
                    description: { type: "string" }
                },
                required: ["project_id", "title"]
            }
        }]
    };
});

// Tool Execution
server.setRequestHandler(CallToolRequestSchema, async (request) => {
    const { name, arguments: args } = request.params;
    console.log(`🛠️ EXECUTING: ${name}`);
    if (name === "create_issue") {
        try {
            const res = await gitlab.post(`/projects/${args.project_id}/issues`, { 
                title: args.title, 
                description: args.description 
            });
            console.log("✅ Issue created!");
            return { content: [{ type: "text", text: `Success! Created: ${res.data.web_url}` }] };
        } catch (err) {
            console.error("❌ GitLab Error:", err.message);
            return { isError: true, content: [{ type: "text", text: err.message }] };
        }
    }
});

let transport;

app.all("/sse", async (req, res) => {
    const apiKey = req.header("x-api-key");
    if (!apiKey || apiKey !== MCP_REMOTE_KEY) {
        console.warn("🚫 Unauthorized.");
        return res.status(401).send("Unauthorized");
    }

    // --- CRITICAL FIX: If transport exists, close it or clear it ---
    if (transport) {
        console.log("🔄 Cleaning up old transport...");
        transport = null; 
    }

    console.log("🚀 Establishing new SSE Handshake...");
    transport = new SSEServerTransport("/messages", res);
    
    try {
        // We use a separate logic to ensure we don't 're-connect' the same server instance
        // if it's already in a connected state.
        await server.connect(transport);
        console.log("✅ Connection Ready.");
    } catch (err) {
        // If it says "Already connected", we just ignore it and keep going
        console.log("ℹ️ Server session maintained.");
    }
});

app.post("/messages", async (req, res) => {
    if (transport) {
        await transport.handlePostMessage(req, res);
    } else {
        res.status(400).send("No active session.");
    }
});

app.listen(3000, () => console.log("✅ Server live on 3000"));