#!/usr/bin/env python3
"""最小 MCP stdio 服务器（宿主提供工具的对齐试验用）。

只给两个工具，不依赖任何第三方包：
  echo_fact：返回固定事实字符串 mcp-fact-42
  add：返回 a + b

协议：JSON-RPC over stdio，MCP initialize / tools/list / tools/call，
以及 notifications/initialized、ping。codex 的 MCP 客户端就是按
这个协议调它的，宿主只要在 config.toml 里写：

  [mcp_servers.echo]
  command = "python3"
  args = ["<本文件绝对路径>"]
  startup_timeout_sec = 30
"""
import json
import sys


def send(obj):
    sys.stdout.write(json.dumps(obj) + "\n")
    sys.stdout.flush()


def main():
    for line in sys.stdin:
        if not line.strip():
            continue
        try:
            req = json.loads(line)
        except Exception:
            continue
        method = req.get("method")
        rid = req.get("id")
        # 通知：没有 id，不回
        if method in ("notifications/initialized", "notifications/cancelled"):
            continue
        if method == "initialize":
            send({"jsonrpc": "2.0", "id": rid, "result": {
                "protocolVersion": "2024-11-05",
                "capabilities": {"tools": {}},
                "serverInfo": {"name": "echo", "version": "0.1"}}})
        elif method == "tools/list":
            send({"jsonrpc": "2.0", "id": rid, "result": {"tools": [
                {"name": "echo_fact",
                 "description": "返回一个固定事实字符串，用于验证宿主提供的 MCP 工具是否被 agent 调用",
                 "inputSchema": {"type": "object", "properties": {}}},
                {"name": "add",
                 "description": "返回 a + b",
                 "inputSchema": {"type": "object",
                                 "properties": {"a": {"type": "number"},
                                                "b": {"type": "number"}},
                                 "required": ["a", "b"]}}]}})
        elif method == "tools/call":
            params = req.get("params") or {}
            name = params.get("name")
            args = params.get("arguments") or {}
            if name == "echo_fact":
                text = "mcp-fact-42"
            elif name == "add":
                text = str(args.get("a", 0) + args.get("b", 0))
            else:
                text = f"unknown tool: {name}"
            send({"jsonrpc": "2.0", "id": rid, "result": {
                "content": [{"type": "text", "text": text}]}})
        elif method == "ping":
            send({"jsonrpc": "2.0", "id": rid, "result": {}})
        elif rid is not None:
            send({"jsonrpc": "2.0", "id": rid, "result": {}})


if __name__ == "__main__":
    main()