#!/usr/bin/env python3
"""Minimal MCP stdio server fixture for harness-mcp integration tests.

Speaks newline-delimited JSON-RPC (the framing rmcp's child-process transport uses) and
implements just enough of the protocol to be discovered and called: `initialize`,
`notifications/initialized`, `tools/list`, and `tools/call`. Exposes one tool, `echo`,
which returns its `text` argument, plus `boom`, which returns an error result.
"""
import json
import sys

PROTOCOL_VERSION = "2024-11-05"

TOOLS = [
    {
        "name": "echo",
        "description": "Returns the text it is given.",
        "inputSchema": {
            "type": "object",
            "properties": {"text": {"type": "string"}},
            "required": ["text"],
        },
    },
    {
        "name": "boom",
        "description": "Always fails.",
        "inputSchema": {"type": "object", "properties": {}},
    },
]


def reply(msg_id, result):
    sys.stdout.write(json.dumps({"jsonrpc": "2.0", "id": msg_id, "result": result}) + "\n")
    sys.stdout.flush()


def main():
    # readline() rather than `for line in sys.stdin`: the latter's read-ahead buffer blocks
    # until it fills, which would stall the JSON-RPC handshake line-by-line.
    while True:
        line = sys.stdin.readline()
        if line == "":  # EOF: parent closed stdin
            break
        line = line.strip()
        if not line:
            continue
        msg = json.loads(line)
        method = msg.get("method")
        msg_id = msg.get("id")

        if method == "initialize":
            reply(msg_id, {
                "protocolVersion": PROTOCOL_VERSION,
                "capabilities": {"tools": {}},
                "serverInfo": {"name": "echo-fixture", "version": "0.1.0"},
            })
        elif method == "notifications/initialized":
            pass  # notification: no response
        elif method == "tools/list":
            reply(msg_id, {"tools": TOOLS})
        elif method == "tools/call":
            params = msg.get("params") or {}
            name = params.get("name")
            args = params.get("arguments") or {}
            if name == "echo":
                reply(msg_id, {
                    "content": [{"type": "text", "text": args.get("text", "")}],
                    "isError": False,
                })
            elif name == "boom":
                reply(msg_id, {
                    "content": [{"type": "text", "text": "kaboom"}],
                    "isError": True,
                })
            else:
                reply(msg_id, {
                    "content": [{"type": "text", "text": f"unknown tool {name}"}],
                    "isError": True,
                })
        elif msg_id is not None:
            # Unknown request: empty result keeps the client happy.
            reply(msg_id, {})


if __name__ == "__main__":
    main()