// Minimal stdio MCP server that gives a Claude Code session its typed
// tools: `node mcp-server.mjs <tools.json> <tool socket>`. Newline-delimited
// JSON-RPC 2.0 with initialize, tools/list, tools/call and ping. Each call
// goes to the runner's tool socket; the server holds no capability. A
// reply over REPLY_CAP is a tool error (tools.mjs, replyText).

import { readFileSync } from "node:fs";
import { createInterface } from "node:readline";
import { callTool, replyText } from "./tools.mjs";

const [toolsFile, socket] = process.argv.slice(2);
if (!toolsFile || !socket) {
  process.stderr.write("usage: mcp-server.mjs <tools.json> <tool socket>\n");
  process.exit(2);
}
const tools = JSON.parse(readFileSync(toolsFile, "utf8"));
const byName = new Map(tools.map((t) => [t.name, t]));

const send = (message) => process.stdout.write(JSON.stringify({ jsonrpc: "2.0", ...message }) + "\n");
const reply = (id, result) => send({ id, result });
const error = (id, code, message) => send({ id, error: { code, message } });

async function handle(m) {
  const id = m.id;
  switch (m.method) {
    case "initialize":
      return reply(id, {
        protocolVersion: m.params?.protocolVersion ?? "2025-06-18",
        capabilities: { tools: {} },
        serverInfo: { name: "mosaic", version: "1" },
      });
    case "ping":
      return reply(id, {});
    case "tools/list":
      return reply(id, { tools: tools.map((t) => ({ name: t.name, description: t.description, inputSchema: t.parameters })) });
    case "tools/call": {
      const name = m.params?.name;
      if (!byName.has(name)) return error(id, -32602, `unknown tool: ${name}`);
      try {
        const result = await callTool(socket, name, m.params?.arguments ?? {});
        return reply(id, { content: [{ type: "text", text: replyText(result) }] });
      } catch (e) {
        return reply(id, { content: [{ type: "text", text: e.message }], isError: true });
      }
    }
    default:
      if (id !== undefined) return error(id, -32601, `method not found: ${m.method}`);
  }
}

createInterface({ input: process.stdin }).on("line", (line) => {
  if (!line.trim()) return;
  let m;
  try {
    m = JSON.parse(line);
  } catch {
    return error(null, -32700, "parse error");
  }
  handle(m).catch((e) => m.id !== undefined && error(m.id, -32603, e.message));
});