import readline from 'node:readline';

// 受信順に依存せず、応答・通知・サーバー要求を振り分ける。
export class RpcClient {
  constructor(proc, { onNotification = () => {}, onServerRequest, timeoutMs = 15000 } = {}) {
    this.proc = proc;
    this.pending = new Map();
    this.nextId = 1;
    this.timeoutMs = timeoutMs;
    this.closed = false;
    this.rl = readline.createInterface({ input: proc.stdout });
    this.rl.on('line', line => {
      try {
        const m = JSON.parse(line);
        const hasId = Object.hasOwn(m, 'id');
        if (m.method && hasId) {
          // 両方向の id は別物。同じ値でも pending の応答として扱わない。
          Promise.resolve().then(() => onServerRequest?.(m)).then(result => {
            this.send(result === undefined
              ? { id: m.id, error: { code: -32601, message: 'Unsupported server request' } }
              : { id: m.id, result });
          }).catch(() => {
            if (!this.closed) this.send({ id: m.id, error: { code: -32603, message: 'Client handler failed' } });
          });
        } else if (m.method) {
          onNotification(m);
        } else if (hasId) {
          const p = this.pending.get(m.id);
          if (!p) return;
          clearTimeout(p.timer);
          this.pending.delete(m.id);
          m.error ? p.reject(new Error(`${m.error.code}: ${m.error.message}`)) : p.resolve(m.result);
        }
      } catch (error) { this.fail(error); }
    });
    proc.on('error', error => this.fail(error));
    proc.on('exit', (code, signal) => this.fail(new Error(`server exit: ${code ?? signal}`)));
    proc.stdin.on('error', error => this.fail(error));
    proc.stdout.on('error', error => this.fail(error));
  }
  send(message) {
    if (this.closed) throw new Error('connection closed');
    this.proc.stdin.write(JSON.stringify(message) + '\n');
  }
  request(method, params = {}) {
    if (this.closed) return Promise.reject(new Error('connection closed'));
    const id = this.nextId++;
    return new Promise((resolve, reject) => {
      const timer = setTimeout(() => {
        this.pending.delete(id);
        reject(new Error(`timeout: ${method}; 結果不明のため自動再送しません`));
      }, this.timeoutMs);
      this.pending.set(id, { resolve, reject, timer });
      try { this.send({ id, method, params }); }
      catch (error) { clearTimeout(timer); this.pending.delete(id); reject(error); }
    });
  }
  notify(method, params = {}) { this.send({ method, params }); }
  fail(error) {
    this.closed = true;
    for (const p of this.pending.values()) { clearTimeout(p.timer); p.reject(error); }
    this.pending.clear();
  }
  close() {
    this.fail(new Error('client closed'));
    this.rl.close();
    this.proc.stdin.end();
    this.proc.kill();
  }
}