/**
 * Unit coverage for the daemon-side client-liveness primitives (#692, Layer 2).
 *
 * These back the daemon's defense against a phantom client — one whose process
 * died without the socket ever signalling close (a Windows named-pipe hazard).
 * The wire parsing and the liveness decision are pure, so they're tested here;
 * the full handshake + sweep is exercised end-to-end in `mcp-daemon.test.ts`.
 */
import { describe, it, expect } from 'vitest';
import { Daemon, parseClientHelloLine, peerIsDead } from '../src/mcp/daemon';

describe('parseClientHelloLine', () => {
  it('parses a well-formed client-hello', () => {
    expect(parseClientHelloLine('{"codegraph_client":1,"pid":1234,"hostPid":56}'))
      .toEqual({ pid: 1234, hostPid: 56 });
  });

  it('accepts a null host pid and a missing host pid', () => {
    expect(parseClientHelloLine('{"codegraph_client":1,"pid":1234,"hostPid":null}'))
      .toEqual({ pid: 1234, hostPid: null });
    expect(parseClientHelloLine('{"codegraph_client":1,"pid":1234}'))
      .toEqual({ pid: 1234, hostPid: null });
  });

  it('returns null for a JSON-RPC message (no marker) so it is treated as data', () => {
    expect(parseClientHelloLine('{"jsonrpc":"2.0","id":1,"method":"initialize"}')).toBeNull();
  });

  it('rejects a wrong-typed marker, a non-numeric pid, and a non-integer marker', () => {
    expect(parseClientHelloLine('{"codegraph_client":true,"pid":1}')).toBeNull();
    expect(parseClientHelloLine('{"codegraph_client":2,"pid":1}')).toBeNull();
    expect(parseClientHelloLine('{"codegraph_client":1,"pid":"1"}')).toBeNull();
  });

  it('returns null for invalid / empty / non-object JSON', () => {
    expect(parseClientHelloLine('not json')).toBeNull();
    expect(parseClientHelloLine('')).toBeNull();
    expect(parseClientHelloLine('42')).toBeNull();
    expect(parseClientHelloLine('null')).toBeNull();
  });
});

describe('peerIsDead', () => {
  const aliveAll = () => true;
  const deadAll = () => false;
  const deadOnly = (...pids: number[]) => (pid: number) => !pids.includes(pid);

  it('never reaps a client with an unknown pid (no client-hello)', () => {
    expect(peerIsDead({ pid: null, hostPid: null }, deadAll)).toBe(false);
    expect(peerIsDead({ pid: null, hostPid: 99 }, deadAll)).toBe(false);
  });

  it('keeps a client whose proxy is alive', () => {
    expect(peerIsDead({ pid: 100, hostPid: null }, aliveAll)).toBe(false);
  });

  it('reaps a client whose proxy process is gone', () => {
    expect(peerIsDead({ pid: 100, hostPid: null }, deadOnly(100))).toBe(true);
  });

  it('reaps when the proxy is alive but its host is gone', () => {
    // proxy 100 alive, host 42 dead
    expect(peerIsDead({ pid: 100, hostPid: 42 }, deadOnly(42))).toBe(true);
  });

  it('keeps a client when both proxy and host are alive', () => {
    expect(peerIsDead({ pid: 100, hostPid: 42 }, aliveAll)).toBe(false);
  });
});

describe('Daemon.reapDeadClients', () => {
  // Construct with idleTimeoutMs:0 so dropping the last client doesn't arm a real
  // idle timer. The constructor opens no sockets/DB, so this stays a fast unit test.
  const makeDaemon = () => new Daemon('/tmp/codegraph-reap-unit-test', { idleTimeoutMs: 0 }) as any;
  const fakeSession = () => ({ stopped: false, stop() { this.stopped = true; } });

  it('drops clients with a dead peer and leaves live ones attached', () => {
    const d = makeDaemon();
    const dead = fakeSession();
    const live = fakeSession();
    d.clients.add(dead); d.clientPeers.set(dead, { pid: 111, hostPid: null });
    d.clients.add(live); d.clientPeers.set(live, { pid: 222, hostPid: null });

    const reaped = d.reapDeadClients((pid: number) => pid !== 111); // 111 dead, 222 alive

    expect(reaped).toBe(1);
    expect(dead.stopped).toBe(true);
    expect(d.clients.has(dead)).toBe(false);
    expect(d.clientPeers.has(dead)).toBe(false); // peer record cleaned up too
    expect(d.clients.has(live)).toBe(true);
  });

  it('never reaps a client with an unknown pid (no client-hello)', () => {
    const d = makeDaemon();
    const s = fakeSession();
    d.clients.add(s); d.clientPeers.set(s, { pid: null, hostPid: null });

    expect(d.reapDeadClients(() => false)).toBe(0); // everything "dead", but pid unknown
    expect(d.clients.has(s)).toBe(true);
  });

  it('reaps a client whose host pid is gone even if its proxy pid is alive', () => {
    const d = makeDaemon();
    const s = fakeSession();
    d.clients.add(s); d.clientPeers.set(s, { pid: 100, hostPid: 42 });

    expect(d.reapDeadClients((pid: number) => pid !== 42)).toBe(1); // proxy 100 alive, host 42 dead
    expect(d.clients.has(s)).toBe(false);
  });
});

// The inactivity backstop (#692) must reap a phantom daemon but NEVER a
// live-but-quiet session — reaping the latter silently degraded that session
// (and any others sharing the daemon) to an in-process engine, and on a real
// machine it fired far more often on live sessions than on actual phantoms.
describe('Daemon.backstopShouldExit', () => {
  // maxIdleMs small; idleTimeoutMs:0 so a sweep that empties the set doesn't arm
  // a real timer. Force the inactivity window open by backdating lastActivityAt.
  const makeDaemon = () => {
    const d = new Daemon('/tmp/codegraph-backstop-unit-test', { idleTimeoutMs: 0, maxIdleMs: 1000 }) as any;
    d.lastActivityAt = Date.now() - 60_000; // long past the 1000ms window
    return d;
  };
  const fakeSession = () => ({ stopped: false, stop() { this.stopped = true; } });

  it('does NOT reap while a provably-alive client stays connected (the fix)', () => {
    const d = makeDaemon();
    const live = fakeSession();
    d.clients.add(live); d.clientPeers.set(live, { pid: 222, hostPid: null });

    expect(d.backstopShouldExit(() => true)).toBe(false); // 222 alive → keep the daemon
    expect(d.clients.has(live)).toBe(true);
  });

  it('reaps when only an unknown-pid client remains (the phantom the sweep cannot catch)', () => {
    const d = makeDaemon();
    const phantom = fakeSession();
    d.clients.add(phantom); d.clientPeers.set(phantom, { pid: null, hostPid: null });

    // Unknown pid → the sweep leaves it, and after the window it's a probable phantom.
    expect(d.backstopShouldExit(() => false)).toBe(true);
  });

  it('protects a live session even when a phantom is also connected', () => {
    const d = makeDaemon();
    const live = fakeSession();
    const phantom = fakeSession();
    d.clients.add(live); d.clientPeers.set(live, { pid: 222, hostPid: null });
    d.clients.add(phantom); d.clientPeers.set(phantom, { pid: null, hostPid: null });

    // 222 alive, phantom unknown → ANY alive keeps the daemon; the live one wins.
    expect(d.backstopShouldExit((pid: number) => pid === 222)).toBe(false);
    expect(d.clients.has(live)).toBe(true);
  });

  it('sweeps a dead-peer client first; if that empties the set it does not exit', () => {
    const d = makeDaemon();
    const dead = fakeSession();
    d.clients.add(dead); d.clientPeers.set(dead, { pid: 111, hostPid: null });

    // 111 dead → swept by backstopShouldExit; empty set → idle timer owns it, no backstop exit.
    expect(d.backstopShouldExit(() => false)).toBe(false);
    expect(d.clients.has(dead)).toBe(false);
    expect(dead.stopped).toBe(true);
  });

  it('does not exit before the inactivity window elapses', () => {
    const d = makeDaemon();
    d.lastActivityAt = Date.now(); // fresh — inside the 1000ms window
    const phantom = fakeSession();
    d.clients.add(phantom); d.clientPeers.set(phantom, { pid: null, hostPid: null });

    expect(d.backstopShouldExit(() => false)).toBe(false);
    expect(d.clients.has(phantom)).toBe(true); // not even swept yet
  });

  it('does not exit with zero clients (the idle timer owns that case)', () => {
    const d = makeDaemon();
    expect(d.backstopShouldExit(() => false)).toBe(false);
  });
});