/**
 * Tests for the graceful shutdown coordinator (DC-067).
 *
 * Covers:
 *  - Constructor rejects bad inputs
 *  - shutdown() emits 'shutdown' event with the signal name
 *  - shutdown() stops each manager in declaration order
 *  - shutdown() is idempotent — second call logs and returns
 *  - shutdown() force-exits after drainTimeoutMs if server.close never fires
 *  - shutdown() clears the force-exit timer when server.close fires first
 *  - shutdown() catches manager.stop() throws so one bad manager doesn't
 *    prevent the others from being stopped
 *  - installSignalHandlers() registers for SIGTERM and SIGINT by default
 *
 * process.exit is mocked so tests don't actually kill the test runner.
 */
'use strict';

const EventEmitter = require('events');
const {
  createShutdownCoordinator,
  installSignalHandlers,
  DEFAULT_DRAIN_TIMEOUT_MS,
  ShutdownCoordinator,
} = require('../src/utilities/shutdown');

describe('ShutdownCoordinator (DC-067)', () => {
  let exitMock;
  let exitCalls;

  beforeEach(() => {
    exitCalls = [];
    // Use jest.spyOn so the mock is restored in afterEach (via clearMocks +
    // restoreMocks: true in jest.config.js). Direct assignment to process.exit
    // doesn't suppress Jest's process.exit watchlist which fails the test.
    exitMock = jest.spyOn(process, 'exit').mockImplementation((code) => {
      exitCalls.push(code);
      // Returning undefined prevents the test runner from actually exiting.
      return undefined;
    });
  });

  afterEach(() => {
    exitMock.mockRestore();
    jest.clearAllTimers();
  });

  function makeFakeServer({ closeBehavior = 'sync' } = {}) {
    // 'sync' close calls back immediately.
    // 'never' close never calls back (used to test force-exit).
    if (closeBehavior === 'never') {
      return { close: jest.fn() };
    }
    return { close: jest.fn((cb) => { cb(); }) };
  }

  function makeFakeLog() {
    return {
      info: jest.fn(),
      warn: jest.fn(),
      error: jest.fn(),
    };
  }

  describe('constructor', () => {
    test('throws if server is missing', () => {
      expect(() => createShutdownCoordinator({ log: makeFakeLog(), managers: [] }))
        .toThrow('server is required');
    });

    test('throws if log is missing or invalid', () => {
      expect(() => createShutdownCoordinator({ server: makeFakeServer(), managers: [] }))
        .toThrow('log must have info');
      expect(() => createShutdownCoordinator({
        server: makeFakeServer(),
        log: { foo: 'bar' },
        managers: [],
      })).toThrow('log must have info');
      expect(() => createShutdownCoordinator({
        server: makeFakeServer(),
        log: { info: () => {}, warn: () => {} },  // missing error
        managers: [],
      })).toThrow('log must have info');
      // A log with all three methods should NOT throw.
      expect(() => createShutdownCoordinator({
        server: makeFakeServer(),
        log: { info: () => {}, warn: () => {}, error: () => {} },
        managers: [],
      })).not.toThrow();
    });

    test('uses DEFAULT_DRAIN_TIMEOUT_MS when drainTimeoutMs is not finite positive', () => {
      const c = createShutdownCoordinator({
        server: makeFakeServer(),
        log: makeFakeLog(),
        drainTimeoutMs: 0,
        managers: [],
      });
      expect(c.drainTimeoutMs).toBe(DEFAULT_DRAIN_TIMEOUT_MS);

      const c2 = createShutdownCoordinator({
        server: makeFakeServer(),
        log: makeFakeLog(),
        drainTimeoutMs: NaN,
        managers: [],
      });
      expect(c2.drainTimeoutMs).toBe(DEFAULT_DRAIN_TIMEOUT_MS);

      const c3 = createShutdownCoordinator({
        server: makeFakeServer(),
        log: makeFakeLog(),
        drainTimeoutMs: 5000,
        managers: [],
      });
      expect(c3.drainTimeoutMs).toBe(5000);
    });

    test('defaults managers to [] when not an array', () => {
      const c = createShutdownCoordinator({
        server: makeFakeServer(),
        log: makeFakeLog(),
      });
      expect(c.managers).toEqual([]);
    });

    test('is an EventEmitter', () => {
      const c = createShutdownCoordinator({
        server: makeFakeServer(),
        log: makeFakeLog(),
        managers: [],
      });
      expect(c).toBeInstanceOf(EventEmitter);
      expect(c).toBeInstanceOf(ShutdownCoordinator);
    });
  });

  describe('shutdown()', () => {
    test('emits shutdown event with signal name', () => {
      const c = createShutdownCoordinator({
        server: makeFakeServer(),
        log: makeFakeLog(),
        managers: [],
      });
      const handler = jest.fn();
      c.on('shutdown', handler);

      c.shutdown('SIGTERM');

      expect(handler).toHaveBeenCalledTimes(1);
      expect(handler).toHaveBeenCalledWith('SIGTERM');
    });

    test('swallows exceptions thrown by shutdown event listeners', () => {
      const log = makeFakeLog();
      const server = makeFakeServer();
      const c = createShutdownCoordinator({
        server,
        log,
        managers: [],
      });
      c.on('shutdown', () => { throw new Error('listener boom'); });

      // shutdown() must NOT propagate the exception — that would abort
      // the entire shutdown sequence before server.close is even called.
      expect(() => c.shutdown('SIGTERM')).not.toThrow();
      expect(log.error).toHaveBeenCalledWith(
        'shutdown',
        "event listener for 'shutdown' threw",
        expect.objectContaining({ error: 'listener boom' }),
      );
      // server.close should still have been called.
      expect(server.close).toHaveBeenCalledTimes(1);
    });

    test('swallows exceptions thrown by closed event listeners', async () => {
      const log = makeFakeLog();
      const server = makeFakeServer();
      const c = createShutdownCoordinator({
        server,
        log,
        managers: [],
      });
      c.on('closed', () => { throw new Error('closed listener boom'); });

      // process.exit is mocked; we just verify the throw doesn't bubble.
      c.shutdown('SIGTERM');
      await new Promise((resolve) => setImmediate(resolve));
      // The closed listener threw but the exit still got recorded.
      expect(exitCalls).toEqual([0]);
    });

    test('calls server.close() once', () => {
      const server = makeFakeServer();
      const c = createShutdownCoordinator({
        server,
        log: makeFakeLog(),
        managers: [],
      });

      c.shutdown('SIGTERM');

      expect(server.close).toHaveBeenCalledTimes(1);
    });

    test('stops each manager in declaration order AFTER server.close fires', async () => {
      const order = [];
      const managers = [
        { name: 'first', stop: jest.fn(() => { order.push('first'); }) },
        { name: 'second', stop: jest.fn(() => { order.push('second'); }) },
        { name: 'third', stop: jest.fn(() => { order.push('third'); }) },
      ];
      const c = createShutdownCoordinator({
        server: makeFakeServer(),
        log: makeFakeLog(),
        managers,
      });

      c.shutdown('SIGTERM');
      // Wait for the async chain (server.close → _stopManagersInOrder →
      // process.exit) to settle. The mock exit is synchronous so this
      // resolves once all microtasks drain.
      await new Promise((resolve) => setImmediate(resolve));

      expect(order).toEqual(['first', 'second', 'third']);
    });

    test('does NOT stop managers until server.close callback fires', () => {
      const order = [];
      // Use a server whose close callback fires only when we manually call it.
      let deferredCloseCb;
      const server = {
        close: jest.fn((cb) => { deferredCloseCb = cb; }),
      };
      const managers = [
        { name: 'first', stop: jest.fn(() => { order.push('first'); }) },
      ];
      const c = createShutdownCoordinator({
        server,
        log: makeFakeLog(),
        managers,
      });

      c.shutdown('SIGTERM');

      // server.close has been called but its callback hasn't fired yet.
      expect(server.close).toHaveBeenCalledTimes(1);
      // Manager has NOT been stopped yet — server is still draining.
      expect(order).toEqual([]);

      // Now fire the deferred callback to simulate drain completion.
      deferredCloseCb();

      // Manager stopped AFTER server.close fired.
      expect(order).toEqual(['first']);
    });

    test('continues stopping remaining managers if one throws', async () => {
      const order = [];
      const managers = [
        { name: 'first', stop: jest.fn(() => { order.push('first'); }) },
        { name: 'broken', stop: jest.fn(() => { throw new Error('boom'); }) },
        { name: 'third', stop: jest.fn(() => { order.push('third'); }) },
      ];
      const log = makeFakeLog();
      const c = createShutdownCoordinator({
        server: makeFakeServer(),
        log,
        managers,
      });

      c.shutdown('SIGTERM');
      await new Promise((resolve) => setImmediate(resolve));

      expect(order).toEqual(['first', 'third']);
      expect(log.warn).toHaveBeenCalledWith(
        'shutdown',
        'manager stop failed: broken',
        expect.objectContaining({ error: 'boom' }),
      );
    });

    test('is idempotent — second shutdown() returns without re-running', () => {
      const server = makeFakeServer();
      const c = createShutdownCoordinator({
        server,
        log: makeFakeLog(),
        managers: [{ name: 'm', stop: jest.fn() }],
      });

      c.shutdown('SIGTERM');
      c.shutdown('SIGTERM');
      c.shutdown('SIGINT');

      expect(server.close).toHaveBeenCalledTimes(1);
      expect(c.isShuttingDown()).toBe(true);
    });

    test('isShuttingDown() flips false→true on first shutdown call', () => {
      const c = createShutdownCoordinator({
        server: makeFakeServer(),
        log: makeFakeLog(),
        managers: [],
      });
      expect(c.isShuttingDown()).toBe(false);
      c.shutdown('SIGTERM');
      expect(c.isShuttingDown()).toBe(true);
    });

    test('force-exits after drainTimeoutMs if server.close never fires', () => {
      jest.useFakeTimers();
      try {
        const server = makeFakeServer({ closeBehavior: 'never' });
        const log = makeFakeLog();
        const c = createShutdownCoordinator({
          server,
          log,
          drainTimeoutMs: 1000,
          managers: [],
        });

        c.shutdown('SIGTERM');
        expect(exitCalls).toEqual([]);

        jest.advanceTimersByTime(999);
        expect(exitCalls).toEqual([]);

        jest.advanceTimersByTime(2);
        expect(exitCalls).toEqual([0]);
        expect(log.warn).toHaveBeenCalledWith(
          'shutdown',
          expect.stringContaining('drain timeout (1000ms) reached before HTTP server closed'),
        );
      } finally {
        jest.useRealTimers();
      }
    });

    test('force-exits after drainTimeoutMs if manager.stop() hangs after HTTP close', () => {
      jest.useFakeTimers();
      try {
        const server = makeFakeServer();  // calls back immediately
        const log = makeFakeLog();
        // Manager that NEVER resolves — simulates a hung cleanup.
        const hungManager = {
          name: 'hung',
          stop: jest.fn(() => new Promise(() => {})),  // never resolves
        };
        const c = createShutdownCoordinator({
          server,
          log,
          drainTimeoutMs: 1000,
          managers: [hungManager],
        });

        c.shutdown('SIGTERM');
        // After the synchronous shutdown() call: server.close has fired
        // (serverClosed=true), but hungManager.stop() has been called and
        // its promise is pending. managersStopped is still false.
        // process.exit should NOT have been called yet.
        expect(exitCalls).toEqual([]);

        jest.advanceTimersByTime(1001);
        // Now the safety-net timer fires — force-exit because manager hung.
        expect(exitCalls).toEqual([0]);
        expect(log.warn).toHaveBeenCalledWith(
          'shutdown',
          expect.stringContaining('after HTTP close (manager hung)'),
        );
      } finally {
        jest.useRealTimers();
      }
    });

    test('clears force-exit timer when manager drain completes promptly', () => {
      jest.useFakeTimers();
      try {
        const server = makeFakeServer();  // calls back on the same tick
        const log = makeFakeLog();
        // Quick-stopping manager. The close callback awaits stop(),
        // which resolves immediately, so managersStopped flips true
        // and the safety-net timer is cleared before it can fire.
        const fastManager = {
          name: 'fast',
          stop: jest.fn(() => Promise.resolve()),
        };
        const c = createShutdownCoordinator({
          server,
          log,
          drainTimeoutMs: 1000,
          managers: [fastManager],
        });

        c.shutdown('SIGTERM');

        // Flush microtasks so the close callback's await stop() resolves,
        // managersStopped flips true, the timer is cleared, and
        // process.exit(0) is recorded exactly once.
        return Promise.resolve().then(() => Promise.resolve()).then(() => {
          expect(exitCalls).toEqual([0]);

          // Advance well past the drain timeout — no extra exit should fire.
          jest.advanceTimersByTime(5000);
          expect(exitCalls).toEqual([0]);
        });
      } finally {
        jest.useRealTimers();
      }
    });
  });

  describe('installSignalHandlers()', () => {
    test('registers listeners on the given signals', () => {
      const c = createShutdownCoordinator({
        server: makeFakeServer(),
        log: makeFakeLog(),
        managers: [],
      });
      const shutdownSpy = jest.spyOn(c, 'shutdown');

      installSignalHandlers(c);

      // Emit fake signals through process.emit to verify the listener was
      // registered (process.on listens to the process EventEmitter).
      process.emit('SIGTERM');
      process.emit('SIGINT');

      expect(shutdownSpy).toHaveBeenCalledWith('SIGTERM');
      expect(shutdownSpy).toHaveBeenCalledWith('SIGINT');
    });

    test('accepts custom signal list', () => {
      const c = createShutdownCoordinator({
        server: makeFakeServer(),
        log: makeFakeLog(),
        managers: [],
      });
      const shutdownSpy = jest.spyOn(c, 'shutdown');

      installSignalHandlers(c, ['SIGHUP']);

      process.emit('SIGHUP');
      expect(shutdownSpy).toHaveBeenCalledWith('SIGHUP');
    });

    test('is idempotent — calling installSignalHandlers twice does not double-register', () => {
      const c = createShutdownCoordinator({
        server: makeFakeServer(),
        log: makeFakeLog(),
        managers: [],
      });
      const shutdownSpy = jest.spyOn(c, 'shutdown');

      installSignalHandlers(c);
      installSignalHandlers(c);  // second call
      installSignalHandlers(c);  // third call

      // The installedSignals tracker should have one entry per signal.
      expect(c._installedSignals).toEqual(['SIGTERM', 'SIGINT']);

      process.emit('SIGTERM');
      expect(shutdownSpy).toHaveBeenCalledTimes(1);
    });
  });
});