/**
 * Tests for WorkerPool (TRUEREF-0022).
 *
 * Real node:worker_threads Workers are replaced by FakeWorker (an EventEmitter)
 * so no subprocess is ever spawned.  We maintain our own registry of created
 * FakeWorker instances so we can inspect postMessage calls and emit events.
 */

import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
import { writeFileSync, unlinkSync, existsSync } from 'node:fs';
import { EventEmitter } from 'node:events';

// ---------------------------------------------------------------------------
// Hoist FakeWorker + registry so vi.mock can reference them.
// ---------------------------------------------------------------------------

const { createdWorkers, FakeWorker } = vi.hoisted(() => {
	// eslint-disable-next-line @typescript-eslint/no-require-imports
	const { EventEmitter } = require('node:events') as typeof import('node:events');

	const createdWorkers: InstanceType<typeof FakeWorkerClass>[] = [];

	class FakeWorkerClass extends EventEmitter {
		threadId = Math.floor(Math.random() * 100_000);
		// Auto-emit 'exit' with code 0 when a shutdown message is received
		postMessage = vi.fn((msg: { type: string }) => {
			if (msg.type === 'shutdown') {
				// Emit exit asynchronously so shutdown() loop can process it
				setImmediate(() => {
					this.emit('exit', 0);
					this.threadId = 0; // signal exited
				});
			}
		});
		terminate = vi.fn(() => {
			this.threadId = 0;
		});

		constructor(_script: string, _opts?: unknown) {
			super();
			createdWorkers.push(this);
		}
	}

	return { createdWorkers, FakeWorker: FakeWorkerClass };
});

// ---------------------------------------------------------------------------
// Mock node:worker_threads BEFORE importing WorkerPool.
// ---------------------------------------------------------------------------

vi.mock('node:worker_threads', () => {
	return { Worker: FakeWorker };
});

import { WorkerPool, type WorkerPoolOptions } from './worker-pool.js';

// ---------------------------------------------------------------------------
// Test helpers
// ---------------------------------------------------------------------------

const FAKE_SCRIPT = '/tmp/fake-worker-pool-test.mjs';
const MISSING_SCRIPT = '/tmp/this-file-does-not-exist-worker-pool.mjs';

function makeOpts(overrides: Partial<WorkerPoolOptions> = {}): WorkerPoolOptions {
	return {
		concurrency: 2,
		workerScript: FAKE_SCRIPT,
		embedWorkerScript: MISSING_SCRIPT,
		dbPath: ':memory:',
		onProgress: vi.fn(),
		onJobDone: vi.fn(),
		onJobFailed: vi.fn(),
		onEmbedDone: vi.fn(),
		onEmbedFailed: vi.fn(),
		...overrides
	} as unknown as WorkerPoolOptions;
}

// ---------------------------------------------------------------------------
// Setup / teardown
// ---------------------------------------------------------------------------

beforeEach(() => {
	// Create the fake script so existsSync returns true
	writeFileSync(FAKE_SCRIPT, '// placeholder\n');
	// Clear registry and reset all mocks
	createdWorkers.length = 0;
	vi.clearAllMocks();
});

afterEach(() => {
	if (existsSync(FAKE_SCRIPT)) unlinkSync(FAKE_SCRIPT);
});

// ---------------------------------------------------------------------------
// Fallback mode (no real workers)
// ---------------------------------------------------------------------------

describe('WorkerPool fallback mode', () => {
	it('enters fallback mode when workerScript does not exist', () => {
		const pool = new WorkerPool(makeOpts({ workerScript: MISSING_SCRIPT }));

		expect(pool.isFallbackMode).toBe(true);
	});

	it('does not throw when constructed in fallback mode', () => {
		expect(() => new WorkerPool(makeOpts({ workerScript: MISSING_SCRIPT }))).not.toThrow();
	});

	it('enqueue is a no-op in fallback mode — callbacks are never called', () => {
		const opts = makeOpts({ workerScript: MISSING_SCRIPT });
		const pool = new WorkerPool(opts);

		pool.enqueue('job-1', '/repo/1');

		expect(opts.onJobDone).not.toHaveBeenCalled();
		expect(opts.onProgress).not.toHaveBeenCalled();
	});

	it('spawns no workers in fallback mode', () => {
		new WorkerPool(makeOpts({ workerScript: MISSING_SCRIPT }));

		expect(createdWorkers).toHaveLength(0);
	});
});

// ---------------------------------------------------------------------------
// Normal mode
// ---------------------------------------------------------------------------

describe('WorkerPool normal mode', () => {
	it('isFallbackMode is false when workerScript exists', () => {
		const pool = new WorkerPool(makeOpts({ concurrency: 1 }));

		expect(pool.isFallbackMode).toBe(false);
	});

	it('spawns `concurrency` parse workers on construction', () => {
		new WorkerPool(makeOpts({ concurrency: 3 }));

		expect(createdWorkers).toHaveLength(3);
	});

	// -------------------------------------------------------------------------
	// enqueue dispatches to an idle worker
	// -------------------------------------------------------------------------

	it('enqueue sends { type: "run", jobId } to an idle worker', () => {
		const pool = new WorkerPool(makeOpts({ concurrency: 1 }));

		pool.enqueue('job-42', '/repo/1');

		expect(createdWorkers).toHaveLength(1);
		expect(createdWorkers[0].postMessage).toHaveBeenCalledWith({ type: 'run', jobId: 'job-42' });
	});

	// -------------------------------------------------------------------------
	// "done" message — onJobDone called, next queued job dispatched
	// -------------------------------------------------------------------------

	it('calls onJobDone and dispatches the next queued job when a worker emits "done"', () => {
		const opts = makeOpts({ concurrency: 1 });
		const pool = new WorkerPool(opts);

		// Enqueue two jobs — second must wait because concurrency=1
		pool.enqueue('job-A', '/repo/1');
		pool.enqueue('job-B', '/repo/2');

		const worker = createdWorkers[0];

		// Simulate job-A completing
		worker.emit('message', { type: 'done', jobId: 'job-A' });

		expect(opts.onJobDone).toHaveBeenCalledWith('job-A');
		// The same worker should now run job-B
		expect(worker.postMessage).toHaveBeenCalledWith({ type: 'run', jobId: 'job-B' });
	});

	// -------------------------------------------------------------------------
	// "failed" message — onJobFailed called
	// -------------------------------------------------------------------------

	it('calls onJobFailed when a worker emits a "failed" message', () => {
		const opts = makeOpts({ concurrency: 1 });
		const pool = new WorkerPool(opts);

		pool.enqueue('job-fail', '/repo/1');

		const worker = createdWorkers[0];
		worker.emit('message', { type: 'failed', jobId: 'job-fail', error: 'parse error' });

		expect(opts.onJobFailed).toHaveBeenCalledWith('job-fail', 'parse error');
	});

	// -------------------------------------------------------------------------
	// Per-repo serialization
	// -------------------------------------------------------------------------

	it('does not dispatch a second job for the same repo while first is running', () => {
		const opts = makeOpts({ concurrency: 2 });
		const pool = new WorkerPool(opts);

		pool.enqueue('job-1', '/repo/same');
		pool.enqueue('job-2', '/repo/same');

		// Only job-1 should have been dispatched (run message sent)
		const runCalls = createdWorkers.flatMap((w) =>
			w.postMessage.mock.calls.filter((c) => (c[0] as { type: string })?.type === 'run')
		);
		expect(runCalls.filter((c) => (c[0] as unknown as { jobId: string }).jobId === 'job-1')).toHaveLength(1);
		expect(runCalls.filter((c) => (c[0] as unknown as { jobId: string }).jobId === 'job-2')).toHaveLength(0);
	});

	it('starts jobs for different repos concurrently', () => {
		const opts = makeOpts({ concurrency: 2 });
		const pool = new WorkerPool(opts);

		pool.enqueue('job-alpha', '/repo/alpha');
		pool.enqueue('job-beta', '/repo/beta');

		const runCalls = createdWorkers.flatMap((w) =>
			w.postMessage.mock.calls.filter((c) => (c[0] as { type: string })?.type === 'run')
		);
		const dispatchedIds = runCalls.map((c) => (c[0] as unknown as { jobId: string }).jobId);
		expect(dispatchedIds).toContain('job-alpha');
		expect(dispatchedIds).toContain('job-beta');
	});

	// -------------------------------------------------------------------------
	// Worker crash (exit code != 0)
	// -------------------------------------------------------------------------

	it('calls onJobFailed and spawns a replacement worker when a worker exits with code 1', () => {
		const opts = makeOpts({ concurrency: 1 });
		const pool = new WorkerPool(opts);

		pool.enqueue('job-crash', '/repo/1');

		const originalWorker = createdWorkers[0];
		// Simulate crash while the job is running
		originalWorker.emit('exit', 1);

		expect(opts.onJobFailed).toHaveBeenCalledWith('job-crash', expect.stringContaining('1'));
		// A replacement worker must have been spawned
		expect(createdWorkers.length).toBeGreaterThan(1);
	});

	it('does NOT call onJobFailed when a worker exits cleanly (code 0)', () => {
		const opts = makeOpts({ concurrency: 1 });
		const pool = new WorkerPool(opts);

		// Exit without any running job
		const worker = createdWorkers[0];
		worker.emit('exit', 0);

		expect(opts.onJobFailed).not.toHaveBeenCalled();
	});

	// -------------------------------------------------------------------------
	// setMaxConcurrency — scale up
	// -------------------------------------------------------------------------

	it('spawns additional workers when setMaxConcurrency is increased', () => {
		const pool = new WorkerPool(makeOpts({ concurrency: 1 }));
		const before = createdWorkers.length; // 1

		pool.setMaxConcurrency(3);

		expect(createdWorkers.length).toBe(before + 2);
	});

	// -------------------------------------------------------------------------
	// setMaxConcurrency — scale down
	// -------------------------------------------------------------------------

	it('sends "shutdown" to idle workers when setMaxConcurrency is decreased', () => {
		const opts = makeOpts({ concurrency: 3 });
		const pool = new WorkerPool(opts);

		pool.setMaxConcurrency(1);

		const shutdownWorkers = createdWorkers.filter((w) =>
			w.postMessage.mock.calls.some((c) => (c[0] as { type: string })?.type === 'shutdown')
		);
		// Two workers should have received shutdown
		expect(shutdownWorkers.length).toBeGreaterThanOrEqual(2);
	});

	// -------------------------------------------------------------------------
	// shutdown
	// -------------------------------------------------------------------------

	it('sends "shutdown" to all workers on pool.shutdown()', () => {
		const opts = makeOpts({ concurrency: 2 });
		const pool = new WorkerPool(opts);

		// Don't await — shutdown() is async but the postMessage calls happen synchronously
		void pool.shutdown();

		for (const worker of createdWorkers) {
			const hasShutdown = worker.postMessage.mock.calls.some(
				(c) => (c[0] as { type: string })?.type === 'shutdown'
			);
			expect(hasShutdown).toBe(true);
		}
	});

	// -------------------------------------------------------------------------
	// Enqueue after shutdown is a no-op
	// -------------------------------------------------------------------------

	it('ignores enqueue calls after shutdown is initiated', () => {
		const opts = makeOpts({ concurrency: 1 });
		const pool = new WorkerPool(opts);

		// Don't await — shutdown() sets shuttingDown=true synchronously
		void pool.shutdown();

		// Reset postMessage mocks to isolate post-shutdown calls
		for (const w of createdWorkers) w.postMessage.mockClear();

		pool.enqueue('job-late', '/repo/1');

		const runCalls = createdWorkers.flatMap((w) =>
			w.postMessage.mock.calls.filter((c) => (c[0] as { type: string })?.type === 'run')
		);
		expect(runCalls).toHaveLength(0);
	});
});