import { Worker } from 'node:worker_threads';
import { existsSync } from 'node:fs';
import type { ParseWorkerRequest, ParseWorkerResponse, EmbedWorkerRequest, EmbedWorkerResponse, WorkerInitData } from './worker-types.js';

export interface WorkerPoolOptions {
	concurrency: number;
	workerScript: string;
	embedWorkerScript: string;
	dbPath: string;
	embeddingProfileId?: string;
	onProgress: (jobId: string, msg: ParseWorkerResponse) => void;
	onJobDone: (jobId: string) => void;
	onJobFailed: (jobId: string, error: string) => void;
	onEmbedDone: (jobId: string) => void;
	onEmbedFailed: (jobId: string, error: string) => void;
}

interface QueuedJob {
	jobId: string;
	repositoryId: string;
	versionId?: string | null;
}

interface RunningJob {
	jobId: string;
	repositoryId: string;
}

interface EmbedQueuedJob {
	jobId: string;
	repositoryId: string;
	versionId: string | null;
}

export class WorkerPool {
	private workers: Worker[] = [];
	private idleWorkers: Worker[] = [];
	private embedWorker: Worker | null = null;
	private embedReady = false;
	private jobQueue: QueuedJob[] = [];
	private runningJobs = new Map<Worker, RunningJob>();
	private runningRepoIds = new Set<string>();
	private embedQueue: EmbedQueuedJob[] = [];
	private options: WorkerPoolOptions;
	private fallbackMode = false;
	private shuttingDown = false;

	constructor(options: WorkerPoolOptions) {
		this.options = options;

		// Check if worker script exists
		if (!existsSync(options.workerScript)) {
			console.warn(`Worker script not found at ${options.workerScript}, entering fallback mode`);
			this.fallbackMode = true;
			return;
		}

		// Spawn parse workers
		for (let i = 0; i < options.concurrency; i++) {
			const worker = this.spawnParseWorker();
			this.workers.push(worker);
			this.idleWorkers.push(worker);
		}

		// Optionally spawn embed worker
		if (options.embeddingProfileId && existsSync(options.embedWorkerScript)) {
			this.embedWorker = this.spawnEmbedWorker();
		}
	}

	private spawnParseWorker(): Worker {
		const worker = new Worker(this.options.workerScript, {
			workerData: {
				dbPath: this.options.dbPath
			} satisfies WorkerInitData
		});

		worker.on('message', (msg: ParseWorkerResponse) => this.onWorkerMessage(worker, msg));
		worker.on('exit', (code: number) => this.onWorkerExit(worker, code));

		return worker;
	}

	private spawnEmbedWorker(): Worker {
		const worker = new Worker(this.options.embedWorkerScript, {
			workerData: {
				dbPath: this.options.dbPath,
				embeddingProfileId: this.options.embeddingProfileId
			} satisfies WorkerInitData
		});

		worker.on('message', (msg: EmbedWorkerResponse) => this.onEmbedWorkerMessage(msg));

		return worker;
	}

	public enqueue(jobId: string, repositoryId: string, versionId?: string | null): void {
		if (this.shuttingDown) {
			console.warn('WorkerPool is shutting down, ignoring enqueue request');
			return;
		}

		if (this.fallbackMode) {
			console.warn(`WorkerPool in fallback mode for job ${jobId} - delegating to main thread`);
			return;
		}

		this.jobQueue.push({ jobId, repositoryId, versionId });
		this.dispatch();
	}

	private dispatch(): void {
		while (this.idleWorkers.length > 0 && this.jobQueue.length > 0) {
			// Find first job whose repositoryId is not currently running
			const jobIdx = this.jobQueue.findIndex((j) => !this.runningRepoIds.has(j.repositoryId));

			if (jobIdx === -1) {
				// No eligible job found (all repos have running jobs)
				break;
			}

			const job = this.jobQueue.splice(jobIdx, 1)[0];
			const worker = this.idleWorkers.pop()!;

			this.runningJobs.set(worker, { jobId: job.jobId, repositoryId: job.repositoryId });
			this.runningRepoIds.add(job.repositoryId);

			const msg: ParseWorkerRequest = { type: 'run', jobId: job.jobId };
			worker.postMessage(msg);
		}
	}

	private onWorkerMessage(worker: Worker, msg: ParseWorkerResponse): void {
		if (msg.type === 'progress') {
			this.options.onProgress(msg.jobId, msg);
		} else if (msg.type === 'done') {
			const runningJob = this.runningJobs.get(worker);
			if (runningJob) {
				this.runningJobs.delete(worker);
				this.runningRepoIds.delete(runningJob.repositoryId);
			}
			this.idleWorkers.push(worker);
			this.options.onJobDone(msg.jobId);

			// If embedding configured, enqueue embed request
			if (this.embedWorker && this.options.embeddingProfileId) {
				const runningJobData = runningJob || { jobId: msg.jobId, repositoryId: '' };
				this.enqueueEmbed(msg.jobId, runningJobData.repositoryId, null);
			}

			this.dispatch();
		} else if (msg.type === 'failed') {
			const runningJob = this.runningJobs.get(worker);
			if (runningJob) {
				this.runningJobs.delete(worker);
				this.runningRepoIds.delete(runningJob.repositoryId);
			}
			this.idleWorkers.push(worker);
			this.options.onJobFailed(msg.jobId, msg.error);
			this.dispatch();
		}
	}

	private onWorkerExit(worker: Worker, code: number): void {
		if (this.shuttingDown) {
			return;
		}

		// Remove from idle if present
		const idleIdx = this.idleWorkers.indexOf(worker);
		if (idleIdx !== -1) {
			this.idleWorkers.splice(idleIdx, 1);
		}

		// Check if there's a running job
		const runningJob = this.runningJobs.get(worker);
		if (runningJob && code !== 0) {
			this.runningJobs.delete(worker);
			this.runningRepoIds.delete(runningJob.repositoryId);
			this.options.onJobFailed(runningJob.jobId, `Worker crashed with code ${code}`);
		} else if (runningJob) {
			this.runningJobs.delete(worker);
			this.runningRepoIds.delete(runningJob.repositoryId);
		}

		// Remove from workers array
		const workerIdx = this.workers.indexOf(worker);
		if (workerIdx !== -1) {
			this.workers.splice(workerIdx, 1);
		}

		// Spawn replacement worker if not shutting down and we haven't reached target
		if (!this.shuttingDown && this.workers.length < this.options.concurrency) {
			const newWorker = this.spawnParseWorker();
			this.workers.push(newWorker);
			this.idleWorkers.push(newWorker);
			this.dispatch();
		}
	}

	private onEmbedWorkerMessage(msg: EmbedWorkerResponse): void {
		if (msg.type === 'ready') {
			this.embedReady = true;
			// Process any queued embed requests
			this.processEmbedQueue();
		} else if (msg.type === 'embed-progress') {
			// Progress message - could be tracked but not strictly required
		} else if (msg.type === 'embed-done') {
			this.options.onEmbedDone(msg.jobId);
		} else if (msg.type === 'embed-failed') {
			this.options.onEmbedFailed(msg.jobId, msg.error);
		}
	}

	private processEmbedQueue(): void {
		if (!this.embedWorker || !this.embedReady) {
			return;
		}

		while (this.embedQueue.length > 0) {
			const job = this.embedQueue.shift();
			if (job) {
				const msg: EmbedWorkerRequest = {
					type: 'embed',
					jobId: job.jobId,
					repositoryId: job.repositoryId,
					versionId: job.versionId
				};
				this.embedWorker.postMessage(msg);
			}
		}
	}

	public enqueueEmbed(jobId: string, repositoryId: string, versionId: string | null): void {
		if (!this.embedWorker) {
			return; // no-op if embedding not configured
		}

		if (this.embedReady) {
			const msg: EmbedWorkerRequest = {
				type: 'embed',
				jobId,
				repositoryId,
				versionId
			};
			this.embedWorker.postMessage(msg);
		} else {
			this.embedQueue.push({ jobId, repositoryId, versionId });
		}
	}

	public setMaxConcurrency(n: number): void {
		const current = this.workers.length;

		if (n > current) {
			// Spawn additional workers
			for (let i = current; i < n; i++) {
				const worker = this.spawnParseWorker();
				this.workers.push(worker);
				this.idleWorkers.push(worker);
			}
		} else if (n < current) {
			// Shut down excess idle workers
			const excess = current - n;
			for (let i = 0; i < excess; i++) {
				if (this.idleWorkers.length > 0) {
					const worker = this.idleWorkers.pop()!;
					const workerIdx = this.workers.indexOf(worker);
					if (workerIdx !== -1) {
						this.workers.splice(workerIdx, 1);
					}
					const msg: ParseWorkerRequest = { type: 'shutdown' };
					worker.postMessage(msg);
				}
			}
		}
	}

	public async shutdown(): Promise<void> {
		this.shuttingDown = true;

		const msg: ParseWorkerRequest = { type: 'shutdown' };

		// Send shutdown to all parse workers
		for (const worker of this.workers) {
			try {
				worker.postMessage(msg);
			} catch {
				// Worker might already be exited
			}
		}

		// Send shutdown to embed worker if exists
		if (this.embedWorker) {
			try {
				const embedMsg: EmbedWorkerRequest = { type: 'shutdown' };
				this.embedWorker.postMessage(embedMsg);
			} catch {
				// Worker might already be exited
			}
		}

		// Wait for workers to exit with timeout
		const timeout = 5000;
		const startTime = Date.now();

		const checkAllExited = (): boolean => {
			return this.workers.length === 0 && (!this.embedWorker || !this.embedWorker.threadId);
		};

		while (!checkAllExited() && Date.now() - startTime < timeout) {
			await new Promise((resolve) => setTimeout(resolve, 100));
		}

		// Force kill any remaining workers
		for (const worker of this.workers) {
			try {
				worker.terminate();
			} catch {
				// Already terminated
			}
		}

		if (this.embedWorker) {
			try {
				this.embedWorker.terminate();
			} catch {
				// Already terminated
			}
		}

		this.workers = [];
		this.idleWorkers = [];
		this.embedWorker = null;
	}

	public get isFallbackMode(): boolean {
		return this.fallbackMode;
	}
}