tonemark/src/lib/server/downloader.ts

import { execFile } from 'child_process';
import { promisify } from 'util';
import { existsSync } from 'fs';
import { mkdir, writeFile } from 'fs/promises';
import { join } from 'path';
import { fetchTranscript, type TranscriptResponse } from 'youtube-transcript';

const execFileAsync = promisify(execFile);
const DATA_DIR = process.env.DATA_DIR ?? '/tmp/.whisper-pwa';
const TMP_DIR = join(DATA_DIR, 'downloads');
const UPLOADS_DIR = join(DATA_DIR, 'uploads');

export async function ensureTmpDir() {
	if (!existsSync(TMP_DIR)) await mkdir(TMP_DIR, { recursive: true });
}

async function ensureUploadsDir(jobId: string): Promise<string> {
	const dir = join(UPLOADS_DIR, jobId);
	if (!existsSync(dir)) await mkdir(dir, { recursive: true });
	return dir;
}

/** Path to a job's persistent upload file. Survives cleanupJobTmp. */
export function getUploadPath(jobId: string, filename: string): string {
	return join(UPLOADS_DIR, jobId, filename);
}

/** Delete a job's persistent upload dir (call on success). */
export async function cleanupUploadDir(jobId: string): Promise<void> {
	const dir = join(UPLOADS_DIR, jobId);
	try {
		const { rm } = await import('fs/promises');
		await rm(dir, { recursive: true, force: true });
	} catch { /* ignore */ }
}

export interface CaptionResult {
	type: 'captions';
	segments: Array<{ index: number; start: number; end: number; text: string; words: [] }>;
	title: string;
}

export interface AudioResult {
	type: 'audio';
	audioPath: string;
	title: string;
}

export type DownloadResult = CaptionResult | AudioResult;

/** Try to get auto-generated captions from YouTube. Returns null if unavailable. */
async function tryGetCaptions(url: string, _outDir: string): Promise<CaptionResult | null> {
	try {
		const transcript = await fetchTranscript(url, { lang: 'en' });
		const segments = transcriptEntriesToSegments(transcript);
		const title = await getYouTubeTitle(url);
		return { type: 'captions', segments, title };
	} catch {
		return null;
	}
}

async function getYouTubeTitle(url: string): Promise<string> {
	try {
		const { stdout } = await execFileAsync('yt-dlp', [
			'--dump-single-json',
			'--skip-download',
			'--no-playlist',
			url
		]);
		return JSON.parse(stdout).title ?? 'Untitled';
	} catch {
		return 'Untitled';
	}
}

/** Download best audio from YouTube. Returns path to audio file. */
async function downloadAudio(url: string, outDir: string): Promise<{ audioPath: string; title: string }> {
	await execFileAsync('yt-dlp', [
		'-f', 'bestaudio',
		'--write-info-json',
		'--no-playlist',
		'-o', join(outDir, 'audio.%(ext)s'),
		url
	]);

	const { readdirSync, readFileSync } = await import('fs');
	const files = readdirSync(outDir);
	const audioFile = files.find((f) => f.startsWith('audio.') && !f.endsWith('.json'));
	if (!audioFile) throw new Error('yt-dlp did not produce an audio file');

	let title = 'Untitled';
	const jsonFile = files.find((f) => f.endsWith('.info.json'));
	if (jsonFile) {
		try {
			title = JSON.parse(readFileSync(join(outDir, jsonFile), 'utf8')).title ?? title;
		} catch { /* ignore */ }
	}

	return { audioPath: join(outDir, audioFile), title };
}

/** Download a YouTube URL: try captions first, fall back to audio. */
export async function downloadYouTube(url: string, jobId: string): Promise<DownloadResult> {
	await ensureTmpDir();
	const outDir = join(TMP_DIR, jobId);
	await mkdir(outDir, { recursive: true });

	const captions = await tryGetCaptions(url, outDir);
	if (captions && captions.segments.length > 0) return captions;

	const { audioPath, title } = await downloadAudio(url, outDir);
	return { type: 'audio', audioPath, title };
}

/** Save an uploaded file to persistent storage (survives cleanupJobTmp). */
export async function saveUploadedFile(
	buffer: Buffer,
	filename: string,
	jobId: string
): Promise<string> {
	const outDir = await ensureUploadsDir(jobId);
	const dest = join(outDir, filename);
	await writeFile(dest, buffer);
	return dest;
}

export async function cleanupJobTmp(jobId: string) {
	const outDir = join(TMP_DIR, jobId);
	try {
		const { rm } = await import('fs/promises');
		await rm(outDir, { recursive: true, force: true });
	} catch { /* ignore */ }
}

export function transcriptEntriesToSegments(
	entries: TranscriptResponse[]
): Array<{ index: number; start: number; end: number; text: string; words: [] }> {
	const useMilliseconds = entries.some((entry) => entry.offset > 1000 || entry.duration > 1000);
	return entries
		.map((entry) => {
			const start = useMilliseconds ? entry.offset / 1000 : entry.offset;
			const duration = useMilliseconds ? entry.duration / 1000 : entry.duration;
			return {
				index: 0,
				start,
				end: start + duration,
				text: entry.text.trim(),
				words: [] as []
			};
		})
		.filter((entry) => entry.text.length > 0)
		.map((entry, index) => ({ ...entry, index }));
}