tonemark/src/lib/server/audio.ts

import { execFile } from 'child_process';
import { promisify } from 'util';
import { existsSync } from 'fs';
import { mkdir, unlink, rename } from 'fs/promises';
import { join } from 'path';
import { DATA_DIR } from './data-dir.js';
import type { AudioMode, AudioAnalysis } from '$lib/types.js';

const execFileAsync = promisify(execFile);

const TMP_DIR = join(DATA_DIR, 'audio');

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

export function tmpPath(jobId: string, suffix: string) {
	return join(TMP_DIR, `${jobId}${suffix}`);
}

export async function cleanup(...paths: string[]) {
	await Promise.allSettled(paths.map((p) => unlink(p).catch(() => {})));
}

/** Run ffmpeg volumedetect and return mean/max dB. */
export async function analyzeVolume(inputPath: string): Promise<AudioAnalysis> {
	const { stderr } = await execFileAsync('ffmpeg', [
		'-i', inputPath,
		'-af', 'volumedetect',
		'-vn', '-sn', '-dn',
		'-f', 'null', '-'
	]);
	const meanMatch = stderr.match(/mean_volume:\s*([-\d.]+)\s*dB/);
	const maxMatch = stderr.match(/max_volume:\s*([-\d.]+)\s*dB/);
	return {
		meanVolume: meanMatch ? parseFloat(meanMatch[1]) : -99,
		maxVolume: maxMatch ? parseFloat(maxMatch[1]) : -99
	};
}

/**
 * Detect leading silence duration (ms).
 * Only trims if silence begins at/near time 0 (< 0.5s).
 * Capped at 30s to prevent accidental over-trimming.
 */
async function detectLeadingSilenceMs(inputPath: string): Promise<number> {
	try {
		const { stderr } = await execFileAsync('ffmpeg', [
			'-i', inputPath,
			'-af', 'silencedetect=n=-40dB:d=0.1',
			'-vn', '-sn', '-dn',
			'-f', 'null', '-'
		]);
		const startMatch = stderr.match(/silence_start:\s*([\d.]+)/);
		const endMatch = stderr.match(/silence_end:\s*([\d.]+)/);
		// Only trim if silence genuinely starts at the very beginning of the file
		if (startMatch && endMatch && parseFloat(startMatch[1]) < 0.5) {
			return Math.min(Math.floor(parseFloat(endMatch[1]) * 1000), 30_000);
		}
	} catch {
		// ignore
	}
	return 0;
}

/** Build ffmpeg -af filter chain for the given mode and mean volume. */
export function buildFilterChain(mode: AudioMode, meanVolume: number): string | null {
	const isQuiet = meanVolume < -30;

	switch (mode) {
		case 'none':
			return null;

		case 'standard':
			return 'highpass=f=80,lowpass=f=8000,loudnorm=I=-16:LRA=11:TP=-1.5';

		case 'aggressive':
			return [
				'highpass=f=80',
				isQuiet ? 'volume=24dB,dynaudnorm=f=500:g=15' : null,
				'lowpass=f=8000',
				'afftdn=nf=-30',
				'agate=threshold=0.01:attack=5:release=50',
				'loudnorm=I=-16:LRA=11:TP=-1.5'
			]
				.filter(Boolean)
				.join(',');

		case 'auto':
		default:
			if (isQuiet) {
				return [
					'highpass=f=80',
					'volume=24dB',
					'dynaudnorm=f=500:g=15',
					'lowpass=f=8000',
					'afftdn=nf=-25',
					'loudnorm=I=-16:LRA=11:TP=-1.5'
				].join(',');
			}
			return 'highpass=f=80,lowpass=f=8000,loudnorm=I=-16:LRA=11:TP=-1.5';
	}
}

/**
 * Prepare audio for Whisper: convert to 16kHz mono WAV, trim leading silence,
 * apply the appropriate filter chain.
 * Returns path to the prepared WAV file.
 */
export async function prepareAudio(
	inputPath: string,
	jobId: string,
	mode: AudioMode
): Promise<{ wavPath: string; analysis: AudioAnalysis }> {
	await ensureTmpDir();

	// Step 1: analyse volume on the original file
	const analysis = await analyzeVolume(inputPath);

	// Step 2: detect leading silence
	const silenceMs = await detectLeadingSilenceMs(inputPath);

	const wavPath = tmpPath(jobId, '.wav');
	const filterChain = buildFilterChain(mode, analysis.meanVolume);

	const args: string[] = ['-y'];

	// Trim leading silence
	if (silenceMs > 0) {
		args.push('-ss', (silenceMs / 1000).toFixed(3));
	}

	args.push('-i', inputPath, '-ar', '16000', '-ac', '1');

	if (filterChain) {
		args.push('-af', filterChain);
	}

	args.push('-c:a', 'pcm_s16le', wavPath);

	await execFileAsync('ffmpeg', args);
	return { wavPath, analysis };
}

/** Move a file to a new path (cross-device safe). */
export async function moveFile(src: string, dest: string) {
	try {
		await rename(src, dest);
	} catch {
		const { copyFile } = await import('fs/promises');
		await copyFile(src, dest);
		await unlink(src);
	}
}