apps/api/src/services/ai/ffmpeg.ts

import { exec } from 'child_process';
import { promisify } from 'util';
import { writeFile, readFile, unlink } from 'fs/promises';
import { join } from 'path';
import { randomBytes } from 'crypto';

const execAsync = promisify(exec);

/**
 * Converts an audio buffer to MP3 using local FFmpeg if the file is OGG/OPUS.
 * This ensures compatibility with OpenAI Whisper, which frequently rejects native WhatsApp OPUS files.
 * Returns the original buffer if ffmpeg fails or isn't installed to attempt best-effort transcription.
 */
export async function convertToMp3IfNeeded(inputBuffer: Buffer, filename: string): Promise<{ buffer: Buffer; format: string }> {
    // We only strictly convert OGG or OPUS files (which are typical for WhatsApp).
    // If it's already an MP4/AAC or M4A, Whisper usually accepts it fine.
    if (!filename.toLowerCase().endsWith('.ogg') && !filename.toLowerCase().endsWith('.opus') && !filename.toLowerCase().endsWith('.oga')) {
        return { buffer: inputBuffer, format: filename.split('.').pop()! };
    }

    const tempId = randomBytes(8).toString('hex');
    const inputPath = join('/tmp', `in_${tempId}_${filename}`);
    const outputPath = join('/tmp', `out_${tempId}.mp3`);

    try {
        console.log(`[FFMPEG] Starting conversion for ${filename}...`);

        // Write the inbound buffer to a temp file
        await writeFile(inputPath, inputBuffer);

        // Run FFmpeg to convert it to a standard 128k MP3
        // -y overwrites without prompting
        // -i specifies input file
        // -vn disables video just in case
        // -ar sets audio sample rate
        // -ac sets channels to mono (perfect for voice)
        // -b:a sets audio bitrate to 64k (sufficient for voice, saves bandwidth)
        await execAsync(`ffmpeg -y -i "${inputPath}" -vn -ar 44100 -ac 1 -b:a 64k "${outputPath}"`);

        // Read the converted file back into a buffer
        const mp3Buffer = await readFile(outputPath);
        console.log(`[FFMPEG] ✅ Successfully converted ${filename} to MP3.`);

        return { buffer: mp3Buffer, format: 'mp3' };

    } catch (err: unknown) {
        console.error(`[FFMPEG] ⚠️ Conversion failed for ${filename}. Proceeding with original buffer. Error: ${(err instanceof Error ? (err instanceof Error ? err.message : String(err)) : String(err))}`);
        // If FFMPEG isn't installed or fails, we return the original buffer
        return { buffer: inputBuffer, format: filename.split('.').pop()! };
    } finally {
        // Cleanup temp files asynchronously
        unlink(inputPath).catch(() => { });
        unlink(outputPath).catch(() => { });
    }
}