const path = require('path');
const { spawn } = require('child_process');
const { tmpdir } = require('os');
const { unlink, open } = require('fs/promises');
const EventEmitter = require('events');

class PCMStream extends EventEmitter {

    constructor(file, start, format, channels, sampleRate) {
        super();
        this.file = file;
        this.start = start || 0;
        this.discarded = 0;
        this.ffmpeg = {
            format: format || 'pcm_s16le',
            channels: channels || 2,
            sampleRate: sampleRate || 44100
        };
        this.fifo = {};
    }

    async prepare() {
        if (this.file === undefined) {
            throw new Error('cannot prepare pcm stream from an undefined file');
        }
        this.file = path.resolve(this.file);
        await this.#createFifo();
        await this.#spawnFFmpeg();
        await this.#readFifo();
    }

    resume() {
        this.fifo?.stream.on('data', async (data) => {
            if (this.start ===  0 || this.discarded >= this.start) {
                this.emit('data', data);
                return;
            }
            let tmp = data.length + this.discarded;
            if (tmp < this.start) {
                this.discarded = tmp;
                return;
            }
            tmp = this.start - this.discarded;
            this.discarded += tmp;
            data = data.slice(tmp);
            this.emit('data', data);
        });
        this.fifo?.stream?.resume();
    }

    pause() {
        this.fifo?.stream?.pause();
        this.fifo?.stream?.removeAllListeners('data');
    }

    isPaused() {
        return this.fifo?.stream?.isPaused();
    }

    async #spawnFFmpeg() {
        if (this.file === undefined) {
            throw new Error('can not convert an undefined file to pcm');
        }
        const args = [
            '-y',
            '-i',
            this.file,
            '-acodec',
            this.ffmpeg.format,
            '-ac',
            this.ffmpeg.channels,
            '-ar',
            this.ffmpeg.sampleRate,
            '-f',
            's16le',
            this.fifo.file
        ];
        return new Promise((resolve, reject) => {
            this.ffmpeg.process = spawn('ffmpeg', args);
            this.ffmpeg.process.on('spawn', () => {
                logger.debug('successfully spawned process \'ffmpeg\' (args: ' + args + ') for pcm conversion...');
                this.ffmpeg.timestamp = Date.now();
                resolve();
            });
            this.ffmpeg.process.on('error', async (error) => {
                logger.error('encountered an error spawning process \'ffmpeg\' (args: ' + args + ') for pcm conversion: ' + error);
                await this.destroy();
                reject(error);
            });
            this.ffmpeg.process.on('close', async (code, signal) => {
                let msg = 'process \'ffmpeg\' (args: ' + args + ') closed';
                if (code !== undefined) {
                    msg += ' with code \'' + code + '\'';
                } else {
                    msg += ' with signal \'' + signal + '\'';
                }
                msg += ' after ' + (Date.now() - this.ffmpeg.timestamp) + 'ms';
                logger.debug(msg);
                await this.destroy();
                this.emit('close');
            });
        });
    }

    async #createFifo() {
        let fifo = path.join(tmpdir(), 'kannon.fifo');
        try {
            await unlink(fifo);
        } catch (error) {
            logger.debug('theres no fifo file to delete...');
        }
        this.fifo.process = spawn('mkfifo', [fifo]);
        return new Promise((resolve, reject) => {
            this.fifo.process.on('spawn', () => {
                logger.debug('successfully spawned process \'mkfifo\' (args: ' + fifo + ')...');
                this.fifo.file = fifo;
            });
            this.fifo.process.on('error', async (error) => {
                logger.error('encountered an error spawning process \'mkfifo\' (args: \'' + fifo + '\'): ' + error);
                await this.destroy();
                reject(error);
            });
            this.fifo.process.on('close', (code, signal) => {
                let msg = 'process \'mkfifo\' (args: \'' + fifo + '\') closed';
                if (code !== undefined) {
                    msg += ' with code \'' + code + '\'';
                } else {
                    msg += ' with signal ' + signal + '\'';
                }
                logger.debug(msg);
                resolve();
            });
        });
    }

    async #readFifo() {
        if (this.fifo.file === undefined) {
            throw new Error('can not read from undefined fifo file');
        }
        const timestamp = Date.now();
        this.fifo.fd = await open(this.fifo.file);
        this.fifo.stream = this.fifo.fd.createReadStream();
        return new Promise((resolve, reject) => {
            this.fifo.stream.on('error', async (error) => {
                logger.error('encountered an error reading from fifo file \'' + this.fifo + '\': ' + error);
                await this.destroy();
                reject(error);
            });
            this.fifo.stream.on('close', () => {
                logger.debug('read stream for fifo file \'' + this.fifo.file + '\' closed after ' + (Date.now() - timestamp) + 'ms (read ' + this.fifo.stream.bytesRead + ' bytes)');
            });
            this.fifo.stream.on('readable', () => {
                this.fifo.stream.removeAllListeners('readable');
                resolve();
            });
            this.fifo.stream.on('drain', () => {
                logger.warn('FIFO STREAM DRAINED');
            });
        });
    }

    async #deleteFifo() {
        if (this.fifo.file === undefined) {
            return;
        }
        try {
            await unlink(this.fifo.file);
        } catch (error) {
            logger.error('encountered an error deleting the fifo file \'' + this.fifo.file + '\': ' + error);
        }
    }

    async destroy() {
        if (this.ffmpeg.process.killed != true) {
            this.ffmpeg.process.kill();
            this.ffmpeg.process = undefined;
        }
        if (this.fifo.process.killed !== true) {
            this.fifo.process.kill();
            this.fifo.process = undefined;
        }
        if (this.fifo.stream.destroyed !== true) {
            this.fifo.stream.destroy();
            this.fifo.stream = undefined;
        }
        if (this.fifo.fd.closed !== true) {
            this.fifo.fd.close();
            this.fifo.fd = undefined;
        }
        await this.#deleteFifo();
        this.destroyed = true;
    }
}

module.exports = PCMStream;