import { once } from "events";
import { Socket } from "net";
import { Readable } from "stream";
import { readLength } from "./read-length";

export interface StreamParser {
    container: string;
    outputArguments: string[];
    parse: (socket: Socket) => AsyncGenerator<StreamChunk>;
}

export interface StreamParserOptions {
    acodec?: string[];
    vcodec?: string[];
}

export interface StreamChunk {
    startStream?: Buffer;
    chunk: Buffer;
    type?: string;
}

export function createMpegTsParser(options?: StreamParserOptions): StreamParser {
    return {
        container: 'mpegts',
        outputArguments: [
            '-f', 'mpegts',
            ...(options?.vcodec || []),
            ...(options?.acodec || []),
        ],
        async *parse(socket: Socket): AsyncGenerator<StreamChunk> {
            let pending: Buffer[] = [];
            let pendingSize = 0;
            while (true) {
                const data: Buffer = socket.read();
                if (!data) {
                    await once(socket, 'readable');
                    continue;
                }
                pending.push(data);
                pendingSize += data.length;
                if (pendingSize < 188)
                    continue;

                const concat = Buffer.concat(pending);

                if (concat[0] != 0x47) {
                    throw new Error('Invalid sync byte in mpeg-ts packet. Terminating stream.')
                }

                const remaining = concat.length % 188;
                const left = concat.slice(0, concat.length - remaining);
                const right = concat.slice(concat.length - remaining);
                pending = [right];
                pendingSize = right.length;
                yield {
                    chunk: left,
                };
            }
        }
    }
}

export interface MP4Atom {
    header: Buffer;
    length: number;
    type: string;
    data: Buffer;
}

export async function* parseFragmentedMP4(readable: Readable): AsyncGenerator<MP4Atom> {
    while (true) {
        const header = await readLength(readable, 8);
        const length = header.readInt32BE(0) - 8;
        const type = header.slice(4).toString();
        const data = await readLength(readable, length);

        yield {
            header,
            length,
            type,
            data,
        };
    }
}

export function createFragmentedMp4Parser(options?: StreamParserOptions): StreamParser {
    return {
        container: 'mp4',
        outputArguments: [
            '-f', 'mp4',
            ...(options?.vcodec || []),
            ...(options?.acodec || []),
            '-movflags', 'frag_keyframe+empty_moov+default_base_moof',
        ],
        async *parse(socket: Socket): AsyncGenerator<StreamChunk> {
            const parser = parseFragmentedMP4(socket);
            let ftyp: MP4Atom;
            let moov: MP4Atom;
            let startStream: Buffer;
            for await (const atom of parser) {
                if (!ftyp) {
                    ftyp = atom;
                }
                else if (!moov) {
                    moov = atom;
                }

                yield{
                    startStream,
                    chunk: Buffer.concat([atom.header, atom.data]),
                    type: atom.type,
                };

                if (ftyp && moov && !startStream) {
                    startStream = Buffer.concat([ftyp.header, ftyp.data, moov.header, moov.data])
                }
            }
        }
    }
}