/*
This Transport layers builds on WebTorrent

Y Lists have listeners and generate events - see docs at ...
*/

// WebTorrent components

//Require in consumer;
//const WebTorrent = require('webtorrent');
const stream = require('readable-stream');
const Url = require('url');
const path = require('path');
const debug = require('debug')('dweb-transports:webtorrent');

// Other Dweb modules
const errors = require('./Errors'); // Standard Dweb Errors
const Transport = require('./Transport.js'); // Base class for TransportXyz
const Transports = require('./Transports'); // Manage all Transports that are loaded

let defaultoptions = {
};

class TransportWEBTORRENT extends Transport {
    /*
    WebTorrent specific transport

    Fields:
    webtorrent: object returned when starting webtorrent
     */

    constructor(options) {
        super(options);
        this.webtorrent = undefined;    // Undefined till start WebTorrent
        this.options = options;         // Dictionary of options
        this.name = "WEBTORRENT";       // For console log etc
        this.supportURLs = ['magnet'];
        this.supportFunctions = ['fetch', 'createReadStream', "seed"];
        this.supportFeatures = ['noCache']; // Note doesnt actually support noCache, but immutable is same
        this.status = Transport.STATUS_LOADED;
    }

    p_webtorrentstart() {
        /*
        Start WebTorrent and wait until for ready.
         */
        let self = this;
        return new Promise((resolve, reject) => {
            this.webtorrent = new WebTorrent(this.options);
            this.webtorrent.once("ready", () => {
                debug("ready");
                resolve();
            });
            this.webtorrent.once("error", (err) => reject(err));
            this.webtorrent.on("warning", (err) => {
                console.warn("WebTorrent Torrent WARNING: " + err.message);
            });
        })
    }

    //TODO-SPLIT define load()

    static setup0(options) {
        /*
        First part of setup, create obj, add to Transports but dont attempt to connect, typically called instead of p_setup if want to parallelize connections.
        */
        let combinedoptions = Transport.mergeoptions(defaultoptions, options.webtorrent);
        debug("setup0: options=%o", combinedoptions);
        let t = new TransportWEBTORRENT(combinedoptions);
        Transports.addtransport(t);

        return t;
    }

    async p_setup1(cb) {
        try {
            this.status = Transport.STATUS_STARTING;
            if (cb) cb(this);
            await this.p_webtorrentstart();
            await this.p_status();
        } catch(err) {
            console.error(this.name, "failed to connect", err.message);
            this.status = Transport.STATUS_FAILED;
        }
        if (cb) cb(this);
        return this;
    }

    stop(refreshstatus, cb) {
        this.webtorrent.destroy((err) => {
            this.status = Transport.STATUS_FAILED;
            if (refreshstatus) refreshstatus(this);
            if (err) {
                debug("Webtorrent error during stopping %o", err);
            } else {
                debug("Webtorrent stopped");
            }
            cb(err, this);
        });
    }

    async p_status() {
        /*
        Return a string for the status of a transport. No particular format, but keep it short as it will probably be in a small area of the screen.
         */
        if (this.webtorrent && this.webtorrent.ready) {
            this.status = Transport.STATUS_CONNECTED;
        } else if (this.webtorrent) {
            this.status = Transport.STATUS_STARTING;
        } else {
            this.status = Transport.STATUS_FAILED;
        }
        return super.p_status();
    }

    webtorrentparseurl(url) {
        /* Parse a URL
        url:    URL as string or already parsed into Url - should start magnet: or in future might support dweb:/magnet/; some other formats might be supported
        returns:    torrentid, path
         */
        if (!url) {
            throw new errors.CodingError("TransportWEBTORRENT.p_rawfetch: requires url");
        }

        const urlstring = (typeof url === "string" ? url : url.href);
        const index = urlstring.indexOf('/');

        if (index === -1) {
            throw new errors.CodingError("TransportWEBTORRENT.p_rawfetch: invalid url - missing path component. Should look like magnet:xyzabc/path/to/file");
        }

        const torrentId = urlstring.slice(0, index);
        const path = urlstring.slice(index + 1);

        return { torrentId, path }
    }

    async p_webtorrentadd(torrentId, opts) {
        return new Promise((resolve, reject) => {
            // Check if this torrentId is already added to the webtorrent client
            let torrent = this.webtorrent.get(torrentId);

            // If not, then add the torrentId to the torrent client
            if (!torrent) {
                // This can be added in to rewrite a known torrent for example to test a different tracker.
                //let testid = "magnet:?xt=urn:btih:ELHVM7F4VEOTZQFDHCX7OZXUXKINUIPJ&tr=http%3A%2F%2Fbt1.archive.org%3A6969%2Fannounce&tr=http%3A%2F%2Fbt2.archive.org%3A6969%2Fannounce&tr=wss%3A%2F%2Ftracker.btorrent.xyz&tr=wss%3A%2F%2Ftracker.openwebtorrent.com&tr=wss%3A%2F%2Ftracker.fastcast.nz&ws=https%3A%2F%2Fdweb.me%2Farc%2Farchive.org%2Fdownload%2F&xs=https%3A%2F%2Fdweb.me%2Farc%2Farchive.org%2Ftorrent%2Fcommute";
                //let testidnewtrack = "magnet:?xt=urn:btih:ELHVM7F4VEOTZQFDHCX7OZXUXKINUIPJ&tr=http%3A%2F%2Fbt1.archive.org%3A6969%2Fannounce&tr=http%3A%2F%2Fbt2.archive.org%3A6969%2Fannounce&tr=wss%3A%2F%2Fdweb.archive.org:6969&ws=https%3A%2F%2Fdweb.me%2Farc%2Farchive.org%2Fdownload%2F&xs=https%3A%2F%2Fdweb.me%2Farc%2Farchive.org%2Ftorrent%2Fcommute";
                //if (torrentId === testid) torrentId = testidnewtrack;
                torrent = this.webtorrent.add(torrentId, opts);

                torrent.once("error", (err) => {
                    reject(new errors.TransportError("Torrent encountered a fatal error " + err.message));
                });

                torrent.on("warning", (err) => {
                    console.warn("WebTorrent Torrent WARNING: " + err.message + " (" + torrent.name + ")");
                });
            }

            if (torrent.ready) {
                resolve(torrent);
            } else {
                torrent.once("ready", () => {
                    resolve(torrent);
                });
            }
        });
    }

    webtorrentfindfile (torrent, path) {
        /*
        Given a torrent object and a path to a file within the torrent, find the given file.
         */
        const filePath = torrent.name + '/' + path;
        const file = torrent.files.find(file => {
            return file.path === filePath;
        });
        if (!file) {
            //debugger;
            throw new errors.TransportError("Requested file (" + path + ") not found within torrent ");
        }
        return file;
    }

    p_rawfetch(url) {
        /*
        Fetch some bytes based on a url of the form:

            magnet:xyzabc/path/to/file

        (Where xyzabc is the typical magnet uri contents)

        No assumption is made about the data in terms of size or structure.         Returns a new Promise that resolves to a buffer.

        :param string url: URL of object being retrieved
        :resolve buffer: Return the object being fetched.
        :throws:        TransportError if url invalid - note this happens immediately, not as a catch in the promise
         */
        return new Promise((resolve, reject) => {
            // Logged by Transports
            const { torrentId, path } = this.webtorrentparseurl(url);
            this.p_webtorrentadd(torrentId)
                .then((torrent) => {
                    torrent.deselect(0, torrent.pieces.length - 1, false); // Dont download entire torrent as will pull just the file we want (warning - may give problems if multiple reads from same webtorrent)
                    const file = this.webtorrentfindfile(torrent, path);
                    file.getBuffer((err, buffer) => {
                        if (err) {
                            return reject(new errors.TransportError("Torrent encountered a fatal error " + err.message + " (" + torrent.name + ")"));
                        }
                        resolve(buffer);
                    });
                })
                .catch((err) => reject(err));
        });
    }

    seed({fileRelativePath, directoryPath, torrentRelativePath }, cb) {
        /* Add a file to webTorrent - this will be called each time a file is cached and adds the torrent to WT handling so its seeding this (and other) files in directory */
        if (!torrentRelativePath) { // If no torrentfile available then just skip WebTorrent, MirrorFS will often seed the file (eg to IPFS) while its fetching the torrent and then seed that.
            cb(null);
        } else {
            const torrentfile = path.join(directoryPath, torrentRelativePath);
            this.p_addTorrentFromTorrentFile(torrentfile, directoryPath)
                .then(res => { debug("Added %s/%s to webtorrent", directoryPath, fileRelativePath); cb(null)})
                .catch(err => {
                    if (err.message.includes("Cannot add duplicate torrent")) { // Ignore silently if already added
                        cb(null);
                    } else {
                        debug("addWebTorrent failed %s/%s", directoryPath, fileRelativePath); cb(err);
                    }
                });
        }
    }

    async _p_fileTorrentFromUrl(url) {
        /*
        Then open a webtorrent for the file specified in the path part of the url
        url:    of form magnet:... or magnet/:...
        return: Web Torrent file
         */
        try {
            const {torrentId, path} = this.webtorrentparseurl(url);
            const torrent = await this.p_webtorrentadd(torrentId);
            torrent.deselect(0, torrent.pieces.length - 1, false); // Dont download entire torrent as will pull just the file we want (warning - may give problems if multiple reads from same webtorrent)
            const file = this.webtorrentfindfile(torrent, path);
            if (typeof window !== "undefined") {   // Check running in browser
                window.WEBTORRENT_TORRENT = torrent;
                window.WEBTORRENT_FILE = file;
                torrent.once('close', () => {
                    window.WEBTORRENT_TORRENT = null;
                    window.WEBTORRENT_FILE = null;
                })
            }
            return file
        } catch(err) {
            // Logged by Transports
            throw(err);
        }

    }

    async p_addTorrentFromTorrentFile(torrentFilePath, filesPath) {
        // TODO-API: doc
        try {
            const opts = { path: filesPath };
            const oldTorrent = this.webtorrent.get(torrentFilePath);
            if (oldTorrent) {
                oldTorrent.rescanFiles();
            } else {
                const torrent = await this.p_webtorrentadd(torrentFilePath, opts);
                torrent.deselect(0, torrent.pieces.length - 1, false); // Dont download entire torrent as will pull just the file we want (warning - may give problems if multiple reads from same webtorrent)
            }
        } catch(err) {
            // Logged by Transports
            throw(err);
        }

    }

    async p_f_createReadStream(url, {wanturl=false}={}) {
        /*
        Fetch bytes progressively, using a node.js readable stream, based on a url of the form:
        No assumption is made about the data in terms of size or structure.

        This is the initialisation step, which returns a function suitable for <VIDEO>

        Returns a new Promise that resolves to function for a node.js readable stream.

        Node.js readable stream docs: https://nodejs.org/api/stream.html#stream_readable_streams

        :param string url: URL of object being retrieved of form  magnet:xyzabc/path/to/file  (Where xyzabc is the typical magnet uri contents)
        :param boolean wanturl True if want the URL of the stream (for service workers)
        :resolves to: f({start, end}) => stream (The readable stream.)
        :throws:        TransportError if url invalid - note this happens immediately, not as a catch in the promise
         */
        // Logged by Transports
        try {
            let filet = await this._p_fileTorrentFromUrl(url);
            let self = this;
            if (wanturl) {
                return url;
            } else {
                return function (opts) { return self.createReadStream(filet, opts); };
            }
        } catch(err) {
            // Logged by Transports
            throw(err);
        }
    }

    createReadStream(file, opts) {
        /*
        The function, encapsulated and inside another function by p_f_createReadStream (see docs)

        :param file:    Webtorrent "file" as returned by webtorrentfindfile
        :param opts: { start: byte to start from; end: optional end byte }
        :returns stream: The readable stream.
         */
        debug("reading from stream %s %o", file.name, opts);
        let through;
        try {
            through = new stream.PassThrough();
            const fileStream = file.createReadStream(opts);
            fileStream.pipe(through);
            return through;
        } catch(err) {
            debug("createReadStream error %s", err);
            if (typeof through.destroy === 'function')
                through.destroy(err);
            else through.emit('error', err)
        }
    }

    async p_createReadableStream(url, opts) {
        //Return a readable stream (suitable for a HTTP response) from a node type stream from webtorrent.
        // This is used by dweb-serviceworker for WebTorrent only
        let filet = await this._p_fileTorrentFromUrl(url);
        return new ReadableStream({
            start (controller) {
                debug("start %s %o", url, opts);
                // Create a webtorrent file stream
                const filestream = filet.createReadStream(opts);
                // When data comes out of webtorrent node.js style stream, put it into the WHATWG stream
                filestream.on('data', value => {
                    controller.enqueue(value)
                });
                filestream.on('end', () => {
                    controller.close()
                })
            },
            cancel (reason) {
                throw new errors.TransportError(`cancelled ${url}, ${opts} ${reason}`);
            }
        });
    }



    static async p_test(opts) {
        try {
            let transport = await this.p_setup(opts); // Assumes IPFS already setup
            console.log(transport.name, "p_test setup", opts, "complete");
            let res = await transport.p_status();
            console.assert(res === Transport.STATUS_CONNECTED);

            // Creative commons torrent, copied from https://webtorrent.io/free-torrents
            let bigBuckBunny = 'magnet:?xt=urn:btih:dd8255ecdc7ca55fb0bbf81323d87062db1f6d1c&dn=Big+Buck+Bunny&tr=udp%3A%2F%2Fexplodie.org%3A6969&tr=udp%3A%2F%2Ftracker.coppersurfer.tk%3A6969&tr=udp%3A%2F%2Ftracker.empire-js.us%3A1337&tr=udp%3A%2F%2Ftracker.leechers-paradise.org%3A6969&tr=udp%3A%2F%2Ftracker.opentrackr.org%3A1337&tr=wss%3A%2F%2Ftracker.btorrent.xyz&tr=wss%3A%2F%2Ftracker.fastcast.nz&tr=wss%3A%2F%2Ftracker.openwebtorrent.com&ws=https%3A%2F%2Fwebtorrent.io%2Ftorrents%2F&xs=https%3A%2F%2Fwebtorrent.io%2Ftorrents%2Fbig-buck-bunny.torrent/Big Buck Bunny.en.srt';

            let data1 = await transport.p_rawfetch(bigBuckBunny);
            data1 = data1.toString();
            assertData(data1);

            const stream = await transport.createReadStream(bigBuckBunny);

            const chunks = [];
            stream.on("data", (chunk) => {
                chunks.push(chunk);
            });
            stream.on("end", () => {
                const data2 = Buffer.concat(chunks).toString();
                assertData(data2);
            });

            function assertData(data) {
                // Test for a string that is contained within the file
                let expectedWithinData = "00:00:02,000 --> 00:00:05,000";

                console.assert(data.indexOf(expectedWithinData) !== -1, "Should fetch 'Big Buck Bunny.en.srt' from the torrent");

                // Test that the length is what we expect
                console.assert(data.length, 129, "'Big Buck Bunny.en.srt' was " + data.length);
            }
        } catch (err) {
            console.log("Exception thrown in", transport.name, "p_test():", err.message);
            throw err;
        }
    }

}
Transports._transportclasses["WEBTORRENT"] = TransportWEBTORRENT;
TransportWEBTORRENT.requires = ['https://cdn.jsdelivr.net/npm/webtorrent@latest/webtorrent.min.js'];

exports = module.exports = TransportWEBTORRENT;