/* global RTCRtpScriptTransform */

import { getLogger } from '@jitsi/logger';

const logger = getLogger(__filename);

// Flag to set on senders / receivers to avoid setting up the encryption transform
// more than once.
const kJitsiE2EE = Symbol('kJitsiE2EE');

/**
 * Context encapsulating the cryptography bits required for E2EE.
 * This uses the WebRTC Insertable Streams API which is explained in
 *   https://github.com/alvestrand/webrtc-media-streams/blob/master/explainer.md
 * that provides access to the encoded frames and allows them to be transformed.
 *
 * The encoded frame format is explained below in the _encodeFunction method.
 * High level design goals were:
 * - do not require changes to existing SFUs and retain (VP8) metadata.
 * - allow the SFU to rewrite SSRCs, timestamp, pictureId.
 * - allow for the key to be rotated frequently.
 */
export default class E2EEcontext {
    /**
     * Build a new E2EE context instance, which will be used in a given conference.
     * @param {boolean} [options.sharedKey] - whether there is a uniques key shared amoung all participants.
     */
    constructor({ sharedKey } = {}) {
        // Determine the URL for the worker script. Relative URLs are relative to
        // the entry point, not the script that launches the worker.
        let baseUrl = '';
        const ljm = document.querySelector('script[src*="lib-jitsi-meet"]');

        if (ljm) {
            const idx = ljm.src.lastIndexOf('/');

            baseUrl = `${ljm.src.substring(0, idx)}/`;
        }

        let workerUrl = `${baseUrl}lib-jitsi-meet.e2ee-worker.js`;

        // If there is no baseUrl then we create the worker in a normal way
        // as you cant load scripts inside blobs from relative paths.
        // See: https://www.html5rocks.com/en/tutorials/workers/basics/#toc-inlineworkers-loadingscripts
        if (baseUrl && baseUrl !== '/') {
            // Initialize the E2EE worker. In order to avoid CORS issues, start the worker and have it
            // synchronously load the JS.
            const workerBlob
                = new Blob([ `importScripts("${workerUrl}");` ], { type: 'application/javascript' });

            workerUrl = window.URL.createObjectURL(workerBlob);
        }

        this._worker = new Worker(workerUrl, { name: 'E2EE Worker' });

        this._worker.onerror = e => logger.error(e);

        this._worker.postMessage({
            operation: 'initialize',
            sharedKey
        });
    }

    /**
     * Cleans up all state associated with the given participant. This is needed when a
     * participant leaves the current conference.
     *
     * @param {string} participantId - The participant that just left.
     */
    cleanup(participantId) {
        this._worker.postMessage({
            operation: 'cleanup',
            participantId
        });
    }

    /**
     * Cleans up all state associated with all participants in the conference. This is needed when disabling e2ee.
     *
     */
    cleanupAll() {
        this._worker.postMessage({
            operation: 'cleanupAll'
        });
    }

    /**
     * Handles the given {@code RTCRtpReceiver} by creating a {@code TransformStream} which will inject
     * a frame decoder.
     *
     * @param {RTCRtpReceiver} receiver - The receiver which will get the decoding function injected.
     * @param {string} kind - The kind of track this receiver belongs to.
     * @param {string} participantId - The participant id that this receiver belongs to.
     */
    handleReceiver(receiver, kind, participantId) {
        if (receiver[kJitsiE2EE]) {
            return;
        }
        receiver[kJitsiE2EE] = true;

        if (window.RTCRtpScriptTransform) {
            const options = {
                operation: 'decode',
                participantId
            };

            receiver.transform = new RTCRtpScriptTransform(this._worker, options);
        } else {
            const receiverStreams = receiver.createEncodedStreams();

            this._worker.postMessage({
                operation: 'decode',
                readableStream: receiverStreams.readable,
                writableStream: receiverStreams.writable,
                participantId
            }, [ receiverStreams.readable, receiverStreams.writable ]);
        }
    }

    /**
     * Handles the given {@code RTCRtpSender} by creating a {@code TransformStream} which will inject
     * a frame encoder.
     *
     * @param {RTCRtpSender} sender - The sender which will get the encoding function injected.
     * @param {string} kind - The kind of track this sender belongs to.
     * @param {string} participantId - The participant id that this sender belongs to.
     */
    handleSender(sender, kind, participantId) {
        if (sender[kJitsiE2EE]) {
            return;
        }
        sender[kJitsiE2EE] = true;

        if (window.RTCRtpScriptTransform) {
            const options = {
                operation: 'encode',
                participantId
            };

            sender.transform = new RTCRtpScriptTransform(this._worker, options);
        } else {
            const senderStreams = sender.createEncodedStreams();

            this._worker.postMessage({
                operation: 'encode',
                readableStream: senderStreams.readable,
                writableStream: senderStreams.writable,
                participantId
            }, [ senderStreams.readable, senderStreams.writable ]);
        }
    }

    /**
     * Set the E2EE key for the specified participant.
     *
     * @param {string} participantId - the ID of the participant who's key we are setting.
     * @param {Uint8Array | boolean} key - they key for the given participant.
     * @param {Number} keyIndex - the key index.
     */
    setKey(participantId, key, keyIndex) {
        this._worker.postMessage({
            operation: 'setKey',
            key,
            keyIndex,
            participantId
        });
    }
}