ruffle/web/js-src/public-api.js

import { Version } from "./version.js";

/**
 * Represents the Ruffle public API.
 * 
 * The public API exists primarily to allow multiple installs of Ruffle on a
 * page (e.g. an extension install and a local one) to cooperate. In an ideal
 * situation, all Ruffle sources on the page install themselves into a single
 * public API, and then the public API picks the newest version by default.
 * 
 * This API *is* versioned, in case we need to upgrade it. However, it must be
 * backwards- and forwards-compatible with all known sources.
 */
export class PublicAPI {
    /**
     * Construct the Ruffle public API.
     * 
     * Do not use this function to negotiate a public API. Instead, use
     * `public_api` to register your Ruffle source with an existing public API
     * if it exists.
     * 
     * Constructing a Public API will also trigger it to initialize Ruffle once
     * the page loads, if the API has not already been superceded.
     * 
     * @param {object} prev What used to be in the public API slot.
     * 
     * This is used to upgrade from a prior version of the public API, or from
     * a user-defined configuration object placed in the public API slot.
     */
    constructor(prev) {
        this.sources = {};
        this.config = {};
        this.invoked = false;
        this.newest_name = false;

        if (prev !== undefined) {
            if (prev.constructor.name === PublicAPI.name) {
                /// We're upgrading from a previous API to a new one.
                this.sources = prev.sources;
                this.config = prev.config;
                this.invoked = prev.invoked;
                this.conflict = prev.conflict;
                this.newest_name = prev.newest_name;

                prev.superceded();
            } else if (prev.constructor === Object && prev.config !== undefined) {
                /// We're the first, install user configuration
                this.config = prev.config;
            } else {
                /// We're the first, but conflicting with someone else.
                this.conflict = prev;
            }
        }

        if (document.readyState === "loading") {
            window.addEventListener("DOMContentLoaded", this.init.bind(this));
        } else {
            window.setTimeout(this.init.bind(this), 0);
        }
    }

    /**
     * The version of the public API.
     * 
     * This allows a page with an old version of the Public API to be upgraded
     * to a new version of the API. The public API is intended to be changed
     * very infrequently, if at all, but this provides an escape mechanism for
     * newer Ruffle sources to upgrade older installations.
     */
    get version() {
        return "0.1.0";
    }

    /**
     * Register a given source with the Ruffle Public API.
     * 
     * @param {string} name The name of the source.
     * @param {object} api The public API object. This must conform to the shape
     * of `SourceAPI`.
     */
    register_source(name, api) {
        this.sources[name] = api;
    }
    
    /**
     * Determine the name of the newest registered source in the Public API.
     * 
     * @returns {(string|bool)} The name of the source, or `false` if no source
     * has yet to be registered.
     */
    newest_source_name() {
        let newest_name = false, newest_version = Version.from_semver("0.0.0");

        for (let k in this.sources) {
            if (this.sources.hasOwnProperty(k)) {
                let k_version = Version.from_semver(this.sources[k].version);
                if (k_version.has_precedence_over(newest_version)) {
                    newest_name = k;
                    newest_version = k_version;
                }
            }
        }

        return newest_name;
    }

    /**
     * Negotiate and start Ruffle.
     * 
     * This function reads the config parameter to determine which polyfills
     * should be enabled. If the configuration parameter is missing, then we
     * use a built-in set of defaults sufficient to fool sites with static
     * content and weak plugin detection.
     */
    init() {
        if (!this.invoked) {
            this.invoked = true;
            this.newest_name = this.newest_source_name();

            if (this.newest_name === false) {
                throw new Error("No registered Ruffle source!");
            }

            let polyfills = this.config.polyfills;
            if (polyfills === undefined) {
                polyfills = ["plugin-detect", "static-content"];
            }
            
            this.sources[this.newest_name].polyfill(polyfills);
        }
    }

    /**
     * Indicates that this version of the public API has been superceded by a
     * newer version.
     * 
     * This should only be called by a newer version of the Public API.
     * Identical versions of the Public API should not supercede older versions
     * of that same API.
     * 
     * Unfortunately, we can't disable polyfills after-the-fact, so this
     * only lets you disable the init event...
     */
    superceded() {
        this.invoked = true;
    }

    /**
     * Join a source into the public API, if it doesn't already exist.
     * 
     * @param {*} prev_ruffle The previous iteration of the Ruffle API.
     * 
     * The `prev_ruffle` param lists the previous object in the RufflePlayer
     * slot. We perform some checks to see if this is a Ruffle public API or a
     * conflicting object. If this is conflicting, then a new public API will
     * be constructed (see the constructor information for what happens to
     * `prev_ruffle`).
     * 
     * Note that Public API upgrades are deliberately not enabled in this
     * version of Ruffle, since there is no Public API to upgrade from.
     * 
     * @param {string|undefined} source_name The name of this particular
     * Ruffle source.
     * 
     * @param {object|undefined} source_api The Ruffle source to add.
     * 
     * If both parameters are provided they will be used to define a new Ruffle
     * source to register with the public API.
     * 
     * @returns {object} The Ruffle Public API.
     */
    static negotiate(prev_ruffle, source_name, source_api) {
        let public_api;
        if (prev_ruffle !== undefined && prev_ruffle.constructor.name == PublicAPI.name) {
            public_api = prev_ruffle;
        } else {
            public_api = new PublicAPI(prev_ruffle);
        }
        
        if (source_name !== undefined && source_api !== undefined) {
            public_api.register_source(source_name, source_api);
        }

        return public_api;
    };
}