1 files changed, 105 insertions, 0 deletions
diff --git a/ext/js/core/event-dispatcher.js b/ext/js/core/event-dispatcher.js
new file mode 100644
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+++ b/ext/js/core/event-dispatcher.js
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+/*
+ * Copyright (C) 2023-2024  Yomitan Authors
+ * Copyright (C) 2019-2022  Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ * The following typedef is required because the JSDoc `implements` tag doesn't work with `import()`.
+ * https://github.com/microsoft/TypeScript/issues/49905
+ * @typedef {import('core').EventDispatcherOffGeneric} EventDispatcherOffGeneric
+ */
+
+/**
+ * Base class controls basic event dispatching.
+ * @template {import('core').EventSurface} TSurface
+ * @implements {EventDispatcherOffGeneric}
+ */
+export class EventDispatcher {
+    /**
+     * Creates a new instance.
+     */
+    constructor() {
+        /** @type {Map<import('core').EventNames<TSurface>, import('core').EventHandlerAny[]>} */
+        this._eventMap = new Map();
+    }
+
+    /**
+     * Triggers an event with the given name and specified argument.
+     * @template {import('core').EventNames<TSurface>} TName
+     * @param {TName} eventName The string representing the event's name.
+     * @param {import('core').EventArgument<TSurface, TName>} details The argument passed to the callback functions.
+     * @returns {boolean} `true` if any callbacks were registered, `false` otherwise.
+     */
+    trigger(eventName, details) {
+        const callbacks = this._eventMap.get(eventName);
+        if (typeof callbacks === 'undefined') { return false; }
+
+        for (const callback of callbacks) {
+            callback(details);
+        }
+        return true;
+    }
+
+    /**
+     * Adds a single event listener to a specific event.
+     * @template {import('core').EventNames<TSurface>} TName
+     * @param {TName} eventName The string representing the event's name.
+     * @param {import('core').EventHandler<TSurface, TName>} callback The event listener callback to add.
+     */
+    on(eventName, callback) {
+        let callbacks = this._eventMap.get(eventName);
+        if (typeof callbacks === 'undefined') {
+            callbacks = [];
+            this._eventMap.set(eventName, callbacks);
+        }
+        callbacks.push(callback);
+    }
+
+    /**
+     * Removes a single event listener from a specific event.
+     * @template {import('core').EventNames<TSurface>} TName
+     * @param {TName} eventName The string representing the event's name.
+     * @param {import('core').EventHandler<TSurface, TName>} callback The event listener callback to add.
+     * @returns {boolean} `true` if the callback was removed, `false` otherwise.
+     */
+    off(eventName, callback) {
+        const callbacks = this._eventMap.get(eventName);
+        if (typeof callbacks === 'undefined') { return false; }
+
+        const ii = callbacks.length;
+        for (let i = 0; i < ii; ++i) {
+            if (callbacks[i] === callback) {
+                callbacks.splice(i, 1);
+                if (callbacks.length === 0) {
+                    this._eventMap.delete(eventName);
+                }
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Checks if an event has any listeners.
+     * @template {import('core').EventNames<TSurface>} TName
+     * @param {TName} eventName The string representing the event's name.
+     * @returns {boolean} `true` if the event has listeners, `false` otherwise.
+     */
+    hasListeners(eventName) {
+        const callbacks = this._eventMap.get(eventName);
+        return (typeof callbacks !== 'undefined' && callbacks.length > 0);
+    }
+}