/*************************************************************
 *
 *  Copyright (c) 2017 The MathJax Consortium
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

/**
 * @fileoverview  Implements a list sorted by a numeric priority
 *
 * @author dpvc@mathjax.org (Davide Cervone)
 */

/*****************************************************************/
/**
 *  The PrioritizedListItem<DataClass> interface
 *
 * @template DataClass   The class of data stored in the item
 */

export interface PrioritizedListItem<DataClass> {

    /**
     * The priority of this item
     */
    priority: number;

    /**
     * The data for the list item
     */
    item: DataClass;
}

/*****************************************************************/
/**
 *  Implements the PrioritizedList<DataClass> class
 *
 * @template DataClass   The class of data stored in the list
 */

export class PrioritizedList<DataClass> {

    /**
     * The default priority for items added to the list
     */
    public static DEFAULTPRIORITY: number = 5;

    /**
     * The list of items, sorted by priority (smallest number first)
     */
    protected items: PrioritizedListItem<DataClass>[] = [];

    /**
     * @constructor
     */
    constructor() {
        this.items = [];
    }

    /**
     * Make the list iterable, and return the data for the items in the list
     *
     * @return {{next: Function}}  The object containing the iterator's next() function
     */
    public [Symbol.iterator](): Iterator<PrioritizedListItem<DataClass>> {
        let i = 0;
        let items = this.items;
        return {
            next(): IteratorResult<PrioritizedListItem<DataClass>> {
                return {value: items[i++], done: (i > items.length)};
            }
        };
    }

    /**
     * Add an item to the list
     *
     * @param {DataClass} item   The data for the item to be added
     * @param {number} priority  The priority for the item
     * @return {DataClass}       The data itself
     */
    public add(item: DataClass, priority: number = PrioritizedList.DEFAULTPRIORITY) {
        let i = this.items.length;
        do {
            i--;
        } while (i >= 0 && priority < this.items[i].priority);
        this.items.splice(i + 1, 0, {item: item, priority: priority});
        return item;
    }

    /**
     * Remove an item from the list
     *
     * @param {DataClass} item   The data for the item to be removed
     */
    public remove(item: DataClass) {
        let i = this.items.length;
        do {
            i--;
        } while (i >= 0 && this.items[i].item !== item);
        if (i >= 0) {
            this.items.splice(i, 1);
        }
    }

    /**
     * Typescript < 2.3 targeted at ES5 doesn't handle
     *
     *     for (const x of this) {...}
     *
     * so use toArray() to convert to array, when needed
     *
     * @return {PrioritizedListItem<DataClass>[]}  The list converted to an array
     */
    public toArray() {
        return Array.from(this);
    }

}