ringbuffer.js

/*                                 ISC License
 *
 * Copyright (c) 2016-2020, Erayd LTD
 *
 * Permission to use, copy, modify, and/or distribute this software for any purpose
 * with or without fee is hereby granted, provided that the above copyright notice
 * and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT,
 * OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
 * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

"use strict";
const events = require("events");

module.exports = class Ringbuffer extends events.EventEmitter {
    constructor(size) {
        super();
        var head = 0;
        var items = 0;
        var buffer = new Array(size);

        // basic properties
        Object.defineProperties(this, {
            // get the size of the buffer
            size: { value: size, writable: false, enumerable: true },

            // get the current number of items in the buffer
            length: { get: () => items, enumerable: true },

            // get the current number of free slots in the buffer
            free: { get: () => size - items, enumerable: true },

            // methods
            push: { value: push, writable: false },
            unshift: { value: unshift, writable: false },
            pop: { value: pop, writable: false },
            shift: { value: shift, writable: false },
            peek: { value: peek, writable: false },
            peekStart: { value: peekStart, writable: false }
        });

        // push item onto the end of the buffer
        function push(value) {
            if (items === size) throw new Error("Buffer is full");

            var pos = (head + items++) % size;
            buffer[pos] = value;

            if (items === 1) this.emit("data", this);
            if (items === size) this.emit("full", this);
        }

        // push item onto the start of the buffer
        function unshift(value) {
            if (items === size) throw new Error("Buffer is full");

            var pos = head ? --head : (head = size - 1);
            buffer[pos] = value;
            items++;

            if (items === 1) this.emit("data", this);
            if (items === size) this.emit("full", this);
        }

        // pop an item off the end of the buffer
        function pop() {
            if (!items) throw new Error("No items in buffer");

            var pos = (head + --items) % size;
            var value = buffer[pos];
            buffer[pos] = undefined;

            if (!items) this.emit("empty", this);
            if (items < size) this.emit("free", this);
            return value;
        }

        // pop an item off the start of the buffer
        function shift() {
            if (!items) throw new Error("No items in buffer");

            var value = buffer[head];
            buffer[head] = undefined;
            if (++head == size) head = 0;
            items--;

            if (!items) this.emit("empty", this);
            if (items < size) this.emit("free", this);
            return value;
        }

        // peek at the end of the buffer
        function peek() {
            if (!items) throw new Error("No items in buffer");

            return buffer[(head + (items - 1)) % size];
        }

        // peek at the start of the buffer
        function peekStart() {
            if (!items) throw new Error("No items in buffer");

            return buffer[head];
        }
    }
};