escher-vis/js/src/UndoStack.js

Escher: A Web Application for Building, Sharing, and Embedding Data-Rich Visualizations of Biological Pathways

/** UndoStack. A constructor that can be used to store undo info. */

var utils = require('./utils');


var UndoStack = utils.make_class();
UndoStack.prototype = {
    init: init,
    push: push,
    undo: undo,
    redo: redo
};
module.exports = UndoStack;


// definitions
function init() {
    var stack_size = 40;
    this.stack = Array(stack_size);
    this.current = -1;
    this.oldest = -1;
    this.newest = -1;
    this.end_of_stack = true;
    this.top_of_stack = true;
}


function _incr(a, l) {
    return a + 1 > l - 1 ? 0 : a + 1;
}


function _decr(a, l) {
    return a - 1 < 0 ? l - 1 : a -  1;
}


function push(undo_fn, redo_fn) {
    this.current = _incr(this.current, this.stack.length);
    // change the oldest
    if (this.end_of_stack)
        this.oldest = this.current;
    else if (this.oldest == this.current)
        this.oldest = _incr(this.oldest, this.stack.length);
    this.stack[this.current] = { undo: undo_fn, redo: redo_fn };
    this.newest = this.current;

    // top of the stack
    this.top_of_stack = true;
    this.end_of_stack = false;
}


function undo() {
    // check that we haven't reached the end
    if (this.end_of_stack) return console.warn('End of stack.');
    // run the lastest stack function
    this.stack[this.current].undo();
    if (this.current == this.oldest) {
        // if the next index is less than the oldest, then the stack is dead
        this.end_of_stack = true;
    } else {
        // reference the next fn
        this.current = _decr(this.current, this.stack.length);
    }

    // not at the top of the stack
    this.top_of_stack = false;
}


function redo() {
    // check that we haven't reached the end
    if (this.top_of_stack) return console.warn('Top of stack.');

    if (!this.end_of_stack)
        this.current = _incr(this.current, this.stack.length);
    this.stack[this.current].redo();

    // if at top of stack
    if (this.current == this.newest)
        this.top_of_stack = true;

    // not at the end of the stack
    this.end_of_stack = false;
}