/**
 *
 */
var MergeSort = function() {
    //===== Inits.
    this.actions = [];
    this.comparisons = 0;

    //===== Action management.
    //
    this.reset = function(arr, start, end) {
        var len = arr.length;

        this
            .instruct(Itemgroup.background, 0, 0, '#f00', 0, len)

            .instruct(Itemgroup.opacity, 0, 0, 0, len, 1)
            .instruct(Itemgroup.opacity, 0, 0, -1, start - 1, 0.2)
            .instruct(Itemgroup.opacity, 0, 0, end + 1, len, 0.2)

            .instruct(Itemgroup.message, 0, 0, 1, `Comparisons: ${this.comparisons}`)
            .instruct(Itemgroup.message, 0, 0, 2, '')
            .instruct(Itemgroup.message, 0, 0, 3, '')
            .instruct(Itemgroup.message, 0, 0, 4, '')
            .instruct(Itemgroup.message, 0, 0, 5, '');
    };

    //
    this.splitSingle = function(index) {
        this
            .instruct(Itemgroup.message, 0, 100, 2, `Single element [${index}]`);
    };

    //
    this.preSort = function(start, mid, end) {
        this
            .instruct(Itemgroup.message, 0, 0, 2, `Sorting [${start}] - [${end}]`)
            .instruct(Itemgroup.message, 0, 0, 3, 'Slicing and recursing:')
            .instruct(Itemgroup.message, 0, 100, 4, `[${start}]-[${mid}] and [${mid + 1}]-[${end}]`);
    };

    //
    this.preMerge = function(start, mid, end, len) {
        this
            .instruct(Itemgroup.message, 0, 0, 2, ``)
            .instruct(Itemgroup.message, 0, 0, 3, 'Merging slices:')
            .instruct(Itemgroup.message, 0, 0, 4, `[${start}]-[${mid}] and [${mid + 1}]-[${end}]`)

            .instruct(Itemgroup.opacity, 1, 0, 0, len, 0)
            .instruct(Itemgroup.opacity, 1, 0, start, end, 1)
            .instruct(Itemgroup.opacity, 2, 0, 0, len, 0)
    };

    //
    this.postMerge = function(len) {
        this
            .instruct(Itemgroup.opacity, 1, 0, 0, len, 0)
    };

    //
    this.midMerge = function(index, value, message) {
        this
            .instruct(Itemgroup.opacity, 1, 0, index, index, 1)
            .instruct(Itemgroup.text, 1, 0, index, value)
            .instruct(Itemgroup.message, 0, 100, 5, `Pushing ${value} to sub-result.`);
    };

    //
    this.updateComparisons = function() {
        this.instruct(Itemgroup.message, 0, 0, 1, `Comparisons: ${this.comparisons}`);
    };
};

MergeSort.prototype = Object.create(Sorter.prototype);

/**
 *
 */
MergeSort.prototype.init = function() {
    var len = this.shuffled.length;

    this
        .instruct(Itemgroup.items, 0, 0, len)
        .instruct(Itemgroup.items, 1, 0, len)
        .instruct(Itemgroup.items, 2, 0, len)

    for (var i = 0; i < len; i++) {
        this.instruct(Itemgroup.text, 0, 0, i, this.shuffled[i]);
    }

    this
        .instruct(Itemgroup.foreground, 0, 0, 0, len, Visualizer.fg0)
        .instruct(Itemgroup.background, 0, 0, 0, len, Visualizer.bg0)

        .instruct(Itemgroup.opacity, 1, 0, 0, 0, len)
        .instruct(Itemgroup.foreground, 1, 0, 0, len, Visualizer.fg1)
        .instruct(Itemgroup.background, 1, 0, 0, len, Visualizer.bg1)

        .instruct(Itemgroup.opacity, 2, 0, 0, 0, len)
        .instruct(Itemgroup.foreground, 2, 0, 0, len, Visualizer.fg2)
        .instruct(Itemgroup.background, 2, 100, 0, len, Visualizer.bg2)


    this
        .instruct(Itemgroup.swap, 0, 1000, 0, 1)
        .instruct(Itemgroup.swap, 0, 1000, 1, 2)
        .instruct(Itemgroup.swap, 0, 1000, 2, 3)
        .instruct(Itemgroup.swap, 0, 1000, 3, 2)
        .instruct(Itemgroup.swap, 0, 1000, 2, 1)
        .instruct(Itemgroup.swap, 0, 1000, 1, 0)
};

/**
 *
 */
MergeSort.prototype.sort = function(arr, start, end) {
    this.reset(arr, start, end);

    if (arr.length === 0) {
        return arr;
    }

    if (start === end) {
        this.splitSingle(start);
        return [arr[start]];
    }


    var mid = start + Math.floor((end - start) / 2);

    this.preSort(start, mid, end);
    var arr1 = this.sort(arr, start, mid);
    var arr2 = this.sort(arr, mid + 1, end);

    this.preMerge(start, mid, end, arr.length);
    var result = this.merge(arr1, arr2);
    this.postMerge(arr.length);

    return result;
};

/**
 *
 */
MergeSort.prototype.merge = function(arr1, arr2) {
    var result = [];
    var n;

    while (arr1.length > 0 || arr2.length > 0) {
        if (arr1.length === 0) {
            n = arr2.shift();
            result.push(n);
            this.midMerge(result.length, n, 'One element left to merge.');
        }
        else if (arr2.length === 0) {
            n = arr1.shift();
            result.push(n);
            this.midMerge(result.length, n, 'One element left to merge.');
        }
        else if (arr1[0] <= arr2[0]) {
            n = arr1.shift()
            result.push(n);
            this.midMerge(result.length, n, `${n} <= ${arr2[0]}`);
        }
        else {
            n = arr2.shift();
            result.push(n);
            this.midMerge(result.length, n, `${arr1[0]} > ${n}`);
        }

        this.comparisons++;
        this.updateComparisons();
    }

    return result;
};