/**
 *
 */
var MergeSort = function(VisualizerInstance) {
    //===== Inits.
    this.V = VisualizerInstance;
    this.comparisons = 0;

    //===== Action management.
    //
    this.initSort = function(arr, start, end) {
        this.V
            .instruct(this.V.unhighlight, 0)
            .instruct(this.V.unfade, 0)
            .instruct(this.V.fade, 0, -1, start - 1)
            .instruct(this.V.fade, 0, end + 1, arr.length)
            .instruct(this.V.message, 0, 1, `Comparisons: ${this.comparisons}`)
            .instruct(this.V.message, 0, 2, '')
            .instruct(this.V.message, 0, 3, '')
            .instruct(this.V.message, 0, 4, '')
            .instruct(this.V.message, 0, 5, '');
    };

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

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

    //
    this.preMerge = function(arr1, arr2, start, mid, end) {
        var i, j, x, y, v;
        var len1 = arr1.length;
        var len2 = arr2.length;

        for (var i = 0; i < len1; i++) {
            x = Visualizer.padding + (i + start) * (Visualizer.itemW + Visualizer.spacerW);
            y = Visualizer.padding * 2 + Visualizer.itemH;
            v = arr1[i].value;
            this.V.instruct(this.V.item, 0, 'secondary', x, y, v, '#05350D')
        }

        for (var j = 0; j < len2; j++) {
            x = Visualizer.padding + (j + len1 + start) * (Visualizer.itemW + Visualizer.spacerW);
            y = Visualizer.padding * 2 + Visualizer.itemH;
            v = arr2[j].value;
            this.V.instruct(this.V.item, 0, 'secondary', x, y, v, '#028E2D')
        }

        this.V
            // .instruct(this.V.fade, 0, 0, arr.length)
            .instruct(this.V.message, 0, 2, ``)
            .instruct(this.V.message, 0, 3, 'Merging slices:')
            .instruct(this.V.message, 0, 4, `[${start}]-[${mid}] and [${mid + 1}]-[${end}]`)
            .instruct(this.V.removeTertiary, 0);
    };

    //
    this.postMerge = function() {
        this.V.instruct(this.V.removeSecondary, 0);
    };

    //
    this.midMerge = function(index, value, message) {
        var x = Visualizer.padding + index * (Visualizer.itemW + Visualizer.spacerW);
        var y = Visualizer.padding * 3 + Visualizer.itemH * 2

        this.V
            .instruct(this.V.item, 0, 'tertiary', x, y, value, '#8E5500')
            .instruct(this.V.message, 0, 4, message)
            .instruct(this.V.message, 100, 5, `Pushing ${value} to sub-result.`);
    };

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

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

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

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

    if (start === end) {
        this.splitSingle(start);
        return new Array(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(arr1, arr2, start, mid, end);
    var result = this.merge(arr1, arr2);

    this.postMerge();
    return result;
};

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

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

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

    return result;
};