/**
 *
 */
var MergeSort = function() {
    var _this = this;

    this.ui = {
        //
        reset: function reset(len) {
            _this
                .instruct(Itemgroup.background, 0, 0, '#f00', 0, len)

                .instruct(Itemgroup.opacity, 0, 0, 0, len, 1)

                .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, 'Starting sort.');
        },

        //
        presort: function presort(start, mid, end, len) {
            _this
                .instruct(Itemgroup.message, 0, 0, 2, `Sorting [${start}] - [${end}]`)
                .instruct(Itemgroup.message, 0, 0, 3, 'Slicing and recursing...')
                // .instruct(Itemgroup.message, 0, 0, 4, `[${start}]-[${mid}] and [${mid + 1}]-[${end}]`)

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

                .instruct(Itemgroup.opacity, 1, 0, 0, len, 0)
                .instruct(Itemgroup.opacity, 2, 100, 0, len, 0)
        },

        //
        premerge: function premerge(arr1, arr2, start, mid, end, len) {
            var len1 = arr1.length;
            var len2 = arr2.length;

            for (var i = 0; i < len1; i++) {
                _this
                    .instruct(Itemgroup.text, 1, 0, i, arr1[i]);
            }

            for (var j = 0; j < len2; j++) {
                _this
                    .instruct(Itemgroup.text, 1, 0, len1 + j, arr2[j]);
            }

            _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.message, 0, 0, 5, '')

                .instruct(Itemgroup.background, 1, 0, 0, len1 - 1, Visualizer.bg1)
                .instruct(Itemgroup.background, 1, 0, len1, len1 + len2 - 1, '#751806')

                .instruct(Itemgroup.opacity, 0, 0, 0, len, 0.2)
                .instruct(Itemgroup.opacity, 1, 0, 0, len, 0)
                .instruct(Itemgroup.opacity, 2, 0, 0, len, 0)

                .instruct(Itemgroup.opacity, 1, 100, 0, len1 + len2 - 1, 1)
        },

        //
        midmerge: function midmerge(indexG1, indexG2, value, message) {
            _this
                .instruct(Itemgroup.opacity, 1, 0, indexG1, indexG1, 0)

                .instruct(Itemgroup.opacity, 2, 0, indexG2, indexG2, 1)
                .instruct(Itemgroup.text, 2, 0, indexG2, value)

                .instruct(Itemgroup.message, 0, 0, 4, message)
                .instruct(Itemgroup.message, 0, 100, 5, `${value} pushed onto sub-result.`);
        },

        //
        updateComparisons: function updateComparisons() {
            _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.actions = [];
    this.comparisons = 0;

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

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

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

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

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

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

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

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

    return result;
};

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

    // (For reporting only, to keep track of "split" group.)
    var arr1index = 0;
    var arr2index = arr1.length;

    while (arr1.length > 0 || arr2.length > 0) {
        if (arr1.length === 0) {
            n = arr2.shift();
            result.push(n);

            this.ui.midmerge(arr2index, result.length - 1, n, '(last element)');
            arr2index++;
        }
        else if (arr2.length === 0) {
            n = arr1.shift();
            result.push(n);

            this.ui.midmerge(arr1index, result.length - 1, n, '(last element)');
            arr1index++;
        }
        else if (arr1[0] <= arr2[0]) {
            n = arr1.shift()
            result.push(n);

            this.ui.midmerge(arr1index, result.length - 1, n, `Compare heads: ${n} <= ${arr2[0]}`);
            arr1index++;
        }
        else {
            n = arr2.shift();
            result.push(n);

            this.ui.midmerge(arr2index, result.length - 1, n, `Compare heads: ${arr1[0]} > ${n}`);
            arr2index++;
        }

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

    return result;
};