/**
 *
 */
var ShellSort = function() {
    //===== Action management.
    //
    this.preSort = function(arr, i, gap) {
        this
            .instruct(Itemgroup.background, 1, 0, 0, arr.length, Visualizer.bg0)

            .instruct(Itemgroup.message, 0, 0, 1, `Comparisons: ${this.comparisons}`)
            .instruct(Itemgroup.message, 0, 0, 2, `Swaps: ${this.swaps}`)
            .instruct(Itemgroup.message, 0, 0, 3, `Gap: ${gap}`)
            .instruct(Itemgroup.message, 0, 0, 4, ``)
            .instruct(Itemgroup.message, 0, 100, 5, `Starting sort at index ${i}.`)
    };

    //
    this.midSort = function(arr, i, j, gap) {
        this
            .instruct(Itemgroup.background, 1, 0, 0, arr.length, Visualizer.bg0)
            .instruct(Itemgroup.background, 1, 0, j, j, Visualizer.bg1)
            .instruct(Itemgroup.background, 1, 0, (j - gap), (j - gap), Visualizer.bg1)

            .instruct(Itemgroup.message, 0, 0, 4, `Comparing [${j - gap}] and [${j}]`)
            .instruct(Itemgroup.message, 0, 100, 5, ``)
    };

    //
    this.swap = function(arr, j, gap) {
        this
            .instruct(Itemgroup.message, 0, 100, 4, `${arr[j]} < ${arr[j - gap]}, swap required.`)
            .instruct(Itemgroup.swap, 1, 300, j - gap, j)

        if (j - gap > 0) {
            this
                .instruct(Itemgroup.message, 0, 100, 5, `Continuing downstream...`)
        }
    };

    //
    this.noswap = function(arr, j, gap) {
        this
            .instruct(Itemgroup.message, 0, 0, 4, `${arr[j]} > ${arr[j - gap]}, no swap required.`)
            .instruct(Itemgroup.message, 0, 100, 5, ``)
    };

    //
    this.postSort = function(arr) {
        this
            .instruct(Itemgroup.background, 1, 0, 0, arr.length, Visualizer.bg0)
            .instruct(Itemgroup.message, 0, 0, 3, ``)
            .instruct(Itemgroup.message, 0, 0, 4, ``)
            .instruct(Itemgroup.message, 0, 100, 5, `Ready for insertion sort.`)
    };
};

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

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

    this.actions = [];
    this.swaps = 0;
    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, 1, 0, i, this.shuffled[i]);
    }

    this
        .instruct(Itemgroup.foreground, 1, 0, 0, len, Visualizer.fg0)
        .instruct(Itemgroup.background, 1, 0, 0, len, Visualizer.bg0)

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


/**
 *
 */
ShellSort.prototype.sort = function(arr) {
    var len = arr.length;
    var gap = Math.floor(len / 3);
    var i, j;

    for (i = 0; i < gap; i++) {
        this.preSort(arr, i, gap);
        this.gapSort(arr, i, gap);
    }

    this.postSort(arr);

    return arr;
};

/**
 *
 */
ShellSort.prototype.gapSort = function(arr, start, gap) {
    var i, j;
    var len = arr.length;

    for (i = start; i < len; i += gap) {
        for (j = i; j > start; j -= gap) {
            this.midSort(arr, i, j, gap);
            this.comparisons++;

            if (arr[j - gap] > arr[j]) {
                this.swaps++;
                tmp = arr[j - gap];
                arr[j - gap] = arr[j];
                arr[j] = tmp;

                this.swap(arr, j, gap);
            }
            else {
                this.noswap(arr, j, gap);
                break;
            }
        }
    }
};