/**
 *
 */
var Itemgroup = {
    /**
     *
     */
    items: function items(group, delay, n) {
        var g;
        var all = [];

        group.selectAll('g').remove();

        // Items start with no background by default.
        for (var i = 0; i < n; i++) {
            g = group.append('g')
                .attr('class', `i${i}`)
                .attr('transform', function transform(d) {
                    return `translate(${i * (Visualizer.itemW + Visualizer.spacerW) + Visualizer.padding}, ${Visualizer.padding})`;
                });;

            g.append('rect')
                .attr('class', 'item')
                .attr('height', Visualizer.itemH)
                .attr('width', Visualizer.itemW)
                .attr('fill', 'transparent');

            // Item labels
            g.append('text')
                .attr('fill', '#aaa')
                .attr('font-size', 10)
                .attr('font-family', 'sans-serif')
                .attr('transform', function transform(d) {
                    return `rotate(90 0,0), translate(5, -3)`;
                });

            all.push(g);
        };

        return all;
    },

    /**
     *
     */
    swap: function swap(group, delay, indexA, indexB) {
        var x, a, b;
        var len = group.selectAll('g')[0].length;

        // Animate a node swap which will be quietly undone after completion.
        group.selectAll('g').transition().duration(delay - 100)
            .attr('transform', function transform(d, i) {
                x = i * (Visualizer.itemW + Visualizer.spacerW) + Visualizer.padding;

                if (i === indexA) {
                    x = indexB * (Visualizer.itemW + Visualizer.spacerW) + Visualizer.padding;
                    a = d3.select(this).select('text').text();

                    if (indexA === indexB) {
                        b = a;
                    }
                }
                else if (i === indexB) {
                    x = indexA * (Visualizer.itemW + Visualizer.spacerW) + Visualizer.padding;
                    b = d3.select(this).select('text').text();
                }

                return `translate(${x}, ${Visualizer.padding})`;
            })
            .each('end', function(d, i) {
                if (i !== len - 1) {
                    return;
                }

                // Undo the animation by restoring the original positions and swapping the values.
                group.selectAll('g')
                    .attr('transform', function transform(d, i) {
                        x = i * (Visualizer.itemW + Visualizer.spacerW) + Visualizer.padding;
                        return `translate(${x}, ${Visualizer.padding})`;
                    })
                    .each(function(d, i) {
                        if (i === indexA) {
                            d3.select(this).select('text').text(b);
                        }
                        else if (i === indexB) {
                            d3.select(this).select('text').text(a);
                        }
                    });
            });
    },

    /**
     *
     */
    background: function background(group, delay, start, end, color) {
        group.selectAll('g').each(function(d, i) {
            if (i >= start && i <= end) {
                d3.select(this).select('rect').attr('fill', color);
            }
        });
    },

    /**
     *
     */
    foreground: function foreground(group, delay, start, end, color) {
        group.selectAll('g').each(function(d, i) {
            if (i >= start && i <= end) {
                d3.select(this).select('text').attr('fill', color);
            }
        });
    },

    /**
     *
     */
    text: function text(group, delay, which, text) {
        group.selectAll('g')
            .filter(function filter(d, i) { return i === which; })
            .select('text').text(text);
    },

    /**
     *
     */
    opacity: function opacity(group, delay, start, end, opacity) {
        group.selectAll('g').each(function(d, i) {
            if (i >= start && i <= end) {
                d3.select(this).attr('opacity', opacity);
            }
        });
    },

    /**
     * Message updates.
     */
    message: function message(group, delay, which, msg) {
        var msg = msg || '&nbsp;';
        this.parent.querySelector(`.message:nth-child(${which})`).innerHTML = msg;
    },
};