var width = 500;
var height = 300;

var maxValue = d3.select('#maximum')
    .node()
    .value;

var margin = {
    top: 20,
    left: 30,
    right: 30,
    bottom: 30
};

var svg = d3.select("#vis")
    .append("svg")
    .attr('width', width)
    .attr('height', height)
    .append('g')
    .attr('transform', 'translate(' + margin.left + ',' + margin.top + ')');

width = width - margin.left - margin.right;
height = height - margin.top - margin.bottom;

var yscale = d3.scaleLinear()
    .range([height, 0])
    .domain([0, maxValue]);

var xscale = d3.scaleBand()
    .range([0, width])
    .padding(0.1);

var xaxis = d3.axisBottom()
    .scale(xscale);

var yaxis = d3.axisLeft()
    .scale(yscale);

svg.append('g')
    .attr('transform', 'translate(0, ' + (height) + ')')
    .attr('class', 'x axis');

svg.append('g')
    .attr('class', 'y axis');

function update() {

    maxValue = d3.select('#maximum')
        .node()
        .value;
    var exampleData = createRandomData(maxValue);

    xscale.domain(d3.range(exampleData.length));

    yscale.domain([0, maxValue]);

    var bars = svg.selectAll(".bar")
        .data(exampleData);

    bars
        .exit()
        .transition()
        .attr('height', 0)
        .attr('y', height)
        .remove();

    var new_bars = bars
        .enter()
        .append('rect')
        .attr('class', 'bar')
        .attr("fill", "red")
        .attr('height', 0)
        .attr('y', height);

    new_bars.merge(bars)
        .transition()
        .attr("height", function(d, i) {
            return height - yscale(d);
        })
        .attr("y", function(d, i) {
            return yscale(d);
        })
        .attr("width", xscale.bandwidth())
        .attr("x", function(d, i) {
            return xscale(i);
        })


    var labels = svg.selectAll('.label')
        .data(exampleData);

    labels
        .exit()
        .transition()
        .attr('y', height)
        .attr('opacity', 0)
        .remove();

    var new_labels = labels
        .enter()
        .append('text')
        .attr('class', 'label')
        .attr('opacity', 0)
        .attr('text-anchor', 'middle')
        .attr('y', height);

    new_labels.merge(labels)
        .transition()
        .attr('opacity', 1)
        .attr('x', function(d, i) {
            return xscale(i) + xscale.bandwidth() / 2;
        })
        .attr('y', function(d) {
            return yscale(d) - 2;
        })
        .text(function(d) {
            return d;
        });

    svg.select('.x.axis')
        .transition()
        .call(xaxis);

    svg.select('.y.axis')
        .transition()
        .call(yaxis);
}

function createRandomData(maxValue) {
    var numDataItems = Math.floor((Math.random() * 30) + 1);
    var d = [];
    for (var i = 0; i < numDataItems; i++) {
        d.push(Math.floor((Math.random() * maxValue) + 1));
    }
    return d;
}

update();