var updateData = function() {
  // get the textarea "value" (i.e. the entered text)
  var text = d3.select("body").select("textarea").node().value;

  // make sure we got the right text
  console.log(text);

  // get letter count
  var count = countLetters(text);

  // some browsers support console.table()
  try {
    console.table(count.entries());

  }
  catch (e) {
    console.log(count);
  }

  return count;
};

/*
 * our massive function to draw a bar chart. note some stuff in here
 * is bonus material (for transitions and updating the text)
 */
var drawBarChart = function() {
  // get the data to visualize
  var count = updateData();

  // get the svg to draw on
  var svg = d3.select("body").select("svg");

  /*
   * we will need to map our data domain to our svg range, which
   * means we need to calculate the min and max of our data
   */

  var countMin = 0; // always include 0 in a bar chart!

  /* d3.documents:
    # map.values() = Returns an array of values for every entry in this map.
    The order of the returned values is arbitrary.
  */

  var countMax = d3.max(count.values());  // count.values() = [value1, value2, etc..] (values from each entries[key] in d3.map)
  console.log("count bounds:", [countMin, countMax]);

  /*
   * before we draw, we should decide what kind of margins we
   * want. this will be the space around the core plot area,
   * where the tick marks and axis labels will be placed
   * http://bl.ocks.org/mbostock/3019563
   */
  var margin = {
    top:    15,
    /* original code */
    // right:  35, // leave space for y-axis

    /* P1_3 new code */
    right: 11,  // since 10 -> 25 = (15 units), deduct 35 - 24 = 11

    bottom: 30, // leave space for x-axis

    /* original code */
    // left:   10

    /* P1_3 new code */
    left: 25
  };

  // now we can calculate how much space we have to plot
  var bounds = svg.node().getBoundingClientRect();  // get the svg's bounding (dimension info, width, height etc..)
  console.log(bounds)
  var plotWidth = bounds.width - margin.right - margin.left;
  var plotHeight = bounds.height - margin.top - margin.bottom;

  /*
   * okay now somehow we have to figure out how to map a count value
   * to a bar height, decide bar widths, and figure out how to space
   * bars for each letter along the x-axis
   *
   * this is where the scales in d3 come in very handy
   * https://github.com/d3/d3-scale#api-reference
   */

  /*
   * the counts are easiest because they are numbers and we can use
   * a simple linear scale, but the complicating matter is the
   * coordinate system in svgs:
   * https://developer.mozilla.org/en-US/docs/Web/SVG/Tutorial/Positions
   *
   * so we want to map our min count (0) to the max height of the plot area
   */

  // Y  scale
  var countScale = d3.scaleLinear()
    .domain([countMin, countMax])   // domain([d1, d2])
                                    // d1 map to range r1
    // Note: computer graphics formed by matrix.
    // Ex [(0,0), (0,1)]
    //    [(1,0), (1,1)]
    // Y axis goes from 0 (top)-> increasing number (bottom)]
    .range([plotHeight, 0])         // range([r1, r2])
    .nice(); // rounds the domain a bit for nicer output

  /*
   * the letters need an ordinal scale instead, which is used for
   * categorical data. we want a bar space for all letters, not just
   * the ones we found, and spaces between bars.
   * https://github.com/d3/d3-scale#band-scales
   */
   // X scale
  var letterScale = d3.scaleBand()  // Explain: Constructs a new band scale with the empty domain, the unit range [0, 1], no padding, no rounding and center alignment.
    .domain(letters)
    .rangeRound([0, plotWidth])     // explain: https://github.com/d3/d3-interpolate#interpolateRound (makes a's bar, b's bar has interpolate space in between)
    .paddingInner(0.1);             // space between bars
                                    // visualize the paddingInner in https://github.com/d3/d3-scale/blob/master/README.md#scaleImplicit under Band Scales section

  // try using these scales in the console
  console.log("count scale [0, 36]:", [countScale(0), countScale(36)]);     // countScale(0) = Given a value in the input domain, returns the start of the corresponding band derived from the output range. If the given value is not in the scale’s domain, returns undefined.
                                                                            // visualize in https://github.com/d3/d3-scale/blob/master/README.md#scaleImplicit under Band Scales section
                                                                            // give the value to domain (ex: bandwidth 1, bandwidth 2 etc..), return the corresponding position and range of it
  console.log("letter scale [a, z]:", [letterScale('a'), letterScale('z')]);

  // we are actually going to draw on the "plot area"
  var plot = svg.select("g#plot");  // the id=plot generated by svg in live web pages under #id = plot (can inspect with javascript developer tools on web to spot this)

  // explain: plot.size() < 1 (to let svg generate #id = plot), first time execute these so plot.size() still < 1
  if (plot.size() < 1) {
    // this is the first time we called this function
    // we need to setup the plot area
    plot = svg.append("g").attr("id", "plot");

    // notice in the "elements" view we now have a g element!

    // shift the plot area over by our margins to leave room
    // for the x- and y-axis
    plot.attr("transform", "translate(" + margin.left + "," + margin.top + ")");

    /* IMPORTANT NOTES */
    // explain: plot.attr() in http://jonathansoma.com/tutorials/d3/using-attr-and-style/
    // transform + translate explain: https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/transform
    // note: the translate has same properties as how computer graphics work (matrix) translate(the margin-left, the margin-top)
  }

  // now lets draw our x- and y-axis
  // these require our x (letter) and y (count) scales
  var xAxis = d3.axisBottom(letterScale); // bottom oriented axis = X-axis <<Example below:>>
                                          //  _|_|_|

  /* orignal code */
  // var yAxis = d3.axisRight(countScale);   // right oriented axis = Y-axis  <<Example below:>>
                                          //    |_
                                          //    |_
                                          //    |
                                          /* P1_3 new code */

  /* P1_3 new code */
  var yAxis = d3.axisLeft(countScale);

  // check if we have already drawn our axes, else first time, draw it in these piece of code
  // plot.select("g#y-axis"), here can be either g#y-axis or g#x-axis, doesn't matter since plot of graph shoul come along with x & y axis
  // this is just for checking
  if (plot.select("g#y-axis").size() < 1) {

    // drawig x axis
    var xGroup = plot.append("g").attr("id", "x-axis");
    // the drawing is triggered by call()
    xGroup.call(xAxis);
    // notice it is at the top of our svg
    // we need to translate/shift it down to the bottom
    xGroup.attr("transform", "translate(0," + plotHeight + ")");

    // do the same for our y axix
    var yGroup = plot.append("g").attr("id", "y-axis");
    yGroup.call(yAxis);

    /* original code */
    // yGroup.attr("transform", "translate(" + plotWidth + ",0)");
    yGroup.attr("transform", "translate(0,0)");
  }
  else {
    /* IMPORTANT NOTES */
    // we need to do this so our chart updates
    // as we type new letters in our box
    plot.select("g#y-axis").call(yAxis);
  }

  // now how about some bars!

  /*
   * time to bind each data element to a rectangle in our visualization
   * hence the name data-driven documents (d3)
   */
  var bars = plot.selectAll("rect")
    .data(count.entries(), function(d) { return d.key; });

  // setting the "key" is important... this is how d3 will tell
  // what is existing data, new data, or old data

  /*
   * okay, this is where things get weird. d3 uses an enter, update,
   * exit pattern for dealing with data. think of it as new data,
   * existing data, and old data. for the first time, everything is new!
   * http://bost.ocks.org/mike/join/
   */

  // we use the enter() selection to add new bars for new data
  bars.enter().append("rect")
    // we will style using css
    .attr("class", "bar")
    // the width of our bar is determined by our band scale
    .attr("width", letterScale.bandwidth())
    // we must now map our letter to an x pixel position
    .attr("x", function(d) {
      return letterScale(d.key);
    })
    // and do something similar for our y pixel position
    .attr("y", function(d) {
      return countScale(d.value);
    })
    // here it gets weird again, how do we set the bar height?
    .attr("height", function(d) {
      return plotHeight - countScale(d.value);
    });

  // notice there will not be bars created for missing letters!

  // so what happens when we change the text?
  // well our data changed, and there will be a new enter selection!
  // only new letters will get new bars

  // but we have to bind this draw function to textarea events
  // (see index.html)

  // for bars that already existed, we must use the update selection
  // and then update their height accordingly
  // we use transitions for this to avoid change blindness
  bars.transition()
    .attr("y", function(d) { return countScale(d.value); })
    .attr("height", function(d) { return plotHeight - countScale(d.value); });

  // what about letters that disappeared?
  // we use the exit selection for those to remove the bars
  bars.exit().transition()
    .attr("y", function(d) { return countScale(countMin); })
    .attr("height", function(d) { return plotHeight - countScale(countMin); })
    .remove();
};