D3 Examples - Indented Tree Concept for CK12

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<!DOCTYPE html>
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html;charset=utf-8">  
    <script type="text/javascript" src="https://cdn.jsdelivr.net/npm/d3@1.29.5/d3.js"></script>
    <script type="text/javascript" src="https://cdn.jsdelivr.net/npm/d3@1.29.5/d3.layout.js"></script>
<style>
    
    
rect {
  cursor: pointer;
  fill: #fff;
  stroke: steelblue;
  stroke-width: 1.5px;
}
​
text {
cursor:pointer; 
font-size:13px;
}
​
path.link {
  fill: none;
  stroke: #ccc;
  stroke-width: 1.5px;
}
</style>
</head>
<body>
    <div id="chart"></div>
​
<script type="text/javascript">
​
var w = 960,
    h = 3500,
    i = 0,
    barHeight = 35,
    barWidth = w * .6,
    duration = 400,
    root;
​
var tree = d3.layout.tree()
    .size([h, 100]);
​
var diagonal = d3.svg.diagonal()
    .projection(function(d) { return [d.y, d.x]; });
​
var vis = d3.select("#chart").append("svg:svg")
    .attr("width", w)
    .attr("height", h)
  .append("svg:g")
    .attr("transform", "translate(20,30)");
​
d3.json("math_map_compact.json", function(json) {
  json.x0 = 0;
  json.y0 = 0;
  update(root = json);
});
​
function update(source) {
​
  // Compute the flattened node list. TODO use d3.layout.hierarchy.
  var nodes = tree.nodes(root);
  
  // Compute the "layout".
  nodes.forEach(function(n, i) {
    n.x = i * barHeight;
  });
  
  // Update the nodes…
  var node = vis.selectAll("g.node")
      .data(nodes, function(d) { return d.id || (d.id = ++i); });
  
  var nodeEnter = node.enter().append("svg:g")
      .attr("class", "node")
      .attr("transform", function(d) { return "translate(" + source.y0 + "," + source.x0 + ")"; })
      .style("opacity", 1e-6);
​
  // Enter any new nodes at the parent's previous position.
  nodeEnter.append("svg:rect")
      .attr("y", -barHeight / 2)
      .attr("height", barHeight)
      .attr("width", barWidth)
      .attr("rx",2)
      .attr("ry",2)
      .style("fill", color)
      .on("click", click);
  
  nodeEnter.append("svg:a")
        .attr("xlink:href","https://www.ck12.org")
    .append("svg:text")
      .attr("x",10)
      .attr("dy", 3.5)
      .attr("dx", 10)
      .attr("fill","#000")
      //.attr("fill",function(d) {return (d.children) ? "#000" : "#ccc";})
      //.attr("stroke", function(d) {return (d.children) ? "#000" : "#ccc";})
      .text(function(d) { return d.name; });
      //.on("click",follow);
  
  // Transition nodes to their new position.
  nodeEnter.transition()
      .duration(duration)
      .attr("transform", function(d) { return "translate(" + d.y + "," + d.x + ")"; })
      .style("opacity", 1);
  
  node.transition()
      .duration(duration)
      .attr("transform", function(d) { return "translate(" + d.y + "," + d.x + ")"; })
      .style("opacity", 1)
    .select("rect")
      .style("fill", color);
  
  // Transition exiting nodes to the parent's new position.
  node.exit().transition()
      .duration(duration)
      .attr("transform", function(d) { return "translate(" + source.y + "," + source.x + ")"; })
      .style("opacity", 1e-6)
      .remove();
  
  // Update the links…
  var link = vis.selectAll("path.link")
      .data(tree.links(nodes), function(d) { return d.target.id; });
  
  // Enter any new links at the parent's previous position.
  link.enter().insert("svg:path", "g")
      .attr("class", "link")
      .attr("d", function(d) {
        var o = {x: source.x0, y: source.y0};
        return diagonal({source: o, target: o});
      })
    .transition()
      .duration(duration)
      .attr("d", diagonal);
  
  // Transition links to their new position.
  link.transition()
      .duration(duration)
      .attr("d", diagonal);
  
  // Transition exiting nodes to the parent's new position.
  link.exit().transition()
      .duration(duration)
      .attr("d", function(d) {
        var o = {x: source.x, y: source.y};
        return diagonal({source: o, target: o});
      })
      .remove();
  
  // Stash the old positions for transition.
  nodes.forEach(function(d) {
    d.x0 = d.x;
    d.y0 = d.y;
  });
}
​
// Toggle children on click.
function click(d) {
  if (d.children) {
    d._children = d.children;
    d.children = null;
  } else {
    d.children = d._children;
    d._children = null;
  }
  update(d);
}
​
function color(d) {
  return d._children ? "#3182bd" : d.children ? "#c6dbef" : "#fd8d3c";
}
​
    </script>
  </body>
</html>
    