roadmap/assets/js/graph.js

async function drawGraph(
  baseUrl,
  pathColors,
  depth,
  enableDrag,
  enableLegend,
  enableZoom
) {
  const container = document.getElementById('graph-container')

  const { index, links, content } = await fetchData
  const curPage = window.location.href.replace(baseUrl, "").replace(/\/$/g, "")

  const parseIdsFromLinks = (links) => [
    ...new Set(links.flatMap((link) => [link.source, link.target])),
  ]

  // Links is mutated by d3. We want to use links later on, so we make a copy and pass that one to d3
  // Note: shallow cloning does not work because it copies over references from the original array
  const copyLinks = JSON.parse(JSON.stringify(links))

  const neighbours = new Set()
  const wl = [curPage || '/', '__SENTINEL']
  if (depth >= 0) {
    while (depth >= 0 && wl.length > 0) {
      // compute neighbours
      const cur = wl.shift()
      if (cur === '__SENTINEL') {
        depth--
        wl.push('__SENTINEL')
      } else {
        neighbours.add(cur)
        const outgoing = index.links[cur] || []
        const incoming = index.backlinks[cur] || []
        wl.push(
          ...outgoing.map((l) => l.target),
          ...incoming.map((l) => l.source)
        )
      }
    }
  } else {
    parseIdsFromLinks(copyLinks).forEach((id) => neighbours.add(id))
  }

  const data = {
    nodes: [...neighbours].map((id) => ({ id })),
    links: copyLinks.filter(
      (l) => neighbours.has(l.source) && neighbours.has(l.target)
    ),
  }

  const color = (d) => {
    if (d.id === curPage || (d.id === '/' && curPage === '')) {
      return 'var(--g-node-active)'
    }

    for (const pathColor of pathColors) {
      const path = Object.keys(pathColor)[0]
      const colour = pathColor[path]
      if (d.id.startsWith(path)) {
        return colour
      }
    }

    return 'var(--g-node)'
  }

  const drag = (simulation) => {
    function dragstarted(event, d) {
      if (!event.active) simulation.alphaTarget(1).restart()
      d.fx = d.x
      d.fy = d.y
    }

    function dragged(event, d) {
      d.fx = event.x
      d.fy = event.y
    }

    function dragended(event, d) {
      if (!event.active) simulation.alphaTarget(0)
      d.fx = null
      d.fy = null
    }

    const noop = () => { }
    return d3
      .drag()
      .on('start', enableDrag ? dragstarted : noop)
      .on('drag', enableDrag ? dragged : noop)
      .on('end', enableDrag ? dragended : noop)
  }

  const height = Math.max(container.offsetHeight, 250)
  const width = container.offsetWidth

  const simulation = d3
    .forceSimulation(data.nodes)
    .force('charge', d3.forceManyBody().strength(-30))
    .force(
      'link',
      d3
        .forceLink(data.links)
        .id((d) => d.id)
        .distance(40)
    )
    .force('center', d3.forceCenter())

  const svg = d3
    .select('#graph-container')
    .append('svg')
    .attr('width', width)
    .attr('height', height)
    .attr('viewBox', [-width / 2, -height / 2, width, height])

  if (enableLegend) {
    const legend = [
      { Current: 'var(--g-node-active)' },
      { Note: 'var(--g-node)' },
      ...pathColors,
    ]
    legend.forEach((legendEntry, i) => {
      const key = Object.keys(legendEntry)[0]
      const colour = legendEntry[key]
      svg
        .append('circle')
        .attr('cx', -width / 2 + 20)
        .attr('cy', height / 2 - 30 * (i + 1))
        .attr('r', 6)
        .style('fill', colour)
      svg
        .append('text')
        .attr('x', -width / 2 + 40)
        .attr('y', height / 2 - 30 * (i + 1))
        .text(key)
        .style('font-size', '15px')
        .attr('alignment-baseline', 'middle')
    })
  }

  // draw links between nodes
  const link = svg
    .append('g')
    .selectAll('line')
    .data(data.links)
    .join('line')
    .attr('class', 'link')
    .attr('stroke', 'var(--g-link)')
    .attr('stroke-width', 2)
    .attr('data-source', (d) => d.source.id)
    .attr('data-target', (d) => d.target.id)

  // svg groups
  const graphNode = svg
    .append('g')
    .selectAll('g')
    .data(data.nodes)
    .enter()
    .append('g')

  // calculate radius
  const nodeRadius = (d) => {
    const numOut = index.links[d.id]?.length || 0
    const numIn = index.backlinks[d.id]?.length || 0
    return 3 + (numOut + numIn) / 4
  }

  // draw individual nodes
  const node = graphNode
    .append('circle')
    .attr('class', 'node')
    .attr('id', (d) => d.id)
    .attr('r', nodeRadius)
    .attr('fill', color)
    .style('cursor', 'pointer')
    .on('click', (_, d) => {
      // SPA navigation
      window.navigate(
        new URL(`${baseUrl}${decodeURI(d.id).replace(/\s+/g, '-')}/`),
        '.singlePage'
      )
    })
    .on('mouseover', function(_, d) {
      d3.selectAll('.node')
        .transition()
        .duration(100)
        .attr('fill', 'var(--g-node-inactive)')

      const neighbours = parseIdsFromLinks([
        ...(index.links[d.id] || []),
        ...(index.backlinks[d.id] || []),
      ])
      const neighbourNodes = d3
        .selectAll('.node')
        .filter((d) => neighbours.includes(d.id))
      const currentId = d.id
      const linkNodes = d3
        .selectAll('.link')
        .filter((d) => d.source.id === currentId || d.target.id === currentId)

      // highlight neighbour nodes
      neighbourNodes.transition().duration(200).attr('fill', color)

      // highlight links
      linkNodes
        .transition()
        .duration(200)
        .attr('stroke', 'var(--g-link-active)')

      // show text for self
      d3.select(this.parentNode)
        .raise()
        .select('text')
        .transition()
        .duration(200)
        .style('opacity', 1)
    })
    .on('mouseleave', function(_, d) {
      d3.selectAll('.node').transition().duration(200).attr('fill', color)

      const currentId = d.id
      const linkNodes = d3
        .selectAll('.link')
        .filter((d) => d.source.id === currentId || d.target.id === currentId)

      linkNodes.transition().duration(200).attr('stroke', 'var(--g-link)')

      d3.select(this.parentNode)
        .select('text')
        .transition()
        .duration(200)
        .style('opacity', 0)
    })
    .call(drag(simulation))

  // draw labels
  const labels = graphNode
    .append('text')
    .attr('dx', 0)
    .attr('dy', (d) => nodeRadius(d) + 8 + 'px')
    .attr('text-anchor', 'middle')
    .text((d) => content[d.id]?.title || d.id.replace('-', ' '))
    .style('opacity', 0)
    .style('pointer-events', 'none')
    .style('font-size', '0.4em')
    .raise()
    .call(drag(simulation))

  // set panning

  if (enableZoom) {
    svg.call(
      d3
        .zoom()
        .extent([
          [0, 0],
          [width, height],
        ])
        .scaleExtent([0.25, 4])
        .on('zoom', ({ transform }) => {
          link.attr('transform', transform)
          node.attr('transform', transform)
          const scale = transform.k
          const scaledOpacity = Math.max((scale - 1) / 3.75, 0)
          labels.attr('transform', transform).style('opacity', scaledOpacity)
        })
    )
  }

  // progress the simulation
  simulation.on('tick', () => {
    link
      .attr('x1', (d) => d.source.x)
      .attr('y1', (d) => d.source.y)
      .attr('x2', (d) => d.target.x)
      .attr('y2', (d) => d.target.y)
    node.attr('cx', (d) => d.x).attr('cy', (d) => d.y)
    labels.attr('x', (d) => d.x).attr('y', (d) => d.y)
  })
}