Sankey.svelte component

<!--
  @component
  Generates an SVG Sankey chart using [d3-sankey](https://github.com/d3/d3-sankey). The data must be an object with `nodes` and `links` arrays, the shape [sankey](https://github.com/d3/d3-sankey#sankey) takes.
 -->
<script>
  import * as Sankey from 'd3-sankey';
  import { getLayerCakeContext } from 'layercake';

  /** @typedef {import('d3-sankey').SankeyGraph<any, any>} SankeyGraph */
  /** @typedef {import('d3-sankey').SankeyNodeMinimal<any, any>} SankeyNode */
  /** @typedef {import('d3-sankey').SankeyLinkMinimal<any, any>} SankeyLink */
  /** @typedef {(node: SankeyNode, n: number) => number} SankeyAlignment */
  /** @typedef {(a: SankeyLink, b: SankeyLink) => number} LinkSortFunction */

  /** @type {import('layercake').LayerCakeContext<any, SankeyGraph>} */
  const k = getLayerCakeContext();

  /**
   * @typedef {Object} Props
   * @property {(d: any) => string} [getLinkStroke=() => 'rgba(0, 0, 0, .2)'] - Returns the stroke color for a link.
   * @property {(d: any) => string} [getNodeFill=() => '#333'] - Returns the fill color for a node.
   * @property {(d: any) => string} [getTextFill=() => '#263238'] - Returns the fill color for a node's label.
   * @property {number} [nodeWidth=5] - The width of each node in pixels, passed to [sankey.nodeWidth](https://github.com/d3/d3-sankey#sankey_nodeWidth).
   * @property {number} [nodePadding=10] - The gap between nodes in pixels, passed to [sankey.nodePadding](https://github.com/d3/d3-sankey#sankey_nodePadding).
   * @property {LinkSortFunction|undefined} [linkSort] - How to sort the links, passed to [sankey.linkSort](https://github.com/d3/d3-sankey#sankey_linkSort).
   * @property {(d: any) => number | string} [nodeId=d => d.id] - Returns a node's id, passed to [sankey.nodeId](https://github.com/d3/d3-sankey#sankey_nodeId).
   * @property {SankeyAlignment} [nodeAlign=Sankey.sankeyLeft] - Where the nodes line up, passed to [sankey.nodeAlign](https://github.com/d3/d3-sankey#alignments).
   */

  /** @type {Props} */
  let {
    getLinkStroke = () => 'rgba(0, 0, 0, .2)',
    getNodeFill = () => '#333',
    getTextFill = () => '#263238',
    nodeWidth = 5,
    nodePadding = 10,
    linkSort = undefined,
    nodeId = d => d.id,
    nodeAlign = Sankey.sankeyLeft
  } = $props();

  const linkPath = Sankey.sankeyLinkHorizontal();

  // The layout writes positions onto the nodes and links, so it gets copies of
  // them and hands back a fresh graph each time. Your data stays as it was.
  let sankeyData = $derived.by(() => {
    const sankey = Sankey.sankey()
      .nodeAlign(nodeAlign)
      .nodeWidth(nodeWidth)
      .nodePadding(nodePadding)
      .nodeId(nodeId)
      .size([k.width, k.height])
      .linkSort(linkSort);
    const graph = {
      nodes: k.data.nodes.map(d => ({ ...d })),
      links: k.data.links.map(d => ({ ...d }))
    };
    return /** @type {SankeyGraph} */ (sankey(graph));
  });

  let fontSize = $derived(k.width <= 320 ? 8 : 12);
</script>

<g class="sankey-layer">
  <g class="link-group">
    {#each sankeyData.links as d}
      <path
        d={linkPath(d)}
        fill="none"
        stroke={getLinkStroke(d)}
        stroke-opacity="0.5"
        stroke-width={d.width}
      />
    {/each}
  </g>
  <g class="rect-group">
    {#each sankeyData.nodes as d}
      <rect x={d.x0} y={d.y0} height={d.y1 - d.y0} width={d.x1 - d.x0} fill={getNodeFill(d)} />
      <text
        x={d.x0 < k.width / 4 ? d.x1 + 6 : d.x0 - 6}
        y={(d.y1 + d.y0) / 2}
        dy={fontSize / 2 - 2}
        style="fill: {getTextFill(d)};
              font-size: {fontSize}px;
              text-anchor: {d.x0 < k.width / 4 ? 'start' : 'end'};"
      >
        {d.id}
      </text>
    {/each}
  </g>
</g>

<style>
  text {
    pointer-events: none;
  }
</style>