# All files / src/components/knowledge KnowledgeGraph.tsx

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     /**
     * Force-directed knowledge graph visualization using d3-force + SVG.
     *
     * Renders nodes as styled SVG elements with CSS theming support,
     * glassmorphic cards, glow effects, and smooth transitions.
     *
     * @module
     */

    import { useCallback, useRef, useEffect, useState, type JSX } from "react";
    import {
      forceSimulation,
      forceLink,
      forceManyBody,
      forceCenter,
      forceCollide,
      type Simulation,
      type SimulationNodeDatum,
      type SimulationLinkDatum,
    } from "d3-force";
    import { drag, type D3DragEvent } from "d3-drag";
    import { select, type Selection } from "d3-selection";
    import { zoom, zoomIdentity, type ZoomBehavior } from "d3-zoom";
    import "d3-transition";
    import type { GraphNode, GraphLink } from "../../hooks/types.js";
    import styles from "./KnowledgeGraph.module.scss";

    // ---------------------------------------------------------------------------
    // Types
    // ---------------------------------------------------------------------------

    interface SimNode extends SimulationNodeDatum, GraphNode {}

    interface SimLink extends SimulationLinkDatum<SimNode> {
      type: string;
    }

    // ---------------------------------------------------------------------------
    // Constants
    // ---------------------------------------------------------------------------

    const NODE_COLORS: Record<string, string> = {
      reference: "#4A9EFF",
      decision: "#22C55E",
      insight: "#EAB308",
      concept: "#A855F7",
      snippet: "#6B7280",
    };

    function getNodeColor(node: GraphNode): string {
      Iif (node.kind === "reference") {
        return NODE_COLORS.reference;
      }
      return NODE_COLORS[node.category ?? "insight"] ?? NODE_COLORS.insight;
    }

    const NODE_WIDTH: number = 200;
    const NODE_HEIGHT: number = 52;
    const NODE_RADIUS: number = 12;

    /** Padding around the bounding box when computing zoom-to-fit. */
    const FIT_PADDING: number = 40;

    /** Minimum drag distance (px) before a mouseup is treated as a drag-end rather than a click. */
    const DRAG_CLICK_THRESHOLD: number = 3;

    // ---------------------------------------------------------------------------
    // Helpers
    // ---------------------------------------------------------------------------

    interface ZoomToFitResult {
      translateX: number;
      translateY: number;
      scale: number;
    }

    /**
     * Compute the transform needed to fit all nodes within the viewport.
     *
     * Returns translate + scale that centers the node bounding box with padding.
     * Scale is capped at 1.0 so small graphs are never zoomed in past 100%.
     */
    function computeZoomToFit(
      nodes: readonly { x?: number; y?: number }[],
      viewport: { width: number; height: number },
    ): ZoomToFitResult | undefined {
      Iif (viewport.width <= 0 || viewport.height <= 0) {
        return undefined;
      }

      // Single-pass min/max to avoid stack overflow with large node counts
      let minX: number = Infinity;
      let maxX: number = -Infinity;
      let minY: number = Infinity;
      let maxY: number = -Infinity;
      for (const n of nodes) {
        const nx: number = n.x ?? 0;
        const ny: number = n.y ?? 0;
        if (nx < minX) {
          minX = nx;
        }
        if (nx > maxX) {
          maxX = nx;
        }
        if (ny < minY) {
          minY = ny;
        }
        if (ny > maxY) {
          maxY = ny;
        }
      }

      const x0: number = minX - NODE_WIDTH / 2 - FIT_PADDING;
      const x1: number = maxX + NODE_WIDTH / 2 + FIT_PADDING;
      const y0: number = minY - NODE_HEIGHT / 2 - FIT_PADDING;
      const y1: number = maxY + NODE_HEIGHT / 2 + FIT_PADDING;

      const bboxWidth: number = x1 - x0;
      const bboxHeight: number = y1 - y0;

      const scale: number = Math.min(viewport.width / bboxWidth, viewport.height / bboxHeight, 1.0);

      const bboxCenterX: number = (x0 + x1) / 2;
      const bboxCenterY: number = (y0 + y1) / 2;

      return {
        translateX: viewport.width / 2 - bboxCenterX * scale,
        translateY: viewport.height / 2 - bboxCenterY * scale,
        scale,
      };
    }

    // ---------------------------------------------------------------------------
    // Component
    // ---------------------------------------------------------------------------

    interface KnowledgeGraphProps {
      graphData: { nodes: GraphNode[]; links: GraphLink[] };
      selectedNodeId?: string;
      onNodeClick: (nodeId: string) => void;
      onNodeDoubleClick: (nodeId: string) => void;
    }

    export function KnowledgeGraph({
      graphData,
      selectedNodeId,
      onNodeClick,
      onNodeDoubleClick,
    }: KnowledgeGraphProps): JSX.Element {
      const svgRef = useRef<SVGSVGElement>(null);
      const gRef = useRef<SVGGElement>(null);
      const simRef = useRef<Simulation<SimNode, SimLink> | undefined>(undefined);
      const zoomRef = useRef<ZoomBehavior<SVGSVGElement, unknown> | undefined>(undefined);
      const linkElsRef = useRef<Selection<SVGLineElement, SimLink, SVGGElement, unknown> | undefined>(
        undefined,
      );
      const nodeElsRef = useRef<Selection<SVGGElement, SimNode, SVGGElement, unknown> | undefined>(
        undefined,
      );
      const selectedNodeIdRef = useRef(selectedNodeId);
      selectedNodeIdRef.current = selectedNodeId;
      const didAutoFitRef = useRef(false);
      const [dimensions, setDimensions] = useState({ width: 800, height: 600 });
      const dragDistanceRef = useRef(0);

      // Track container size
      useEffect(() => {
        const container: HTMLElement | null = svgRef.current?.parentElement ?? null;
        Iif (!container) {
          return;
        }
        const observer: ResizeObserver = new ResizeObserver((entries) => {
          for (const entry of entries) {
            setDimensions({ width: entry.contentRect.width, height: entry.contentRect.height });
          }
        });
        observer.observe(container);
        setDimensions({ width: container.clientWidth, height: container.clientHeight });
        return () => {
          observer.disconnect();
        };
      }, []);

      // Setup zoom
      useEffect(() => {
        Iif (!svgRef.current || !gRef.current) {
          return;
        }
        const svgEl: SVGSVGElement = svgRef.current;
        const gEl: SVGGElement = gRef.current;

        const zoomBehavior: ZoomBehavior<SVGSVGElement, unknown> = zoom<SVGSVGElement, unknown>()
          .scaleExtent([0.1, 4])
          .filter((event: Event) => {
            // Prevent zoom on double-click (we use it for expand)
            Iif (event.type === "dblclick") {
              return false;
            }
            return true;
          })
          .on("zoom", (event) => {
            select(gEl).attr("transform", String(event.transform));
          });

        select(svgEl).call(zoomBehavior);
        zoomRef.current = zoomBehavior;
        return () => {
          select(svgEl).on(".zoom", null);
        };
      }, []);

      // Stable callback refs so d3 event handlers don't go stale
      const onClickRef = useRef(onNodeClick);
      onClickRef.current = onNodeClick;
      const onDblClickRef = useRef(onNodeDoubleClick);
      onDblClickRef.current = onNodeDoubleClick;

      // Run simulation
      useEffect(() => {
        Iif (!gRef.current) {
          return;
        }
        const g: SVGGElement = gRef.current;

        // Stop previous
        if (simRef.current) {
          simRef.current.stop();
          simRef.current = undefined;
        }

        // Reset auto-fit flag when graph data changes so the next simulation run fits the view
        didAutoFitRef.current = false;

        if (graphData.nodes.length === 0) {
          select(g).selectAll("*").remove();
          return;
        }

        // Clone data for d3 mutation
        const simNodes: SimNode[] = graphData.nodes.map((n) => ({ ...n }));
        const nodeMap: Map<string, SimNode> = new Map(simNodes.map((n) => [n.id, n]));
        const simLinks: SimLink[] = graphData.links
          .filter((l) => nodeMap.has(l.source) && nodeMap.has(l.target))
          .map((l) => ({ source: l.source, target: l.target, type: l.type }));

        // Clear previous elements
        select(g).selectAll("*").remove();

        // Create link elements
        const linkEls: Selection<SVGLineElement, SimLink, SVGGElement, unknown> = select(g)
          .selectAll<SVGLineElement, SimLink>("line")
          .data(simLinks)
          .enter()
          .append("line")
          .attr("class", styles.link);

        // Edge type tooltip on hover
        linkEls.append("title").text((d: SimLink) => d.type);

        linkElsRef.current = linkEls;

        // Create node groups
        const nodeEls: Selection<SVGGElement, SimNode, SVGGElement, unknown> = select(g)
          .selectAll<SVGGElement, SimNode>("g.kg-node")
          .data(simNodes)
          .enter()
          .append("g")
          .attr("class", `kg-node ${styles.node}`)
          .on("click", (_event: MouseEvent, d: SimNode) => {
            // Suppress click if the user just finished dragging
            Iif (dragDistanceRef.current > DRAG_CLICK_THRESHOLD) {
              return;
            }
            onClickRef.current(d.id);
          })
          .on("dblclick", (_event: MouseEvent, d: SimNode) => {
            onDblClickRef.current(d.id);
          });

        nodeElsRef.current = nodeEls;

        // Node card background
        nodeEls
          .append("rect")
          .attr("class", styles.nodeCard)
          .attr("width", NODE_WIDTH)
          .attr("height", NODE_HEIGHT)
          .attr("rx", NODE_RADIUS)
          .attr("ry", NODE_RADIUS)
          .style("--node-color", (d: SimNode) => getNodeColor(d));

        // Category indicator bar
        nodeEls
          .append("rect")
          .attr("class", styles.nodeIndicator)
          .attr("width", 4)
          .attr("height", NODE_HEIGHT)
          .attr("rx", 2)
          .attr("fill", (d: SimNode) => getNodeColor(d));

        // Node label
        nodeEls
          .append("text")
          .attr("class", styles.nodeLabel)
          .attr("x", NODE_WIDTH / 2)
          .attr("y", NODE_HEIGHT / 2 - 4)
          .attr("text-anchor", "middle")
          .attr("dominant-baseline", "central")
          .text((d: SimNode) => (d.label.length > 26 ? d.label.substring(0, 24) + "..." : d.label));

        // Category badge
        nodeEls
          .append("text")
          .attr("class", styles.nodeBadge)
          .attr("x", NODE_WIDTH / 2)
          .attr("y", NODE_HEIGHT - 8)
          .attr("text-anchor", "middle")
          .text((d: SimNode) =>
            (d.kind === "reference" ? (d.sourceType ?? "ref") : (d.category ?? "")).toUpperCase(),
          );

        // Simulation
        const sim: Simulation<SimNode, SimLink> = forceSimulation(simNodes)
          .force(
            "link",
            forceLink<SimNode, SimLink>(simLinks)
              .id((d) => d.id)
              .distance(140),
          )
          .force("charge", forceManyBody().strength(-400))
          .force("center", forceCenter(dimensions.width / 2, dimensions.height / 2))
          .force("collide", forceCollide<SimNode>(NODE_WIDTH / 2 + 16))
          .on("tick", () => {
            linkEls
              .attr("x1", (d: SimLink) => (d.source as SimNode).x ?? 0)
              .attr("y1", (d: SimLink) => (d.source as SimNode).y ?? 0)
              .attr("x2", (d: SimLink) => (d.target as SimNode).x ?? 0)
              .attr("y2", (d: SimLink) => (d.target as SimNode).y ?? 0);

            nodeEls.attr(
              "transform",
              (d: SimNode) =>
                `translate(${(d.x ?? 0) - NODE_WIDTH / 2},${(d.y ?? 0) - NODE_HEIGHT / 2})`,
            );
          });

        simRef.current = sim;

        // Drag behavior — lets users grab and reposition nodes
        const dragBehavior = drag<SVGGElement, SimNode>()
          .on("start", (_event: D3DragEvent<SVGGElement, SimNode, SimNode>, d: SimNode) => {
            d.fx = d.x;
            d.fy = d.y;
            dragDistanceRef.current = 0;
          })
          .on("drag", (event: D3DragEvent<SVGGElement, SimNode, SimNode>, d: SimNode) => {
            d.fx = event.x;
            d.fy = event.y;
            dragDistanceRef.current += Math.abs(event.dx) + Math.abs(event.dy);
            // Only reheat simulation once we confirm an actual drag gesture
            Iif (dragDistanceRef.current > DRAG_CLICK_THRESHOLD && sim.alphaTarget() === 0) {
              sim.alphaTarget(0.3).restart();
            }
          })
          .on("end", (event: D3DragEvent<SVGGElement, SimNode, SimNode>, d: SimNode) => {
            Iif (!event.active) {
              sim.alphaTarget(0);
            }
            // Release node so it re-settles in the force layout
            d.fx = undefined;
            d.fy = undefined;
          });
        nodeEls.call(dragBehavior);

        // Zoom to fit all nodes once the force simulation has fully converged.
        // One-shot: skip if already fitted (drag reheat would re-trigger), or if a node is selected.
        sim.on("end", () => {
          if (
            svgRef.current &&
            zoomRef.current &&
            simNodes.length > 0 &&
            !didAutoFitRef.current &&
            !selectedNodeIdRef.current
          ) {
            didAutoFitRef.current = true;
            const fit: ZoomToFitResult | undefined = computeZoomToFit(simNodes, dimensions);
            Iif (!fit) {
              return;
            }
            const { translateX, translateY, scale }: ZoomToFitResult = fit;
            const zb: ZoomBehavior<SVGSVGElement, unknown> = zoomRef.current;
            const t = zoomIdentity.translate(translateX, translateY).scale(scale);
            // eslint-disable-next-line @typescript-eslint/unbound-method -- d3 zoom API pattern
            select(svgRef.current).transition().duration(500).call(zb.transform, t);
          }
        });

        return () => {
          sim.stop();
        };
      }, [graphData, dimensions]);

      // Update selection styling without rebuilding simulation
      useEffect(() => {
        if (!gRef.current || !nodeElsRef.current || !linkElsRef.current) {
          return;
        }

        if (!selectedNodeId) {
          // No selection — full opacity on everything
          nodeElsRef.current.classed(styles.dimmed, false).classed(styles.selected, false);
          linkElsRef.current.classed(styles.dimmedLink, false);
          return;
        }

        // Build set of connected node IDs
        const connectedIds: Set<string> = new Set([selectedNodeId]);
        linkElsRef.current.each((d: SimLink) => {
          const srcId: string = (d.source as SimNode).id;
          const tgtId: string = (d.target as SimNode).id;
          if (srcId === selectedNodeId || tgtId === selectedNodeId) {
            connectedIds.add(srcId);
            connectedIds.add(tgtId);
          }
        });

        // Update node classes
        nodeElsRef.current
          .classed(styles.selected, (d: SimNode) => d.id === selectedNodeId)
          .classed(styles.dimmed, (d: SimNode) => !connectedIds.has(d.id));

        // Dim unconnected links
        linkElsRef.current.classed(styles.dimmedLink, (d: SimLink) => {
          const srcId: string = (d.source as SimNode).id;
          const tgtId: string = (d.target as SimNode).id;
          return !connectedIds.has(srcId) || !connectedIds.has(tgtId);
        });
      }, [selectedNodeId, graphData]);

      // Center on selected node
      const handleCenterOnNode = useCallback(() => {
        if (!selectedNodeId || !simRef.current || !svgRef.current || !zoomRef.current) {
          return;
        }
        const node: SimNode | undefined = simRef.current
          .nodes()
          .find((n: SimNode) => n.id === selectedNodeId);
        if (node && Number.isFinite(node.x) && Number.isFinite(node.y)) {
          const zb: ZoomBehavior<SVGSVGElement, unknown> = zoomRef.current;
          const t = zoomIdentity
            .translate(dimensions.width / 2, dimensions.height / 2)
            .scale(1.2)
            .translate(-(node.x ?? 0), -(node.y ?? 0));
          // eslint-disable-next-line @typescript-eslint/unbound-method -- d3 zoom API pattern
          select(svgRef.current).transition().duration(500).call(zb.transform, t);
        }
      }, [selectedNodeId, dimensions]);

      useEffect(() => {
        handleCenterOnNode();
      }, [handleCenterOnNode]);

      return (
        <div className={styles.graphContainer} data-testid="knowledge-graph">
          <svg ref={svgRef} width={dimensions.width} height={dimensions.height} className={styles.svg}>
            <defs>
              <filter id="glow">
                <feGaussianBlur stdDeviation="3" result="coloredBlur" />
                <feMerge>
                  <feMergeNode in="coloredBlur" />
                  <feMergeNode in="SourceGraphic" />
                </feMerge>
              </filter>
            </defs>
            <g ref={gRef} />
          </svg>
        </div>
      );
    }