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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>
);
}
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