# All files / src/components/streams useCoordinationLayout.ts

96.42% Statements 27/28
100% Branches 2/2
83.33% Functions 5/6
100% Lines 26/26

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     /**
     * Dagre positioning layer for the Coordination graph. Takes the pure
     * {@link buildCoordinationGraph} model (dagre-free, unit-testable) and assigns
     * deterministic node positions via a left-to-right bipartite dagre layout.
     *
     * @module
     */

    import { useMemo } from "react";
    import dagre from "@dagrejs/dagre";
    import type { Node } from "@xyflow/react";
    import type { Session, StreamData } from "../../hooks/types.js";
    import {
      buildCoordinationGraph,
      STREAM_NODE_TYPE,
      type CoordNodeData,
      type CoordinationLayoutResult,
    } from "./coordinationGraphModel.js";

    export {
      buildCoordinationGraph,
      sessionNodeId,
      streamNodeId,
      COORD_EDGE_TYPE,
      SESSION_NODE_TYPE,
      STREAM_NODE_TYPE,
    } from "./coordinationGraphModel.js";
    export type {
      CoordEdgeData,
      CoordNodeData,
      CoordinationLayoutResult,
      SessionNodeData,
      StreamNodeData,
    } from "./coordinationGraphModel.js";

    /** Width of a session node (pixels). */
    const SESSION_NODE_WIDTH: number = 200;
    /** Height of a session node (pixels). */
    const SESSION_NODE_HEIGHT: number = 64;
    /** Width of a stream hub node (pixels). */
    const STREAM_NODE_WIDTH: number = 180;
    /** Height of a stream hub node (pixels). */
    const STREAM_NODE_HEIGHT: number = 56;
    /** Separation between sibling nodes within a rank (pixels). */
    const NODE_SEPARATION: number = 40;
    /** Separation between rank levels (pixels). */
    const RANK_SEPARATION: number = 70;

    /** Node dimensions for dagre, keyed by node type. */
    function nodeDimensions(type: string | undefined): { width: number; height: number } {
      if (type === STREAM_NODE_TYPE) {
        return { width: STREAM_NODE_WIDTH, height: STREAM_NODE_HEIGHT };
      }
      return { width: SESSION_NODE_WIDTH, height: SESSION_NODE_HEIGHT };
    }

    /** Assign dagre positions to a pure coordination graph model. */
    function layoutGraph(model: CoordinationLayoutResult): CoordinationLayoutResult {
      if (model.nodes.length === 0) {
        return model;
      }

      const graph = new dagre.graphlib.Graph({ multigraph: true });
      graph.setDefaultEdgeLabel(() => ({}));
      graph.setGraph({ rankdir: "LR", nodesep: NODE_SEPARATION, ranksep: RANK_SEPARATION });

      for (const node of model.nodes) {
        const { width, height } = nodeDimensions(node.type);
        graph.setNode(node.id, { width, height });
      }
      for (const edge of model.edges) {
        graph.setEdge(edge.source, edge.target, {}, edge.id);
      }

      dagre.layout(graph);

      const nodes: Node<CoordNodeData>[] = model.nodes.map((node) => {
        const pos = graph.node(node.id) as { x: number; y: number };
        const { width, height } = nodeDimensions(node.type);
        return { ...node, position: { x: pos.x - width / 2, y: pos.y - height / 2 } };
      });

      return { nodes, edges: model.edges };
    }

    /**
     * Build and lay out the coordination graph, memoized on its inputs. Sessions
     * with no visible streams are intentionally omitted — the graph shows
     * coordination, not the full session inventory.
     */
    export function useCoordinationLayout(
      streams: StreamData[],
      sessions: Session[],
    ): CoordinationLayoutResult {
      return useMemo(() => layoutGraph(buildCoordinationGraph(streams, sessions)), [streams, sessions]);
    }