Function addEdge

packages/effect/src/Graph.ts:1145–1197

(
  mutable: MutableGraph<N, E, T>,
  source: NodeIndex,
  target: NodeIndex,
  data: E
)

 * @category mutations
 */
export const addEdge = <N, E, T extends Kind = "directed">(
  mutable: MutableGraph<N, E, T>,
  source: NodeIndex,
  target: NodeIndex,
  data: E
): EdgeIndex => {
  // Validate that both nodes exist
  if (!mutable.nodes.has(source)) {
    throw missingNode(source)
  }
  if (!mutable.nodes.has(target)) {
    throw missingNode(target)
  }

  const edgeIndex = mutable.nextEdgeIndex

  // Create edge data
  const edgeData = new Edge({ source, target, data })
  mutable.edges.set(edgeIndex, edgeData)

  // Update adjacency lists
  const sourceAdjacency = mutable.adjacency.get(source)
  if (sourceAdjacency !== undefined) {
    sourceAdjacency.push(edgeIndex)
  }

  const targetReverseAdjacency = mutable.reverseAdjacency.get(target)
  if (targetReverseAdjacency !== undefined) {
    targetReverseAdjacency.push(edgeIndex)
  }

  // For undirected graphs, add reverse connections
  if (mutable.type === "undirected") {
    const targetAdjacency = mutable.adjacency.get(target)
    if (targetAdjacency !== undefined) {
      targetAdjacency.push(edgeIndex)
    }

    const sourceReverseAdjacency = mutable.reverseAdjacency.get(source)
    if (sourceReverseAdjacency !== undefined) {
      sourceReverseAdjacency.push(edgeIndex)
    }
  }

  // Update allocators
  mutable.nextEdgeIndex = mutable.nextEdgeIndex + 1

  // Only invalidate cycle flag if the graph was acyclic
  // Adding edges cannot remove cycles from cyclic graphs
  invalidateCycleFlagOnAddition(mutable)

  return edgeIndex
}

/**
 * Removes a node and all its incident edges from a mutable graph.