/**
 * Graph path utilities: compute which nodes/edges are "on the path" of an update.
 * Used to show connection ant trail only along the full chain (upstream → updating → downstream).
 * Works with any node types; any node can signal it is updating via startConnectionPathUpdate(id).
 */

export type GraphEdge = { source: string; target: string }

/** Nodes reachable from seedIds by following edges forward (source → target). */
export function getDownstreamNodeIds(edges: GraphEdge[], seedIds: string[]): Set<string> {
  const out = new Set<string>(seedIds)
  let added = true
  while (added) {
    added = false
    for (const e of edges) {
      if (out.has(e.source) && !out.has(e.target)) {
        out.add(e.target)
        added = true
      }
    }
  }
  return out
}

/** Nodes that can reach any seed by following edges backward (target → source). */
export function getUpstreamNodeIds(edges: GraphEdge[], seedIds: string[]): Set<string> {
  const out = new Set<string>(seedIds)
  let added = true
  while (added) {
    added = false
    for (const e of edges) {
      if (out.has(e.target) && !out.has(e.source)) {
        out.add(e.source)
        added = true
      }
    }
  }
  return out
}

/**
 * All node ids that lie on the path of an update.
 * - If triggerNodeIds is non-empty: path = nodes that are both downstream of a trigger and
 *   upstream of an updating node (only the chain that actually triggered the update).
 * - Otherwise: path = upstream ∪ updating ∪ downstream of updating (legacy full upstream/downstream).
 * An edge should show the update animation iff both its source and target are in this set.
 */
export function getPathNodeIds(
  edges: GraphEdge[],
  updatingNodeIds: string[],
  triggerNodeIds?: string[]
): Set<string> {
  if (updatingNodeIds.length === 0) return new Set()
  const upstream = getUpstreamNodeIds(edges, updatingNodeIds)
  if (triggerNodeIds != null && triggerNodeIds.length > 0) {
    const downstreamOfTrigger = getDownstreamNodeIds(edges, triggerNodeIds)
    const path = new Set<string>()
    upstream.forEach((id) => {
      if (downstreamOfTrigger.has(id)) path.add(id)
    })
    return path
  }
  const downstream = getDownstreamNodeIds(edges, updatingNodeIds)
  const path = new Set<string>(upstream)
  downstream.forEach((id) => path.add(id))
  return path
}