// Dependency graph over a SysML model.
//
// Nodes: every Block, Property, Constraint, Requirement.
// Edges encode the structural and traceability relationships from
// docs/sysml-modeling.md §8.
//
// Used by the UI for cross-surface highlighting now (M4) and by Socrates'
// impact analysis later (M7).

import type { SysMLModel } from "./model";

export type DepNodeKind = "block" | "property" | "constraint" | "requirement";

export interface DepNode {
  id: string;          // unique within graph; for properties: `${blockId}.${propertyId}`
  kind: DepNodeKind;
  label: string;
}

export type DepEdgeKind =
  | "contains"          // block → property
  | "relates"           // block → block (per association.kind)
  | "applies-to"        // constraint → block
  | "satisfies"         // requirement → block
  | "derives-from";     // requirement → requirement

export interface DepEdge {
  from: string;
  to: string;
  kind: DepEdgeKind;
  /** For "relates" edges, the underlying association kind. */
  associationKind?: string;
}

export interface DepGraph {
  nodes: Map<string, DepNode>;
  /** Adjacency list, indexed by `from`. */
  out: Map<string, DepEdge[]>;
  /** Reverse adjacency, indexed by `to`. Useful for "what depends on this?". */
  in: Map<string, DepEdge[]>;
}

export function buildDepGraph(model: SysMLModel): DepGraph {
  const nodes = new Map<string, DepNode>();
  const out = new Map<string, DepEdge[]>();
  const inEdges = new Map<string, DepEdge[]>();

  function addNode(node: DepNode) {
    nodes.set(node.id, node);
    if (!out.has(node.id)) out.set(node.id, []);
    if (!inEdges.has(node.id)) inEdges.set(node.id, []);
  }

  function addEdge(edge: DepEdge) {
    const o = out.get(edge.from);
    if (o) o.push(edge);
    else out.set(edge.from, [edge]);
    const i = inEdges.get(edge.to);
    if (i) i.push(edge);
    else inEdges.set(edge.to, [edge]);
  }

  for (const b of model.blocks) {
    addNode({ id: b.id, kind: "block", label: b.label });
    for (const p of b.properties) {
      const pid = `${b.id}.${p.id}`;
      addNode({ id: pid, kind: "property", label: p.name });
      addEdge({ from: b.id, to: pid, kind: "contains" });
    }
  }

  for (const a of model.associations) {
    addEdge({
      from: a.fromBlockId,
      to: a.toBlockId,
      kind: "relates",
      associationKind: a.kind,
    });
  }

  for (const c of model.constraints) {
    addNode({ id: c.id, kind: "constraint", label: c.label });
    for (const target of c.appliesTo) {
      addEdge({ from: c.id, to: target, kind: "applies-to" });
    }
  }

  for (const r of model.requirements) {
    addNode({ id: r.id, kind: "requirement", label: r.tag });
    for (const rel of r.relations) {
      if (rel.kind === "satisfy") {
        addEdge({ from: r.id, to: rel.blockId, kind: "satisfies" });
      } else if (rel.kind === "derive") {
        addEdge({ from: r.id, to: rel.fromReqId, kind: "derives-from" });
      }
    }
  }

  return { nodes, out, in: inEdges };
}

/**
 * BFS the dep graph downstream from `seedId`, returning the closure (excluding
 * the seed itself by default). Use for "if I change X, what's affected?".
 */
export function dependentsOf(graph: DepGraph, seedId: string): Set<string> {
  const visited = new Set<string>();
  const queue: string[] = [seedId];
  while (queue.length) {
    const cur = queue.shift()!;
    const out = graph.out.get(cur) ?? [];
    for (const edge of out) {
      if (!visited.has(edge.to)) {
        visited.add(edge.to);
        queue.push(edge.to);
      }
    }
    // Reverse direction too — things that depend ON this element should also
    // appear in the closure (an Assumption linked to this block, etc., once
    // those are added in M8).
    const inEdges = graph.in.get(cur) ?? [];
    for (const edge of inEdges) {
      if (!visited.has(edge.from)) {
        visited.add(edge.from);
        queue.push(edge.from);
      }
    }
  }
  visited.delete(seedId);
  return visited;
}

export function neighborhood(graph: DepGraph, seedId: string, radius = 2): Set<string> {
  const visited = new Set<string>([seedId]);
  let frontier = new Set<string>([seedId]);
  for (let i = 0; i < radius; i++) {
    const next = new Set<string>();
    for (const id of frontier) {
      for (const e of graph.out.get(id) ?? []) {
        if (!visited.has(e.to)) { visited.add(e.to); next.add(e.to); }
      }
      for (const e of graph.in.get(id) ?? []) {
        if (!visited.has(e.from)) { visited.add(e.from); next.add(e.from); }
      }
    }
    frontier = next;
  }
  visited.delete(seedId);
  return visited;
}