/**
 * Retrieval-class routing (Task 308).
 *
 * Consumes the `retrievalClass` field produced by Task 304's
 * gateway-classifier (landed) and returns a per-class index plan: which
 * labels to filter to, which fusion weights to favour, and whether to
 * skip the lookup entirely.
 *
 * No new Haiku call here — this module is a pure deterministic mapping
 * over the gateway's existing classification.
 */

export type RetrievalClass =
  | "entity"
  | "temporal"
  | "event"
  | "general"
  | "none";

export interface IndexPlan {
  /** When true, the caller short-circuits and returns no results. */
  skip: boolean;
  /** Restrict vector + BM25 to these labels. Undefined means no filter. */
  labelFilter?: string[];
  /** Weight on the vector half of the (weighted-sum) fusion. */
  vectorWeight: number;
  /** Weight on the BM25 half of the (weighted-sum) fusion. */
  bm25Weight: number;
}

/**
 * Return the index plan for a retrieval class. Unknown values fall back
 * to `general` rather than throwing — the routing is a soft hint and the
 * caller's old behaviour is the safe default.
 */
export function pickIndexMix(retrievalClass: string | undefined): IndexPlan {
  switch (retrievalClass) {
    case "entity":
      return {
        skip: false,
        labelFilter: ["Person", "Company", "Concept"],
        vectorWeight: 0.85,
        bm25Weight: 0.15,
      };
    case "temporal":
      return {
        skip: false,
        labelFilter: ["Event"],
        vectorWeight: 0.2,
        bm25Weight: 0.8,
      };
    case "event":
      return {
        skip: false,
        labelFilter: ["Event"],
        vectorWeight: 0,
        bm25Weight: 1,
      };
    case "none":
      return { skip: true, vectorWeight: 0, bm25Weight: 0 };
    case "general":
    default:
      if (retrievalClass && retrievalClass !== "general") {
        process.stderr.write(
          `[graph-search:unknown-class] rc=${retrievalClass} fallback=general\n`,
        );
      }
      return { skip: false, vectorWeight: 0.7, bm25Weight: 0.3 };
  }
}