/**
 * Candidate cards are keyed only on scoreable facts + birth profile + inference.
 * An occupation_note that does not score must not stale the snapshot.
 */

export type CandidateSnapshotSource = Readonly<{
  birthProfileFingerprint: string;
  scoreableEvidenceFingerprint: string;
  inferenceRevision: number;
  candidateSetVersion: string;
  scoringPolicyVersion: string;
}>;

export type SnapshotStaleReason =
  | "birth_profile_changed"
  | "scoreable_evidence_changed"
  | "candidate_set_superseded"
  | "inference_revision_changed"
  | "fingerprint_missing";

export const SNAPSHOT_STALE_COPY: Readonly<Record<SnapshotStaleReason, string>> = {
  birth_profile_changed: "出生资料已变化，候选已失效",
  scoreable_evidence_changed: "可评分证据已变化，请重新比较候选",
  candidate_set_superseded: "已有更新的候选结果",
  inference_revision_changed: "候选后验已更新，请使用当前结果",
  fingerprint_missing: "候选快照缺少证据指纹，请重新比较候选",
};

export function classifySnapshotStaleReason(
  snapshot: CandidateSnapshotSource | null | undefined,
  current: CandidateSnapshotSource,
): SnapshotStaleReason | null {
  if (!snapshot) return "candidate_set_superseded";
  if (!snapshot.scoreableEvidenceFingerprint || !current.scoreableEvidenceFingerprint) {
    return "fingerprint_missing";
  }
  if (
    snapshot.birthProfileFingerprint
    && current.birthProfileFingerprint
    && snapshot.birthProfileFingerprint !== current.birthProfileFingerprint
  ) {
    return "birth_profile_changed";
  }
  if (snapshot.scoreableEvidenceFingerprint !== current.scoreableEvidenceFingerprint) {
    return "scoreable_evidence_changed";
  }
  if (snapshot.candidateSetVersion !== current.candidateSetVersion) {
    return "candidate_set_superseded";
  }
  if (snapshot.inferenceRevision !== current.inferenceRevision) {
    return "inference_revision_changed";
  }
  return null;
}

/** Cards stay current when only non-scoreable notes (occupation_note) change. */
export function scoreableSnapshotIsCurrent(
  snapshot: CandidateSnapshotSource | null | undefined,
  current: CandidateSnapshotSource,
): boolean {
  if (!snapshot) return false;
  if (!snapshot.scoreableEvidenceFingerprint || !current.scoreableEvidenceFingerprint) return false;
  return snapshot.scoreableEvidenceFingerprint === current.scoreableEvidenceFingerprint
    && snapshot.candidateSetVersion === current.candidateSetVersion
    && snapshot.inferenceRevision === current.inferenceRevision;
}

/** No stored snapshot is not stale; a stored snapshot with a missing fingerprint is. */
export function storedSnapshotIsCurrent(
  snapshot: CandidateSnapshotSource | null | undefined,
  current: CandidateSnapshotSource,
): boolean {
  if (!snapshot) return true;
  return scoreableSnapshotIsCurrent(snapshot, current);
}

export function snapshotIsCurrent(
  snapshot: CandidateSnapshotSource | null | undefined,
  current: CandidateSnapshotSource,
): boolean {
  return classifySnapshotStaleReason(snapshot, current) === null;
}

export function candidateSnapshotSource(input: CandidateSnapshotSource): CandidateSnapshotSource {
  return {
    birthProfileFingerprint: input.birthProfileFingerprint,
    scoreableEvidenceFingerprint: input.scoreableEvidenceFingerprint,
    inferenceRevision: input.inferenceRevision,
    candidateSetVersion: input.candidateSetVersion,
    scoringPolicyVersion: input.scoringPolicyVersion,
  };
}