Strategy

type SearchResult = {
  id: string;
  score: number;
  ageDays: number;
  deprecated: boolean;
};

// A policy compares two results. Negative: a first. Zero: tied. Positive: b first.
type RankingPolicy = (a: SearchResult, b: SearchResult) => number;

// Deprecated pages sink below current ones; then the highest score first.
function byRelevance(a: SearchResult, b: SearchResult): number {
  if (a.deprecated !== b.deprecated) return a.deprecated ? 1 : -1;
  return b.score - a.score;
}
function byRecent(a: SearchResult, b: SearchResult): number {
  return a.ageDays - b.ageDays;
}

// The caller's choice, by name.
function choosePolicy(name: string): RankingPolicy {
  switch (name) {
    case 'relevance':
      return byRelevance;
    case 'recent':
      return byRecent;
    default:
      throw new Error(`unknown ranking policy: ${name}`);
  }
}

// The shared workflow: copy, ask the policy, and settle its ties by ID.
function rankResults(items: SearchResult[], policy: RankingPolicy): SearchResult[] {
  const ranked = [...items];
  function compare(a: SearchResult, b: SearchResult): number {
    const order = policy(a, b);
    const tied = order === 0;
    if (!tied) return order;
    return a.id < b.id ? -1 : a.id > b.id ? 1 : 0;
  }
  ranked.sort(compare);
  return ranked;
}