import { PredictionQuery, PredictionResponse } from "./types/predictions.js";

interface CacheEntry {
  response: PredictionResponse;
  expiresAt: number;
}

/**
 * In-memory cache for prediction responses with TTL-based expiry.
 */
export class PredictionCache {
  private readonly cache = new Map<string, CacheEntry>();
  private readonly ttlMs: number;

  constructor(ttlMs: number) {
    this.ttlMs = ttlMs;
  }

  /** Build a deterministic cache key from a prediction query. */
  private buildKey(query: PredictionQuery): string {
    return `${query.task_type}:${query.model}:${query.provider}:${query.complexity}`;
  }

  /** Get a cached prediction. Returns null if not cached or expired. */
  get(query: PredictionQuery): PredictionResponse | null {
    const key = this.buildKey(query);
    const entry = this.cache.get(key);

    if (!entry) {
      return null;
    }

    if (Date.now() > entry.expiresAt) {
      this.cache.delete(key);
      return null;
    }

    return entry.response;
  }

  /** Store a prediction response with TTL. */
  set(query: PredictionQuery, response: PredictionResponse): void {
    const key = this.buildKey(query);
    this.cache.set(key, {
      response,
      expiresAt: Date.now() + this.ttlMs,
    });
  }

  /** Clear all cached predictions. */
  clear(): void {
    this.cache.clear();
  }

  /** Number of entries currently in cache (including potentially expired). */
  get size(): number {
    return this.cache.size;
  }
}