import { createHash } from 'crypto';
import { existsSync, mkdirSync, statSync, createReadStream, writeFileSync } from 'fs';
import { join } from 'path';
import type { Readable } from 'stream';

const MAX_AGE_MS = 24 * 60 * 60 * 1000; // 24 hours

export class ScreenshotCache {
  private dir: string;

  constructor(dir: string) {
    this.dir = dir;
    if (!existsSync(dir)) {
      mkdirSync(dir, { recursive: true });
    }
  }

  /**
   * Build a cache key by quantizing view params and hashing.
   * lat/lon are rounded to 2 decimals and zoom to an integer so nearby views
   * share a cache entry; all other params are sorted for order-independence.
   */
  buildKey(params: URLSearchParams): string {
    const normalized: Record<string, string> = {};

    const lat = params.get('lat');
    const lon = params.get('lon');
    const zoom = params.get('zoom');
    if (lat && lon && zoom) {
      normalized.lat = parseFloat(lat).toFixed(2);
      normalized.lon = parseFloat(lon).toFixed(2);
      normalized.zoom = Math.round(parseFloat(zoom)).toString();
    }

    const quantized = new Set(['lat', 'lon', 'zoom']);
    const keys = [...new Set(params.keys())].filter((k) => !quantized.has(k)).sort();
    for (const key of keys) {
      normalized[key] = params.getAll(key).sort().join(',');
    }

    const input = JSON.stringify(normalized);
    const hash = createHash('sha256').update(input).digest('hex').substring(0, 16);
    return hash;
  }

  getPath(key: string): string {
    return join(this.dir, `${key}.jpg`);
  }

  /**
   * Returns a readable stream if a fresh cached file exists, null otherwise.
   */
  get(key: string): Readable | null {
    const path = this.getPath(key);
    if (!existsSync(path)) return null;

    try {
      const stat = statSync(path);
      const age = Date.now() - stat.mtimeMs;
      if (age > MAX_AGE_MS) return null;
      return createReadStream(path);
    } catch {
      return null;
    }
  }

  /**
   * Write screenshot bytes to cache.
   */
  set(key: string, data: Buffer): void {
    const path = this.getPath(key);
    writeFileSync(path, data);
  }
}