/*
 * Service-worker core: pure helpers with NO side effects (no `self`, no
 * `caches`, no `fetch`). Split out from `sw.js` so the tricky bits — HTTP Range
 * parsing, LRU eviction, cache-key normalization — can be unit-tested in Node.
 *
 * This is an ES module: `sw.js` imports it (the SW is registered with
 * { type: 'module' }) and tests import it natively — one source, no drift.
 */

// Bump the version to invalidate every cached blob on a breaking change.
export const AUDIO_CACHE = 'mcma-audio-v1';
// Synthetic same-origin key holding the LRU index ({ key: {size, lastAccess} }).
export const INDEX_URL = '/__mcma_audio_index__';
// Soft cap on total cached audio. LRU eviction keeps us under this.
export const MAX_BYTES = 500 * 1024 * 1024; // 500 MB

// Cover art (album/artist/playlist images) gets its own cache with a simple
// count cap — covers are small and stable, so no per-byte LRU is needed.
export const COVER_CACHE = 'mcma-covers-v1';
export const MAX_COVERS = 600;

// Backend stream route: /api/v1/streaming/tracks/<trackId>?token=...
const STREAM_RE = /\/streaming\/tracks\/([^/?#]+)/;

/** The track (content) id from a stream URL, or null if it isn't one. */
export function trackIdFromUrl(url) {
  const m = STREAM_RE.exec(url);
  return m ? m[1] : null;
}

/**
 * Canonical cache key for a stream URL: origin + path, query dropped. The auth
 * token rides in the query and rotates on refresh, so keying by content path
 * (origin keeps two backends from colliding) makes the cache token-stable —
 * the same track is one entry regardless of which token fetched it.
 */
export function cacheKeyFor(url) {
  try {
    const u = new URL(url);
    return u.origin + u.pathname;
  } catch {
    return String(url).split('?')[0];
  }
}

/**
 * Parse an HTTP `Range` header against a known resource size. Returns inclusive
 * { start, end } byte offsets, or null for "no range / serve the whole thing".
 * Handles `bytes=a-b`, `bytes=a-` (open-ended) and `bytes=-n` (last n bytes).
 */
export function parseRangeHeader(rangeHeader, size) {
  if (!rangeHeader) return null;
  const m = /^bytes=(\d*)-(\d*)$/.exec(String(rangeHeader).trim());
  if (!m) return null;
  let start = m[1] === '' ? null : parseInt(m[1], 10);
  let end = m[2] === '' ? null : parseInt(m[2], 10);
  if (start === null && end === null) return null;
  if (start === null) {
    // suffix range: the final `end` bytes
    start = Math.max(0, size - end);
    end = size - 1;
  } else if (end === null) {
    end = size - 1;
  }
  if (Number.isNaN(start) || Number.isNaN(end)) return null;
  if (end >= size) end = size - 1;
  if (start < 0 || start > end) return null;
  return { start, end };
}

/**
 * Choose which cached entries to evict (least-recently-used first) so that the
 * existing total plus an incoming blob fits under `maxBytes`. Returns the list
 * of keys to delete; empty when there's already room.
 *
 * `index` is { [key]: { size, lastAccess } }.
 */
export function selectEvictions(index, incomingSize, maxBytes) {
  let total = incomingSize;
  for (const k in index) total += index[k].size || 0;
  if (total <= maxBytes) return [];

  const entries = Object.keys(index)
    .map((k) => ({
      key: k,
      lastAccess: index[k].lastAccess || 0,
      size: index[k].size || 0,
    }))
    .sort((a, b) => a.lastAccess - b.lastAccess); // oldest first

  const evict = [];
  for (const e of entries) {
    if (total <= maxBytes) break;
    evict.push(e.key);
    total -= e.size;
  }
  return evict;
}