/**
 * Service Worker
 *
 * Handles caching of:
 * - App shell (HTML, CSS, JS)
 * - Map tiles (passive runtime caching, per-host buckets)
 * - API responses (network-first)
 *
 * Note: Database operations are handled by the SharedWorker (shared-db-worker.js),
 *       NOT by this service worker. They serve different purposes:
 *       - Service Worker: Caching, offline asset serving, push notifications
 *       - SharedWorker: Shared database connection across tabs
 */

// v3: lower per-cache limits (5000 → 1500) and counter-based eviction to
//     prevent Safari memory-pressure reloads.
// v4: raise OSM and Topographic limits to 8000 to support active offline
//     downloads (Phase 2). Other providers stay at 1500.
// v5: switch LayerSwitcher icon path to base-URL-aware; force shell refresh.
// v6: rename /icons/ → /app-icons/ to dodge Apache's default mod_alias
//     mapping (Alias /icons/ /usr/share/apache2/icons/) which intercepts
//     the path server-side. Force shell refresh so deployed clients
//     re-fetch the new HTML/manifest with the new path.
// v7: HTML pages now use network-first (was cache-first) so new deploys
//     are picked up immediately without needing another SW version bump.
//     Hashed JS / CSS / WASM stay cache-first (they're immutable per build).
// v8: GPS trail recording feature (reusable src/geotracker/ engine, expandable
//     My Location control, navbar GPS readout, gps_trails SQLocal tables) plus
//     mobile drawing-toolbar wrap, base-map "None" option, and the Safari
//     100svh dock fix. New hashed bundle + updated shell — bump to evict the
//     old module/shell caches.
const CACHE_VERSION = 'v8';
const SHELL_CACHE   = `shell-${CACHE_VERSION}`;
const MODULES_CACHE = `modules-${CACHE_VERSION}`;
const API_CACHE     = `api-${CACHE_VERSION}`;

// ----------------------------------------------------------------------------
// Tile caches — one per provider so users can clear them independently.
// Limits are per-cache (not global). 5 000 tiles ≈ ~150 MB at ~30 KB/tile,
// which covers a Ghana district at zoom 10–15 (typical field-work range).
// ----------------------------------------------------------------------------
const TILES_OSM         = `tiles-osm-${CACHE_VERSION}`;
const TILES_TOPO        = `tiles-topo-${CACHE_VERSION}`;
const TILES_SATELLITE   = `tiles-satellite-${CACHE_VERSION}`;
const TILES_CARTO_LIGHT = `tiles-carto-light-${CACHE_VERSION}`;
const TILES_CARTO_DARK  = `tiles-carto-dark-${CACHE_VERSION}`;

// Per-provider tile limits.
//   • OSM and Topographic are the providers offered for active offline
//     download (Phase 2 dialog), so they get a higher cap (~240 MB each at
//     ~30 KB/tile) — enough for a typical Ghana district at zoom 10–15.
//   • The other providers serve passive caching only (whatever the user has
//     already viewed), so 1 500 tiles ≈ 45 MB is plenty.
//
// Total max ≈ 5 × ~150 MB = ~750 MB on disk in the worst case, but only the
// two downloadable buckets are likely to fill. Eviction sweeps run every 100
// inserts (see EVICTION_CHECK_INTERVAL) so memory pressure stays bounded.
const TILE_LIMITS = {
  [TILES_OSM]:         8000,
  [TILES_TOPO]:        8000,
  [TILES_SATELLITE]:   1500,
  [TILES_CARTO_LIGHT]: 1500,
  [TILES_CARTO_DARK]:  1500,
};

// Per-cache running insert counter, in memory. Avoids calling cache.keys()
// (which materialises every Request object in the cache) on every put — that
// was the cause of the Safari "reloaded due to memory pressure" failures.
//
// We only run a real eviction sweep every EVICTION_CHECK_INTERVAL inserts.
const _tileInsertCounters = new Map(); // cacheName → number of inserts since last eviction
const EVICTION_CHECK_INTERVAL = 100;

// Friendly name shown in the UI (matches Settings card labels)
const TILE_CACHE_LABELS = {
  [TILES_OSM]:         'OpenStreetMap',
  [TILES_TOPO]:        'Topographic',
  [TILES_SATELLITE]:   'Satellite',
  [TILES_CARTO_LIGHT]: 'Carto Light',
  [TILES_CARTO_DARK]:  'Carto Dark',
};

const ALL_TILE_CACHES = Object.keys(TILE_LIMITS);

// Approximate average tile size — used for storage estimation.
// Real measurements: PNG tiles range 5–80 KB; 30 KB is a good middle ground.
const AVG_TILE_BYTES = 30 * 1024;

// ----------------------------------------------------------------------------
// App shell assets — precached on install.
// ----------------------------------------------------------------------------
const SHELL_ASSETS = [
  '/',
  '/index.html',
  '/offline.html',
  '/manifest.json'
];

// ============================================================================
// INSTALL EVENT
// ============================================================================

self.addEventListener('install', (event) => {
  console.log('[SW] Installing...');

  event.waitUntil(
    caches.open(SHELL_CACHE)
      .then((cache) => {
        console.log('[SW] Precaching app shell');
        return cache.addAll(SHELL_ASSETS);
      })
      .then(() => self.skipWaiting())
  );
});

// ============================================================================
// ACTIVATE EVENT
// ============================================================================

self.addEventListener('activate', (event) => {
  console.log('[SW] Activating...');

  event.waitUntil(
    caches.keys()
      .then((cacheNames) => {
        // Build the set of caches that should remain
        const keep = new Set([SHELL_CACHE, MODULES_CACHE, API_CACHE, ...ALL_TILE_CACHES]);

        return Promise.all(
          cacheNames
            // Delete anything that:
            //  • belongs to one of our managed cache prefixes (shell-, tiles-, modules-, api-)
            //  • but is NOT in the current keep set
            // This includes the legacy "tiles-v1" single bucket.
            .filter((name) => {
              const isOurs =
                name.startsWith('shell-') ||
                name.startsWith('tiles-') ||
                name.startsWith('modules-') ||
                name.startsWith('api-');
              return isOurs && !keep.has(name);
            })
            .map((name) => {
              console.log('[SW] Deleting old cache:', name);
              return caches.delete(name);
            })
        );
      })
      .then(() => self.clients.claim())
  );
});

// ============================================================================
// FETCH EVENT
// ============================================================================

self.addEventListener('fetch', (event) => {
  const request = event.request;
  const url = new URL(request.url);

  // Only handle GET requests
  if (request.method !== 'GET') return;

  // Skip chrome-extension and other non-http(s) requests
  if (!url.protocol.startsWith('http')) return;

  // Skip worker files and Vite dev-server node_modules requests —
  // intercepting these breaks module workers (e.g. SQLocal/SQLite).
  if (url.pathname.includes('node_modules') ||
      url.search.includes('worker_file') ||
      request.destination === 'worker') return;

  // ----- TILE REQUESTS — passive cache-then-network (per-host bucket) -----
  const tileCache = getTileCacheName(url);
  if (tileCache) {
    event.respondWith(tileCacheThenNetwork(request, tileCache));
    return;
  }

  // ----- OTHER ROUTES -----
  if (isApiRequest(url)) {
    event.respondWith(networkFirst(request, API_CACHE));
  } else if (isModuleAsset(url)) {
    event.respondWith(staleWhileRevalidate(request, MODULES_CACHE));
  } else if (isHtmlAsset(url)) {
    // HTML uses network-first so a fresh deploy is picked up immediately.
    // Falls back to the cached copy when offline (so the app still loads).
    event.respondWith(networkFirst(request, SHELL_CACHE));
  } else if (isAppAsset(url)) {
    // Hashed JS / CSS / WASM / icons are immutable per build — cache-first
    // is the right strategy here.
    event.respondWith(cacheFirst(request, SHELL_CACHE));
  }
  // Let other requests pass through to network
});

// ============================================================================
// URL CLASSIFICATION
// ============================================================================

/**
 * Classify a URL into the appropriate tile cache.
 * Returns `null` for non-tile requests, or for tile providers we deliberately
 * do NOT cache (e.g. Google — caching is forbidden by their ToS).
 */
function getTileCacheName(url) {
  const host = url.hostname;

  // OpenStreetMap — tile.openstreetmap.org and a/b/c subdomains
  if (host.endsWith('tile.openstreetmap.org')) return TILES_OSM;

  // OpenTopoMap — a/b/c.tile.opentopomap.org
  if (host.endsWith('tile.opentopomap.org') || host.endsWith('opentopomap.org')) return TILES_TOPO;

  // Carto Basemaps — light_all / dark_all distinguished by path
  if (host.endsWith('basemaps.cartocdn.com')) {
    if (url.pathname.includes('/light_all/')) return TILES_CARTO_LIGHT;
    if (url.pathname.includes('/dark_all/'))  return TILES_CARTO_DARK;
    return null; // unknown Carto style
  }

  // Esri — server.arcgisonline.com
  if (host.endsWith('arcgisonline.com')) return TILES_SATELLITE;

  // Google — caching forbidden by ToS, do not store
  if (host.endsWith('google.com') || host.endsWith('googleapis.com')) return null;

  // Other tile providers (WMS endpoints, OWS, custom) — not cached at this layer
  // (the user's "online only" toast handles those).
  return null;
}

function isApiRequest(url) {
  return url.pathname.startsWith('/api/') ||
         url.pathname.endsWith('.php');
}

function isModuleAsset(url) {
  return url.pathname.startsWith('/modules/');
}

/**
 * HTML pages (and the bare PWA root) — fetched network-first so new deploys
 * roll out immediately. We never want a stale shell pointing at hashed
 * asset URLs that no longer exist on the server.
 */
function isHtmlAsset(url) {
  if (url.origin !== self.location.origin) return false;
  if (url.pathname.endsWith('.html')) return true;
  // Treat the bare site root and any trailing-slash path as HTML too,
  // since they map to index.html / index.php server-side.
  if (url.pathname === '/' || url.pathname.endsWith('/')) return true;
  return false;
}

/**
 * Immutable per-build static assets (hashed JS / CSS / WASM / images) —
 * safe to cache-first; each new build produces new URLs so there's no
 * stale-content risk.
 */
function isAppAsset(url) {
  if (url.origin !== self.location.origin) return false;
  if (isHtmlAsset(url)) return false; // HTML handled separately
  return (
    url.pathname.endsWith('.css') ||
    url.pathname.endsWith('.js') ||
    url.pathname.endsWith('.wasm') ||
    url.pathname.endsWith('.json') ||
    !!url.pathname.match(/\.(png|jpg|jpeg|gif|svg|ico|webp|woff2?|ttf|otf)$/)
  );
}

// ============================================================================
// CACHING STRATEGIES
// ============================================================================

/**
 * Cache First — Use cache, fallback to network.
 * Best for: App shell, static assets.
 */
async function cacheFirst(request, cacheName) {
  const cached = await caches.match(request);
  if (cached) return cached;

  try {
    const response = await fetch(request);
    if (response.ok) {
      const cache = await caches.open(cacheName);
      cache.put(request, response.clone());
    }
    return response;
  } catch (error) {
    if (request.mode === 'navigate') {
      return caches.match('/offline.html');
    }
    throw error;
  }
}

/**
 * Network First — Try network, fallback to cache.
 * Best for: API requests, dynamic content.
 */
async function networkFirst(request, cacheName) {
  try {
    const response = await fetch(request);
    if (response.ok) {
      const cache = await caches.open(cacheName);
      cache.put(request, response.clone());
    }
    return response;
  } catch (error) {
    const cached = await caches.match(request);
    if (cached) return cached;
    throw error;
  }
}

/**
 * Stale While Revalidate — Return cache immediately, update in background.
 * Best for: Module assets, frequently updated content.
 */
async function staleWhileRevalidate(request, cacheName) {
  const cache = await caches.open(cacheName);
  const cached = await cache.match(request);

  const fetchPromise = fetch(request).then((response) => {
    if (response.ok) {
      cache.put(request, response.clone());
    }
    return response;
  }).catch(() => cached);

  return cached || fetchPromise;
}

/**
 * Tile Cache then Network — Per-host bucket with size limit.
 * Cache first; on miss, fetch from network and store.
 *
 * Memory-conservative eviction:
 *   • Increments an in-memory counter on every successful insert
 *   • Only calls cache.keys() (which materialises all Request objects) every
 *     EVICTION_CHECK_INTERVAL inserts — so the cost is amortised
 *   • Eviction drops the oldest 10 % when over the per-host limit
 *
 * On network failure (offline), serves a 408 so the map renders a blank tile
 * rather than throwing.
 */
async function tileCacheThenNetwork(request, cacheName) {
  const cache = await caches.open(cacheName);
  const cached = await cache.match(request);
  if (cached) return cached;

  try {
    const response = await fetch(request);

    if (response.ok) {
      // Bump the counter; periodically run a real eviction sweep
      const count = (_tileInsertCounters.get(cacheName) || 0) + 1;
      _tileInsertCounters.set(cacheName, count);

      if (count % EVICTION_CHECK_INTERVAL === 0) {
        // Reset the counter — next sweep is another EVICTION_CHECK_INTERVAL away
        _tileInsertCounters.set(cacheName, 0);
        await maybeEvict(cache, cacheName);
      }

      // Don't await put() — it can run after we return the response, keeping
      // the fetch hot path lightweight.
      cache.put(request, response.clone()).catch((err) => {
        // QuotaExceededError → run an immediate eviction sweep and retry once
        if (err && err.name === 'QuotaExceededError') {
          maybeEvict(cache, cacheName, /* force */ true).catch(() => {});
        }
      });
    }

    return response;
  } catch (error) {
    // Offline — let the map renderer show a blank tile
    return new Response('', { status: 408, statusText: 'Offline' });
  }
}

/**
 * Run an eviction sweep on a cache, dropping the oldest 10 % of entries
 * when over the per-cache limit. Heavy: only call periodically.
 */
async function maybeEvict(cache, cacheName, force = false) {
  try {
    const limit = TILE_LIMITS[cacheName] || 1500;
    const keys = await cache.keys();
    if (force || keys.length >= limit) {
      const drop = Math.max(1, Math.ceil(limit * 0.1));
      const toDelete = keys.slice(0, drop);
      await Promise.all(toDelete.map((k) => cache.delete(k)));
    }
  } catch (err) {
    console.warn('[SW] eviction sweep failed for', cacheName, err);
  }
}

// ============================================================================
// MESSAGE HANDLING
// ============================================================================

/**
 * Reply to a message, preferring the transferred MessageChannel port (the
 * window's pwa.js sends a port for request/response correlation), and
 * falling back to the originating WindowClient if no port was supplied.
 */
function replyTo(event, message) {
  if (event.ports && event.ports[0]) {
    try { event.ports[0].postMessage(message); return; } catch {}
  }
  if (event.source && typeof event.source.postMessage === 'function') {
    event.source.postMessage(message);
  }
}

self.addEventListener('message', (event) => {
  const { type, payload, cacheName } = event.data || {};

  switch (type) {
    case 'SKIP_WAITING':
      self.skipWaiting();
      break;

    case 'CACHE_MODULES':
      cacheModules(payload.modules);
      break;

    case 'CLEAR_USER_CACHE':
      clearUserCaches();
      break;

    case 'GET_CACHE_STATUS':
      getCacheStatus().then((status) => replyTo(event, { type: 'CACHE_STATUS', status }));
      break;

    // ----- Tile-cache management (Phase 1 offline maps) -----
    case 'GET_TILE_STATS':
      getTileStats().then((stats) => replyTo(event, { type: 'TILE_STATS', stats }));
      break;

    case 'CLEAR_TILE_CACHES':
      clearTileCaches().then(() => replyTo(event, { type: 'TILE_CACHES_CLEARED' }));
      break;

    // Clear a single provider's tile cache (Phase 3 — per-provider Clear).
    // Validates the requested name against the known ALL_TILE_CACHES list so
    // a misbehaving caller can't drop unrelated caches.
    case 'CLEAR_TILE_CACHE':
      if (typeof cacheName === 'string' && ALL_TILE_CACHES.includes(cacheName)) {
        caches.delete(cacheName).then((deleted) => {
          _tileInsertCounters.delete(cacheName);
          _cachedStats = null; _cachedStatsAt = 0;     // invalidate stats cache
          replyTo(event, { type: 'TILE_CACHE_CLEARED', cacheName, deleted });
        });
      } else {
        replyTo(event, { type: 'TILE_CACHE_CLEARED', cacheName, deleted: false, error: 'Unknown or invalid cache name' });
      }
      break;
  }
});

// ============================================================================
// HELPER FUNCTIONS
// ============================================================================

/**
 * Cache specific modules on demand.
 */
async function cacheModules(moduleNames) {
  const cache = await caches.open(MODULES_CACHE);

  for (const moduleName of moduleNames) {
    try {
      const moduleAssets = [
        `/modules/${moduleName}/index.js`,
        `/modules/${moduleName}/index.css`,
        `/modules/${moduleName}/index.html`
      ];

      await cache.addAll(moduleAssets.filter(async (url) => {
        try {
          const response = await fetch(url, { method: 'HEAD' });
          return response.ok;
        } catch {
          return false;
        }
      }));

      console.log('[SW] Cached module:', moduleName);
    } catch (error) {
      console.warn('[SW] Failed to cache module:', moduleName, error);
    }
  }
}

/**
 * Clear user-specific caches (call on logout).
 * Tile caches are NOT cleared here — those belong to the device, not the user.
 */
async function clearUserCaches() {
  await caches.delete(API_CACHE);
  await caches.delete(MODULES_CACHE);
  console.log('[SW] Cleared user caches');
}

/**
 * Get summary status of all caches (count of entries in each).
 */
async function getCacheStatus() {
  const cacheNames = await caches.keys();
  const status = {};

  for (const name of cacheNames) {
    const cache = await caches.open(name);
    const keys = await cache.keys();
    status[name] = keys.length;
  }

  return status;
}

/**
 * Get per-provider tile cache statistics.
 *
 * Returns shape:
 *   {
 *     totals: { count, estBytes },
 *     byProvider: [{ key, label, count, limit, estBytes }, ...]
 *   }
 *
 * estBytes is an approximation (count × AVG_TILE_BYTES). For an exact size,
 * the caller can use navigator.storage.estimate() on the page side.
 *
 * Result is cached for STATS_TTL_MS so rapid re-queries (e.g. multiple
 * Settings opens) don't re-enumerate every cache.
 */
const STATS_TTL_MS = 10 * 1000;
let _cachedStats = null;
let _cachedStatsAt = 0;

async function getTileStats({ force = false } = {}) {
  const now = Date.now();
  if (!force && _cachedStats && (now - _cachedStatsAt) < STATS_TTL_MS) {
    return _cachedStats;
  }

  const byProvider = [];
  let totalCount = 0;

  for (const cacheName of ALL_TILE_CACHES) {
    let count = 0;
    if (await caches.has(cacheName)) {
      const cache = await caches.open(cacheName);
      // matchAll returns a smaller payload than keys() on Safari, but neither
      // is free. Done at most once per STATS_TTL_MS thanks to the cache above.
      const keys = await cache.keys();
      count = keys.length;
    }
    byProvider.push({
      key:      cacheName,
      label:    TILE_CACHE_LABELS[cacheName] || cacheName,
      count,
      limit:    TILE_LIMITS[cacheName] || 0,
      estBytes: count * AVG_TILE_BYTES,
    });
    totalCount += count;
  }

  _cachedStats = {
    totals: {
      count:    totalCount,
      estBytes: totalCount * AVG_TILE_BYTES,
    },
    byProvider,
  };
  _cachedStatsAt = now;
  return _cachedStats;
}

/**
 * Delete every tile cache. Frees the device storage used by cached map tiles.
 * Does not affect app-shell, modules, or API caches.
 */
async function clearTileCaches() {
  const results = await Promise.all(
    ALL_TILE_CACHES.map((name) => caches.delete(name))
  );
  // Reset counters and invalidate stats cache
  _tileInsertCounters.clear();
  _cachedStats = null;
  _cachedStatsAt = 0;
  console.log('[SW] Cleared tile caches:', ALL_TILE_CACHES.filter((_, i) => results[i]));
}