const CACHE_NAME = 'erp-shell-v3';
const API_CACHE_NAME = 'erp-api-v1';
const WRITE_QUEUE_DB_NAME = 'erp-write-queue-db';
const WRITE_QUEUE_STORE = 'requests';
const WRITE_QUEUE_SYNC_TAG = 'erp-write-queue-sync';
const OFFLINE_URL = '/offline.html';
const PRECACHE_URLS = ['/', '/manifest.webmanifest', '/pwa-icon.svg', OFFLINE_URL];

const API_CACHE_BLOCKLIST = [
  '/api/token/',
  '/api/token/refresh/',
  '/api/fleet/pusher-auth/',
];

function isCacheableApiGet(request, url) {
  if (request.method !== 'GET') return false;
  if (url.origin !== self.location.origin) return false;
  if (!url.pathname.startsWith('/api/')) return false;
  return !API_CACHE_BLOCKLIST.some((blocked) => url.pathname.startsWith(blocked));
}

function isQueueableApiWrite(request, url) {
  if (!['POST', 'PUT', 'PATCH', 'DELETE'].includes(request.method)) return false;
  if (url.origin !== self.location.origin) return false;
  if (!url.pathname.startsWith('/api/')) return false;
  if (API_CACHE_BLOCKLIST.some((blocked) => url.pathname.startsWith(blocked))) return false;
  const contentType = (request.headers.get('content-type') || '').toLowerCase();
  if (contentType.includes('multipart/form-data')) return false;
  return true;
}

function openWriteQueueDb() {
  return new Promise((resolve, reject) => {
    const request = indexedDB.open(WRITE_QUEUE_DB_NAME, 1);
    request.onupgradeneeded = () => {
      const db = request.result;
      if (!db.objectStoreNames.contains(WRITE_QUEUE_STORE)) {
        db.createObjectStore(WRITE_QUEUE_STORE, { keyPath: 'id', autoIncrement: true });
      }
    };
    request.onsuccess = () => resolve(request.result);
    request.onerror = () => reject(request.error);
  });
}

function serializeHeaders(headers) {
  const serialized = {};
  headers.forEach((value, key) => {
    serialized[key] = value;
  });
  return serialized;
}

function getAllQueuedRequests(db) {
  return new Promise((resolve, reject) => {
    const tx = db.transaction(WRITE_QUEUE_STORE, 'readonly');
    const store = tx.objectStore(WRITE_QUEUE_STORE);
    const request = store.getAll();
    request.onsuccess = () => resolve(request.result || []);
    request.onerror = () => reject(request.error);
  });
}

function addQueuedRequest(db, queuedRequest) {
  return new Promise((resolve, reject) => {
    const tx = db.transaction(WRITE_QUEUE_STORE, 'readwrite');
    const store = tx.objectStore(WRITE_QUEUE_STORE);
    const request = store.add(queuedRequest);
    request.onsuccess = () => resolve(request.result);
    request.onerror = () => reject(request.error);
  });
}

function deleteQueuedRequest(db, id) {
  return new Promise((resolve, reject) => {
    const tx = db.transaction(WRITE_QUEUE_STORE, 'readwrite');
    const store = tx.objectStore(WRITE_QUEUE_STORE);
    const request = store.delete(id);
    request.onsuccess = () => resolve();
    request.onerror = () => reject(request.error);
  });
}

async function queueWriteRequest(request) {
  const body = request.method === 'DELETE' ? null : await request.clone().text();
  const db = await openWriteQueueDb();
  const payload = {
    url: request.url,
    method: request.method,
    headers: serializeHeaders(request.headers),
    body,
    createdAt: Date.now(),
  };
  await addQueuedRequest(db, payload);
}

function createQueuedResponse() {
  return new Response(
    JSON.stringify({
      queued: true,
      offline: true,
      detail: 'Zahtjev je spremljen i bit će sinkroniziran kad veza bude dostupna.',
    }),
    {
      status: 202,
      headers: { 'Content-Type': 'application/json' },
    }
  );
}

async function scheduleWriteQueueSync() {
  if (!self.registration || !self.registration.sync) return;
  await self.registration.sync.register(WRITE_QUEUE_SYNC_TAG);
}

async function replayQueuedRequests() {
  const db = await openWriteQueueDb();
  const queuedRequests = await getAllQueuedRequests(db);
  for (const queued of queuedRequests) {
    const headers = new Headers(queued.headers || {});
    const init = {
      method: queued.method,
      headers,
      credentials: 'same-origin',
    };
    if (queued.body != null && queued.method !== 'DELETE') {
      init.body = queued.body;
    }
    try {
      const response = await fetch(queued.url, init);
      if (response.ok) {
        await deleteQueuedRequest(db, queued.id);
        continue;
      }
      if (response.status >= 500) {
        throw new Error(`Replay failed with status ${response.status}`);
      }
      await deleteQueuedRequest(db, queued.id);
    } catch (error) {
      throw error;
    }
  }
}

self.addEventListener('install', (event) => {
self.addEventListener('install', (event) => {
async function precacheShell() {
  const cache = await caches.open(CACHE_NAME);
  await Promise.all(
    PRECACHE_URLS.map(async (url) => {
      try {
        const response = await fetch(url, { cache: 'reload' });
        if (!response || !response.ok) {
          console.warn('Skipping precache for non-OK response:', url, response && response.status);
          return;
        }
        await cache.put(url, response);
      } catch (error) {
        console.warn('Skipping precache for failed request:', url, error);
      }
    })
  );
}

self.addEventListener('install', (event) => {
  event.waitUntil(precacheShell());
  self.skipWaiting();
});

self.addEventListener('activate', (event) => {
  event.waitUntil(
    Promise.all([
      caches.keys().then((cacheNames) =>
        Promise.all(
          cacheNames
            .filter((name) => name !== CACHE_NAME && name !== API_CACHE_NAME)
            .map((name) => caches.delete(name))
        )
      ),
      replayQueuedRequests().catch((error) => {
        console.error('Initial write-queue replay failed.', error);
      }),
    ])
  );
  self.clients.claim();
});

self.addEventListener('fetch', (event) => {
  const { request } = event;
  const url = new URL(request.url);
  if (isQueueableApiWrite(request, url)) {
    event.respondWith(
      fetch(request.clone()).catch(async () => {
        try {
          await queueWriteRequest(request);
        } catch (error) {
          console.error('Failed to queue offline write request.', error);
          return new Response(
            JSON.stringify({
              queued: false,
              offline: true,
              detail: 'Zahtjev nije moguće spremiti offline.',
            }),
            {
              status: 503,
              headers: { 'Content-Type': 'application/json' },
            }
          );
        }
        try {
          await scheduleWriteQueueSync();
        } catch (error) {
          console.warn('Background sync registration failed.', error);
        }
        return createQueuedResponse();
      })
    );
    return;
  }

  if (request.method !== 'GET') return;

  if (isCacheableApiGet(request, url)) {
    event.respondWith(
      caches.open(API_CACHE_NAME).then(async (cache) => {
        const cached = await cache.match(request);
        const networkFetch = fetch(request)
          .then((response) => {
            if (response && response.ok) {
              cache.put(request, response.clone());
            }
            return response;
          })
          .catch(() => cached);

        return cached || networkFetch;
      })
    );
    return;
  }

  if (url.origin !== self.location.origin) return;

  if (request.mode === 'navigate') {
    event.respondWith(
      fetch(request)
        .then((response) => {
          const copy = response.clone();
          caches.open(CACHE_NAME).then((cache) => cache.put(request, copy));
          return response;
        })
        .catch(async () => {
          const cached = await caches.match(request);
          return cached || caches.match(OFFLINE_URL);
        })
    );
    return;
  }

  if (['style', 'script', 'worker', 'font', 'image'].includes(request.destination)) {
    event.respondWith(
      caches.match(request).then((cached) => {
        const networkFetch = fetch(request)
          .then((response) => {
            const copy = response.clone();
            caches.open(CACHE_NAME).then((cache) => cache.put(request, copy));
            return response;
          })
          .catch(() => cached);
        return cached || networkFetch;
      })
    );
  }
});

self.addEventListener('sync', (event) => {
  if (event.tag !== WRITE_QUEUE_SYNC_TAG) return;
  event.waitUntil(replayQueuedRequests());
});

self.addEventListener('message', (event) => {
  if (event.data !== 'FLUSH_WRITE_QUEUE') return;
  event.waitUntil(replayQueuedRequests());
});