// sw.js
// Drop-in service worker to tee streaming chat responses and write progress to localForage (threads_v1).
// - Adjust TARGET_SUBSTRING if your stream URL differs.
// - The SW writes messages tagged with `sw_streamId` to avoid clobbering unrelated messages.

importScripts('https://cdn.jsdelivr.net/npm/localforage@1.10.0/dist/localforage.min.js');

const TARGET_SUBSTRING = 'openrouter.ai/api/v1/chat/completions'; // change if needed
const THREADS_KEY = 'threads_v1'; // matches your index
const BUFFER_SAVE_BYTES = 32 * 1024; // save every ~32KB of new data (tune)
const SAVE_INTERVAL_MS = 2000; // or at least every 2s even if buffer < size

// utils
const gid = () => Math.random().toString(36).slice(2, 9) + '-' + Date.now().toString(36);

function now() { return Date.now(); }

async function readThreads() {
  try {
    const v = await localforage.getItem(THREADS_KEY);
    return Array.isArray(v) ? v : [];
  } catch (e) {
    console.error('sw: idb read error', e);
    return [];
  }
}
async function writeThreads(arr) {
  try {
    await localforage.setItem(THREADS_KEY, arr);
  } catch (e) {
    console.error('sw: idb write error', e);
    throw e;
  }
}

// choose a thread to attach progress to
function pickThread(threads) {
  if (!threads || threads.length === 0) return null;
  // prefer newest updatedAt
  threads.sort((a,b) => (b.updatedAt||0) - (a.updatedAt||0));
  return threads[0];
}

// update or append assistant message for streamId
async function upsertStreamMessage(streamId, text, meta = {}) {
  // read-modify-write
  const threads = await readThreads();
  let th = pickThread(threads);
  const createdNow = now();

  if (!th) {
    // create a new thread if none found
    th = {
      id: 'sw-' + gid(),
      title: 'Missed while backgrounded',
      pinned: false,
      updatedAt: createdNow,
      messages: []
    };
    threads.unshift(th);
  }

  // look for existing message with sw_streamId
  let msgIndex = -1;
  for (let i = th.messages.length - 1; i >= 0; i--) {
    const m = th.messages[i];
    if (m && m.sw_streamId === streamId) { msgIndex = i; break; }
  }

  const contentParts = [{ type: 'text', text }];
  if (msgIndex >= 0) {
    // update message content
    const existing = th.messages[msgIndex];
    existing.content = text;
    existing.contentParts = contentParts;
    existing.updatedAt = createdNow;
    existing._sw_lastSave = createdNow;
    existing._sw_meta = Object.assign({}, existing._sw_meta || {}, meta);
  } else {
    // append new assistant message (tag with sw_streamId)
    const msg = {
      id: 'swmsg-' + gid(),
      role: 'assistant',
      content: text,
      contentParts,
      kind: 'assistant',
      sw_saved: true,
      sw_streamId: streamId,
      createdAt: createdNow,
      updatedAt: createdNow,
      _sw_meta: Object.assign({}, meta)
    };
    th.messages.push(msg);
  }
  th.updatedAt = createdNow;

  // write back
  await writeThreads(threads);
  return { threadId: th.id };
}

async function finalizeStream(streamId, meta = {}) {
  // mark the message as complete; put complete flag in _sw_meta
  const threads = await readThreads();
  const th = pickThread(threads);
  if (!th) return;
  for (let i = th.messages.length - 1; i >= 0; i--) {
    const m = th.messages[i];
    if (m && m.sw_streamId === streamId) {
      m._sw_meta = Object.assign({}, m._sw_meta || {}, meta, { completeAt: now() });
      m.updatedAt = now();
      th.updatedAt = now();
      break;
    }
  }
  await writeThreads(threads);
  // inform clients
  const clientsList = await self.clients.matchAll({ includeUncontrolled: true, type: 'window' });
  clientsList.forEach(c => {
    try { c.postMessage({ type: 'stream-saved', streamId, meta }); } catch(e){ }
  });
}

// notify utility
async function notifyClients(msg) {
  try {
    const list = await self.clients.matchAll({ includeUncontrolled: true, type: 'window' });
    for (const c of list) {
      try { c.postMessage(msg); } catch (e) {}
    }
  } catch (e) {
    /* ignore */
  }
}

// fetch handler: tee and save
self.addEventListener('fetch', event => {
  try {
    const url = event.request.url || '';
    if (!url.includes(TARGET_SUBSTRING)) {
      return; // not our target; let it pass through
    }

    event.respondWith((async () => {
      // perform the upstream fetch
      const upstream = await fetch(event.request);

      // if no streaming body, return upstream
      if (!upstream || !upstream.body) return upstream;

      const streamId = 'swstream-' + gid();
      const headers = new Headers(upstream.headers);

      // tee so one stream goes to client, one consumed by SW
      const [clientStream, swStream] = upstream.body.tee();

      // background save logic:
      const savePromise = (async () => {
        try {
          const reader = swStream.getReader();
          const dec = new TextDecoder('utf-8');
          let bufferText = '';
          let bufferedBytes = 0;
          let lastSaveAt = 0;

          const saveIfNeeded = async (force = false) => {
            const nowMs = Date.now();
            if (!force && bufferedBytes < BUFFER_SAVE_BYTES && (nowMs - lastSaveAt) < SAVE_INTERVAL_MS) return;
            // upsert into threads
            try {
              await upsertStreamMessage(streamId, bufferText, { partialBytes: bufferedBytes, savedAt: Date.now() });
              lastSaveAt = nowMs;
            } catch (e) {
              console.error('sw: upsert save error', e);
            }
          };

          while (true) {
            const { value, done } = await reader.read();
            if (done) break;
            // value is Uint8Array; decode incrementally
            const chunkText = dec.decode(value, { stream: true });
            bufferText += chunkText;
            bufferedBytes += (value && value.byteLength) ? value.byteLength : chunkText.length;
            // try saving periodically
            await saveIfNeeded(false);
          }

          // final save + finalize
          await saveIfNeeded(true);
          await finalizeStream(streamId, { totalBytes: bufferedBytes });
        } catch (err) {
          console.error('sw: error saving stream', err);
          // try to mark failure
          try { await finalizeStream(streamId, { error: String(err) }); } catch(e){ }
        }
      })();

      // keep worker alive while saving
      event.waitUntil(savePromise);

      // return response to client using the clientStream
      return new Response(clientStream, {
        status: upstream.status,
        statusText: upstream.statusText,
        headers
      });
    })());
  } catch (err) {
    // if anything goes wrong, let the request fallback
    console.error('sw: fetch handler error', err);
  }
});

// ping/pong: support both port reply and broadcast reply
self.addEventListener('message', event => {
  const data = event.data || {};
  try {
    if (data && data.type === 'PING') {
      // prefer replying on message port if provided
      if (event.ports && event.ports[0]) {
        try {
          event.ports[0].postMessage({ type: 'PONG', ts: Date.now(), ok: true });
        } catch (e) { /* ignore */ }
      } else {
        // fallback: send message back to the source (if possible) or broadcast to clients
        if (event.source && typeof event.source.postMessage === 'function') {
          try { event.source.postMessage({ type: 'PONG', ts: Date.now(), ok: true }); } catch(e) {}
        } else {
          notifyClients({ type: 'PONG', ts: Date.now(), ok: true });
        }
      }
      return;
    }

    // support a client request to list SW-saved streams or threads
    if (data && data.type === 'list-sw-streams') {
      (async () => {
        const threads = await readThreads();
        // collect messages that have sw_streamId
        const found = [];
        for (const t of (threads||[])) {
          for (const m of (t.messages||[])) {
            if (m && m.sw_streamId) found.push({ threadId: t.id, threadTitle: t.title, messageId: m.id, sw_streamId: m.sw_streamId, summary: (m.content||'').slice(0,200), updatedAt: m.updatedAt });
          }
        }
        // reply to the source if possible, otherwise broadcast
        if (event.ports && event.ports[0]) {
          event.ports[0].postMessage({ type: 'sw-streams-list', streams: found });
        } else if (event.source && typeof event.source.postMessage === 'function') {
          event.source.postMessage({ type: 'sw-streams-list', streams: found });
        } else {
          notifyClients({ type: 'sw-streams-list', streams: found });
        }
      })();
      return;
    }

    // other messages — ignore or log
  } catch (e) {
    console.error('sw: message handler error', e);
  }
});

// basic install/activate to claim clients quickly
self.addEventListener('install', event => {
  self.skipWaiting();
});
self.addEventListener('activate', event => {
  event.waitUntil((async () => {
    try {
      await self.clients.claim();
    } catch(e) { /* ignore */ }
  })());
});