// Offline tile cache — download OSM tiles to IndexedDB, serve locally
// Exposes window.TileCache

const TileCache = {};
const DB_NAME = "baldav_tiles";
const STORE = "tiles";
let _db = null;

function openDB() {
  if (_db) return Promise.resolve(_db);
  return new Promise((resolve, reject) => {
    const req = indexedDB.open(DB_NAME, 1);
    req.onupgradeneeded = () => req.result.createObjectStore(STORE);
    req.onsuccess = () => { _db = req.result; resolve(_db); };
    req.onerror = () => reject(req.error);
  });
}

function putTile(key, blob) {
  return openDB().then(db => new Promise((resolve, reject) => {
    const tx = db.transaction(STORE, "readwrite");
    tx.objectStore(STORE).put(blob, key);
    tx.oncomplete = resolve;
    tx.onerror = () => reject(tx.error);
  }));
}

function getTile(key) {
  return openDB().then(db => new Promise((resolve, reject) => {
    const tx = db.transaction(STORE, "readonly");
    const req = tx.objectStore(STORE).get(key);
    req.onsuccess = () => resolve(req.result || null);
    req.onerror = () => reject(req.error);
  }));
}

// Count cached tiles
TileCache.count = async function() {
  const db = await openDB();
  return new Promise((resolve, reject) => {
    const tx = db.transaction(STORE, "readonly");
    const req = tx.objectStore(STORE).count();
    req.onsuccess = () => resolve(req.result);
    req.onerror = () => reject(req.error);
  });
};

// Clear all cached tiles
TileCache.clear = async function() {
  const db = await openDB();
  return new Promise((resolve, reject) => {
    const tx = db.transaction(STORE, "readwrite");
    tx.objectStore(STORE).clear();
    tx.oncomplete = resolve;
    tx.onerror = () => reject(tx.error);
  });
};

// Calculate tile coordinates for a bounding box at a given zoom
function getTileRange(bounds, zoom) {
  const n = Math.pow(2, zoom);
  const toTile = (lat, lon) => ({
    x: Math.floor((lon + 180) / 360 * n),
    y: Math.floor((1 - Math.log(Math.tan(lat * Math.PI / 180) + 1 / Math.cos(lat * Math.PI / 180)) / Math.PI) / 2 * n),
  });
  const sw = toTile(bounds.getSouth(), bounds.getWest());
  const ne = toTile(bounds.getNorth(), bounds.getEast());
  return {
    xMin: Math.min(sw.x, ne.x), xMax: Math.max(sw.x, ne.x),
    yMin: Math.min(sw.y, ne.y), yMax: Math.max(sw.y, ne.y),
  };
}

// Count tiles needed for area + zoom range
TileCache.countTilesForArea = function(bounds, zoomMin, zoomMax) {
  let total = 0;
  for (let z = zoomMin; z <= zoomMax; z++) {
    const r = getTileRange(bounds, z);
    total += (r.xMax - r.xMin + 1) * (r.yMax - r.yMin + 1);
  }
  return total;
};

// Download tiles for current map bounds
// onProgress(downloaded, total) callback
TileCache.downloadArea = async function(bounds, zoomMin, zoomMax, onProgress) {
  const tiles = [];
  for (let z = zoomMin; z <= zoomMax; z++) {
    const r = getTileRange(bounds, z);
    for (let x = r.xMin; x <= r.xMax; x++) {
      for (let y = r.yMin; y <= r.yMax; y++) {
        tiles.push({ z, x, y });
      }
    }
  }

  let done = 0;
  const PARALLEL = 4;

  async function downloadOne(tile) {
    const key = `${tile.z}/${tile.x}/${tile.y}`;
    // Skip if already cached
    const existing = await getTile(key);
    if (existing) { done++; if (onProgress) onProgress(done, tiles.length); return; }

    const url = `https://tile.openstreetmap.org/${key}.png`;
    try {
      const resp = await fetch(url);
      if (resp.ok) {
        const blob = await resp.blob();
        await putTile(key, blob);
      }
    } catch { /* skip failed tiles */ }
    done++;
    if (onProgress) onProgress(done, tiles.length);
  }

  // Process in parallel batches
  for (let i = 0; i < tiles.length; i += PARALLEL) {
    const batch = tiles.slice(i, i + PARALLEL);
    await Promise.all(batch.map(downloadOne));
  }

  return done;
};

// Custom Leaflet TileLayer that checks IndexedDB first
TileCache.createLayer = function() {
  return L.TileLayer.extend({
    createTile: function(coords, done) {
      const tile = document.createElement("img");
      const key = `${coords.z}/${coords.x}/${coords.y}`;

      getTile(key).then(blob => {
        if (blob) {
          tile.src = URL.createObjectURL(blob);
          done(null, tile);
        } else {
          // Fallback to network
          tile.crossOrigin = "";
          tile.src = `https://tile.openstreetmap.org/${key}.png`;
          // Cache after download
          tile.onload = () => {
            fetch(tile.src).then(r => r.blob()).then(b => putTile(key, b)).catch(() => {});
            done(null, tile);
          };
          tile.onerror = () => done(new Error("tile failed"), tile);
        }
      }).catch(() => {
        tile.src = `https://tile.openstreetmap.org/${key}.png`;
        tile.onload = () => done(null, tile);
        tile.onerror = () => done(new Error("tile failed"), tile);
      });

      return tile;
    }
  });
};

window.TileCache = TileCache;
console.log("[tilecache.js] window.TileCache ready");