Support copy resume.

lib/mbtiles.js

@@ -392,7 +392,7 @@ MBTiles.prototype.startWriting = function(callback) {
     if (!this._isWritable) {
         this._isWritable = 1;
         this._clearCaches();
-        this._db.exec('PRAGMA journal_mode = OFF; PRAGMA locking_mode = EXCLUSIVE; PRAGMA synchronous=OFF; PRAGMA cache_size = 400000;', callback);
+        this._db.exec('PRAGMA locking_mode = EXCLUSIVE; PRAGMA synchronous=OFF; PRAGMA cache_size = 400000;', callback);
     } else {
         this._isWritable++;
         return callback(null);
@@ -613,3 +613,22 @@ MBTiles.prototype.putInfo = function(data, callback) {
         });
     });
 };
+
+// Copy resume. Optionally retrieve the highest inserted key for resuming a
+// tilelive.copy operation.
+MBTiles.prototype.copyResume = function(callback) {
+    if (typeof callback !== 'function') throw new Error('Callback needed');
+    if (!this.open) return callback(new Error('MBTiles not yet loaded'));
+    var mbtiles = this;
+    Step(function() {
+        mbtiles._db.get('SELECT zoom_level AS z, tile_column AS x, tile_row AS y FROM tiles ORDER BY z DESC, y DESC, x DESC LIMIT 1', this.parallel());
+        mbtiles._db.get('SELECT COUNT(*) AS copied FROM tiles WHERE tile_data IS NOT NULL', this.parallel());
+    }, function(err, coords, copied) {
+        if (err) return callback(err);
+        // Flip Y coordinate back to XYZ for tilelive API.
+        if (coords) coords.y = (1 << coords.z) - 1 - coords.y;
+        if (coords && copied) coords.copied = copied.copied;
+        return callback(null, coords);
+    });
+};
+