convert to eventemitter format with caching

lib/mbtiles.js

@@ -26,13 +26,14 @@ function hash(z, x, y) {
 module.exports = MBTiles;
 MBTiles.utils = require('./utils');
 
+var cache = {};
+
 // Provides access to an mbtiles database file.
 // - uri: A parsed URL hash, the only relevant part is `pathname`.
 // - callback: Will be called when the resources have been acquired
 //       or acquisition failed.
+require('util').inherits(MBTiles, require('events').EventEmitter)
 function MBTiles(uri, callback) {
-    var mbtiles = this;
-    if (typeof callback !== 'function') callback = noop;
     if (typeof uri === 'string') uri = url.parse(uri);
 
     if (!uri.pathname) {
@@ -46,20 +47,42 @@ function MBTiles(uri, callback) {
         delete uri.host;
     }
 
+    if (!cache[uri.pathname]) {
+        cache[uri.pathname] = this;
+        this._open(uri);
+    }
+
+    var mbtiles = cache[uri.pathname];
+    if (!mbtiles.open) {
+        mbtiles.once('open', callback);
+    } else {
+        callback(null, mbtiles);
+    }
+    return undefined;
+}
+
+MBTiles.prototype._open = function(uri) {
+    var mbtiles = this;
+    function error(err) {
+        process.nextTick(function() {
+            mbtiles.emit('open', err);
+        });
+    }
+
     this.filename = uri.pathname;
     Step(function() {
         mbtiles._db = new sqlite3.cached.Database(mbtiles.filename, this);
     }, function(err) {
-        if (err) return callback(err);
+        if (err) return error(err);
         mbtiles._setup(this);
     }, function(err) {
-        if (err) return callback(err);
+        if (err) return error(err);
         fs.stat(mbtiles.filename, this);
     }, function(err, stat) {
-        if (err) return callback(err);
+        if (err) return error(err);
         mbtiles._stat = stat;
         mbtiles.open = true;
-        return callback(null, mbtiles);
+        mbtiles.emit('open', null, mbtiles);
     });
 
     return undefined;