hd key optimization

lib/bcoin/hd.js

@@ -707,24 +707,33 @@ HDPrivateKey.prototype._build = function _build(data) {
   this.fingerPrint = fingerPrint;
   this.publicKey = publicKey;
 
-  this.hdPublicKey = new HDPublicKey({
-    network: this.network,
-    data: {
-      version: network[this.network].prefixes.xpubkey,
-      depth: this.depth,
-      parentFingerPrint: this.parentFingerPrint,
-      childIndex: this.childIndex,
-      chainCode: this.chainCode,
-      checksum: this.checksum,
-      publicKey: this.publicKey
-    }
-  });
   this.hdPrivateKey = this;
-
-  this.xpubkey = this.hdPublicKey.xpubkey;
   this.key = key;
 };
 
+HDPrivateKey.prototype.__defineGetter__('xpubkey', function() {
+  return this.hdPublicKey.xpubkey;
+});
+
+HDPrivateKey.prototype.__defineGetter__('hdPublicKey', function() {
+  if (!this._hdPublicKey) {
+    this._hdPublicKey = new HDPublicKey({
+      network: this.network,
+      data: {
+        key: this.key,
+        version: network[this.network].prefixes.xpubkey,
+        depth: this.depth,
+        parentFingerPrint: this.parentFingerPrint,
+        childIndex: this.childIndex,
+        chainCode: this.chainCode,
+        checksum: this.checksum,
+        publicKey: this.publicKey
+      }
+    });
+  }
+  return this._hdPublicKey;
+});
+
 HDPrivateKey.prototype.derive = function derive(index, hardened) {
   var cached, data, hash, leftPart, chainCode, privateKey, child;
   var off = 0;
@@ -1080,8 +1089,7 @@ HDPublicKey.prototype._build = function _build(data) {
   this.xpubkey = xpubkey;
   this.fingerPrint = fingerPrint;
 
-  this.xprivkey = data.xprivkey;
+  this.key = data.key || bcoin.keypair({ publicKey: this.publicKey });
-  this.key = bcoin.keypair({ publicKey: this.publicKey });
 };
 
 HDPublicKey.prototype.derive = function derive(index, hardened) {