make /attach use the selectors, fix UserError, check /tp has one target

see http://stackoverflow.com/a/32749533 for UserError

src/lib/plugins/commands.js

@@ -118,7 +118,7 @@ module.exports.player=function(player, serv) {
       if (res) player.chat('' + res);
     }
     catch(err) {
-      if (err instanceof UserError) player.chat('Error: ' + err.toString());
+      if (err instanceof UserError) player.chat('Error: ' + err.message);
       else setTimeout(() => {throw err;}, 0);
     }
   }

src/lib/plugins/spawn.js

@@ -6,6 +6,7 @@ var path = require('path');
 var requireIndex = require('requireindex');
 var plugins = requireIndex(path.join(__dirname,'..', 'plugins'));
 var Item = require("prismarine-item")(version);
+var UserError = require('flying-squid').UserError;
 
 var Vec3 = require("vec3").Vec3;
 
@@ -128,19 +129,24 @@ module.exports.player=function(player,serv){
   player.commands.add({
     base: 'attach',
     info: 'attach an entity on an other entity',
-    usage: '/attach <carrierId> <attachedId>',
+    usage: '/attach <carrier> <attached>',
     op: true,
     parse(str)  {
-      var pars=str.split(' ');
-      if(pars.length!=2)
+      var args=str.split(' ');
+      if(args.length!=2)
         return false;
-      var [carrierId,attachedId]=pars.map(a => parseInt(a));
-      return {carrierId:carrierId,attachedId:attachedId};
+
+      let carrier = player.selectorString(args[0]);
+      if(carrier.length==0) throw new UserError("one carrier");
+      let attached = player.selectorString(args[1]);
+      if(attached.length==0) throw new UserError("one attached");
+
+      return {carrier:carrier[0],attached:attached[0]};
     },
-    action({carrierId,attachedId}) {
+    action({carrier,attached}) {
       var p={
-        entityId:attachedId,
-        vehicleId:carrierId,
+        entityId:attached.id,
+        vehicleId:carrier.id,
         leash:false
       };
       player._client.write('attach_entity',p);

src/lib/plugins/tp.js

@@ -1,4 +1,5 @@
 var Vec3 = require("vec3").Vec3;
+var UserError = require('flying-squid').UserError;
 
 module.exports.player = (player, serv) => {
 
@@ -14,7 +15,9 @@ module.exports.player = (player, serv) => {
     action(args) {
       if(args.length === 2) {
         let entities_from = player.selectorString(args[0]);
-        let entity_to = player.selectorString(args[1])[0];
+        let entity_to = player.selectorString(args[1]);
+        if(entity_to.length==0) throw new UserError("at least one target");
+        entity_to = entity_to[0];
 
         entities_from.forEach(e => e.teleport(entity_to.position.scaled(1/32)));
       } else if(args.length === 3) {

src/lib/user_error.js

@@ -1,5 +1,16 @@
-class UserError extends Error {
-  
+class ExtendableError extends Error {
+  constructor(message) {
+    super(message);
+    this.name = this.constructor.name;
+    this.message = message;
+    Error.captureStackTrace(this, this.constructor.name)
+  }
+}
+
+class UserError extends ExtendableError {
+  constructor(message) {
+    super(message);
+  }
 }
 
 module.exports = UserError;