Improve note copying validations and errors

fixes #1956; fixes #1957

app/assets/javascripts/posts.js

@@ -324,13 +324,18 @@
           data: {
             other_post_id: other_post_id
           },
-          complete: function(data) {
-            if (data.status === 200) {
-              Danbooru.notice("Successfully copied notes to <a href='" + other_post_id + "'>post #" + other_post_id + "</a>");
+          success: function(data) {
+            Danbooru.notice("Successfully copied notes to <a href='" + other_post_id + "'>post #" + other_post_id + "</a>");
+          },
+          error: function(data) {
+            if (data.status === 404) {
+              Danbooru.error("Error: Invalid destination post");
+            } else if (data.responseJSON && data.responseJSON.reason) {
+              Danbooru.error("Error: " + data.responseJSON.reason);
             } else {
               Danbooru.error("There was an error copying notes to <a href='" + other_post_id + "'>post #" + other_post_id + "</a>");
             }
-          },
+          }
         });
       }
 

app/controllers/posts_controller.rb

@@ -88,7 +88,13 @@ class PostsController < ApplicationController
     @post = Post.find(params[:id])
     @other_post = Post.find(params[:other_post_id].to_i)
     @post.copy_notes_to(@other_post)
-    render :nothing => true
+    
+    if @post.errors.any?
+      @error_message = @post.errors.full_messages.join("; ")
+      render :json => {:success => false, :reason => @error_message}.to_json, :status => 400
+    else
+      head :no_content
+    end
   end
 
   def unvote

app/models/post.rb

@@ -977,7 +977,14 @@ class Post < ActiveRecord::Base
     end
 
     def copy_notes_to(other_post)
-      return if notes.active.length == 0
+      if id == other_post.id
+        errors.add :base, "Source and destination posts are the same"
+        return false
+      end
+      unless has_notes?
+        errors.add :post, "has no notes"
+        return false
+      end
 
       notes.active.each do |note|
         note.copy_to(other_post)