Improve compare logic for EmailOnPush service

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/mailers/emails/projects.rb

@@ -17,6 +17,7 @@ module Emails
     def repository_push_email(project_id, recipient, author_id, branch, compare)
       @project = Project.find(project_id)
       @author  = User.find(author_id)
+      @compare = compare
       @commits = Commit.decorate(compare.commits)
       @diffs   = compare.diffs
       @branch  = branch

app/views/notify/repository_push_email.html.haml

@@ -21,3 +21,8 @@
     %pre
       = diff.diff
     %br
+
+- if @compare.timeout
+  %h5 Huge diff. To prevent performance issues it was hidden
+- elsif @compare.commits_over_limit?
+  %h5 Diff for big amount of commits is disabled

app/views/notify/repository_push_email.text.haml

@@ -18,3 +18,8 @@ Diff:
     = diff.new_path || diff.old_path
   \=====================================
   = diff.diff
+\
+- if @compare.timeout
+  Huge diff. To prevent performance issues it was hidden
+- elsif @compare.commits_over_limit?
+  Diff for big amount of commits is disabled

app/workers/emails_on_push_worker.rb

@@ -13,13 +13,13 @@ class EmailsOnPushWorker
       return true
     end
 
-    compare = Gitlab::Git::Compare.new(project.repository.raw_repository, before_sha, after_sha)
+    compare = Gitlab::Git::Compare.new(project.repository.raw_repository, before_sha, after_sha, MergeRequestDiff::COMMITS_SAFE_SIZE)
 
     # Do not send emails if git compare failed
     return false unless compare && compare.commits.present?
 
     recipients.split(" ").each do |recipient|
-      Notify.delay.repository_push_email(project_id, recipient, author_id, branch, compare)
+      Notify.repository_push_email(project_id, recipient, author_id, branch, compare).deliver
     end
   end
 end