Merge branch 'feature/merge-request-link-after-push' into 'master'

Merge request link after pushing

## What does this MR do?
Add API to generate new merge request urls if it is a new branch. The API will be called by gitlab-shell 

## What are the relevant issue numbers?

#18266 

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5542

2 files changed, 53 insertions, 0 deletions

diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index b1fb3ce5d69..f6d0d0c98f5 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -104,6 +104,7 @@ class MergeRequest < ActiveRecord::Base
   scope :from_project, ->(project) { where(source_project_id: project.id) }
   scope :merged, -> { with_state(:merged) }
   scope :closed_and_merged, -> { with_states(:closed, :merged) }
+  scope :from_source_branches, ->(branches) { where(source_branch: branches) }
 
   scope :join_project, -> { joins(:target_project) }
   scope :references_project, -> { references(:target_project) }
diff --git a/app/services/merge_requests/get_urls_service.rb b/app/services/merge_requests/get_urls_service.rb
new file mode 100644
index 00000000000..501fd135e16
--- /dev/null
+++ b/app/services/merge_requests/get_urls_service.rb
@@ -0,0 +1,52 @@
+module MergeRequests
+  class GetUrlsService < BaseService
+    attr_reader :project
+
+    def initialize(project)
+      @project = project
+    end
+
+    def execute(changes)
+      branches = get_branches(changes)
+      merge_requests_map = opened_merge_requests_from_source_branches(branches)
+      branches.map do |branch|
+        existing_merge_request = merge_requests_map[branch]
+        if existing_merge_request
+          url_for_existing_merge_request(existing_merge_request)
+        else
+          url_for_new_merge_request(branch)
+        end
+      end
+    end
+
+    private
+
+    def opened_merge_requests_from_source_branches(branches)
+      merge_requests = MergeRequest.from_project(project).opened.from_source_branches(branches)
+      merge_requests.inject({}) do |hash, mr|
+        hash[mr.source_branch] = mr
+        hash
+      end
+    end
+
+    def get_branches(changes)
+      changes_list = Gitlab::ChangesList.new(changes)
+      changes_list.map do |change|
+        next unless Gitlab::Git.branch_ref?(change[:ref])
+        Gitlab::Git.branch_name(change[:ref])
+      end.compact
+    end
+
+    def url_for_new_merge_request(branch_name)
+      merge_request_params = { source_branch: branch_name }
+      url = Gitlab::Routing.url_helpers.new_namespace_project_merge_request_url(project.namespace, project, merge_request: merge_request_params)
+      { branch_name: branch_name, url: url, new_merge_request: true }
+    end
+
+    def url_for_existing_merge_request(merge_request)
+      target_project = merge_request.target_project
+      url = Gitlab::Routing.url_helpers.namespace_project_merge_request_url(target_project.namespace, target_project, merge_request)
+      { branch_name: merge_request.source_branch, url: url, new_merge_request: false }
+    end
+  end
+end