Merge branch 'issue-board-api-support' into 'master'

Issue Board API support

## What does this MR do?

Adds support for Issue Board in the API.

## Are there points in the code the reviewer needs to double check?

~~Double check whether the Issue Board list movement fix is needed.~~ 

*Moved to a separate issue.* [#22890](https://gitlab.com/gitlab-org/gitlab-ce/issues/22890)

## Why was this MR needed?

Currently the API offers partial support to a project's Issue Board indirectly through Labels.
This MR adds support for listing, creating, moving and removing board lists.

## Does this MR meet the acceptance criteria?

- [X] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [X] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [X] API support added
- Tests
  - [X] Added for this feature/bug
  - [X] All builds are passing
- [X] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [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)

## What are the relevant issue numbers?
[#22195](https://gitlab.com/gitlab-org/gitlab-ce/issues/22195)

See merge request !6646

3 files changed, 133 insertions, 1 deletions

diff --git a/lib/api/api.rb b/lib/api/api.rb
index cb47ec8f33f..0bbf73a1b63 100644
--- a/lib/api/api.rb
+++ b/lib/api/api.rb
@@ -43,6 +43,7 @@ module API
     mount ::API::Groups
     mount ::API::Internal
     mount ::API::Issues
+    mount ::API::Boards
     mount ::API::Keys
     mount ::API::Labels
     mount ::API::LicenseTemplates
diff --git a/lib/api/boards.rb b/lib/api/boards.rb
new file mode 100644
index 00000000000..4d5d144a02e
--- /dev/null
+++ b/lib/api/boards.rb
@@ -0,0 +1,115 @@
+module API
+  # Boards API
+  class Boards < Grape::API
+    before { authenticate! }
+
+    resource :projects do
+      # Get the project board
+      get ':id/boards' do
+        authorize!(:read_board, user_project)
+        present [user_project.board], with: Entities::Board
+      end
+
+      segment ':id/boards/:board_id' do
+        helpers do
+          def project_board
+            board = user_project.board
+            if params[:board_id].to_i == board.id
+              board
+            else
+              not_found!('Board')
+            end
+          end
+
+          def board_lists
+            project_board.lists.destroyable
+          end
+        end
+
+        # Get the lists of a project board
+        # Does not include `backlog` and `done` lists
+        get '/lists' do
+          authorize!(:read_board, user_project)
+          present board_lists, with: Entities::List
+        end
+
+        # Get a list of a project board
+        get '/lists/:list_id' do
+          authorize!(:read_board, user_project)
+          present board_lists.find(params[:list_id]), with: Entities::List
+        end
+
+        # Create a new board list
+        #
+        # Parameters:
+        #   id (required)           - The ID of a project
+        #   label_id (required)     - The ID of an existing label
+        # Example Request:
+        #   POST /projects/:id/boards/:board_id/lists
+        post '/lists' do
+          required_attributes! [:label_id]
+
+          unless user_project.labels.exists?(params[:label_id])
+            render_api_error!({ error: "Label not found!" }, 400)
+          end
+
+          authorize!(:admin_list, user_project)
+
+          list = ::Boards::Lists::CreateService.new(user_project, current_user,
+              { label_id: params[:label_id] }).execute
+
+          if list.valid?
+            present list, with: Entities::List
+          else
+            render_validation_error!(list)
+          end
+        end
+
+        # Moves a board list to a new position
+        #
+        # Parameters:
+        #   id (required) - The ID of a project
+        #   board_id (required) - The ID of a board
+        #   position (required) - The position of the list
+        # Example Request:
+        #   PUT /projects/:id/boards/:board_id/lists/:list_id
+        put '/lists/:list_id' do
+          list = project_board.lists.movable.find(params[:list_id])
+
+          authorize!(:admin_list, user_project)
+
+          moved = ::Boards::Lists::MoveService.new(user_project, current_user,
+              { position: params[:position].to_i }).execute(list)
+
+          if moved
+            present list, with: Entities::List
+          else
+            render_api_error!({ error: "List could not be moved!" }, 400)
+          end
+        end
+
+        # Delete a board list
+        #
+        # Parameters:
+        #   id (required) - The ID of a project
+        #   board_id (required) - The ID of a board
+        #   list_id (required) - The ID of a board list
+        # Example Request:
+        #   DELETE /projects/:id/boards/:board_id/lists/:list_id
+        delete "/lists/:list_id" do
+          list = board_lists.find_by(id: params[:list_id])
+
+          authorize!(:admin_list, user_project)
+
+          if list
+            destroyed_list = ::Boards::Lists::DestroyService.new(
+              user_project, current_user).execute(list)
+            present destroyed_list, with: Entities::List
+          else
+            not_found!('List')
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/api/entities.rb b/lib/api/entities.rb
index 04437322ec1..feaa0c213bf 100644
--- a/lib/api/entities.rb
+++ b/lib/api/entities.rb
@@ -432,8 +432,11 @@ module API
       end
     end
 
-    class Label < Grape::Entity
+    class LabelBasic < Grape::Entity
       expose :name, :color, :description
+    end
+
+    class Label < LabelBasic
       expose :open_issues_count, :closed_issues_count, :open_merge_requests_count
 
       expose :subscribed do |label, options|
@@ -441,6 +444,19 @@ module API
       end
     end
 
+    class List < Grape::Entity
+      expose :id
+      expose :label, using: Entities::LabelBasic
+      expose :position
+    end
+
+    class Board < Grape::Entity
+      expose :id
+      expose :lists, using: Entities::List do |board|
+        board.lists.destroyable
+      end
+    end
+
     class Compare < Grape::Entity
       expose :commit, using: Entities::RepoCommit do |compare, options|
         Commit.decorate(compare.commits, nil).last