Add service to move board lists

app/services/boards/lists/move_service.rb

+module Boards
+  module Lists
+    class MoveService
+      def initialize(project, params = {})
+        @board  = project.board
+        @params = params.dup
+      end
+
+      def execute
+        return false if new_position.blank?
+        return false if new_position == old_position
+
+        list.with_lock do
+          reorder_intermediate_lists
+          update_list_position
+        end
+      end
+
+      private
+
+      attr_reader :board, :params
+
+      def list
+        @list ||= board.lists.find(params[:list_id])
+      end
+
+      def old_position
+        @old_position ||= list.position
+      end
+
+      def new_position
+        @new_position ||= params[:position]
+      end
+
+      def reorder_intermediate_lists
+        if old_position < new_position
+          board.lists.where('position > ?',  old_position)
+                     .where('position <= ?', new_position)
+                     .update_all('position = position - 1')
+        else
+          board.lists.where('position >= ?', new_position)
+                     .where('position < ?',  old_position)
+                     .update_all('position = position + 1')
+        end
+      end
+
+      def update_list_position
+        list.update_attribute(:position, new_position)
+      end
+    end
+  end
+end

spec/services/boards/lists/move_service_spec.rb

+require 'spec_helper'
+
+describe Boards::Lists::MoveService, services: true do
+  describe '#execute' do
+    let(:project) { create(:project_with_board) }
+    let(:board)   { project.board }
+
+    it 'keeps position of lists when new position is nil' do
+      list1 = create(:list, board: board, position: 1)
+      list2 = create(:list, board: board, position: 2)
+      list3 = create(:list, board: board, position: 3)
+      list4 = create(:list, board: board, position: 4)
+      list5 = create(:list, board: board, position: 5)
+
+      service = described_class.new(project, { list_id: list2.id, position: nil })
+
+      expect(service.execute).to eq false
+      expect(list1.reload.position).to eq 1
+      expect(list2.reload.position).to eq 2
+      expect(list3.reload.position).to eq 3
+      expect(list4.reload.position).to eq 4
+      expect(list5.reload.position).to eq 5
+    end
+
+    it 'keeps position of lists when new positon is equal to old position' do
+      list1 = create(:list, board: board, position: 1)
+      list2 = create(:list, board: board, position: 2)
+      list3 = create(:list, board: board, position: 3)
+      list4 = create(:list, board: board, position: 4)
+      list5 = create(:list, board: board, position: 5)
+
+      service = described_class.new(project, { list_id: list2.id, position: 2 })
+
+      expect(service.execute).to eq false
+      expect(list1.reload.position).to eq 1
+      expect(list2.reload.position).to eq 2
+      expect(list3.reload.position).to eq 3
+      expect(list4.reload.position).to eq 4
+      expect(list5.reload.position).to eq 5
+    end
+
+    it 'decrements position of intermediate lists when new position is greater than old position' do
+      list1 = create(:list, board: board, position: 1)
+      list2 = create(:list, board: board, position: 2)
+      list3 = create(:list, board: board, position: 3)
+      list4 = create(:list, board: board, position: 4)
+      list5 = create(:list, board: board, position: 5)
+
+      service = described_class.new(project, { list_id: list2.id, position: 5 })
+
+      expect(service.execute).to eq true
+      expect(list1.reload.position).to eq 1
+      expect(list2.reload.position).to eq 5
+      expect(list3.reload.position).to eq 2
+      expect(list4.reload.position).to eq 3
+      expect(list5.reload.position).to eq 4
+    end
+
+    it 'increments position of intermediate lists when when new position is lower than old position' do
+      list1 = create(:list, board: board, position: 1)
+      list2 = create(:list, board: board, position: 2)
+      list3 = create(:list, board: board, position: 3)
+      list4 = create(:list, board: board, position: 4)
+      list5 = create(:list, board: board, position: 5)
+
+      service = described_class.new(project, { list_id: list5.id, position: 2 })
+
+      expect(service.execute).to eq true
+      expect(list1.reload.position).to eq 1
+      expect(list2.reload.position).to eq 3
+      expect(list3.reload.position).to eq 4
+      expect(list4.reload.position).to eq 5
+      expect(list5.reload.position).to eq 2
+    end
+  end
+end