Initial commit

app/models/helpers/reorder_position.rb

@@ -0,0 +1,91 @@
+# frozen_string_literal: true
+
+module Helpers
+  module ReorderPosition
+
+    # Function which insert object inside existing list
+    def insert_position(model)
+      # Get current currency amount
+      count = model.class.count
+
+      # If position value greater than currency amount
+      # System should add this object in the end of the list
+      # For example:
+      # List size eq to 15 and user want to set position to 24, system will set it on 16 position
+      if model.position > count
+        # Use update_column in favor of update to skip callback methods
+        model.update_column(:position, count)
+      elsif model.position == count
+        # System shouldn't reorder objects if new object has last position in the list
+        return
+      else
+        # As soon as create doesnt have old position value
+        # System will move the list up to the highest position(count)
+        # So techically old position == highest_position = count
+        highest_position = count
+        # Current model position
+        new_position = model.position
+
+        shuffle_positions_on_intermediate_items(model, highest_position, new_position)
+      end
+    end
+
+    # Function which update object inside existing list
+    def update_position(model)
+      # Get current currency amount
+      count = model.class.count
+
+      # Previous model position
+      old_position = model.position_was
+      # If new position value greater than currency amount
+      # System should add this object in the end of the list
+      new_position = model.position > count ? count : model.position
+
+      shuffle_positions_on_intermediate_items(model, old_position, new_position)
+    end
+
+    private
+
+    def shuffle_positions_on_intermediate_items(model, old_position, new_position)
+      # https://apidock.com/rails/String/tableize
+      # Currency => currencies   Market => markets
+      table_name = model.class.name.tableize
+
+      # Define SQL query for reordering positions
+      sql = if old_position > new_position
+              increment_positions_on_lower_items(model.id, table_name, old_position, new_position)
+            else
+              decrement_positions_on_higher_items(model.id, table_name, old_position, new_position)
+            end
+
+      ActiveRecord::Base.transaction do
+        # Use update_column in favor of update to skip callback methods
+        # Set position as 0 before reordering
+        # Top list position starts from 1, so 0 is safe place for those updating
+        model.update_column(:position, 0)
+        # Reorder ojects in the list
+        ActiveRecord::Base.connection.execute(sql)
+        # Update object with desired position
+        model.update_column(:position, new_position)
+      end
+    end
+
+    # Updates objects positions between old position and new position
+    # If old position > new position
+    def increment_positions_on_lower_items(model_id, table_name, old_position, new_position)
+      "UPDATE #{table_name} SET position = (#{table_name}.position + 1) "\
+      "WHERE (#{table_name}.id != '#{model_id}') "\
+      "AND (#{table_name}.position >= #{new_position}) "\
+      "AND (#{table_name}.position < #{old_position})"
+    end
+
+    # Updates objects positions between old position and new position
+    # If old position < new position
+    def decrement_positions_on_higher_items(model_id, table_name, old_position, new_position)
+      "UPDATE #{table_name} SET position = (#{table_name}.position - 1) "\
+      "WHERE (#{table_name}.id != '#{model_id}') "\
+      "AND (#{table_name}.position > #{old_position}) "\
+      "AND (#{table_name}.position <= #{new_position})"
+    end
+  end
+end