Models for column positioning

app/models/column.rb

@@ -1,4 +1,6 @@
 class Column < ApplicationRecord
+  include Positioned
+
   belongs_to :collection, touch: true
   has_many :cards, dependent: :nullify
 

app/models/concerns/column/positioned.rb

@@ -0,0 +1,35 @@
+module Column::Positioned
+  extend ActiveSupport::Concern
+
+  included do
+    scope :sorted, -> { order(position: :asc) }
+
+    before_create :set_position
+  end
+
+  def move_left
+    if column = collection.columns.where("position < ?", position).sorted.last
+      swap_position_with(column)
+    end
+  end
+
+  def move_right
+    if column = collection.columns.where("position > ?", position).sorted.first
+      swap_position_with(column)
+    end
+  end
+
+  private
+    def set_position
+      max_position = collection.columns.maximum(:position)
+      self.position = max_position + 1
+    end
+
+    def swap_position_with(other_column)
+      transaction do
+        other_column.position, self.position = self.position, other_column.position
+        other_column.save!
+        save!
+      end
+    end
+end

app/views/collections/show/_columns.html.erb

@@ -16,7 +16,7 @@
     <%= render "collections/show/stream", collection: collection, page: page %>
 
     <div class="card-columns__right">
-      <%= render partial: "collections/show/column", collection: collection.columns, cached: true %>
+      <%= render partial: "collections/show/column", collection: collection.columns.sorted, cached: true %>
       <%= render "collections/show/closed", collection: collection %>
 
       <%= render "collections/show/menu/columns", collection: collection %>

db/migrate/20251029142418_add_position_to_columns.rb

@@ -0,0 +1,9 @@
+class AddPositionToColumns < ActiveRecord::Migration[8.2]
+  def change
+    add_column :columns, :position, :integer, default: 0
+
+    execute "UPDATE columns SET position = 0"
+
+    change_column_null :columns, :position, false
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.2].define(version: 2025_10_29_104115) do
+ActiveRecord::Schema[8.2].define(version: 2025_10_29_142418) do
   create_table "accesses", force: :cascade do |t|
     t.datetime "accessed_at"
     t.integer "collection_id", null: false
@@ -191,6 +191,7 @@ ActiveRecord::Schema[8.2].define(version: 2025_10_29_104115) do
     t.string "color", null: false
     t.datetime "created_at", null: false
     t.string "name", null: false
+    t.integer "position", default: 0, null: false
     t.datetime "updated_at", null: false
     t.index ["collection_id"], name: "index_columns_on_collection_id"
   end

db/schema_cache.yml

@@ -562,6 +562,16 @@ columns:
   - *5
   - *6
   - *10
+  - !ruby/object:ActiveRecord::ConnectionAdapters::SQLite3::Column
+    auto_increment:
+    name: position
+    cast_type: *3
+    sql_type_metadata: *4
+    'null': false
+    default: 0
+    default_function:
+    collation:
+    comment:
   - *9
   comments:
   - *22
@@ -2818,4 +2828,4 @@ indexes:
     nulls_not_distinct:
     comment:
     valid: true
-version: 20251029104115
+version: 20251029142418

test/models/column/positioned_test.rb

@@ -0,0 +1,62 @@
+require "test_helper"
+
+class Column::PositionedTest < ActiveSupport::TestCase
+  test "auto position new columns" do
+    collection = collections(:writebook)
+    max_position = collection.columns.maximum(:position)
+
+    new_column = collection.columns.create!(name: "New Column", color: "#000000")
+
+    assert_equal max_position + 1, new_column.position
+  end
+
+  test "move column to the left" do
+    collection = collections(:writebook)
+    columns = collection.columns.sorted.to_a
+
+    column_a = columns[0]
+    column_b = columns[1]
+    original_position_a = column_a.position
+    original_position_b = column_b.position
+
+    column_b.move_left
+
+    assert_equal original_position_b, column_a.reload.position
+    assert_equal original_position_a, column_b.reload.position
+  end
+
+  test "move left when already at leftmost position" do
+    collection = collections(:writebook)
+    leftmost_column = collection.columns.sorted.first
+    original_position = leftmost_column.position
+
+    leftmost_column.move_left
+
+    assert_equal original_position, leftmost_column.reload.position
+  end
+
+  test "move column to the right" do
+    collection = collections(:writebook)
+    columns = collection.columns.sorted.to_a
+
+    column_a = columns[0]
+    column_b = columns[1]
+    original_position_a = column_a.position
+    original_position_b = column_b.position
+
+    column_a.move_right
+
+    assert_equal original_position_b, column_a.reload.position
+    assert_equal original_position_a, column_b.reload.position
+  end
+
+  test "move right when already at rightmost position" do
+    collection = collections(:writebook)
+    rightmost_column = collection.columns.sorted.last
+    original_position = rightmost_column.position
+
+    rightmost_column.move_right
+
+    assert_equal original_position, rightmost_column.reload.position
+  end
+end