# frozen_string_literal: true

module RuboCop
  module Cop
    module Migration
      # Checks that migrations updating the schema of large tables,
      # as defined in the configuration, do so safely. As of writing,
      # this involves utilizing the `uses_departure!` helper.
      #
      # @example
      #  # good
      #  class ExampleMigration < ActiveRecord::Migration[6.1]
      #    uses_departure! if Rails.env.staging? || Rails.env.production?
      #
      #    add_column :users, :new_field, :integer, nullable: true
      #  end
      #
      # @example
      #  # bad
      #  class ExampleMigration < ActiveRecord::Migration[6.1]
      #    add_column :users, :new_field, :integer, nullable: true
      #  end
      class LargeTableSchemaUpdate < RuboCop::Cop::Base
        MSG = "Use departure to change the schema of large table `%s`"

        # @!method uses_departure?(node)
        def_node_search :uses_departure?, <<~PATTERN
          (send nil? :uses_departure!)
        PATTERN

        # @!method schema_changes(node)
        def_node_search :schema_changes, <<~PATTERN
          $(send nil? _ (sym $_) ...)
        PATTERN

        def on_class(node)
          return unless in_migration?(node)
          return if uses_departure?(node)

          schema_changes(node).each do |change_node, table_name|
            next unless large_tables.include?(table_name.to_s)

            add_offense(change_node.loc.expression, message: format(MSG, table_name), severity: :warning)
          end
        end

        private

        def large_tables
          cop_config["Tables"] || []
        end

        def in_migration?(node)
          filename = node.location.expression.source_buffer.name
          directory = File.dirname(filename)
          directory.end_with?("db/migrate")
        end
      end
    end
  end
end