Rails: update integer enum to string

gen.rb

require 'active_support/core_ext/string'
require 'pp'

current_ts_prefix = '20170602000'
migrations = []

[
    {
      model: 'Document',
      table: 'documents',
      column: 'source',
      index: [[:user, :source, :slug], unique: true],
      default: 'enum1',
      null: false,
      enums: %w(enum1 enum2)
    },
].each.with_index do |conf, i|
        str_col_name = "#{conf[:column]}_str"
        migrate_case_sql = "CASE #{conf[:enums].map.with_index { |k, i| "WHEN `#{conf[:column]}` = #{i} THEN '#{k}'" }.join(' ')} END"
        migrate_case_reverse_sql = "CASE #{conf[:enums].map.with_index { |k, i| "WHEN `#{str_col_name}` = '#{k}' THEN #{i}" }.join(' ')} END"
        define_missing_class = "class ::#{conf[:model]} < ActiveRecord::Base; end unless defined? #{conf[:model]}"


        # add column
        filename = "add_#{str_col_name}_to_#{conf[:table]}"
        classname = filename.camelize
        migrations << [
            "#{current_ts_prefix}0#{i}1_#{filename}.rb", <<-EOS
            # #{classname}
            # - #{conf[:column]}の文字列版のカラムを#{str_col_name}として追加
            class #{classname} < ActiveRecord::Migration[5.0]
              def change
                add_column :#{conf[:table]}, :#{str_col_name}, :string, default: #{conf[:default].nil? ? 'nil' : "'#{conf[:default]}'"}, null: #{conf[:null] ? 'true' : 'false' } 
              end
            end
            EOS
        ]

        # migrate data
        filename = "migrate_#{conf[:table]}_#{conf[:column]}_to_#{str_col_name}"
        classname = filename.camelize
        migrations << [
            "#{current_ts_prefix}0#{i}2_#{filename}.rb", <<-EOS
            # #{classname}
            # - #{conf[:column]}のデータを#{str_col_name}に変換してUPDATEする
            class #{classname} < ActiveRecord::Migration[5.0]
              #{define_missing_class} # クラスが無い場合があるのでその場で宣言
              def up
                #{conf[:model]}.update_all("`#{str_col_name}` = (#{migrate_case_sql})")
              end

              def down
                #{conf[:model]}.update_all("`#{conf[:column]}` = (#{migrate_case_reverse_sql})")
              end
            end
            EOS
        ]

        # rename column
        filename = "rename_#{conf[:table]}_#{str_col_name}_to_#{conf[:column]}"
        classname = filename.camelize
        migrations << [
            "#{current_ts_prefix}0#{i}3_#{filename}.rb", <<-EOS
            # #{classname}
            # - integerの#{conf[:column]}を削除して、stringの#{str_col_name}を#{conf[:column]}にリネームする
            class #{classname} < ActiveRecord::Migration[5.0]
              def up
                #{conf[:index].present? && conf[:index][0].length > 1 ? "remove_index :#{conf[:table]}, #{conf[:index][0]}" : '' }
                remove_column :#{conf[:table]}, :#{conf[:column]}
                rename_column :#{conf[:table]}, :#{str_col_name}, :#{conf[:column]}
                #{conf[:index].present? ? "add_index :#{conf[:table]}, #{conf[:index].map(&:to_s).join(', ')}" : '' }
              end

              def down
                #{conf[:index].present? && conf[:index][0].length > 1 ? "remove_index :#{conf[:table]}, #{conf[:index][0]}" : '' }
                rename_column :#{conf[:table]}, :#{conf[:column]}, :#{str_col_name}
                add_column :#{conf[:table]}, :#{conf[:column]}, :integer, default: #{conf[:default].nil? ? 'nil' : conf[:enums].index(conf[:default])}, null: #{conf[:null] ? 'true' : 'false'}
                #{conf[:index].present? ? "add_index :#{conf[:table]}, #{conf[:index].map(&:to_s).join(', ')}" : '' }
              end
            end
            EOS
        ]
end

migrations.each do |fname, body|
    fpath = File.join('db', 'migrate', fname)
    File.open(fpath, 'w') { |f| f.write(body) }
    pp "#{fpath} created."
end