module RailsConnector
  module Migrations
    class Migrator
      attr_reader :migrations
      attr_reader :workspace_lock

      def initialize
        @migrations = determine_migrations
        @migration_store = MigrationStore.instance
        @workspace_lock = WorkspaceLock.instance

        validate
      end

      def migrate
        workspace.as_current do
          runnable.each do |migration|
            migration.migrate
            @migration_store.add_version(migration.version)
          end
        end
      end

      def publish
        remove_workspace_with do
          CmsRestApi.put("workspaces/#{workspace.id}/publish", {})
        end
      end

      def abort
        remove_workspace_with do
          CmsRestApi.delete("workspaces/#{workspace.id}")
        end
      end

      private

      def workspace
        workspace = migration_workspace

        if workspace
          if workspace_lock.exists?
            workspace_lock.validate(workspace)
          end
        else
          CmsRestApi.post('workspaces', :workspace => { :title => 'rtc', :id => 'rtc' })

          workspace = migration_workspace
          workspace_lock.write(workspace)
        end

        workspace
      end

      def migration_workspace
        Workspace.find('rtc')
      rescue ResourceNotFound
      end

      def remove_workspace_with(&block)
        workspace = migration_workspace

        if workspace
          workspace_lock.validate(workspace)

          yield

          workspace_lock.remove
        else
          raise RailsConnectorError.new('Migration workspace does not exist')
        end
      end

      def determine_migrations
        files = Dir[*migrations_paths.map { |path| "#{path}/**/[0-9]*_*.rb" }]

        migrations = files.map do |file|
          version, name = file.scan(/([0-9]+)_([_a-z0-9]*)\.rb\z/).first

          unless version
            raise RailsConnectorError.new("Illegal name for migration file: #{file}\n\t(only lower case letters, numbers, and '_' allowed)")
          end

          version = version
          name = name.camelize

          require(File.expand_path(file))
          name.constantize.new(name, version)
        end

        migrations.sort_by(&:version)
      end

      def migrations_paths
        ["#{Rails.root}/cms/migrate"]
      end

      def runnable
        migrations.reject do |migration|
          migrated_versions.include?(migration.version)
        end
      end

      def migrated_versions
        @migration_store.versions
      end

      def validate
        name, _ = migrations.group_by(&:name).find { |_, value| value.length > 1 }

        if name
          raise RailsConnectorError.new("Multiple migrations have the name #{name}")
        end

        version, _ = migrations.group_by(&:version).find { |_, value| value.length > 1 }

        if version
          raise RailsConnectorError.new("Multiple migrations have the version number #{version}")
        end
      end
    end
  end
end