module Gitlab
  module Ci
    class Config
      module Entry
        ##
        # Base abstract class for each configuration entry node.
        #
        class Node
          InvalidError = Class.new(StandardError)

          attr_reader :config, :metadata
          attr_accessor :key, :parent, :description

          def initialize(config, **metadata)
            @config = config
            @metadata = metadata
            @entries = {}

            self.class.aspects.to_a.each do |aspect|
              instance_exec(&aspect)
            end
          end

          def [](key)
            @entries[key] || Entry::Undefined.new
          end

          def compose!(deps = nil)
            return unless valid?

            yield if block_given?
          end

          def leaf?
            @entries.none?
          end

          def descendants
            @entries.values
          end

          def ancestors
            @parent ? @parent.ancestors + [@parent] : []
          end

          def valid?
            errors.none?
          end

          def errors
            []
          end

          def value
            if leaf?
              @config
            else
              meaningful = @entries.select do |_key, value|
                value.specified? && value.relevant?
              end

              Hash[meaningful.map { |key, entry| [key, entry.value] }]
            end
          end

          def specified?
            true
          end

          def relevant?
            true
          end

          def location
            name = @key.presence || self.class.name.to_s.demodulize
                                        .underscore.humanize.downcase

            ancestors.map(&:key).append(name).compact.join(':')
          end

          def inspect
            val = leaf? ? config : descendants
            unspecified = specified? ? '' : '(unspecified) '
            "#<#{self.class.name} #{unspecified}{#{key}: #{val.inspect}}>"
          end

          def self.default
          end

          def self.aspects
            @aspects ||= []
          end

          private

          attr_reader :entries
        end
      end
    end
  end
end