module Eco
  module API
    class Session
      class Batch
        # Helper class to build a hierarchical model of policies
        # @example Usage:
        #     class PolicyModel < Eco::API::Session::Batch::BasePolicy
        #       MODEL = {attr1: ["prop1a", "prop1b", {"prop1c": ["prop1c1"]}]}
        #       self.model = MODEL
        #       policy_attrs *model_attrs
        #     end
        #
        #     policies = PolicyModel.new("batch_policy")
        #     policies.attr1c do |attr1c|
        #       attr1c.prop1c1.max = 30
        #     end
        #
        # @attr_reader attr [Symbol] the Symbol `name` of the current policy
        # @attr_reader max [Integer] `max` **allowed**  number of occurrences of the property
        # @attr_reader min [Integer] `min` **required** number of occurrences of the property
        class BasePolicy
          extend Eco::API::Common::ClassHierarchy

          class << self

            # If the class for `key` exists, it returns it. Otherwise it generates it.
            # @note for this to work, `key` should be one of the submodels of the current class' `model`
            # @return [Eco::API::Session::Batch::BasePolicy] or subclass thereof
            def policy_class(key)
              key             = key.to_sym.freeze
              class_name      = to_constant(key)

              new_class(class_name, inherits: Eco::API::Session::Batch::BasePolicy) do |klass|
                klass.model = model[key]
                klass.policy_attrs *klass.model_attrs
              end
            end

            # Attributes of this level of the model that should be included
            # @param attrs [Array<Symbol>, Array<String>] each of the subpolicies of the model that should be available
            def policy_attrs(*attrs)
              attrs = attrs.map(&:to_sym)

              attrs.each do |attr|
                method = attr.to_s.freeze
                var    = "@#{method}".freeze

                define_method(method) do |&block|
                  unless policy = self[attr]
                    klass  = self.class.policy_class(attr)
                    policy = self[attr] = klass.new(attr, _parent: self)
                  end

                  if block
                    block.call(policy)
                    self
                  else
                    policy
                  end
                end

              end
            end

          end

          include Enumerable

          attr_reader   :attr
          attr_accessor :max, :min

          def initialize(attr = nil, _parent: self)
            @_parent  = _parent
            @attr     = attr.to_sym
            @policies = {}
          end

          def attr(as_namespace: false)
            return @attr if !as_namespace || root?
            "#{@_parent.attr(as_namespace: true)}:#{@attr}"
          end

          # @note if there's no `min` defined, it always returns `true`
          # @param value [Integer] value to check if it's in the minimum required
          # @return [Boolen] `true` if `value` is grater or equal to `min`
          def min?(value)
            !min || !value|| (min <= value)
          end

          # @note if there's no `max` defined, it always returns `true`
          # @param value [Integer] value to check if it's in the maximum allowed
          # @return [Boolen] `true` if `value` is lesser or equal to `min`
          def max?(value)
            !max || !value || (max >= value)
          end

          # return [Integer] number of declared subpolicies
          def length
            count
          end

          # @return [Boolean] `true` if there are no active subpolicies, `false` otherwise
          def empty?
            count == 0
          end

          # @return [Boolean] `true` if there are active subpolicies, `false` otherwise
          def subpolicies?
            !empty?
          end

          def each(&block)
            return to_enum(:each) unless block
            items.each(&block)
          end

          # @return [Array<Eco::API::Session::Batch::BasePolicy>] the active subpolicies
          def items
            @policies.values
          end

          # @param attr [Symbol, String] name of the policy
          # @return [Boolean] if `attr` is an active subpolicy
          def active?(attr)
            @policies.key?(attr.to_sym)
          end

          # @param attr [Symbol, String] name of the policy
          # @return [Array<Eco::API::Session::Batch::BasePolicy>] the used subpolicies
          def [](attr)
            @policies[attr.to_sym]
          end

          # @param attr [Symbol, String] name of the policy
          # @param value [Expected object of Eco::API::Session::Batch::BasePolicy] a subpolicy to assign to a name `attr`
          def []=(attr, value)
            raise "Expected object of Eco::API::Session::Batch::BasePolicy. Given #{value.class}" unless value.is_a?(Eco::API::Session::Batch::BasePolicy)
            @policies[attr.to_sym] = value
          end

          # @param model [Hash] plain hash (or hashable object) with the stats to check policy compliance against
          # @param recurse [Boolean] to determine if we only check the current policy or also all active subpolicies
          # @return [Boolean] `true` if `model` is compliant with the current policy
          def compliant?(model, recurse: true)
            unless hash = model_to_hash(model)
              raise "Expected 'model' to be a Hash (or hashable) object. Given: #{model}"
            end
            value   = model_attr(hash)
            good    = !model_attr?(hash) || (min?(value) && max?(value))
            #pp "batch_policy: '#{attr}' - #{value}: 'min' #{min?(value)}; 'max' #{max?(value)}"
            good  &&= all? {|active| active.compliant?(model, recurse: recurse)} if recurse
            good
          end

          def validate!(model)
            unless compliant?(model)
              msg = self.uncompliance(model)
              raise "Uncompliance Exception\n#{msg}"
            end
          end

          # @param model [Hash] plain hash (or hashable object) with the stats to check policy compliance against
          # @return [Array<Eco::API::Session::Batch::BasePolicy>] **non-compliant** policies for the `model`
          def uncompliant(model)
            each_with_object([]) do |active, arr|
              arr.concat(active.uncompliant(model))
            end.tap do |arr|
              arr.unshift(self) unless compliant?(model, recurse: false)
            end
          end

          # @param model [Hash] plain hash (or hashable object) with the stats to check policy compliance against
          # @param recurse [Boolean] to determine if we only check the current policy or also all active subpolicies
          # @return [String] message with what failed to meet compliance
          def uncompliance(model, recurse: true)
            unless hash = model_to_hash(model)
              raise "Expected 'model' to be a Hash (or hashable) object. Given: #{model}"
            end
            msg = ""
            unless compliant?(hash, recurse: false)
              value = model_attr(hash)
              msg += "'#{attr(as_namespace: true)}' fails to meet: "
              msg += " [ min(#{min}) >=  #{value}] " unless min?(value)
              msg += " [ max(#{max}) <=  #{value}] " unless max?(value)
              msg += "\n"
            end

            if recurse
              map do |active|
                active.uncompliance(hash, recurse: true)
              end.compact.tap do |msgs|
                msg += "\n" + msgs.join("\n") unless msgs.empty?
              end
            end
            msg
          end

          protected

          # Internal helper to know if we are at the top/root of the hierarchical model
          # @return [Boolean] `true` if this object is the top `root`, `false` otherwise
          def root?
            @_parent == self
          end

          def to_h
            @policies
          end

          def model_attr?(hash)
            hash.key?(self.attr) || hash.key?(self.attr.to_s)
          end

          def model_attr(hash)
            return hash[self.attr] if hash.key?(self.attr)
            hash[self.attr.to_s]   if model_attr?(hash)
          end

          private

          def model_to_hash(model)
            return model if model.is_a?(Hash)
            model.to_h if model.respond_to?(:to_h)
          end

        end
      end
    end
  end
end