require "formalist/element"
require "formalist/types"

module Formalist
  class Elements
    class Many < Element
      permitted_children :attr, :compound_field, :group, :field

      # @api private
      attr_reader :name

      attribute :label, Types::String
      attribute :action_label, Types::String
      attribute :placeholder, Types::String
      attribute :validation, Types::Validation

      # @api private
      attr_reader :child_template

      # @api private
      def initialize(*args, attributes, children, input, errors)
        super

        @name = Types::ElementName.(args.first)
        @input = input.fetch(name, [])
        @errors = errors[@name]
        @child_template = build_child_template(children)
        @children = build_children(children)
      end

      # Until we can put defaults on `Types::Bool`, supply them here
      # @api private
      def attributes
        {
          allow_create: true,
          allow_update: true,
          allow_destroy: true,
          allow_reorder: true,
        }.merge(super)
      end

      # Converts a collection of "many" repeating elements into an abstract
      # syntax tree.
      #
      # It takes the following format:
      #
      # ```
      # [:many, [params]]
      # ```
      #
      # With the following parameters:
      #
      # 1. Collection name
      # 2. Custom form element type (or `:many` otherwise)
      # 3. Collection-level error messages
      # 4. Form element attributes
      # 5. Child element "template" (i.e. the form elements comprising a
      #    single entry in the collection of "many" elements, without any user
      #    data associated)
      # 6. Child elements, one for each of the entries in the input data (or
      #    none, if there is no or empty input data)
      #
      # @see Formalist::Element::Attributes#to_ast "Form element attributes" structure
      #
      # @example "locations" collection
      #   many.to_ast
      #   # => [:many, [
      #     :locations,
      #     :many,
      #     ["locations size cannot be less than 3"],
      #     [:object, [
      #       [:allow_create, [:value, [true]]],
      #       [:allow_update, [:value, [true]]],
      #       [:allow_destroy, [:value, [true]]],
      #       [:allow_reorder, [:value, [true]]]
      #     ]],
      #     [
      #       [:field, [:name, :field, nil, [], [], [:object, []]]],
      #       [:field, [:address, :field, nil, [], [], [:object, []]]]
      #     ],
      #     [
      #       [
      #         [:field, [:name, :field, "Icelab Canberra", [], [], [:object, []]]],
      #         [:field, [:address, :field, "Canberra, ACT, Australia", [], [], [:object, []]]]
      #       ],
      #       [
      #         [:field, [:name, :field, "Icelab Melbourne", [], [], [:object, []]]],
      #         [:field, [:address, :field, "Melbourne, VIC, Australia", [], [], [:object, []]]]
      #       ]
      #     ]
      #   ]]
      #
      # @return [Array] the collection as an abstract syntax tree.
      def to_ast
        local_errors = errors.is_a?(Array) ? errors : []

        [:many, [
          name,
          type,
          local_errors,
          Element::Attributes.new(attributes).to_ast,
          child_template.map(&:to_ast),
          children.map { |el_list| el_list.map(&:to_ast) },
        ]]
      end

      private

      def build_child_template(definitions)
        definitions.map { |el| el.({}, {})}
      end

      def build_children(definitions)
        # Child errors look like this: {0=>{:summary=>["must be filled"]}
        child_errors = errors.is_a?(Hash) ? errors : {}

        input.each_with_index.map { |child_input, index|
          errors = child_errors.fetch(index, {})

          definitions.map { |el| el.(child_input, errors) }
        }
      end
    end
  end
end