# frozen_string_literal: true

module Praxis
  class Renderer
    attr_reader :include_nil
    attr_reader :cache

    class CircularRenderingError < StandardError
      attr_reader :object
      attr_reader :context

      def initialize(object, context)
        @object = object
        @context = context

        first = Attributor.humanize_context(context[0..10])
        last = Attributor.humanize_context(context[-5..-1])
        pretty_context = "#{first}...#{last}"
        super("SystemStackError in rendering #{object.class} with context: #{pretty_context}")
      end
    end

    def initialize(include_nil: false)
      @cache = Hash.new do |hash, key|
        hash[key] = {}
      end

      @include_nil = include_nil
    end

    # Renders an object using a given list of fields.
    #
    # @param [Object] object the object to render
    # @param [Hash] fields the correct set of fields, as from FieldExpander
    def render(object, fields, context: Attributor::DEFAULT_ROOT_CONTEXT)
      if object.is_a? Praxis::Blueprint
        @cache[object._cache_key][fields] ||= _render(object, fields, context: context)
      else
        if object.class < Attributor::Collection
          object.each_with_index.collect do |sub_object, i|
            sub_context = context + ["at(#{i})"]
            render(sub_object, fields, context: sub_context)
          end
        else
          _render(object, fields, context: context)
        end
      end
    rescue SystemStackError
      raise CircularRenderingError.new(object, context)      
    end

    def _render(object, fields, context: Attributor::DEFAULT_ROOT_CONTEXT)
      if fields == true
        return case object
               when Attributor::Dumpable
                 object.dump
               else
                 object
               end
      end

      fields.each_with_object({}) do |(key, subfields), hash|
        begin
          value = object._get_attr(key)
        rescue => e
          raise Attributor::DumpError.new(context: context, name: key, type: object.class, original_exception: e)
        end

        if value.nil?
          hash[key] = nil if self.include_nil
          next
        end

        if subfields == true
          hash[key] = case value
                      when Attributor::Dumpable
                        value.dump
                      else
                        value
                      end
        else
          new_context = context + [key]
          hash[key] = render(value, subfields, context: new_context)
        end
      end
    end
  end
end