# frozen_string_literal: true

module Html2rss
  module AttributePostProcessors
    ##
    # Returns a defined part of a String.
    #
    # Both parameters must be an Integer and they can be negative.
    # The +end+ parameter can be omitted, in that case it will not cut the
    # String at the end.
    #
    # A Regexp or a MatchString is not supported.
    #
    # See the [`String#[]`](https://ruby-doc.org/core/String.html#method-i-5B-5D)
    # documentation for more information.
    #
    # Imagine this HTML:
    #    <h1>Foo bar and baz<h1>
    #
    # YAML usage example:
    #    selectors:
    #      title:
    #        selector: h1
    #        post_process:
    #          name: substring
    #          start: 4
    #          end: 6
    #
    # Would return:
    #    'bar'
    class Substring < Base
      def self.validate_args!(value, context)
        assert_type value, String, :value, context:

        options = context[:options]
        assert_type options[:start], Integer, :start, context:

        end_index = options[:end]
        assert_type(end_index, Integer, :end, context:) if end_index
      end

      ##
      # Extracts the substring from the original string based on the provided start and end indices.
      #
      # @return [String] The extracted substring.
      def get
        value[range]
      end

      ##
      # Determines the range for the substring extraction based on the provided start and end indices.
      #
      # @return [Range] The range object representing the start and end/Infinity (integers).
      def range
        return (start_index..) unless end_index?

        if start_index == end_index
          raise ArgumentError,
                'The `start` value must be unequal to the `end` value.'
        end

        (start_index..end_index)
      end

      private

      def end_index?  = !context[:options][:end].to_s.empty?
      def end_index   = context[:options][:end].to_i
      def start_index = context[:options][:start].to_i
    end
  end
end