require 'mime-types'
module PictureTag
  # Handles srcset generation, which also handles file generation.
  module Srcsets
    # Basic functionality for a srcset, which also handles file generation.
    # Classes including this module must implement the to_a method, which
    # accomplishes the following:
    # - Return an array of srcset entries.
    # - Call generate_file for each entry, giving it the desired width in
    #   pixels.
    class Basic
      attr_reader :source_image, :media

      def initialize(source_image, input_format)
        @source_image = source_image
        @input_format = input_format
        @media = source_image.media_preset
      end

      def format
        # Input format might be 'original', which is handled by the generated
        # image.
        @format ||= files.first.format
      end

      def files
        @files ||= widths.collect { |w| generate_file(w) }
      end

      def to_a
        files.collect { |f| build_srcset_entry(f) }
      end

      def to_s
        to_a.join(', ')
      end

      # Allows us to add a type attribute to whichever element contains this
      # srcset.
      def mime_type
        MIME::Types.type_for(format).first.to_s
      end

      # Some srcsets have them, for those that don't return nil.
      def sizes
        nil
      end

      # Check our source image size vs requested sizes
      def check_widths(targets)
        if targets.any? { |t| t > @source_image.width }
          handle_small_source(targets, @source_image.width)
        else
          targets
        end
      end

      # Generates an HTML attribute
      def media_attribute
        "(#{PictureTag.media_presets[@media]})"
      end

      private

      def handle_small_source(targets, image_width)
        Utils.warning(
          " #{@source_image.shortname} is #{image_width}px wide, smaller than" \
          " at least one size in the set #{targets}. Will not enlarge."
        )

        small_targets = targets.dup.delete_if { |t| t >= image_width }

        small_targets.push image_width

        small_targets
      end

      def generate_file(width)
        GeneratedImage.new(
          source_file: @source_image,
          width: width,
          format: @input_format
        )
      end
    end
  end
end