# frozen_string_literal: true

require 'rmagick'

module Lipstick
  module Images
    # Creates an AAF standard email banner, with three elements, positioned as
    # follows:
    #
    # 1. AAF Logo. Vertically centered and left-aligned within the content box,
    #    and with a blank space to the right.
    # 2. Application title. Vertically centered, and left-aligned to the logo's
    #    right margin.
    # 3. Environment string. Positioned 10 pixels below the app title, and
    #    left-aligned to the logo's right margin.
    #
    # The "box" containing these three elements is horizontally centered in the
    # resulting image.
    #
    # Text metrics work as follows, using "Alimony" as the example word:
    #
    # * (x, y) is the position of the bottom left tip of 'A'
    # * `ascent` is the letter height from that point (i.e. the height of 'A')
    # * `descent` is a negative value; the letter height *below* that point
    #   (i.e. the height of the 'tail' of 'y')
    # * `height` is greater than `(ascent - descent)`, making it useless for our
    #   purposes here.
    #
    # For image compositing, (x, y) is the position of the top-left corner.
    class EmailBanner
      def initialize(image:, title:, environment:,
                     background_color:, resize_to:)
        @title = title
        @environment = environment
        @image = image
        @background_color = background_color
        @resize_to = resize_to
      end

      def to_png
        bgcolor = @background_color

        canvas = Magick::ImageList.new
        canvas.new_image(WIDTH, HEIGHT) do |f|
          f.format = 'PNG'
          f.background_color = bgcolor
        end

        annotate_title(canvas)
        annotate_environment(canvas)

        canvas.composite!(logo, logo_x, logo_y, Magick::SrcOverCompositeOp)

        canvas.to_blob
      end

      private

      WIDTH = 600
      HEIGHT = 150
      MID_Y = HEIGHT / 2
      private_constant :WIDTH, :HEIGHT, :MID_Y

      def title_format
        @title_format ||= Magick::Draw.new do |title|
          title.font_family = 'Helvetica'
          title.pointsize = 24
          title.gravity = Magick::ForgetGravity
          title.fill = 'white'
        end
      end

      def environment_format
        @environment_format ||= Magick::Draw.new do |title|
          title.font_family = 'Helvetica'
          title.pointsize = 20
          title.gravity = Magick::ForgetGravity
          title.fill = '#dd7727'
        end
      end

      def blank_environment?
        !@environment&.present?
      end

      def annotate_title(canvas)
        title_format.annotate(canvas, 0, 0, title_x, title_y, @title)
      end

      def annotate_environment(canvas)
        return if blank_environment?

        environment_format.annotate(canvas, 0, 0, env_x, env_y, @environment)
      end

      def logo
        @logo ||= Magick::Image.read(@image.pathname.to_s).first
                               .resize_to_fill(@resize_to[0], @resize_to[1])
      end

      def gap
        @gap ||= environment_format.get_type_metrics('AAF').width
      end

      def logo_w
        logo.bounding_box.width
      end

      def logo_x
        margin_x
      end

      # y position to vertically center logo
      def logo_y
        ((HEIGHT - logo.bounding_box.height) / 2).round
      end

      def title_metrics
        title_format.get_type_metrics(@title)
      end

      def env_metrics
        return OpenStruct.new(width: 0, height: 0) if blank_environment?

        environment_format.get_type_metrics(@environment)
      end

      # Halve the total margin to horizontally center the whole content area.
      def margin_x
        # | whitespace | logo | whitespace | text | whitespace |
        # |<---------->|
        ((WIDTH - total_w) / 2).round
      end

      def title_x
        # | whitespace | logo | whitespace | text | whitespace |
        #                                    ^ this position
        margin_x + logo_w + gap
      end

      # y position to vertically center title
      def title_y
        MID_Y + (title_metrics.ascent / 2).round
      end

      def env_x
        title_x
      end

      # `ascent` is a positive value, and `descent` is a negative value. They
      # describe the full height of the letters. See RMagick documentation.
      def env_y
        MID_Y + title_metrics.ascent - title_metrics.descent + 10
      end

      # Center using the largest width for aesthetics.
      def text_w
        [title_metrics.width, env_metrics.width].max
      end

      def total_w
        # | whitespace | logo | whitespace | text | whitespace |
        #              |<------------------------>|
        logo_w + gap + text_w
      end
    end
  end
end