class Prawn::SVG::Properties
  Config = Struct.new(:default, :inheritable?, :keywords, :keyword_restricted?, :attr, :ivar)

  EM = 16
  FONT_SIZES = {
    'xx-small' => EM / 4,
    'x-small'  => EM / 4 * 2,
    'small'    => EM / 4 * 3,
    'medium'   => EM / 4 * 4,
    'large'    => EM / 4 * 5,
    'x-large'  => EM / 4 * 6,
    'xx-large' => EM / 4 * 7
  }.freeze

  PROPERTIES = {
    'clip-path'         => Config.new('none', false, %w[inherit none]),
    'color'             => Config.new('', true),
    'display'           => Config.new('inline', false, %w[inherit inline none], true),
    'fill'              => Config.new('black', true, %w[inherit none currentColor]),
    'fill-opacity'      => Config.new('1', true),
    'fill-rule'         => Config.new('nonzero', true, %w[inherit nonzero evenodd]),
    'font-family'       => Config.new('sans-serif', true),
    'font-size'         => Config.new('medium', true,
      %w[inherit xx-small x-small small medium large x-large xx-large larger smaller]),
    'font-style'        => Config.new('normal', true, %w[inherit normal italic oblique], true),
    'font-variant'      => Config.new('normal', true, %w[inherit normal small-caps], true),
    'font-weight'       => Config.new('normal', true, %w[inherit normal bold 100 200 300 400 500 600 700 800 900], true), # bolder/lighter not supported
    'letter-spacing'    => Config.new('normal', true, %w[inherit normal]),
    'marker-end'        => Config.new('none', true, %w[inherit none]),
    'marker-mid'        => Config.new('none', true, %w[inherit none]),
    'marker-start'      => Config.new('none', true, %w[inherit none]),
    'opacity'           => Config.new('1', false),
    'overflow'          => Config.new('visible', false, %w[inherit visible hidden scroll auto], true),
    'stop-color'        => Config.new('black', false, %w[inherit none currentColor]),
    'stroke'            => Config.new('none', true, %w[inherit none currentColor]),
    'stroke-dasharray'  => Config.new('none', true, %w[inherit none]),
    'stroke-linecap'    => Config.new('butt', true, %w[inherit butt round square], true),
    'stroke-linejoin'   => Config.new('miter', true, %w[inherit miter round bevel], true),
    'stroke-opacity'    => Config.new('1', true),
    'stroke-width'      => Config.new('1', true),
    'text-anchor'       => Config.new('start', true, %w[inherit start middle end], true),
    'text-decoration'   => Config.new('none', true, %w[inherit none underline], true),
    'dominant-baseline' => Config.new('auto', true, %w[inherit auto middle], true)
  }.freeze

  PROPERTIES.each do |name, value|
    value.attr = name.gsub('-', '_')
    value.ivar = "@#{value.attr}"
  end

  PROPERTY_CONFIGS = PROPERTIES.values
  NAMES = PROPERTIES.keys
  ATTR_NAMES = PROPERTIES.keys.map { |name| name.gsub('-', '_') }

  attr_accessor(*ATTR_NAMES)

  def load_default_stylesheet
    PROPERTY_CONFIGS.each do |config|
      instance_variable_set(config.ivar, config.default)
    end

    self
  end

  def set(name, value)
    if (config = PROPERTIES[name.to_s.downcase])
      value = value.strip
      keyword = value.downcase
      keywords = config.keywords || ['inherit']

      if keywords.include?(keyword)
        value = keyword
      elsif config.keyword_restricted?
        value = config.default
      end

      instance_variable_set(config.ivar, value)
    end
  end

  def to_h
    PROPERTIES.each.with_object({}) do |(name, config), result|
      result[name] = instance_variable_get(config.ivar)
    end
  end

  def load_hash(hash)
    hash.each { |name, value| set(name, value) if value }
  end

  def compute_properties(other)
    PROPERTY_CONFIGS.each do |config|
      value = other.send(config.attr)

      if value && value != 'inherit'
        value = compute_font_size_property(value).to_s if config.attr == 'font_size'
        instance_variable_set(config.ivar, value)

      elsif value.nil? && !config.inheritable?
        instance_variable_set(config.ivar, config.default)
      end
    end
  end

  def numerical_font_size
    # px = pt for PDFs
    FONT_SIZES[font_size] || font_size.to_f
  end

  private

  def compute_font_size_property(value)
    if value[-1] == '%'
      numerical_font_size * (value.to_f / 100.0)
    elsif value == 'larger'
      numerical_font_size + 4
    elsif value == 'smaller'
      numerical_font_size - 4
    elsif value.match(/(\d|\.)em\z/i)
      numerical_font_size * value.to_f
    elsif value.match(/(\d|\.)rem\z/i)
      value.to_f * EM
    else
      FONT_SIZES[value] || value.to_f
    end
  end
end