Issue-2464: Add color luminosity options

lib/faker/default/color.rb

@@ -6,14 +6,21 @@ class << self
       ##
       # Produces a hex color code.
       #
+      # @param lightness [Symbol] Allows the client to specify light or dark colors
+      #
       # @return [String]
       #
       # @example
       #   Faker::Color.hex_color #=> "#31a785"
+      # @example
+      #   Faker::Color.hex_color(:light) #=> "#FFEE99"
+      # @example
+      #   Faker::Color.hex_color(:dark) #=> "#665500"
       #
-      # @faker.version 1.5.0
-      def hex_color
-        format('#%06x', (rand * 0xffffff))
+      # @faker.version next
+      def hex_color(lightness = nil)
+        lightness_lookup = { light: 0.8, dark: 0.2 }
+        hsl_to_hex(hsl_color(lightness: lightness_lookup[lightness]))
       end
 
       ##
@@ -51,14 +58,17 @@ def rgb_color
       # Produces an array of floats representing an HSL color.
       # The array is in the form of `[hue, saturation, lightness]`.
       #
+      # @param lightness [Float] Value to use for lightness
       # @return [Array(Float, Float, Float)]
       #
       # @example
       #   Faker::Color.hsl_color #=> [69.87, 0.66, 0.3]
+      # @example
+      #   Faker::Color.hsl_color(lightness: 0.6) #=> [69.87, 0.66, 0.6]
       #
-      # @faker.version 1.5.0
-      def hsl_color
-        [sample((0..360).to_a), rand.round(2), rand.round(2)]
+      # @faker.version next
+      def hsl_color(lightness: nil)
+        [sample((0..360).to_a), rand.round(2), lightness || rand.round(2)]
       end
 
       ##
@@ -74,6 +84,46 @@ def hsl_color
       def hsla_color
         hsl_color << rand.round(1)
       end
+
+      private
+
+      ##
+      # Produces a hex code representation of an HSL color
+      #
+      # @param a_hsl_color [Array(Float, Float, Float)] The array that represents the HSL color
+      #
+      # @return [String]
+      #
+      # @example
+      #   hsl_to_hex([50, 100,80]) #=> #FFEE99
+      #
+      # @see https://en.wikipedia.org/wiki/HSL_and_HSV#HSL_to_RGB
+      # @see https://github.com/jpmckinney/color-generator/blob/master/lib/color-generator.rb
+      #
+      def hsl_to_hex(a_hsl_color)
+        h, s, l = a_hsl_color
+        c = (1 - (2 * l - 1).abs) * s
+        h_prime = h / 60
+        x = c * (1 - (h_prime % 2 - 1).abs)
+        m = l - 0.5 * c
+
+        rgb = case h_prime.to_i
+              when 0 # 0 <= H' < 1
+                [c, x, 0]
+              when 1 # 1 <= H' < 2
+                [x, c, 0]
+              when 2 # 2 <= H' < 3
+                [0, c, x]
+              when 3 # 3 <= H' < 4
+                [0, x, c]
+              when 4 # 4 <= H' < 5
+                [x, 0, c]
+              else # 5 <= H' < 6
+                [c, 0, x]
+              end.map { |value| ((value + m) * 255).round }
+
+        format('#%02x%02x%02x', rgb[0], rgb[1], rgb[2])
+      end
     end
   end
 end

test/faker/default/test_faker_color.rb

@@ -15,6 +15,20 @@ def test_hex_color
     assert_match(/^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$/, @tester.hex_color)
   end
 
+  # @see https://www.rapidtables.com/convert/color/rgb-to-hsl.html
+  def helper_hex_lightness(hex_color)
+    result = hex_color.scan(/([A-Fa-f0-9]{2})/).flatten.map { |x| x.hex / 255.0 }
+    (result.max + result.min) / 2
+  end
+
+  def test_hex_color_light
+    assert_in_delta(0.8, helper_hex_lightness(@tester.hex_color(:light)))
+  end
+
+  def test_hex_color_dark
+    assert_in_delta(0.2, helper_hex_lightness(@tester.hex_color(:dark)))
+  end
+
   def test_single_rgb_color
     assert @tester.single_rgb_color.between?(0, 255)
   end
@@ -38,6 +52,11 @@ def test_hsl_color
     assert @result[2].between?(0.0, 1.0)
   end
 
+  def test_hsl_color_with_a_speficied_lightness
+    @result = @tester.hsl_color(lightness: 0.5)
+    assert_in_delta(0.5, @result[2])
+  end
+
   def test_hsla_color
     @result = @tester.hsla_color
     assert_equal(4, @result.length)