bahaghari/lib: implement basic HSL color namespace

subprojects/bahaghari/lib/colors/hsl.nix

@@ -0,0 +1,135 @@
+# Similar to RGB, we're also going to base our implementation from looking
+# after the W3 CSS Color Module Level 4 specification simply because it is the
+# most common one.
+{ pkgs, lib, self }:
+
+let inherit (self.colors) rgb;
+in rec {
+  valueHueMin = 0.0;
+  valueHueMax = 360.0;
+  valueParamMin = 0.0;
+  valueParamMax = 100.0;
+
+  /* Generates an HSL colorspace object to be generated with its method for
+     convenience.
+
+     Type: HSL :: Attrs -> Attrs
+
+     Example:
+       HSL { h = 242.0; s = 25; l = 50; }
+       => {
+         # The individual hue, saturation, and luminance levels.
+
+         # And several methods.
+         methods = {
+           toRgb = <function>;
+           lighten = <function>;
+         };
+       }
+  */
+  HSL = { h, s, l, ... }@color:
+    assert lib.assertMsg (isHsl color)
+      "bahaghariLib.colors.hsl.HSL: given color does not have valid HSL value";
+    {
+      inherit h s l;
+    } // lib.optionalAttrs (color ? a) { inherit (color) a; };
+
+  /* Returns a boolean if the object is a valid HSL Nix object.
+
+     Type: isHsl :: Attrs -> Bool
+
+     Example:
+       isHsl { h = 43; s = 89; l = 79; }
+       => true
+
+       # The hue value is over 360 so it isn't valid.
+       isHsl { h = 467; s = 78; l = 50; }
+       => false
+
+       # The lightness is over 100 so not valid either.
+       isHsl { h = 360; s = 86; l = 120; }
+       => false
+  */
+  isHsl = { h, s, l, ... }@color:
+    let
+      isValidHue = self.math.isWithinRange valueHueMin valueHueMax;
+      isValidPercentage = self.math.isWithinRange valueParamMin valueParamMax;
+    in
+      isValidHue h && isValidPercentage s && isValidPercentage l;
+
+  /* Converts an HSL object to RGB instance.
+
+     Formula is directly taken from the following resource:
+     https://www.rapidtables.com/convert/color/hsl-to-rgb.html
+
+     Type: toRgb :: Attrs -> Attrs
+
+     Example:
+       toRgb { h = 234; s = 65; l = 73; }
+       => { r = 43; g = 52; b = 56 }
+  */
+  toRgb = { h, s, l, ... }@color:
+    let
+      inherit (self.colors.rgb) RGB valueMax;
+      inherit (self.math) abs sub mod';
+
+      l' = l / valueParamMax;
+      s' = s / valueParamMax;
+
+      # This may as well turn into Scheme code.
+      C = (1 - (abs ((2 * l') - 1))) * s';
+      X = C * (1 - (abs (sub (mod' (h / 60.0) 2) 1)));
+      m = l' - (C / 2);
+
+      isHueWithin = min: max:
+        (h >= min) && (h < max);
+      rgb' =
+        if (isHueWithin 0 60) then
+          { r = C; g = X; b = 0; }
+        else if (isHueWithin 60 120) then
+          { r = X; g = C; b = 0; }
+        else if (isHueWithin 120 180) then
+          { r = 0; g = C; b = X; }
+        else if (isHueWithin 180 240) then
+          { r = 0; g = X; b = C; }
+        else if (isHueWithin 240 300) then
+          { r = X; g = 0; b = C; }
+        else if (isHueWithin 300 360) then
+          { r = C; g = 0; b = X; }
+        else throw "WHAT IN THE HELL";
+
+      scaleValue = x: self.math.round ((x + m) * valueMax);
+    in
+      RGB {
+        r = scaleValue rgb'.r;
+        g = scaleValue rgb'.g;
+        b = scaleValue rgb'.b;
+      };
+
+  /* Converts an HSL object into an RGB hex string.
+
+     Type: toHex :: Attrs -> String
+
+     Example:
+       toHex { h = 34; s = 76; l = 100; }
+       => "FFFFFF"
+  */
+  toHex = color: rgb.toHex (toRgb color);
+
+  /* Converts an HSL object into an RGBA hex string.
+
+     Type: toHex :: Attrs -> String
+
+     Example:
+       toHex { h = 34; s = 76; l = 100; }
+       => "FFFFFF"
+  */
+  toHex' = color: rgb.toHex' (toRgb color);
+
+  lighten = { h, s, l, ... }:
+    percentage:
+    HSL {
+      inherit h s;
+      l = l + percentage;
+    };
+}

subprojects/bahaghari/lib/default.nix

@@ -34,6 +34,7 @@ pkgs.lib.makeExtensible
     # some unbeknownst and probably irrational reason.
     colors = {
       rgb = callLibs ./colors/rgb.nix;
+      hsl = callLibs ./colors/hsl.nix;
     };
 
     # Dedicated module sets are not supposed to have any of its functions as a

subprojects/bahaghari/tests/lib/default.nix

@@ -13,4 +13,5 @@ in
   trivial = callLib ./trivial;
   tinted-theming = callLib ./tinted-theming;
   rgb = callLib ./rgb.nix;
+  hsl = callLib ./hsl.nix;
 }

subprojects/bahaghari/tests/lib/hsl.nix

@@ -0,0 +1,59 @@
+{ pkgs, lib, self }:
+
+let
+  inherit (self.colors.rgb) RGB;
+  inherit (self.colors.hsl) HSL;
+
+  hslSample = HSL {
+    h = 254;
+    s = 100;
+    l = 45;
+  };
+in lib.runTests {
+  testsBasicHsl = {
+    expr = HSL {
+      h = 245;
+      s = 16;
+      l = 60;
+    };
+    expected = {
+      h = 245;
+      s = 16;
+      l = 60;
+    };
+  };
+
+  testsBasicHsl2 = {
+    expr = HSL {
+      h = 350;
+      s = 16;
+      l = 60;
+      a = 100;
+    };
+    expected = {
+      h = 350;
+      s = 16;
+      l = 60;
+      a = 100;
+    };
+  };
+
+  testsToRgb = {
+    expr = self.colors.hsl.toRgb hslSample;
+    expected = RGB {
+      r = 54;
+      g = 0;
+      b = 230;
+    };
+  };
+
+  testsToHex = {
+    expr = self.colors.hsl.toHex hslSample;
+    expected = "3600E6";
+  };
+
+  testsToHex' = {
+    expr = self.colors.hsl.toHex' hslSample;
+    expected = "3600E6FF";
+  };
+}