Implement builtin functions hue(), saturation(), and lightness()

src/builtin/color.rs

@@ -1,7 +1,5 @@
 use std::collections::BTreeMap;
 
-use num_bigint::BigInt;
-
 use super::Builtin;
 use crate::color::Color;
 use crate::common::QuoteKind;
@@ -104,23 +102,41 @@ pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
         Some(Value::Color(Color::from_hsla(hue, saturation, luminance, alpha)))
     });
     decl!(f "red", |args, _| {
-        match arg!(args, 0, "red") {
+        match arg!(args, 0, "color") {
-            Value::Color(c) => Some(Value::Dimension(Number::from(BigInt::from(c.red())), Unit::None)),
+            Value::Color(c) => Some(Value::Dimension(Number::from(c.red()), Unit::None)),
             _ => todo!("non-color given to builtin function `red()`")
         }
     });
     decl!(f "green", |args, _| {
-        match arg!(args, 0, "green") {
+        match arg!(args, 0, "color") {
-            Value::Color(c) => Some(Value::Dimension(Number::from(BigInt::from(c.green())), Unit::None)),
+            Value::Color(c) => Some(Value::Dimension(Number::from(c.green()), Unit::None)),
             _ => todo!("non-color given to builtin function `green()`")
         }
     });
     decl!(f "blue", |args, _| {
-        match arg!(args, 0, "blue") {
+        match arg!(args, 0, "color") {
-            Value::Color(c) => Some(Value::Dimension(Number::from(BigInt::from(c.blue())), Unit::None)),
+            Value::Color(c) => Some(Value::Dimension(Number::from(c.blue()), Unit::None)),
             _ => todo!("non-color given to builtin function `blue()`")
         }
     });
+    decl!(f "hue", |args, _| {
+        match arg!(args, 0, "color") {
+            Value::Color(c) => Some(Value::Dimension(c.hue(), Unit::Deg)),
+            _ => todo!("non-color given to builtin function `hue()`")
+        }
+    });
+    decl!(f "saturation", |args, _| {
+        match arg!(args, 0, "color") {
+            Value::Color(c) => Some(Value::Dimension(c.saturation(), Unit::Percent)),
+            _ => todo!("non-color given to builtin function `saturation()`")
+        }
+    });
+    decl!(f "lightness", |args, _| {
+        match arg!(args, 0, "color") {
+            Value::Color(c) => Some(Value::Dimension(c.lightness(), Unit::Percent)),
+            _ => todo!("non-color given to builtin function `lightness()`")
+        }
+    });
     decl!(f "opacity", |args, _| {
         match arg!(args, 0, "color") {
             Value::Color(c) => Some(Value::Dimension(c.alpha() / Number::from(255), Unit::None)),

src/color/mod.rs

@@ -40,6 +40,68 @@ impl Color {
         self.green
     }
 
+    /// Calculate hue from RGBA values
+    /// Algorithm adapted from http://www.niwa.nu/2013/05/math-behind-colorspace-conversions-rgb-hsl/
+    pub fn hue(&self) -> Number {
+        let red = Number::ratio(self.red, 255);
+        let green = Number::ratio(self.green, 255);
+        let blue = Number::ratio(self.blue, 255);
+        let min = red.clone().min(green.clone().min(blue.clone()));
+        let max = red.clone().max(green.clone().max(blue.clone()));
+        if &min == &max {
+            return Number::from(0);
+        }
+
+        let mut hue = if &red == &max {
+            (green - blue) / (max - min)
+        } else if &green == &max {
+            Number::from(2) + (blue - red) / (max - min)
+        } else {
+            Number::from(4) + (red - green) / (max - min)
+        };
+
+        if hue < Number::from(0) {
+            hue += Number::from(360);
+        }
+
+        (hue * Number::from(60)).round()
+    }
+
+    /// Calculate saturation from RGBA values
+    /// Algorithm adapted from http://www.niwa.nu/2013/05/math-behind-colorspace-conversions-rgb-hsl/
+    pub fn saturation(&self) -> Number {
+        let red = Number::ratio(self.red, 255);
+        let green = Number::ratio(self.green, 255);
+        let blue = Number::ratio(self.blue, 255);
+        let mut min = red.clone().min(green.clone().min(blue.clone()));
+        min = Number::ratio((min * Number::from(100)).to_integer(), 100);
+        let mut max = red.max(green.max(blue));
+        max = Number::ratio((max * Number::from(100)).to_integer(), 100);
+        let luminance = (min.clone() + max.clone()) / Number::from(2);
+        if &min == &max {
+            return Number::from(0);
+        }
+
+        let saturation = if luminance < Number::ratio(1, 2) {
+            (max.clone() - min.clone()) / (max + min)
+        } else {
+            (max.clone() - min.clone()) / (Number::from(2) - max - min)
+        } * Number::from(100);
+
+        saturation.round()
+    }
+
+    /// Calculate luminance from RGBA values
+    /// Algorithm adapted from http://www.niwa.nu/2013/05/math-behind-colorspace-conversions-rgb-hsl/
+    pub fn lightness(&self) -> Number {
+        let red = Number::ratio(self.red, 255);
+        let green = Number::ratio(self.green, 255);
+        let blue = Number::ratio(self.blue, 255);
+        let min = red.clone().min(green.clone().min(blue.clone()));
+        let max = red.max(green.max(blue));
+        (((min + max) / Number::from(2)) * Number::from(100)).round()
+    }
+
     pub fn alpha(&self) -> Number {
         self.alpha.clone()
     }
@@ -77,7 +139,7 @@ impl Color {
             luminance.clone() + saturation.clone() - luminance.clone() * saturation.clone()
         };
         let temporary_2 = Number::from(2) * luminance.clone() - temporary_1.clone();
-        hue = hue / Number::from(360);
+        hue /= Number::from(360);
         let mut temporary_r = hue.clone() + Number::ratio(1, 3);
         let mut temporary_g = hue.clone();
         let mut temporary_b = hue.clone() - Number::ratio(1, 3);

src/value/number.rs

@@ -1,6 +1,6 @@
 use std::convert::From;
 use std::fmt::{self, Display, Write};
-use std::ops::{Add, AddAssign, Div, Mul, Sub, SubAssign};
+use std::ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Sub, SubAssign};
 
 use num_bigint::BigInt;
 use num_rational::BigRational;
@@ -132,6 +132,12 @@ impl Mul for Number {
     }
 }
 
+impl MulAssign for Number {
+    fn mul_assign(&mut self, other: Self) {
+        self.val *= other.val
+    }
+}
+
 impl Div for Number {
     type Output = Self;
 
@@ -141,3 +147,9 @@ impl Div for Number {
         }
     }
 }
+
+impl DivAssign for Number {
+    fn div_assign(&mut self, other: Self) {
+        self.val /= other.val
+    }
+}

src/value/ops.rs

@@ -31,7 +31,7 @@ impl Add for Value {
                 Self::Null => Value::Ident(c.to_string(), QuoteKind::None),
                 Self::Color(..) => todo!("figure out if it's possible to add colors"),
                 _ => Value::Ident(format!("{}{}", c, other), QuoteKind::None),
-            }
+            },
             // Self::BinaryOp(..) => todo!(),
             // Self::Paren(..) => todo!(),
             Self::Ident(s1, quotes1) => match other {
@@ -97,7 +97,7 @@ impl Sub for Value {
                 }
                 Self::Null => Value::Ident(format!("{}-", c), QuoteKind::None),
                 Self::Dimension(..) => todo!("investigate adding numbers and colors"),
-                _ => Value::Ident(format!("{}-{}", c, other), QuoteKind::None)
+                _ => Value::Ident(format!("{}-{}", c, other), QuoteKind::None),
             },
             // Self::BinaryOp(..) => todo!(),
             // Self::Paren(..) => todo!(),
@@ -116,7 +116,11 @@ impl Sub for Value {
                         QuoteKind::None,
                     )
                 }
-                Self::Important | Self::True | Self::False | Self::Dimension(..) | Self::Color(..) => {
+                Self::Important
+                | Self::True
+                | Self::False
+                | Self::Dimension(..)
+                | Self::Color(..) => {
                     let quotes = match quotes1 {
                         QuoteKind::Double | QuoteKind::Single => QuoteKind::Double,
                         QuoteKind::None => QuoteKind::None,

tests/color.rs

@@ -156,3 +156,18 @@ test!(
     "a {\n  color: foo - red;\n}\n",
     "a {\n  color: foo-red;\n}\n"
 );
+test!(
+    hue,
+    "$a: hsl(193, 67%, 28%);\n\na {\n  color: hue($a);\n}\n",
+    "a {\n  color: 193deg;\n}\n"
+);
+test!(
+    saturation,
+    "$a: hsl(193, 67%, 28%);\n\na {\n  color: saturation($a);\n}\n",
+    "a {\n  color: 67%;\n}\n"
+);
+test!(
+    lightness,
+    "$a: hsl(193, 67%, 28%);\n\na {\n  color: lightness($a);\n}\n",
+    "a {\n  color: 28%;\n}\n"
+);