feat(filter): add auto_lightness filter

auto_lightness filter increases lightness if under 50.0 and decreases
lightness if above 50.0

src/filters/lightness.rs

@@ -8,6 +8,73 @@ use crate::color::{
     parse::{check_string_value, parse_color},
 };
 
+fn adjust_rgb_lightness(color: &mut Rgb, amount: f64, threshold: f64) {
+    let hsl = Hsl::from(color.clone()); // Convert RGB to HSL
+
+    // Adjust lightness based on the threshold
+    if hsl.lightness() < threshold {
+        color.lighten(amount); // Increase lightness
+    } else {
+        color.lighten(-amount); // Decrease lightness
+    }
+}
+
+fn adjust_hsl_lightness(color: &mut Hsl, amount: f64, threshold: f64) {
+    // Adjust lightness based on the threshold
+    if color.lightness() < threshold {
+        color.lighten(amount); // Increase lightness
+    } else {
+        color.lighten(-amount); // Decrease lightness
+    }
+}
+
+pub fn auto_lightness(value: &Value, amount: f64) -> Result<String, String> {
+    let string = check_string_value(value).unwrap();
+    let threshold = 50.0;
+
+    let format = parse_color(string);
+
+    debug!("Setting lightness on string {} by {}", string, amount);
+
+    if format.is_none() {
+        return Ok(string.to_string());
+    }
+
+    match format.unwrap() {
+        "hex" => {
+            let mut color = Rgb::from_hex_str(string).unwrap();
+            adjust_rgb_lightness(&mut color, amount, threshold);
+            Ok(format_hex(&color))
+        }
+        "hex_stripped" => {
+            let mut color = Rgb::from_hex_str(string).unwrap();
+            adjust_rgb_lightness(&mut color, amount, threshold);
+            Ok(format_hex_stripped(&color))
+        }
+        "rgb" => {
+            let mut color = Rgb::from_str(string).unwrap();
+            adjust_rgb_lightness(&mut color, amount, threshold);
+            Ok(format_rgb(&color))
+        }
+        "rgba" => {
+            let mut color = Rgb::from_str(string).unwrap();
+            adjust_rgb_lightness(&mut color, amount, threshold);
+            Ok(format_rgba(&color, true))
+        }
+        "hsl" => {
+            let mut color = Hsl::from_str(string).unwrap();
+            adjust_hsl_lightness(&mut color, amount, threshold);
+            Ok(format_hsl(&color))
+        }
+        "hsla" => {
+            let mut color = Hsl::from_str(string).unwrap();
+            adjust_hsl_lightness(&mut color, amount, threshold);
+            Ok(format_hsla(&color, true))
+        }
+        v => Ok(v.to_string()),
+    }
+}
+
 pub fn set_lightness(value: &Value, amount: f64) -> Result<String, String> {
     let string = check_string_value(value).unwrap();
 

src/template_util/template.rs

@@ -14,7 +14,7 @@ use crate::filters::camel::camel_case;
 use crate::filters::grayscale::grayscale;
 use crate::filters::hue::set_hue;
 use crate::filters::invert::invert;
-use crate::filters::lightness::set_lightness;
+use crate::filters::lightness::{auto_lightness, set_lightness};
 use crate::scheme::{Schemes, SchemesEnum};
 
 #[derive(serde::Serialize, serde::Deserialize, Debug)]
@@ -44,6 +44,7 @@ pub struct ColorVariants {
 pub fn add_engine_filters(engine: &mut Engine) {
     // Color manipulation
     engine.add_filter("set_lightness", set_lightness);
+    engine.add_filter("auto_lightness", auto_lightness);
     engine.add_filter("set_alpha", set_alpha);
     engine.add_filter("set_hue", set_hue);
     engine.add_filter("grayscale", grayscale);