implement builtin function random

README.md

@@ -18,7 +18,7 @@ The large features remaining are
 order of operations
 special case certain functions (min, max, calc, element, expression, progid, url)
 all builtin selector functions (274 tests)
-content-exists, unique-id, random, min, min
+content-exists, unique-id, min, min
 @extend (~600 tests)
 indented syntax (27 tests)
 a special parser for plain css

src/builtin/math.rs

@@ -1,5 +1,10 @@
 use std::collections::HashMap;
 
+#[cfg(feature = "random")]
+use num_traits::{One, Signed, ToPrimitive, Zero};
+#[cfg(feature = "random")]
+use rand::Rng;
+
 use super::Builtin;
 use crate::unit::Unit;
 use crate::value::{Number, Value};
@@ -75,4 +80,50 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
             Ok(Value::bool(unit1.comparable(&unit2)))
         }),
     );
+    // TODO: write tests for this. how?
+    #[cfg(feature = "random")]
+    f.insert(
+        "random".to_owned(),
+        Builtin::new(|mut args, scope, super_selector| {
+            max_args!(args, 1);
+            let limit = match arg!(args, scope, super_selector, 0, "limit" = Value::Null) {
+                Value::Dimension(n, _) => n,
+                Value::Null => {
+                    let mut rng = rand::thread_rng();
+                    return Ok(Value::Dimension(
+                        Number::from(rng.gen_range(0.0, 1.0)),
+                        Unit::None,
+                    ));
+                }
+                v => return Err(format!("$limit: {} is not a number.", v).into()),
+            };
+
+            if limit.is_one() {
+                return Ok(Value::Dimension(Number::one(), Unit::None));
+            }
+
+            if limit.is_decimal() {
+                return Err(format!("$limit: {} is not an int.", limit).into());
+            }
+
+            if limit.is_zero() || limit.is_negative() {
+                return Err(format!("$limit: Must be greater than 0, was {}.", limit).into());
+            }
+
+            let limit = match limit.to_integer().to_u32() {
+                Some(n) => n,
+                None => {
+                    return Err(
+                        format!("max must be in range 0 < max ≤ 2^32, was {}", limit).into(),
+                    )
+                }
+            };
+
+            let mut rng = rand::thread_rng();
+            Ok(Value::Dimension(
+                Number::from(rng.gen_range(0, limit)),
+                Unit::None,
+            ))
+        }),
+    );
 }

src/value/number.rs

@@ -161,6 +161,7 @@ impl From<f64> for Number {
 from_integer!(u16);
 from_integer!(usize);
 from_integer!(i32);
+from_integer!(u32);
 from_integer!(u8);
 
 impl Display for Number {