initial version

bqst-core/src/api.rs

@@ -0,0 +1,54 @@
+use std::fmt::Debug;
+
+use dashu::rational::RBig;
+
+use crate::{PrecDec, prefixes, qty::Qty, unit};
+
+macro_rules! _t {
+    ($e:expr) => {
+        $e.map_err(|e| Box::new(e) as Box<dyn Debug>)
+    };
+}
+
+fn parse_decimal<const B: u32>(s: &str) -> Result<RBig, dashu::base::ParseError> {
+    if let Some((int_part, frac_part)) = s.split_once('.') {
+        let denominator = B.pow(frac_part.len() as u32);
+        let numerator = RBig::from_str_radix(&format!("{}{}", int_part, frac_part), B)?;
+        Ok(numerator / RBig::from(denominator))
+    } else {
+        Ok(RBig::from_str_radix(s, B)?)
+    }
+}
+
+pub fn qty(q: &str) -> Result<Qty, Box<dyn Debug>> {
+    let split_idx = q
+        .char_indices()
+        .rev()
+        .find(|&(_, c)| c.is_ascii_digit())
+        .map(|(i, _)| i + 1) // found digit and digits are 1 byte so no worries byt ugly
+        .unwrap_or(0);
+
+    let (amt, unt) = q.split_at(split_idx);
+    let mut amt: PrecDec = if amt.is_empty() {
+        PrecDec::from(1)
+    } else {
+        _t!(parse_decimal::<10>(amt))?
+    };
+
+    let unt = if let Some((_, rem, exp)) = prefixes::extract_prefix_and_rem(unt.trim()) {
+        let e = PrecDec::from(10isize.pow(exp.unsigned_abs().into()));
+        if exp < 0 {
+            amt /= e;
+        } else {
+            amt *= e;
+        }
+
+        rem
+    } else {
+        unt
+    };
+
+    let unt = _t!(unit::Unit::try_from(unt.trim()))?;
+
+    Ok(Qty { n: amt, u: unt })
+}