init commit

src/util.rs

@@ -0,0 +1,62 @@
+use rand::prelude::*;
+
+enum Tok {
+    Roll(u32),
+    Flat(u32),
+}
+
+use Tok::*;
+
+/// Rolls dice corresponding to a ttrpg dice specifier
+/// ```
+/// assert_eq!(roll("4d6 + 1d4 + 1").1.len(), 2)
+/// ```
+pub fn roll(spec: &str) -> (u32, Vec<u32>) {
+    let mut toks = spec.split_whitespace();
+    let mut rolls = vec![];
+    let mut total = 0;
+    
+    let first = toks.next().unwrap();
+    match parse_tok(first) {
+	Roll(v) => {
+	    total += v;
+	    rolls.push(v);
+	}
+	Flat(v) => total += v,
+    };
+    let toks : Vec<&str> = toks.collect();
+    let mut toks = toks.chunks(2);
+    while let Some(&[op, tok]) = toks.next() {
+	let val = match parse_tok(tok) {
+	    Roll(v) => {
+		rolls.push(v);
+		v
+	    }
+	    Flat(v) => v,
+	};
+	if op == "-" {
+	    total -= val;
+	} else {
+	    total += val;
+	}
+    }
+    (total, rolls)
+}
+
+fn parse_tok(tok: &str) -> Tok {
+    let mut rng = thread_rng();
+    match *tok.split('d')
+        .map(|x| x.parse().unwrap())
+	.collect::<Vec<_>>()
+	.as_slice() {
+	[v] => Flat(v),
+	[n, d] => {
+	    let mut total = 0;
+	    for _ in 0..n {
+		total += rng.gen_range(1..=d)
+	    }
+	    Roll(total)
+	}
+	_ => panic!()
+    }
+}