From 57f490a06fe793a25172ea5f6a13945c363cc6aa Mon Sep 17 00:00:00 2001
From: Scott Worley <scottworley@scottworley.com>
Date: Thu, 13 Jul 2023 12:02:47 -0700
Subject: [PATCH 1/1] PathLengthInfo

---
 Cargo.toml |  1 +
 src/lib.rs | 61 ++++++++++++++++++++++++++++++++++++++++++++++++------
 2 files changed, 56 insertions(+), 6 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 73f846f..fd79b30 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,3 +9,4 @@ repository = "https://git.scottworley.com/pluta-lesnura"
 
 
 [dependencies]
+rand = "0.8.5"
diff --git a/src/lib.rs b/src/lib.rs
index c90799e..a5148a0 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,6 +1,43 @@
-#[must_use]
-pub fn add(left: usize, right: usize) -> usize {
-    left + right
+use rand::Rng;
+
+pub const NUM_RANKS: u8 = 13;
+
+#[derive(Clone, Copy, Eq, PartialEq)]
+pub struct Rank(u8);
+
+#[derive(Clone, Copy)]
+pub struct PathLength(Rank);
+
+#[derive(Clone, Copy, Default)]
+pub struct PathLengthInfo(u16);
+impl PathLengthInfo {
+    #[must_use]
+    pub fn is_showing(&self, i: Rank) -> bool {
+        (self.0 >> i.0) & 1 == 1
+    }
+    fn reveal(&mut self, i: Rank) {
+        self.0 |= 1 << i.0;
+    }
+    pub fn reveal_random(&mut self, true_length: PathLength) -> Option<Rank> {
+        let showing = u8::try_from(self.0.count_ones()).expect("There aren't that many bits");
+        let not_showing = NUM_RANKS - showing;
+        if not_showing <= 1 {
+            return None;
+        }
+
+        let mut show = rand::thread_rng().gen_range(0..not_showing - 1);
+        for i in 0..NUM_RANKS {
+            let r = Rank(i);
+            if !self.is_showing(r) && r != true_length.0 {
+                if show == 0 {
+                    self.reveal(r);
+                    return Some(r);
+                }
+                show -= 1;
+            }
+        }
+        unreachable!()
+    }
 }
 
 #[cfg(test)]
@@ -8,8 +45,20 @@ mod tests {
     use super::*;
 
     #[test]
-    fn it_works() {
-        let result = add(2, 2);
-        assert_eq!(result, 4);
+    fn path_length_info_random_reveal() {
+        let length = PathLength(Rank(7));
+        let mut pli = PathLengthInfo::default();
+        for _ in 0..12 {
+            let old_pli = PathLengthInfo::clone(&pli);
+            match pli.reveal_random(length) {
+                None => panic!("Nothing revealed?"),
+                Some(r) => {
+                    assert!(!old_pli.is_showing(r));
+                    assert!(pli.is_showing(r));
+                }
+            }
+            assert_eq!(pli.0.count_ones(), 1 + old_pli.0.count_ones());
+        }
+        assert!(pli.reveal_random(length).is_none());
     }
 }
-- 
2.44.1