1 files changed, 32 insertions, 0 deletions
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..db8020e
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,32 @@
+use rand::distributions::{Distribution, WeightedIndex};
+use rand::RngCore;
+
+const NUM_OF_LETTERS: usize = 26;
+
+pub struct Model {
+    chars: [[usize; NUM_OF_LETTERS + 1]; NUM_OF_LETTERS + 1],
+}
+
+impl Model {
+    pub fn new() -> Model {
+        let chars = include!(concat!(env!("OUT_DIR"), "/prebuilt_model.rs"));
+        Model { chars }
+    }
+
+    pub fn generate<Rng: RngCore>(&self, rng: &mut Rng, len: usize) -> String {
+        let mut result = String::with_capacity(len);
+        let mut prefix = NUM_OF_LETTERS;
+        for _ in 0..len {
+            let chars = &self.chars[prefix];
+            let c = select_one_char(rng, &chars);
+            result.push(c as char);
+            prefix = (c - b'a') as usize;
+        }
+        result
+    }
+}
+
+fn select_one_char<Rng: RngCore>(rng: &mut Rng, freq: &[usize; NUM_OF_LETTERS + 1]) -> u8 {
+    let dist = WeightedIndex::new(freq).expect("invalid frequency");
+    b'a' + (dist.sample(rng) as u8)
+}