split wasm filter (#186)

* split wasm filter

* fix int and unit tests

* rename public_types => common and move common code there

* rename

* fix int test

crates/common/src/tokenizer.rs

@@ -0,0 +1,39 @@
+use log::debug;
+
+#[derive(Debug, PartialEq, Eq)]
+#[allow(dead_code)]
+pub enum Error {
+    UnknownModel,
+    FailedToTokenize,
+}
+
+#[allow(dead_code)]
+pub fn token_count(model_name: &str, text: &str) -> Result<usize, Error> {
+    debug!("getting token count model={}", model_name);
+    // Consideration: is it more expensive to instantiate the BPE object every time, or to contend the singleton?
+    let bpe = tiktoken_rs::get_bpe_from_model(model_name).map_err(|_| Error::UnknownModel)?;
+    Ok(bpe.encode_ordinary(text).len())
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn encode_ordinary() {
+        let model_name = "gpt-3.5-turbo";
+        let text = "How many tokens does this sentence have?";
+        assert_eq!(
+            8,
+            token_count(model_name, text).expect("correct tokenization")
+        );
+    }
+
+    #[test]
+    fn unrecognized_model() {
+        assert_eq!(
+            Error::UnknownModel,
+            token_count("unknown", "").expect_err("unknown model")
+        )
+    }
+}