feat: start on encoding constants with Flat Encoder

crates/uplc/src/ast.rs

@@ -1,5 +1,9 @@
+use flat::en::{Encode, Encoder};
+
 use crate::builtins::DefaultFunction;
 
+const TERM_TAG_WIDTH: u32 = 4;
+
 #[derive(Debug)]
 pub struct Program {
     pub version: String,
@@ -32,6 +36,22 @@ pub enum Term {
     Builtin(DefaultFunction),
 }
 
+pub fn encode_term_tag(tag: u8, e: &mut Encoder) -> Result<(), String> {
+    safe_encode_bits(TERM_TAG_WIDTH, tag, e)
+}
+
+pub fn safe_encode_bits(num_bits: u32, byte: u8, e: &mut Encoder) -> Result<(), String> {
+    if 2_u8.pow(num_bits) < byte {
+        Err(format!(
+            "Overflow detected, cannot fit {} in {} bits.",
+            byte, num_bits
+        ))
+    } else {
+        e.bits(num_bits as i64, byte);
+        Ok(())
+    }
+}
+
 #[derive(Debug, Clone)]
 pub enum Constant {
     // TODO: figure out the right size for this
@@ -48,3 +68,43 @@ pub enum Constant {
     // tag: 5
     Bool(bool),
 }
+
+impl Encode for Program {
+    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+        self.version.encode(e)?;
+        self.term.encode(e)?;
+
+        Ok(())
+    }
+}
+
+impl Encode for Term {
+    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+        match self {
+            Term::Constant(constant) => {
+                encode_term_tag(4, e)?;
+                constant.encode(e)?;
+            }
+            rest => {
+                todo!("Implement: {:?}", rest)
+            }
+        }
+
+        Ok(())
+    }
+}
+
+impl Encode for &Constant {
+    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+        match self {
+            Constant::Integer(_) => todo!(),
+            Constant::ByteString(bytes) => bytes.encode(e)?,
+            Constant::String(s) => s.encode(e)?,
+            Constant::Char(c) => c.encode(e)?,
+            Constant::Unit => todo!(),
+            Constant::Bool(b) => b.encode(e)?,
+        }
+
+        Ok(())
+    }
+}