use prometeu_bytecode::{HeapRef, Value};

/// Visitor for GC roots. Implementors receive every `HeapRef` discovered
/// during root traversal. No marking/sweeping semantics here.
pub trait RootVisitor {
    fn visit_heap_ref(&mut self, r: HeapRef);
}

/// Helper: if `val` is a `Value::HeapRef`, call the visitor.
pub fn visit_value_for_roots<V: RootVisitor + ?Sized>(val: &Value, visitor: &mut V) {
    if let Value::HeapRef(r) = val {
        visitor.visit_heap_ref(*r);
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::VirtualMachine;

    struct CollectVisitor {
        pub seen: Vec<HeapRef>,
    }
    impl RootVisitor for CollectVisitor {
        fn visit_heap_ref(&mut self, r: HeapRef) {
            self.seen.push(r);
        }
    }

    #[test]
    fn visits_heapref_on_operand_stack() {
        let mut vm = VirtualMachine::default();
        // Place a HeapRef on the operand stack
        vm.push_operand_for_test(Value::HeapRef(HeapRef(123)));

        let mut v = CollectVisitor { seen: vec![] };
        vm.visit_roots(&mut v);

        assert_eq!(v.seen, vec![HeapRef(123)]);
    }
}