use crate::classfile::{ JavaClassFile, AttributeData };

#[derive(Copy, Clone, Debug)]
pub enum LocalVariable {
    Boolean(bool),
    Byte(u8),
    Char(u16),
    Short(u16),
    Int(u32),
    Float(u32),
    Reference(u32),
    ReturnAddress(u32),
    Double0(u32),
    Double1(u32),
    Long0(u32),
    Long1(u32),
    Empty(),
}

#[derive(Debug)]
pub struct OperandStack {
    stack: Box<[LocalVariable]>,
    depth: u16,
}

impl OperandStack {
    fn new(size: u16) -> Self {
        return OperandStack {
            stack: vec![LocalVariable::Empty(); size.into()].into_boxed_slice(),
            depth: 0,
        }
    }
}

#[derive(Debug)]
pub struct StackFrame {
    locals: Box<[LocalVariable]>,
    operand_stack: OperandStack,
    class_id: usize,
    method_index: u16,
    instruction_pointer: u32,
}

impl StackFrame {
    pub fn new(classfile: &JavaClassFile, class_id: usize, method_index: u16) -> Self {
        let method_info = &classfile.methods[method_index as usize];
        let code_data = match &method_info.attributes[method_info.code_attribute_index].data {
            AttributeData::Code(data) => data,
            _ => unreachable!(),
        };

        StackFrame {
            locals: vec![LocalVariable::Empty(); code_data.max_locals.into()].into_boxed_slice(),
            operand_stack: OperandStack::new(code_data.max_stack),
            class_id,
            method_index,
            instruction_pointer: 0,
        }
    }
}