//! This module defines the Application Binary Interface (ABI) of the Prometeu Virtual Machine.
//! It specifies how instructions are encoded in bytes and how they interact with memory.

use crate::opcode::OpCode;

/// Returns the size in bytes of the operands for a given OpCode.
/// 
/// Note: This does NOT include the 2 bytes of the OpCode itself.
/// For example, `PushI32` has a size of 4, but occupies 6 bytes in ROM (2 for OpCode + 4 for value).
pub fn operand_size(opcode: OpCode) -> usize {
    match opcode {
        OpCode::PushConst => 4,
        OpCode::PushI32 => 4,
        OpCode::PushI64 => 8,
        OpCode::PushF64 => 8,
        OpCode::PushBool => 1,
        OpCode::PopN => 4,
        OpCode::Jmp | OpCode::JmpIfFalse | OpCode::JmpIfTrue => 4,
        OpCode::GetGlobal | OpCode::SetGlobal => 4,
        OpCode::GetLocal | OpCode::SetLocal => 4,
        OpCode::Call => 8, // addr(u32) + args_count(u32)
        OpCode::Syscall => 4,
        _ => 0,
    }
}

/// Checks if an instruction is a jump (branch) instruction.
pub fn is_jump(opcode: OpCode) -> bool {
    match opcode {
        OpCode::Jmp | OpCode::JmpIfFalse | OpCode::JmpIfTrue => true,
        _ => false,
    }
}

/// Checks if an instruction has any immediate operands in the instruction stream.
pub fn has_immediate(opcode: OpCode) -> bool {
    operand_size(opcode) > 0
}