use crate::call_frame::CallFrame;
use prometeu_bytecode::abi::{TrapInfo, TRAP_INVALID_LOCAL};
use prometeu_bytecode::FunctionMeta;

/// Computes the absolute stack index for the start of the current frame's locals (including args).
pub fn local_base(frame: &CallFrame) -> usize {
    frame.stack_base
}

/// Computes the absolute stack index for a given local slot.
pub fn local_index(frame: &CallFrame, slot: u32) -> usize {
    frame.stack_base + slot as usize
}

/// Validates that a local slot index is within the valid range for the function.
/// Range: 0 <= slot < (param_slots + local_slots)
pub fn check_local_slot(meta: &FunctionMeta, slot: u32, opcode: u16, pc: u32) -> Result<(), TrapInfo> {
    let limit = meta.param_slots as u32 + meta.local_slots as u32;
    if slot < limit {
        Ok(())
    } else {
        Err(TrapInfo {
            code: TRAP_INVALID_LOCAL,
            opcode,
            message: format!("Local slot {} out of bounds for function (limit {})", slot, limit),
            pc,
            span: None,
        })
    }
}