use prometeu_bytecode::isa::core::{CoreOpCode, CoreOpCodeSpecExt};
use prometeu_hal::{HostContext, HostReturn, NativeInterface, SyscallId};
use prometeu_vm::{BudgetReport, LogicalFrameEndingReason, VirtualMachine};
use prometeu_bytecode::Value;

fn emit(op: CoreOpCode, imm: Option<&[u8]>, out: &mut Vec<u8>) {
    out.extend_from_slice(&(op as u16).to_le_bytes());
    let need = op.spec().imm_bytes as usize;
    match (need, imm) {
        (0, None) => {}
        (n, Some(bytes)) if bytes.len() == n => out.extend_from_slice(bytes),
        (n, Some(bytes)) => panic!("imm size mismatch for {:?}: need {}, got {}", op, n, bytes.len()),
        (n, None) => panic!("missing imm for {:?}: need {} bytes", op, n),
    }
}

struct NoopNative;
impl NativeInterface for NoopNative {
    fn syscall(
        &mut self,
        _id: SyscallId,
        _args: &[Value],
        _ret: &mut HostReturn,
        _ctx: &mut HostContext,
    ) -> Result<(), prometeu_hal::vm_fault::VmFault> {
        Ok(())
    }
}

#[test]
fn vm_executes_valid_program_in_slices() {
    // Program: PUSH_I32 2; PUSH_I32 3; ADD; FRAME_SYNC; HALT
    let mut rom = Vec::new();
    emit(CoreOpCode::PushI32, Some(&2i32.to_le_bytes()), &mut rom);
    emit(CoreOpCode::PushI32, Some(&3i32.to_le_bytes()), &mut rom);
    emit(CoreOpCode::Add, None, &mut rom);
    emit(CoreOpCode::FrameSync, None, &mut rom);
    emit(CoreOpCode::Halt, None, &mut rom);

    // Construct VM directly; assume input is already verified.
    let mut vm = VirtualMachine::new(rom, vec![]);
    vm.prepare_call("0");

    let mut native = NoopNative;
    let mut ctx = HostContext::new(None);

    // First slice should stop at FRAME_SYNC deterministically.
    let report: BudgetReport = vm.run_budget(100, &mut native, &mut ctx).expect("run ok");
    assert_eq!(report.reason, LogicalFrameEndingReason::FrameSync);
    assert!(!vm.is_halted());

    // Second slice proceeds to HALT.
    let report2: BudgetReport = vm.run_budget(100, &mut native, &mut ctx).expect("run ok");
    assert_eq!(report2.reason, LogicalFrameEndingReason::Halted);
    assert!(vm.is_halted());
}