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

#[test]
fn scheduler_wake_and_ready_order_is_deterministic() {
    // Black-box determinism: run a tiny program twice and ensure it yields the same sequence
    // of LogicalFrameEndingReason for identical budgets.

    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: &[prometeu_bytecode::Value],
            _ret: &mut HostReturn,
            _ctx: &mut HostContext,
        ) -> Result<(), prometeu_hal::vm_fault::VmFault> {
            Ok(())
        }
    }

    // Program: FRAME_SYNC; HALT
    let mut rom = Vec::new();
    emit(CoreOpCode::FrameSync, None, &mut rom);
    emit(CoreOpCode::Halt, None, &mut rom);

    let run_once = || -> Vec<LogicalFrameEndingReason> {
        let mut vm = VirtualMachine::new(rom.clone(), vec![]);
        vm.prepare_call("0");
        let mut native = NoopNative;
        let mut ctx = HostContext::new(None);
        let mut reasons = Vec::new();
        let r1: BudgetReport = vm.run_budget(10, &mut native, &mut ctx).unwrap();
        reasons.push(r1.reason);
        let r2: BudgetReport = vm.run_budget(10, &mut native, &mut ctx).unwrap();
        reasons.push(r2.reason);
        reasons
    };

    let a = run_once();
    let b = run_once();
    assert_eq!(a, b, "execution reasons must be deterministic");
}