use crate::run_thread::{ThreadToken, RunThread};
use asm::instr::{Op, Cond};
use crate::fault::Fault;
use crate::frame::StackFrame;
use asm::data::literal::{Value, is_positive, is_negative};

pub type CyclesSpent = usize;

pub struct EvalRes {
    pub cycles: u8,
    pub advance: i64,
}

impl RunThread {
    pub fn eval_op(&mut self) -> Result<EvalRes, Fault> {
        let mut cycles = 1;
        let mut advance = 1;

        let mut frame = &mut self.frame;

        let op = self.program.read(frame.pc);
        debug!("{} | {:?}", frame.pc, op);

        /* Operations can be given different execution times when run in slow mode. */
        /* Presently, all that do anything use 1 cycle. */

        match op {
            Op::Nop => {}
            Op::FarLabel(_) | Op::Routine(_) => {
                /* this is nop, but without any cost - just markers */
                cycles = 0;
            }
            Op::Barrier(msg) => {
                return Err(Fault::Barrier {
                    msg: msg.clone().unwrap_or_else(|| "No msg".into())
                })
            }
            Op::Fault(msg) => {
                return Err(Fault::FaultInstr {
                    msg: msg.clone().unwrap_or_else(|| "No msg".into())
                })
            }
            Op::FarJump(_) => unimplemented!(),
            Op::Call(_, _) => unimplemented!(),
            Op::Ret(_) => unimplemented!(),
            Op::Skip(val) => {
                let steps = frame.read(*val)?;
                advance = i64::from_ne_bytes(steps.to_ne_bytes());
            }
            Op::SkipIf(cond, val) => {
                if frame.status.test(*cond) {
                    let steps = frame.read(*val)?;
                    advance = i64::from_ne_bytes(steps.to_ne_bytes());
                }
            }
            Op::Mov(dst, src) => {
                let val = frame.read(*src)?;
                frame.write(*dst, val)?;
            }
            Op::Cmp(a, b) => {
                frame.status.clear();
                let a = frame.read(*a)?;
                let b = frame.read(*b)?;
                frame.status.equal = a == b;
                frame.status.zero = a == 0 && b == 0;
                frame.status.lower = a < b;
                frame.status.greater = a > b;
                frame.status.positive = is_positive(a) && is_positive(b);
                frame.status.negative = is_negative(a) && is_negative(b);
            }
            Op::Inc(reg) => {
                frame.status.clear();
                let mut val = frame.read(reg.as_rd())?;
                val = val.wrapping_add(1);
                frame.status.overflow = (val == 0);
                frame.status.zero = (val == 0);
                frame.status.positive = is_positive(val);
                frame.status.negative = is_negative(val);
                frame.write(*reg, val)?;
            }
            Op::Dec(reg) => {
                frame.status.clear();
                let mut val = frame.read(reg.as_rd())?;
                frame.status.overflow = (val == 0); // will overflow
                val = val.wrapping_sub(1);
                frame.status.zero = (val == 0);
                frame.status.positive = is_positive(val);
                frame.status.negative = is_negative(val);
                frame.write(*reg, val)?;
            }
        }

        Ok(EvalRes {
            cycles,
            advance,
        })
    }
}