use std::ops::Rem;

use num_traits::PrimInt;

use asm::data::literal::Addr;
use asm::instr::Op;

use crate::fault::Fault;
use crate::frame::StackFrame;
use crate::run_thread::RunThread;

pub type CyclesSpent = usize;

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

impl RunThread {
    // TODO unit tests
    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!("------------------------");
        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(name) => {
                debug!("Far jump to {}", name);
                match self.program.find_far_label(name) {
                    Ok(pos) => {
                        debug!("label is at {}", pos);
                        self.frame.pc = pos;
                    }
                    Err(e) => {
                        return Err(e);
                    }
                }
            }
            Op::Call(name, args) => {
                debug!("Call routine {}", name);
                match self.program.find_routine(name) {
                    Ok(pos) => {
                        debug!("routine is at {}", pos);

                        let mut values = Vec::with_capacity(args.len());
                        for arg in args {
                            values.push(self.frame.read(*arg)?);
                        }

                        let mut frame2 = StackFrame::new(pos, &values);
                        std::mem::swap(&mut self.frame, &mut frame2);
                        self.call_stack.push(frame2);
                        advance = 0;
                    }
                    Err(e) => {
                        return Err(e);
                    }
                }
            }
            Op::Ret(retvals) => {
                match self.call_stack.pop() {
                    Some(previous) => {
                        let mut values = Vec::with_capacity(retvals.len());
                        for arg in retvals {
                            values.push(frame.read(*arg)?);
                        }
                        *frame = previous;
                        frame.set_retvals(&values);
                        advance = 1; // advance past the call
                    }
                    None => {
                        return Err(Fault::CallStackUnderflow);
                    }
                }
            }
            Op::Skip(val) => {
                let steps = frame.read(*val)?;
                advance = i64::from_ne_bytes(steps.to_ne_bytes());
                self.program.validate_jump(frame.pc, Addr((frame.pc.0 as i64 + advance) as u64))?;
            }
            Op::SkipIf(cond, val) => {
                if frame.status.test(*cond) {
                    let steps = frame.read(*val)?;
                    advance = i64::from_ne_bytes(steps.to_ne_bytes());
                    self.program.validate_jump(frame.pc, Addr((frame.pc.0 as i64 + advance) as u64))?;
                }
            }
            Op::Move { dst, src } => {
                frame.status.clear();
                let val = frame.read(*src)?;
                frame.status.update(val);
                frame.write(*dst, val)?;
            }
            Op::Test { a } => {
                frame.status.clear();
                let res = frame.read(*a)?;
                frame.status.update(res);
            }
            Op::Compare { a, b } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let y = frame.read(*b)?;
                frame.status.equal = x == y;
                frame.status.lower = x < y;
                frame.status.greater = x > y;
                // Test flags are set when both arguments have the property
                if x == y {
                    frame.status.update(x);
                }
            }
            Op::Add { dst, a, b } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let y = frame.read(*b)?;
                let (res, ov) = if let Some(v) = x.checked_add(y) {
                    (v, false)
                } else {
                    (x.wrapping_add(y), true)
                };
                frame.status.update(res);
                frame.status.overflow = ov;
                frame.write(*dst, res)?;
            }
            Op::Sub { dst, a, b } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let y = frame.read(*b)?;
                let (res, ov) = if let Some(v) = x.checked_sub(y) {
                    (v, false)
                } else {
                    (x.wrapping_sub(y), true)
                };
                frame.status.update(res);
                frame.status.overflow = ov;
                frame.write(*dst, res)?;
            }
            Op::Mul { dst, a, b } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let y = frame.read(*b)?;
                let (res, ov) = if let Some(v) = x.checked_mul(y) {
                    (v, false)
                } else {
                    (x.wrapping_mul(y), true)
                };
                frame.status.update(res);
                frame.status.overflow = ov;
                frame.write(*dst, res)?;
            }
            Op::Div { dst, rem, a, div } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let d = frame.read(*div)?;
                if d == 0 {
                    frame.status.invalid = true;
                } else {
                    let (res, remainder, ov) = if let Some(v) = x.checked_div(d) {
                        (v, x.rem(d), false)
                    } else {
                        (x.wrapping_div(d), x.wrapping_rem(d), true)
                    };
                    frame.status.update(res);
                    frame.status.overflow = ov;
                    frame.write(*dst, res)?;
                    frame.write(*rem, remainder)?;
                }
            }
            Op::Mod { dst, a, div } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let d = frame.read(*div)?;
                if d == 0 {
                    frame.status.invalid = true;
                } else {
                    let (remainder, ov) = if let Some(v) = x.checked_rem(d) {
                        (v, false)
                    } else {
                        (x.wrapping_rem(d), true)
                    };
                    frame.status.update(remainder);
                    frame.status.overflow = ov;
                    frame.write(*dst, remainder)?;
                }
            }
            Op::And { dst, a, b } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let y = frame.read(*b)?;
                let res = x & y;
                frame.status.update(res);
                frame.write(*dst, res)?;
            }
            Op::Or { dst, a, b } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let y = frame.read(*b)?;
                let res = x | y;
                frame.status.update(res);
                frame.write(*dst, res)?;
            }
            Op::Xor { dst, a, b } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let y = frame.read(*b)?;
                let res = x ^ y;
                frame.status.update(res);
                frame.write(*dst, res)?;
            }
            Op::Cpl { dst, a } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let res = !x;
                frame.status.update(res);
                frame.write(*dst, res)?;
            }
            Op::Rol { dst, a, n } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let y = frame.read(*n)?;
                if y > u32::MAX as u64 {
                    frame.status.invalid = true;
                } else {
                    let res = x.rotate_left(y as u32);
                    frame.status.update(res);
                    frame.write(*dst, res)?;
                }
            }
            Op::Ror { dst, a, n } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let y = frame.read(*n)?;
                if y > u32::MAX as u64 {
                    frame.status.invalid = true;
                } else {
                    let res = x.rotate_right(y as u32);
                    frame.status.update(res);
                    frame.write(*dst, res)?;
                }
            }
            Op::Lsl { dst, a, n } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let y = frame.read(*n)?;
                let res = x << y;
                frame.status.update(res);
                frame.write(*dst, res)?;
            }
            Op::Lsr { dst, a, n } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let y = frame.read(*n)?;
                let res = x >> y;
                frame.status.update(res);
                frame.write(*dst, res)?;
            }
            Op::Asr { dst, a, n } => {
                frame.status.clear();
                let x = frame.read(*a)?;
                let y = frame.read(*n)?;
                if y > u32::MAX as u64 {
                    frame.status.invalid = true;
                } else {
                    let res = x.signed_shr(y as u32);
                    frame.status.update(res);
                    frame.write(*dst, res)?;
                }
            }
            Op::StoreStatus { dst } => {
                let packed = frame.status.store();
                frame.write(*dst, packed)?;
            }
            Op::LoadStatus { src } => {
                let x = frame.read(*src)?;
                frame.status.load(x);
            }
        }

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