use crate::validate;

mod mem;
mod value;

use {
    core::ops,
    hbbytecode::{OpParam, ParamRI, ParamRR, ParamRRI, ParamRRR},
    mem::{ma_size, Memory},
    static_assertions::assert_impl_one,
    value::Value,
};

macro_rules! param {
    ($self:expr, $ty:ty) => {{
        assert_impl_one!($ty: OpParam);
        let data = $self.program.as_ptr()
            .add($self.pc + 1)
            .cast::<$ty>()
            .read();
        $self.pc += 1 + core::mem::size_of::<$ty>();
        data
    }};
}

macro_rules! binary_op {
    ($self:expr, $ty:ident, $handler:expr) => {{
        let ParamRRR(tg, a0, a1) = param!($self, ParamRRR);
        $self.write_reg(tg, $handler(Value::$ty(&$self.read_reg(a0)), Value::$ty(&$self.read_reg(a1))).into());
    }};
}

macro_rules! load {
    ($self:expr, $size:ty) => {{
        let ParamRRI(tg, a0, offset) = param!($self, ParamRRI);
        $self.write_reg(
            tg,
            $self.memory
                .load::<$size>($self.read_reg(a0).int() + offset)
                .ok_or(Exception::LoadAccess)?
        );
    }};
}

macro_rules! store {
    ($self:expr, $size:ty) => {{
        let ParamRRI(src, a0, offset) = param!($self, ParamRRI);
        $self
            .memory
            .store::<$size>($self.read_reg(a0).int() + offset, $self.read_reg(src))
            .map_err(|_| Exception::StoreAccess)?;
    }};
}

pub struct Vm<'a> {
    pub registers: [Value; 60],
    pub memory: Memory,
    pc: usize,
    program: &'a [u8],
}

impl<'a> Vm<'a> {
    /// # Safety
    /// Program code has to be validated
    pub unsafe fn new_unchecked(program: &'a [u8]) -> Self {
        Self {
            registers: [Value::from(0); 60],
            memory: Default::default(),
            pc: 0,
            program,
        }
    }

    pub fn new_validated(program: &'a [u8]) -> Result<Self, validate::Error> {
        validate::validate(program)?;
        Ok(unsafe { Self::new_unchecked(program) })
    }

    pub fn run(&mut self) -> Result<(), Exception> {
        use hbbytecode::opcode::*;
        loop {
            let Some(&opcode) = self.program.get(self.pc)
                else { return Ok(()) };

            unsafe {
                match opcode {
                    NOP => param!(self, ()),
                    ADD => binary_op!(self, int, u64::wrapping_add),
                    SUB => binary_op!(self, int, u64::wrapping_sub),
                    MUL => binary_op!(self, int, u64::wrapping_mul),
                    DIV => binary_op!(self, int, u64::wrapping_div),
                    REM => binary_op!(self, int, u64::wrapping_rem),
                    AND => binary_op!(self, int, ops::BitAnd::bitand),
                    OR => binary_op!(self, int, ops::BitOr::bitor),
                    XOR => binary_op!(self, int, ops::BitXor::bitxor),
                    NOT => {
                        let param = param!(self, ParamRR);
                        self.write_reg(param.0, (!self.read_reg(param.1).int()).into());
                    }
                    ADDF => binary_op!(self, float, ops::Add::add),
                    SUBF => binary_op!(self, float, ops::Sub::sub),
                    MULF => binary_op!(self, float, ops::Mul::mul),
                    DIVF => binary_op!(self, float, ops::Div::div),
                    CP => {
                        let param = param!(self, ParamRR);
                        self.write_reg(param.0, self.read_reg(param.1));
                    }
                    LI => {
                        let param = param!(self, ParamRI);
                        self.write_reg(param.0, param.1.into());
                    }
                    LB => load!(self, ma_size::Byte),
                    LD => load!(self, ma_size::Doublet),
                    LQ => load!(self, ma_size::Quadlet),
                    LO => load!(self, ma_size::Octlet),
                    SB => store!(self, ma_size::Byte),
                    SD => store!(self, ma_size::Doublet),
                    SQ => store!(self, ma_size::Quadlet),
                    SO => store!(self, ma_size::Octlet),
                    JMP => {
                        let ParamRI(reg, offset) = param!(self, ParamRI);
                        self.pc = (self.read_reg(reg).int() + offset) as usize;
                    }
                    _ => core::hint::unreachable_unchecked(),
                }
            }
        }
    }

    #[inline]
    unsafe fn read_reg(&self, n: u8) -> Value {
        if n == 0 {
            0.into()
        } else {
            *self.registers.get_unchecked(n as usize)
        }
    }

    #[inline]
    unsafe fn write_reg(&mut self, n: u8, value: Value) {
        if n != 0 {
            *self.registers.get_unchecked_mut(n as usize) = value;
        }
    }
}

#[derive(Copy, Clone, Debug, PartialEq, Eq)]
#[repr(u8)]
pub enum Exception {
    LoadAccess,
    StoreAccess,
}