use crate::validate;

mod value;

use {
    crate::bytecode::{OpParam, ParamRI, ParamRR, ParamRRR},
    core::ops,
    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.reg_mut(tg) = $handler(Value::$ty($self.reg(a0)), Value::$ty($self.reg(a1))).into();
    }};
}

pub struct Vm<'a> {
    pub registers: [Value; 60],
    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],
            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) {
        use crate::bytecode::opcode::*;
        loop {
            let Some(&opcode) = self.program.get(self.pc)
                else { return };

            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.reg_mut(param.0) = (!self.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),
                    LI => {
                        let param = param!(self, ParamRI);
                        *self.reg_mut(param.0) = param.1.into();
                    }
                    // TODO: LD, ST
                    JMP => {
                        self.pc =
                            self.program.as_ptr().add(self.pc + 1).cast::<u64>().read() as usize;
                    }
                    _ => core::hint::unreachable_unchecked(),
                }
            }
        }
    }

    #[inline]
    unsafe fn reg(&self, n: u8) -> &Value {
        self.registers.get_unchecked(n as usize)
    }

    #[inline]
    unsafe fn reg_mut(&mut self, n: u8) -> &mut Value {
        self.registers.get_unchecked_mut(n as usize)
    }
}