use core::prelude::*;
use core::mem::{size_of, align_of};
use core::cmp::max;
use core::ptr;

use stack::Stack;

#[allow(non_camel_case_types)]
pub type uintptr_t = u64;

#[allow(raw_pointer_derive)]
#[derive(Copy, Clone)]
pub struct Registers {
  rsp: *mut uintptr_t
}

impl Registers {
  #[inline]
  pub unsafe fn new<S, F>(stack: &mut S, f: F) -> Registers where S: Stack, F: FnOnce() {
    let sp_limit = stack.limit();
    let mut sp = stack.top() as *mut uintptr_t;
    let f_ptr = push(&mut sp, f);

    asm!(include_str!("init.s")
          : "={rdi}"(sp)
          : "{rdi}" (sp),
            "{rsi}" (rust_trampoline::<F>),
            "{rdx}" (f_ptr),
            "{rcx}" (sp_limit)
          :
          : "volatile");

    Registers { rsp: sp }
  }

  #[inline(always)]
  pub unsafe fn swap(&mut self) {
    asm!(include_str!("swap.s")
          :
          : "{rdi}" (&mut self.rsp)
          : "rax",   "rbx",   "rcx",   "rdx",   "rsi",   "rdi", //"rbp",   "rsp",
            "r8",    "r9",    "r10",   "r11",   "r12",   "r13",   "r14",   "r15",
            "xmm0",  "xmm1",  "xmm2",  "xmm3",  "xmm4",  "xmm5",  "xmm6",  "xmm7",
            "xmm8",  "xmm9",  "xmm10", "xmm11", "xmm12", "xmm13", "xmm14", "xmm15",
            "xmm16", "xmm17", "xmm18", "xmm19", "xmm20", "xmm21", "xmm22", "xmm23", 
            "xmm24", "xmm25", "xmm26", "xmm27", "xmm28", "xmm29", "xmm30", "xmm31"
            "cc"
          : "volatile");
  }
}

unsafe extern "C" fn rust_trampoline<F: FnOnce()>(f: *const F) {
  ptr::read(f)()
}

unsafe fn push<T>(spp: &mut *mut uintptr_t, value: T) -> *mut T {
  let mut sp = *spp as *mut T;
  sp = offset_mut(sp, -1);
  sp = align_down_mut(sp, max(align_of::<T>(), 16));
  *sp = value;
  *spp = sp as *mut uintptr_t;
  sp
}

fn align_down_mut<T>(sp: *mut T, n: usize) -> *mut T {
  let sp = (sp as usize) & !(n - 1);
  sp as *mut T
}

// ptr::offset_mut is positive ints only
pub fn offset_mut<T>(ptr: *mut T, count: isize) -> *mut T {
  (ptr as isize + count * (size_of::<T>() as isize)) as *mut T
}