use std::mem::{self, size_of, MaybeUninit};
use std::ops::{Deref, DerefMut};
use std::ptr;

use libredox::call::MmapArgs;
use libredox::{error::Result, flag, Fd};
use syscall::PAGE_SIZE;

use crate::MemoryType;

const DMA_MEMTY: MemoryType = {
    if cfg!(any(target_arch = "x86", target_arch = "x86_64")) {
        // x86 ensures cache coherence with DMA memory
        MemoryType::Writeback
    } else if cfg!(target_arch = "aarch64") {
        // aarch64 currently must map DMA memory without caching to ensure coherence
        MemoryType::Uncacheable
    } else {
        panic!("invalid arch")
    }
};

pub(crate) fn phys_contiguous_fd() -> Result<Fd> {
    Fd::open(
        &format!("/scheme/memory/zeroed@{DMA_MEMTY}?phys_contiguous"),
        flag::O_CLOEXEC,
        0,
    )
}

fn alloc_and_map(length: usize) -> Result<(usize, *mut ())> {
    assert_eq!(length % PAGE_SIZE, 0);
    unsafe {
        let fd = phys_contiguous_fd()?;
        let virt = libredox::call::mmap(MmapArgs {
            fd: fd.raw(),
            offset: 0,                   // ignored
            addr: core::ptr::null_mut(), // ignored
            length,
            flags: flag::MAP_PRIVATE,
            prot: flag::PROT_READ | flag::PROT_WRITE,
        })?;
        let phys = syscall::virttophys(virt as usize)?;
        for i in 1..length.div_ceil(PAGE_SIZE) {
            debug_assert_eq!(
                syscall::virttophys(virt as usize + i * PAGE_SIZE),
                Ok(phys + i * PAGE_SIZE),
                "NOT CONTIGUOUS"
            );
        }
        Ok((phys, virt as *mut ()))
    }
}

pub struct Dma<T: ?Sized> {
    phys: usize,
    aligned_len: usize,
    virt: *mut T,
}

impl<T> Dma<T> {
    pub fn new(value: T) -> Result<Self> {
        unsafe {
            let mut zeroed = Self::zeroed()?;
            zeroed.as_mut_ptr().write(value);
            Ok(zeroed.assume_init())
        }
    }
    pub fn zeroed() -> Result<Dma<MaybeUninit<T>>> {
        let aligned_len = size_of::<T>().next_multiple_of(PAGE_SIZE);
        let (phys, virt) = alloc_and_map(aligned_len)?;
        Ok(Dma {
            phys,
            virt: virt.cast(),
            aligned_len,
        })
    }
}

impl<T> Dma<MaybeUninit<T>> {
    pub unsafe fn assume_init(self) -> Dma<T> {
        let Dma {
            phys,
            aligned_len,
            virt,
        } = self;
        mem::forget(self);

        Dma {
            phys,
            aligned_len,
            virt: virt.cast(),
        }
    }
}
impl<T: ?Sized> Dma<T> {
    pub fn physical(&self) -> usize {
        self.phys
    }
}

impl<T> Dma<[T]> {
    pub fn zeroed_slice(count: usize) -> Result<Dma<[MaybeUninit<T>]>> {
        let aligned_len = count
            .checked_mul(size_of::<T>())
            .unwrap()
            .next_multiple_of(PAGE_SIZE);
        let (phys, virt) = alloc_and_map(aligned_len)?;

        Ok(Dma {
            phys,
            aligned_len,
            virt: ptr::slice_from_raw_parts_mut(virt.cast(), count),
        })
    }
    pub unsafe fn cast_slice<U>(self) -> Dma<[U]> {
        let Dma {
            phys,
            virt,
            aligned_len,
        } = self;
        core::mem::forget(self);

        Dma {
            phys,
            virt: virt as *mut [U],
            aligned_len,
        }
    }
}
impl<T> Dma<[MaybeUninit<T>]> {
    pub unsafe fn assume_init(self) -> Dma<[T]> {
        let &Dma {
            phys,
            aligned_len,
            virt,
        } = &self;
        mem::forget(self);

        Dma {
            phys,
            aligned_len,
            virt: virt as *mut [T],
        }
    }
}

impl<T: ?Sized> Deref for Dma<T> {
    type Target = T;

    fn deref(&self) -> &T {
        unsafe { &*self.virt }
    }
}

impl<T: ?Sized> DerefMut for Dma<T> {
    fn deref_mut(&mut self) -> &mut T {
        unsafe { &mut *self.virt }
    }
}

impl<T: ?Sized> Drop for Dma<T> {
    fn drop(&mut self) {
        unsafe {
            ptr::drop_in_place(self.virt);
            let _ = libredox::call::munmap(self.virt as *mut (), self.aligned_len);
        }
    }
}