// SPDX-License-Identifier: MPL-2.0

use alloc::sync::Arc;
use core::ops::Range;

#[cfg(feature = "intel_tdx")]
use ::tdx_guest::tdx_is_enabled;

use super::{check_and_insert_dma_mapping, remove_dma_mapping, DmaError, HasDaddr};
#[cfg(feature = "intel_tdx")]
use crate::arch::tdx_guest;
use crate::{
    arch::iommu,
    error::Error,
    mm::{
        dma::{dma_type, Daddr, DmaType},
        HasPaddr, Paddr, Segment, VmIo, VmReader, VmWriter, PAGE_SIZE,
    },
};

/// A streaming DMA mapping. Users must synchronize data
/// before reading or after writing to ensure consistency.
///
/// The mapping is automatically destroyed when this object
/// is dropped.
#[derive(Debug, Clone)]
pub struct DmaStream {
    inner: Arc<DmaStreamInner>,
}

#[derive(Debug)]
struct DmaStreamInner {
    vm_segment: Segment,
    start_daddr: Daddr,
    /// TODO: remove this field when on x86.
    #[allow(unused)]
    is_cache_coherent: bool,
    direction: DmaDirection,
}

/// `DmaDirection` limits the data flow direction of [`DmaStream`] and
/// prevents users from reading and writing to [`DmaStream`] unexpectedly.
#[derive(Debug, PartialEq, Clone, Copy)]
pub enum DmaDirection {
    /// Data flows to the device
    ToDevice,
    /// Data flows form the device
    FromDevice,
    /// Data flows both from and to the device
    Bidirectional,
}

impl DmaStream {
    /// Establishes DMA stream mapping for a given [`Segment`].
    ///
    /// The method fails if the segment already belongs to a DMA mapping.
    pub fn map(
        vm_segment: Segment,
        direction: DmaDirection,
        is_cache_coherent: bool,
    ) -> Result<Self, DmaError> {
        let frame_count = vm_segment.nframes();
        let start_paddr = vm_segment.start_paddr();
        if !check_and_insert_dma_mapping(start_paddr, frame_count) {
            return Err(DmaError::AlreadyMapped);
        }
        // Ensure that the addresses used later will not overflow
        start_paddr.checked_add(frame_count * PAGE_SIZE).unwrap();
        let start_daddr = match dma_type() {
            DmaType::Direct => {
                #[cfg(feature = "intel_tdx")]
                // SAFETY:
                // This is safe because we are ensuring that the physical address range specified by `start_paddr` and `frame_count` is valid before these operations.
                // The `check_and_insert_dma_mapping` function checks if the physical address range is already mapped.
                // We are also ensuring that we are only modifying the page table entries corresponding to the physical address range specified by `start_paddr` and `frame_count`.
                // Therefore, we are not causing any undefined behavior or violating any of the requirements of the 'unprotect_gpa_range' function.
                if tdx_is_enabled() {
                    unsafe {
                        tdx_guest::unprotect_gpa_range(start_paddr, frame_count).unwrap();
                    }
                }
                start_paddr as Daddr
            }
            DmaType::Iommu => {
                for i in 0..frame_count {
                    let paddr = start_paddr + (i * PAGE_SIZE);
                    // SAFETY: the `paddr` is restricted by the `start_paddr` and `frame_count` of the `vm_segment`.
                    unsafe {
                        iommu::map(paddr as Daddr, paddr).unwrap();
                    }
                }
                start_paddr as Daddr
            }
        };

        Ok(Self {
            inner: Arc::new(DmaStreamInner {
                vm_segment,
                start_daddr,
                is_cache_coherent,
                direction,
            }),
        })
    }

    /// Gets the underlying [`Segment`].
    ///
    /// Usually, the CPU side should not access the memory
    /// after the DMA mapping is established because
    /// there is a chance that the device is updating
    /// the memory. Do this at your own risk.
    pub fn vm_segment(&self) -> &Segment {
        &self.inner.vm_segment
    }

    /// Returns the number of frames
    pub fn nframes(&self) -> usize {
        self.inner.vm_segment.nframes()
    }

    /// Returns the number of bytes
    pub fn nbytes(&self) -> usize {
        self.inner.vm_segment.nbytes()
    }

    /// Synchronizes the streaming DMA mapping with the device.
    ///
    /// This method should be called under one of the two conditions:
    /// 1. The data of the stream DMA mapping has been updated by the device side.
    ///    The CPU side needs to call the `sync` method before reading data (e.g., using [`read_bytes`]).
    /// 2. The data of the stream DMA mapping has been updated by the CPU side
    ///    (e.g., using [`write_bytes`]).
    ///    Before the CPU side notifies the device side to read, it must call the `sync` method first.
    ///
    /// [`read_bytes`]: Self::read_bytes
    /// [`write_bytes`]: Self::write_bytes
    pub fn sync(&self, _byte_range: Range<usize>) -> Result<(), Error> {
        cfg_if::cfg_if! {
            if #[cfg(target_arch = "x86_64")]{
                // The streaming DMA mapping in x86_64 is cache coherent, and does not require synchronization.
                // Reference: <https://lwn.net/Articles/855328/>, <https://lwn.net/Articles/2265/>
                Ok(())
            } else {
                if _byte_range.end > self.nbytes() {
                    return Err(Error::InvalidArgs);
                }
                if self.inner.is_cache_coherent {
                    return Ok(());
                }
                let start_va = self.inner.vm_segment.as_ptr();
                // TODO: Query the CPU for the cache line size via CPUID, we use 64 bytes as the cache line size here.
                for i in _byte_range.step_by(64) {
                    // TODO: Call the cache line flush command in the corresponding architecture.
                    todo!()
                }
                Ok(())
            }
        }
    }
}

impl HasDaddr for DmaStream {
    fn daddr(&self) -> Daddr {
        self.inner.start_daddr
    }
}

impl Drop for DmaStreamInner {
    fn drop(&mut self) {
        let frame_count = self.vm_segment.nframes();
        let start_paddr = self.vm_segment.start_paddr();
        // Ensure that the addresses used later will not overflow
        start_paddr.checked_add(frame_count * PAGE_SIZE).unwrap();
        match dma_type() {
            DmaType::Direct => {
                #[cfg(feature = "intel_tdx")]
                // SAFETY:
                // This is safe because we are ensuring that the physical address range specified by `start_paddr` and `frame_count` is valid before these operations.
                // The `start_paddr()` ensures the `start_paddr` is page-aligned.
                // We are also ensuring that we are only modifying the page table entries corresponding to the physical address range specified by `start_paddr` and `frame_count`.
                // Therefore, we are not causing any undefined behavior or violating any of the requirements of the `protect_gpa_range` function.
                if tdx_is_enabled() {
                    unsafe {
                        tdx_guest::protect_gpa_range(start_paddr, frame_count).unwrap();
                    }
                }
            }
            DmaType::Iommu => {
                for i in 0..frame_count {
                    let paddr = start_paddr + (i * PAGE_SIZE);
                    iommu::unmap(paddr).unwrap();
                }
            }
        }
        remove_dma_mapping(start_paddr, frame_count);
    }
}

impl VmIo for DmaStream {
    /// Reads data into the buffer.
    fn read_bytes(&self, offset: usize, buf: &mut [u8]) -> Result<(), Error> {
        if self.inner.direction == DmaDirection::ToDevice {
            return Err(Error::AccessDenied);
        }
        self.inner.vm_segment.read_bytes(offset, buf)
    }

    /// Writes data from the buffer.
    fn write_bytes(&self, offset: usize, buf: &[u8]) -> Result<(), Error> {
        if self.inner.direction == DmaDirection::FromDevice {
            return Err(Error::AccessDenied);
        }
        self.inner.vm_segment.write_bytes(offset, buf)
    }
}

impl<'a> DmaStream {
    /// Returns a reader to read data from it.
    pub fn reader(&'a self) -> Result<VmReader<'a>, Error> {
        if self.inner.direction == DmaDirection::ToDevice {
            return Err(Error::AccessDenied);
        }
        Ok(self.inner.vm_segment.reader())
    }

    /// Returns a writer to write data into it.
    pub fn writer(&'a self) -> Result<VmWriter<'a>, Error> {
        if self.inner.direction == DmaDirection::FromDevice {
            return Err(Error::AccessDenied);
        }
        Ok(self.inner.vm_segment.writer())
    }
}

impl HasPaddr for DmaStream {
    fn paddr(&self) -> Paddr {
        self.inner.vm_segment.start_paddr()
    }
}

/// A slice of streaming DMA mapping.
#[derive(Debug)]
pub struct DmaStreamSlice<'a> {
    stream: &'a DmaStream,
    offset: usize,
    len: usize,
}

impl<'a> DmaStreamSlice<'a> {
    /// Constructs a `DmaStreamSlice` from the [`DmaStream`].
    ///
    /// # Panics
    ///
    /// If the `offset` is greater than or equal to the length of the stream,
    /// this method will panic.
    /// If the `offset + len` is greater than the length of the stream,
    /// this method will panic.
    pub fn new(stream: &'a DmaStream, offset: usize, len: usize) -> Self {
        assert!(offset < stream.nbytes());
        assert!(offset + len <= stream.nbytes());

        Self {
            stream,
            offset,
            len,
        }
    }

    /// Returns the number of bytes.
    pub fn nbytes(&self) -> usize {
        self.len
    }

    /// Synchronizes the slice of streaming DMA mapping with the device.
    pub fn sync(&self) -> Result<(), Error> {
        self.stream.sync(self.offset..self.offset + self.len)
    }
}

impl VmIo for DmaStreamSlice<'_> {
    fn read_bytes(&self, offset: usize, buf: &mut [u8]) -> Result<(), Error> {
        if buf.len() + offset > self.len {
            return Err(Error::InvalidArgs);
        }
        self.stream.read_bytes(self.offset + offset, buf)
    }

    fn write_bytes(&self, offset: usize, buf: &[u8]) -> Result<(), Error> {
        if buf.len() + offset > self.len {
            return Err(Error::InvalidArgs);
        }
        self.stream.write_bytes(self.offset + offset, buf)
    }
}

impl HasDaddr for DmaStreamSlice<'_> {
    fn daddr(&self) -> Daddr {
        self.stream.daddr() + self.offset
    }
}

impl HasPaddr for DmaStreamSlice<'_> {
    fn paddr(&self) -> Paddr {
        self.stream.paddr() + self.offset
    }
}

#[cfg(ktest)]
mod test {
    use alloc::vec;

    use super::*;
    use crate::{mm::FrameAllocOptions, prelude::*};

    #[ktest]
    fn streaming_map() {
        let vm_segment = FrameAllocOptions::new(1)
            .is_contiguous(true)
            .alloc_contiguous()
            .unwrap();
        let dma_stream =
            DmaStream::map(vm_segment.clone(), DmaDirection::Bidirectional, true).unwrap();
        assert!(dma_stream.paddr() == vm_segment.paddr());
    }

    #[ktest]
    fn duplicate_map() {
        let vm_segment_parent = FrameAllocOptions::new(2)
            .is_contiguous(true)
            .alloc_contiguous()
            .unwrap();
        let vm_segment_child = vm_segment_parent.range(0..1);
        let dma_stream_parent =
            DmaStream::map(vm_segment_parent, DmaDirection::Bidirectional, false);
        let dma_stream_child = DmaStream::map(vm_segment_child, DmaDirection::Bidirectional, false);
        assert!(dma_stream_child.is_err());
    }

    #[ktest]
    fn read_and_write() {
        let vm_segment = FrameAllocOptions::new(2)
            .is_contiguous(true)
            .alloc_contiguous()
            .unwrap();
        let dma_stream = DmaStream::map(vm_segment, DmaDirection::Bidirectional, false).unwrap();

        let buf_write = vec![1u8; 2 * PAGE_SIZE];
        dma_stream.write_bytes(0, &buf_write).unwrap();
        dma_stream.sync(0..2 * PAGE_SIZE).unwrap();
        let mut buf_read = vec![0u8; 2 * PAGE_SIZE];
        dma_stream.read_bytes(0, &mut buf_read).unwrap();
        assert_eq!(buf_write, buf_read);
    }

    #[ktest]
    fn reader_and_wirter() {
        let vm_segment = FrameAllocOptions::new(2)
            .is_contiguous(true)
            .alloc_contiguous()
            .unwrap();
        let dma_stream = DmaStream::map(vm_segment, DmaDirection::Bidirectional, false).unwrap();

        let buf_write = vec![1u8; PAGE_SIZE];
        let mut writer = dma_stream.writer().unwrap();
        writer.write(&mut buf_write.as_slice().into());
        writer.write(&mut buf_write.as_slice().into());
        dma_stream.sync(0..2 * PAGE_SIZE).unwrap();
        let mut buf_read = vec![0u8; 2 * PAGE_SIZE];
        let buf_write = vec![1u8; 2 * PAGE_SIZE];
        let mut reader = dma_stream.reader().unwrap();
        reader.read(&mut buf_read.as_mut_slice().into());
        assert_eq!(buf_read, buf_write);
    }
}