use core::ops::Deref;
use core::default::Default;
use stm32f4xx_hal::stm32::ETHERNET_DMA;

use crate::{
    desc::Descriptor,
    ring::{RingEntry, RingDescriptor},
};


#[derive(Debug, PartialEq)]
pub enum RxError {
    WouldBlock,
    Truncated,
    DmaError,
}

/// Owned by DMA engine
const RXDESC_0_OWN: u32 = 1 << 31;
/// First descriptor
const RXDESC_0_FS: u32 = 1 << 9;
/// Last descriptor
const RXDESC_0_LS: u32 = 1 << 8;
/// Error summary
const RXDESC_0_ES: u32 = 1 << 15;
/// Frame length
const RXDESC_0_FL_MASK: u32 = 0x3FFF;
const RXDESC_0_FL_SHIFT: usize = 16;

const RXDESC_1_RBS_SHIFT: usize = 0;
const RXDESC_1_RBS_MASK: u32 = 0x0fff << RXDESC_1_RBS_SHIFT;
/// Second address chained
const RXDESC_1_RCH: u32 = 1 << 14;
/// End Of Ring
const RXDESC_1_RER: u32 = 1 << 15;

#[repr(C)]
#[derive(Clone)]
pub struct RxDescriptor {
    desc: Descriptor,
}

impl Default for RxDescriptor {
    fn default() -> Self {
        let mut desc = Descriptor::default();
        unsafe { desc.write(1, RXDESC_1_RCH); }
        RxDescriptor { desc }
    }
}

impl RxDescriptor {
    /// Is owned by the DMA engine?
    fn is_owned(&self) -> bool {
        (self.desc.read(0) & RXDESC_0_OWN) == RXDESC_0_OWN
    }

    /// Pass ownership to the DMA engine
    fn set_owned(&mut self) {
        unsafe { self.desc.modify(0, |w| w | RXDESC_0_OWN); }
    }

    fn has_error(&self) -> bool {
        (self.desc.read(0) & RXDESC_0_ES) == RXDESC_0_ES
    }

    /// Descriptor contains first buffer of frame
    fn is_first(&self) -> bool {
        (self.desc.read(0) & RXDESC_0_FS) == RXDESC_0_FS
    }

    /// Descriptor contains last buffers of frame
    fn is_last(&self) -> bool {
        (self.desc.read(0) & RXDESC_0_LS) == RXDESC_0_LS
    }

    fn set_buffer1(&mut self, buffer: *const u8, len: usize) {
        unsafe {
            self.desc.write(2, buffer as u32);
            self.desc.modify(1, |w| {
                (w & !RXDESC_1_RBS_MASK) |
                ((len as u32) << RXDESC_1_RBS_SHIFT)
            });
        }
    }

    // points to next descriptor (RCH)
    fn set_buffer2(&mut self, buffer: *const u8) {
        unsafe { self.desc.write(3, buffer as u32); }
    }

    fn set_end_of_ring(&mut self) {
        unsafe { self.desc.modify(1, |w| w | RXDESC_1_RER); }
    }

    fn get_frame_len(&self) -> usize {
        ((self.desc.read(0) >> RXDESC_0_FL_SHIFT) & RXDESC_0_FL_MASK) as usize
    }
}

pub type RxRingEntry = RingEntry<RxDescriptor>;

impl RingDescriptor for RxDescriptor {
    fn setup(&mut self, buffer: *const u8, len: usize, next: Option<&Self>) {
        self.set_buffer1(buffer, len);
        match next {
            Some(next) =>
                self.set_buffer2(&next.desc as *const Descriptor as *const u8),
            None => {
                self.set_buffer2(0 as *const u8);
                self.set_end_of_ring();
            },
        };
        self.set_owned();
    }
}

impl RxRingEntry {
    fn take_received(&mut self) -> Result<RxPacket, RxError> {
        match self.desc().is_owned() {
            true =>
                Err(RxError::WouldBlock),
            false if self.desc().has_error() => {
                self.desc_mut().set_owned();
                Err(RxError::DmaError)
            },
            false if self.desc().is_first() && self.desc().is_last() => {
                let frame_len = self.desc().get_frame_len();
                // TODO: obtain ethernet frame type (RDESC_1_FT)

                let pkt = RxPacket { entry: self, length: frame_len };
                Ok(pkt)
            },
            false => {
                self.desc_mut().set_owned();
                Err(RxError::Truncated)
            },
        }
    }
}

pub struct RxPacket<'a> {
    entry: &'a mut RxRingEntry,
    length: usize,
}

impl<'a> Deref for RxPacket<'a> {
    type Target = [u8];
    
    fn deref(&self) -> &Self::Target {
        &self.entry.as_slice()[0..self.length]
    }
}

impl<'a> Drop for RxPacket<'a> {
    fn drop(&mut self) {
        self.entry.desc_mut().set_owned();
    }
}

impl<'a> RxPacket<'a> {
    // Pass back to DMA engine
    pub fn free(self) {
        drop(self)
    }
}

/// Rx DMA state
pub struct RxRing<'a> {
    entries: &'a mut [RxRingEntry],
    next_entry: usize,
}

impl<'a> RxRing<'a> {
    /// Allocate
    pub fn new(entries: &'a mut [RxRingEntry]) -> Self {
        RxRing {
            entries,
            next_entry: 0,
        }
    }

    /// Setup the DMA engine (**required**)
    pub fn start(&mut self, eth_dma: &ETHERNET_DMA) {
        // Setup ring
        {
            let mut previous: Option<&mut RxRingEntry> = None;
            for entry in self.entries.iter_mut() {
                previous.map(|previous| previous.setup(Some(entry)));
                previous = Some(entry);
            }
            previous.map(|previous| previous.setup(None));
        }
        self.next_entry = 0;
        let ring_ptr = self.entries[0].desc() as *const RxDescriptor;
        // Register RxDescriptor
        eth_dma.dmardlar.write(|w| {
            w.srl().bits(ring_ptr as u32)
        });

        // Start receive
        eth_dma.dmaomr.modify(|_, w| w.sr().set_bit());

        self.demand_poll(eth_dma);
    }

    /// Demand that the DMA engine polls the current `RxDescriptor`
    /// (when in `RunningState::Stopped`.)
    pub fn demand_poll(&self, eth_dma: &ETHERNET_DMA) {
        eth_dma.dmarpdr.write(|w| unsafe { w.rpd().bits(1) });
    }

    /// Get current `RunningState`
    pub fn running_state(&self, eth_dma: &ETHERNET_DMA) -> RunningState {
        match eth_dma.dmasr.read().rps().bits() {
            //  Reset or Stop Receive Command issued
            0b000 => RunningState::Stopped,
            //  Fetching receive transfer descriptor
            0b001 => RunningState::Running,
            //  Waiting for receive packet
            0b011 => RunningState::Running,
            //  Receive descriptor unavailable
            0b100 => RunningState::Stopped,
            //  Closing receive descriptor
            0b101 => RunningState::Running,
            //  Transferring the receive packet data from receive buffer to host memory
            0b111 => RunningState::Running,
            _ => RunningState::Unknown,
        }
    }

    /// Receive the next packet (if any is ready), or return `None`
    /// immediately.
    pub fn recv_next(&mut self, eth_dma: &ETHERNET_DMA) -> Result<RxPacket, RxError>
    {
        if ! self.running_state(eth_dma).is_running() {
            self.demand_poll(eth_dma);
        }

        let entries_len = self.entries.len();
        let result = self.entries[self.next_entry].take_received();
        match result {
            Err(RxError::WouldBlock) => {}
            _ => {
                self.next_entry += 1;
                if self.next_entry >= entries_len {
                    self.next_entry = 0;
                }
            }
        }

        result
    }
}

/// Running state of the `RxRing`
#[derive(PartialEq, Eq, Debug)]
pub enum RunningState {
    Unknown,
    Stopped,
    Running,
}

impl RunningState {
    /// whether self equals to `RunningState::Running`
    pub fn is_running(&self) -> bool {
        *self == RunningState::Running
    }
}