//! A USB-Serial driver for the nRF52840

use core::ops::Deref;

use bbqueue::{BBBuffer, Consumer, Producer};
use nrf52840_hal::{usbd::{Usbd, UsbPeripheral}, pac::USBD};
// use sportty::{Message, max_encoding_length};
use usb_device::{device::UsbDevice, UsbError};
use usbd_serial::SerialPort;
use heapless::{LinearMap, Deque, Vec};
use crate::alloc::{HeapArray, HEAP};
use postcard::{CobsAccumulator, FeedResult};
use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize)]
pub struct Chunk {
    port: u16,
    buf: Vec<u8, 128>,
}

const USB_BUF_SZ: usize = 4096;
static UART_INC: BBBuffer<USB_BUF_SZ> = BBBuffer::new();
static UART_OUT: BBBuffer<USB_BUF_SZ> = BBBuffer::new();

/// A type alias for the nRF52840 USB Peripheral type
pub type AUsbPeripheral = Usbd<UsbPeripheral<'static>>;

/// A type alias for the nRF52840 USB Device type
pub type AUsbDevice = UsbDevice<'static, AUsbPeripheral>;

/// A type alias for the nRF52840 CDC-ACM USB Serial port type
pub type ASerialPort = SerialPort<'static, AUsbPeripheral>;

/// The handle necessary for servicing USB interrupts
pub struct UsbUartIsr {
    dev: AUsbDevice,
    ser: ASerialPort,
    out: Consumer<'static, USB_BUF_SZ>,
    inc: Producer<'static, USB_BUF_SZ>,
}

impl UsbUartIsr {
    /// Service the USB ISR, which is triggered by either a regular polling timer,
    /// or some kind of USB interrupt.
    pub fn poll(&mut self) {
        // Service the relevant hardware logic
        self.dev.poll(&mut [&mut self.ser]);

        // If there is data to be sent...
        if let Ok(rgr) = self.out.read() {
            match self.ser.write(&rgr) {
                // ... and there is room to send it, then send it.
                Ok(sz) if sz > 0 => {
                    rgr.release(sz);
                },
                // ... and there is no room to send it, then just bail.
                Ok(_) | Err(UsbError::WouldBlock) => {
                    // Just silently drop the read grant
                }
                // ... and there is a USB error, then panic.
                Err(_) => defmt::panic!("Usb Error Write!"),
            }
        }

        // If there is room to receive data...
        if let Ok(mut wgr) = self.inc.grant_max_remaining(128) {
            match self.ser.read(&mut wgr) {
                // ... and there is data to be read, then take it.
                Ok(sz) if sz > 0 => {
                    wgr.commit(sz);
                },
                // ... and there is no data to be read, then just bail.
                Ok(_) | Err(UsbError::WouldBlock) => {
                    // Just silently drop the write grant
                }
                // ... and there is a USB error, then panic.
                Err(_) => defmt::panic!("Usb Error Read!"),
            }
        }
    }
}

/// The "userspace" handle for the driver
pub struct UsbUartSys {
    out: Producer<'static, USB_BUF_SZ>,
    inc: Consumer<'static, USB_BUF_SZ>,
    // TODO: There's probably a smarter way to handle this without having
    // a bigass accumulator struct in here. Either limit max size, or use
    // a smarter stream decoder which can emit partial data on the fly
    acc: CobsAccumulator<256>,

    // Also, we might want to "coverge" older messages into fewer allocs,
    // to avoid small chunks filling up the queue
    ports: LinearMap<u16, Deque<HeapArray<u8>, 16>, 8>,
}

/// A struct containing both the "interrupt" and "userspace" handles
/// for this USB-Serial driver
pub struct UsbUartParts {
    pub isr: UsbUartIsr,
    pub sys: UsbUartSys,
}

/// Obtain the "userspace" and "interrupt" portions of the USB-Serial driver
///
/// This only returns `Ok` once, as this driver is a singleton. Subsequent
/// calls will return an `Err`.
pub fn setup_usb_uart(dev: AUsbDevice, ser: ASerialPort) -> Result<UsbUartParts, ()> {
    let (inc_prod, inc_cons) = UART_INC.try_split().map_err(drop)?;
    let (out_prod, out_cons) = UART_OUT.try_split().map_err(drop)?;

    // Port zero (stdio) is always mapped.
    let mut ports = LinearMap::new();
    ports.insert(0, Deque::new()).ok();

    Ok(UsbUartParts {
        isr: UsbUartIsr {
            dev,
            ser,
            out: out_cons,
            inc: inc_prod,
        },
        sys: UsbUartSys {
            out: out_prod,
            inc: inc_cons,
            acc: CobsAccumulator::new(),
            ports,
        }
    })
}

// Implement the "userspace" traits for the USB UART
impl crate::traits::Serial for UsbUartSys {
    fn register_port(&mut self, port: u16) -> Result<(), ()> {
        if self.ports.contains_key(&port) {
            return Err(());
        }

        self.ports.insert(port, Deque::new()).map_err(drop)?;

        defmt::println!("Registered port {=u16}!", port);

        Ok(())
    }

    fn release_port(&mut self, port: u16) -> Result<(), ()> {
        if port == 0 {
            return Err(());
        }

        if self.ports.remove(&port).is_some() {
            Ok(())
        } else {
            Err(())
        }
    }

    fn process(&mut self) {
        // Process all incoming message and dispatch to queues
        while let Ok(rgr) = self.inc.read() {
            let mut window = rgr.deref();
            let rec_len = rgr.len();

            //////////////////////
            // No early returns here! We need to release the grant!
            while !window.is_empty() {
                match self.acc.feed::<Chunk>(window) {
                    FeedResult::Consumed => {
                        window = &[];
                    },
                    FeedResult::OverFull(rem) => {
                        defmt::println!("Overfull error!");
                        window = rem;
                    },
                    FeedResult::DeserError(rem) => {
                        defmt::println!("Chunk deser error!");
                        window = rem;
                    },
                    FeedResult::Success { data, remaining } => {
                        window = remaining;

                        // TODO: Replace this with `map()` and Results so we can actually
                        // tell which part went wrong
                        let failed = self.ports
                            .get_mut(&data.port)
                            .and_then(|dq| {
                                // Keep the heap locked for as short as possible!
                                let mut hp = HEAP.try_lock()?;
                                let habox = hp.alloc_box_array(0u8, data.buf.len()).ok()?;
                                Some((dq, habox))
                            })
                            .and_then(|(dq, mut habox)| {
                                habox.copy_from_slice(&data.buf);
                                dq.push_back(habox).ok()
                            }).is_none();

                        if failed && self.ports.contains_key(&data.port) {
                            defmt::println!("Failed to receive message for serial port {=u16}. Discarding.", data.port);
                        }
                    },
                }
            }

            rgr.release(rec_len);
            // End of "no early return" zone!
            //////////////////////
        }
    }

    fn recv<'a>(&mut self, port: u16, buf: &'a mut [u8]) -> Result<&'a mut [u8], ()> {
        self.process();

        let deq = self.ports.get_mut(&port).ok_or(())?;
        let mut used = 0;
        let buflen = buf.len();

        while used < buf.len() {
            let msg = match deq.pop_front() {
                None => {
                    // No more queued contents, bail!
                    //
                    // NOTE: `&mut buf[..0]` does correctly give back `&mut []`
                    // (and not a slice panic) as you may expect - I checked :)
                    return Ok(&mut buf[..used]);
                }
                Some(msg) => msg,
            };

            let avail = buflen - used;

            if msg.len() <= avail {
                buf[used..][..msg.len()].copy_from_slice(&msg);
                used += msg.len();
            } else {
                let (now, later) = msg.split_at(avail);
                buf[used..].copy_from_slice(now);

                let mut hp = defmt::unwrap!(HEAP.try_lock());
                let mut habox = defmt::unwrap!(hp.alloc_box_array(0u8, later.len()).ok());
                habox.copy_from_slice(later);

                // Okay to ignore error - We just made space
                deq.push_front(habox).ok();

                used += avail;
            }
        }

        // if we've reached here, we've filled the destination buffer
        Ok(buf)
    }

    fn send<'a>(&mut self, port: u16, buf: &'a [u8]) -> Result<(), &'a [u8]> {
        // Check if port is mapped
        if !self.ports.contains_key(&port) {
            defmt::println!("Unregistered port: {=u16}", port);
            return Err(buf);
        }
        let mut used = 0;
        for ch in buf.chunks(128) {
            let mut dunk = Vec::new();
            dunk.extend_from_slice(ch).ok();
            let msg = Chunk { port, buf: dunk };
            match self.out.grant_exact(256) {
                Ok(mut wgr) => {
                    let enc_used = postcard::to_slice_cobs(&msg, &mut wgr).unwrap().len();
                    wgr.commit(enc_used);
                    used += ch.len();
                },
                Err(_) => {
                    return Err(&buf[..used]);
                },
            }
        }
        // This means that we reached `remaining.is_empty()`, and all
        // data has been successfully sent.
        Ok(())
    }
}

pub fn enable_usb_interrupts(usbd: &USBD) {
    usbd.intenset.write(|w| {
        // rg -o "events_[a-z_0-9]+" ./usbd.rs | sort | uniq
        w.endepin0().set_bit();
        w.endepin1().set_bit();
        w.endepin2().set_bit();
        w.endepin3().set_bit();
        w.endepin4().set_bit();
        w.endepin5().set_bit();
        w.endepin6().set_bit();
        w.endepin7().set_bit();

        w.endepout0().set_bit();
        w.endepout1().set_bit();
        w.endepout2().set_bit();
        w.endepout3().set_bit();
        w.endepout4().set_bit();
        w.endepout5().set_bit();
        w.endepout6().set_bit();
        w.endepout7().set_bit();

        w.ep0datadone().set_bit();
        w.ep0setup().set_bit();
        w.sof().set_bit();
        w.usbevent().set_bit();
        w.usbreset().set_bit();
        w
    });
}



// struct Accumulator<const N: usize> {
//     buf: [u8; N],
//     idx: usize,
// }

// enum AccError<'a> {
//     NoRoomNoRem,
//     NoRoomWithRem(&'a [u8]),
// }

// impl<const N: usize> Accumulator<N> {
//     fn new() -> Self {
//         Self {
//             buf: [0u8; N],
//             idx: 0,
//         }
//     }
//     fn feed<'a>(&mut self, buf: &'a [u8]) -> Result<Option<AccSuccess<'a, N>>, AccError<'a>> {
//         match buf.iter().position(|b| *b == 0) {
//             Some(n) if (self.idx + n) <= N => {
//                 let (now, later) = buf.split_at(n + 1);
//                 self.buf[self.idx..][..now.len()].copy_from_slice(now);
//                 let mut msg = AccMsg {
//                     buf: [0u8; N],
//                     len: self.idx + now.len(),
//                 };
//                 msg.buf[..msg.len].copy_from_slice(&self.buf[..msg.len]);
//                 self.idx = 0;
//                 Ok(Some(AccSuccess {
//                     remainder: later,
//                     msg,
//                 }))
//             },
//             Some(n) if n < buf.len() => {
//                 self.idx = 0;
//                 Err(AccError::NoRoomWithRem(&buf[(n + 1)..]))
//             },
//             Some(_) => {
//                 self.idx = 0;
//                 Err(AccError::NoRoomNoRem)
//             }
//             None if (self.idx + buf.len()) <= N => {
//                 self.buf[self.idx..][..buf.len()].copy_from_slice(buf);
//                 self.idx += buf.len();
//                 Ok(None)
//             },
//             None => {
//                 // No room, and no zero. Truncate the current buf.
//                 self.idx = 0;
//                 Err(AccError::NoRoomNoRem)
//             },
//         }
//     }
// }

// struct AccSuccess<'a, const N: usize> {
//     remainder: &'a [u8],
//     msg: AccMsg<N>,
// }

// struct AccMsg<const N: usize> {
//     buf: [u8; N],
//     len: usize,
// }

// impl<const N: usize> AccMsg<N> {
//     fn as_mut_slice(&mut self) -> &mut [u8] {
//         &mut self.buf[..self.len]
//     }
// }