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    use super::File;
    use crate::mm::UserBuffer;
    use crate::sync::UPIntrFreeCell;
    use alloc::sync::{Arc, Weak};

    use crate::task::suspend_current_and_run_next;

    pub struct Pipe {
        readable: bool,
        writable: bool,
        buffer: Arc<UPIntrFreeCell<PipeRingBuffer>>,
    }

    impl Pipe {
        pub fn read_end_with_buffer(buffer: Arc<UPIntrFreeCell<PipeRingBuffer>>) -> Self {
            Self {
                readable: true,
                writable: false,
                buffer,
            }
        }
        pub fn write_end_with_buffer(buffer: Arc<UPIntrFreeCell<PipeRingBuffer>>) -> Self {
            Self {
                readable: false,
                writable: true,
                buffer,
            }
        }
    }

    const RING_BUFFER_SIZE: usize = 32;

    #[derive(Copy, Clone, PartialEq)]
    enum RingBufferStatus {
        Full,
        Empty,
        Normal,
    }

    pub struct PipeRingBuffer {
        arr: [u8; RING_BUFFER_SIZE],
        head: usize,
        tail: usize,
        status: RingBufferStatus,
        write_end: Option<Weak<Pipe>>,
    }

    impl PipeRingBuffer {
        pub fn new() -> Self {
            Self {
                arr: [0; RING_BUFFER_SIZE],
                head: 0,
                tail: 0,
                status: RingBufferStatus::Empty,
                write_end: None,
            }
        }
        pub fn set_write_end(&mut self, write_end: &Arc<Pipe>) {
            self.write_end = Some(Arc::downgrade(write_end));
        }
        pub fn write_byte(&mut self, byte: u8) {
            self.status = RingBufferStatus::Normal;
            self.arr[self.tail] = byte;
            self.tail = (self.tail + 1) % RING_BUFFER_SIZE;
            if self.tail == self.head {
                self.status = RingBufferStatus::Full;
            }
        }
        pub fn read_byte(&mut self) -> u8 {
            self.status = RingBufferStatus::Normal;
            let c = self.arr[self.head];
            self.head = (self.head + 1) % RING_BUFFER_SIZE;
            if self.head == self.tail {
                self.status = RingBufferStatus::Empty;
            }
            c
        }
        pub fn available_read(&self) -> usize {
            if self.status == RingBufferStatus::Empty {
                0
            } else if self.tail > self.head {
                self.tail - self.head
            } else {
                self.tail + RING_BUFFER_SIZE - self.head
            }
        }
        pub fn available_write(&self) -> usize {
            if self.status == RingBufferStatus::Full {
                0
            } else {
                RING_BUFFER_SIZE - self.available_read()
            }
        }
        pub fn all_write_ends_closed(&self) -> bool {
            self.write_end.as_ref().unwrap().upgrade().is_none()
        }
    }

    /// Return (read_end, write_end)
    pub fn make_pipe() -> (Arc<Pipe>, Arc<Pipe>) {
        let buffer = Arc::new(unsafe { UPIntrFreeCell::new(PipeRingBuffer::new()) });
        let read_end = Arc::new(Pipe::read_end_with_buffer(buffer.clone()));
        let write_end = Arc::new(Pipe::write_end_with_buffer(buffer.clone()));
        buffer.exclusive_access().set_write_end(&write_end);
        (read_end, write_end)
    }

    impl File for Pipe {
        fn readable(&self) -> bool {
            self.readable
        }
        fn writable(&self) -> bool {
            self.writable
        }
        fn read(&self, buf: UserBuffer) -> usize {
            assert!(self.readable());
            let mut buf_iter = buf.into_iter();
            let mut read_size = 0usize;
            loop {
                let mut ring_buffer = self.buffer.exclusive_access();
                let loop_read = ring_buffer.available_read();
                if loop_read == 0 {
                    if ring_buffer.all_write_ends_closed() {
                        return read_size;
                    }
                    drop(ring_buffer);
                    suspend_current_and_run_next();
                    continue;
                }
                // read at most loop_read bytes
                for _ in 0..loop_read {
                    if let Some(byte_ref) = buf_iter.next() {
                        unsafe {
                            *byte_ref = ring_buffer.read_byte();
                        }
                        read_size += 1;
                    } else {
                        return read_size;
                    }
                }
            }
        }
        fn write(&self, buf: UserBuffer) -> usize {
            assert!(self.writable());
            let mut buf_iter = buf.into_iter();
            let mut write_size = 0usize;
            loop {
                let mut ring_buffer = self.buffer.exclusive_access();
                let loop_write = ring_buffer.available_write();
                if loop_write == 0 {
                    drop(ring_buffer);
                    suspend_current_and_run_next();
                    continue;
                }
                // write at most loop_write bytes
                for _ in 0..loop_write {
                    if let Some(byte_ref) = buf_iter.next() {
                        ring_buffer.write_byte(unsafe { *byte_ref });
                        write_size += 1;
                    } else {
                        return write_size;
                    }
                }
            }
        }
    }