use std::error::Error;
use std::io;
use std::thread;
use std::time::{Duration, Instant};
use embedded_hal::serial::{Read, Write};
use esp_idf_hal::serial::{self, Rx, Tx};

#[derive(Debug)]
pub enum SerialError {
    ReadError,
    WriteError(String),
    TimeoutError,
}

impl Error for SerialError {}

impl std::fmt::Display for SerialError {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "{:?}", self)
    }
}

pub type Result<T> = std::result::Result<T, SerialError>;

pub struct RxIter<UART: serial::Uart> {
    inner: Rx<UART>,
    timeout: Duration,
}

impl<UART: serial::Uart> RxIter<UART> {
    pub fn reset(&mut self, timeout: Duration) -> &mut Self {
        self.timeout = timeout;
        self
    }

    fn clear(&mut self) -> () {
        println!("clearing serial rx");
        self.reset(Duration::from_millis(500)).for_each(drop);
    }
}

impl<UART: serial::Uart> Iterator for RxIter<UART> {
    type Item = u8;

    /// `nb` returns Ok(byte), or one of Err(WouldBlock) and Err(Other) which isn't of anyone's
    /// interest, so the retry mechanism is triggered on _any_ error every 200ms until a byte is
    /// received, or the timeout is reached.
    fn next(&mut self) -> Option<Self::Item> {
        let start = Instant::now();
        loop {
            match self.inner.read() {
                Ok(b) => {
                    self.timeout = self.timeout.saturating_sub(start.elapsed());
                    break Some(b)
                },
                Err(_) => {
                    if start.elapsed() > self.timeout {
                        self.timeout = Duration::ZERO;
                        break None
                    }
                    thread::sleep(Duration::from_millis(200));
                }
            }
        }
    }
}

pub struct SerialIO<UART: serial::Uart> {
    pub rx: RxIter<UART>,
    pub tx: Tx<UART>,
}

impl<UART: serial::Uart> SerialIO<UART> {
    pub fn new(tx: Tx<UART>, rx: Rx<UART>) -> Self {
        Self {
            rx: RxIter { inner: rx, timeout: Duration::from_millis(0) },
            tx,
        }
    }

    pub fn send_bytes(&mut self, payload: &[u8], eos: Option<u8>) -> Result<usize> {
        //self.rx.clear();
        for b in payload.iter() {
            nb::block!(self.tx.write(*b))
                .map_err(|err| SerialError::WriteError(format!("Error writing '{}' to serial, Original error {}", b, err)))?;
        }
        eos.map(|b| nb::block!(self.tx.write(b)));
        Ok(payload.len() + if eos.is_none() { 0 } else { 1 })
    }

    /// Reads a whole line (that ends with \\n) within the given `timeout` passed on input.
    pub fn read_line(&mut self, timeout: Duration) -> Result<String> {
        let mut line: String = self.rx.reset(timeout)
            .map(|b| char::from(b))
            .take_while(|c| *c != '\n')
            .collect();

        // \r must come right before \n on read; take_while excludes the matched element.
        if line.ends_with('\r') {
            line.push('\n');
            Ok(line)
        }
        else if self.rx.timeout.as_millis() == 0 {
            Err(SerialError::TimeoutError)
        }
        else {
            Err(SerialError::ReadError)
        }
    }
}

impl<UART: serial::Uart> io::Read for SerialIO<UART> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let buf_size = buf.len();
        let count = self.rx.reset(Duration::from_millis(1000))
            .enumerate()
            .map(|(i, b)| {
                buf[i] = b;
                i
            })
            .take_while(|i| i < &buf_size)
            .count();
        Ok(count)
    }
}

impl<UART: serial::Uart> io::Write for SerialIO<UART> {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.send_bytes(buf, None)
            .map_err(|_| io::Error::from(io::ErrorKind::Other))
    }

    fn flush(&mut self) -> io::Result<()> {
        self.tx.flush()
            .map_err(|err| io::Error::from(io::ErrorKind::Other))
    }
}