// Copyright lowRISC contributors.
// Licensed under the Apache License, Version 2.0, see LICENSE for details.
// SPDX-License-Identifier: Apache-2.0

use anyhow::Result;
use regex::{Captures, Regex};
use std::fs::File;
use std::io::{Read, Write};
use std::os::unix::io::AsRawFd;
use std::time::{Duration, Instant, SystemTime};

use crate::io::uart::Uart;
use crate::util::file;

#[derive(Default)]
pub struct UartConsole {
    pub logfile: Option<File>,
    pub timeout: Option<Duration>,
    pub deadline: Option<Instant>,
    pub exit_success: Option<Regex>,
    pub exit_failure: Option<Regex>,
    pub timestamp: bool,
    pub buffer: String,
    pub newline: bool,
}

#[derive(Clone, Copy, Debug)]
pub enum ExitStatus {
    None,
    CtrlC,
    Timeout,
    ExitSuccess,
    ExitFailure,
}

// Creates a vtable for impementors of Read and AsRawFd traits.
pub trait ReadAsRawFd: Read + AsRawFd {}
impl<T: Read + AsRawFd> ReadAsRawFd for T {}

impl UartConsole {
    const CTRL_C: u8 = 3;
    const BUFFER_LEN: usize = 1024;

    // Runs an interactive console until CTRL_C is received.
    pub fn interact(
        &mut self,
        uart: &dyn Uart,
        mut stdin: Option<&mut dyn ReadAsRawFd>,
        mut stdout: Option<&mut dyn Write>,
    ) -> Result<ExitStatus> {
        if let Some(timeout) = &self.timeout {
            self.deadline = Some(Instant::now() + *timeout);
        }
        loop {
            match self.interact_once(uart, &mut stdin, &mut stdout)? {
                ExitStatus::None => {}
                status => return Ok(status),
            }
        }
    }

    // Maintain a buffer for the exit regexes to match against.
    fn append_buffer(&mut self, data: &[u8]) {
        self.buffer.push_str(&String::from_utf8_lossy(data));
        while self.buffer.len() > UartConsole::BUFFER_LEN {
            self.buffer.remove(0);
        }
    }

    // Read from the uart and process the data read.
    fn uart_read(
        &mut self,
        uart: &dyn Uart,
        timeout: Duration,
        stdout: &mut Option<&mut dyn Write>,
    ) -> Result<()> {
        let mut buf = [0u8; 256];
        let len = uart.read_timeout(&mut buf, timeout)?;
        if len == 0 {
            return Ok(());
        }
        for i in 0..len {
            if self.timestamp && self.newline {
                let t = humantime::format_rfc3339_millis(SystemTime::now());
                stdout
                    .as_mut()
                    .map_or(Ok(()), |out| out.write_fmt(format_args!("[{}]", t)))?;
                self.newline = false;
            }
            stdout
                .as_mut()
                .map_or(Ok(()), |out| out.write_all(&buf[i..i + 1]))?;
            self.newline = buf[i] == b'\n';
        }
        stdout.as_mut().map_or(Ok(()), |out| out.flush())?;

        // If we're logging, save it to the logfile.
        self.logfile
            .as_mut()
            .map_or(Ok(()), |f| f.write_all(&buf[..len]))?;
        self.append_buffer(&buf[..len]);
        Ok(())
    }

    fn process_input(
        &self,
        uart: &dyn Uart,
        stdin: &mut Option<&mut (dyn ReadAsRawFd)>,
    ) -> Result<ExitStatus> {
        if let Some(ref mut input) = stdin.as_mut() {
            if file::wait_fd_read_timeout(input.as_raw_fd(), Duration::from_millis(0)).is_ok() {
                let mut buf = [0u8; 256];
                let len = input.read(&mut buf)?;
                if len == 1 && buf[0] == UartConsole::CTRL_C {
                    return Ok(ExitStatus::CtrlC);
                }
                uart.write(&buf[..len])?;
            }
        }
        Ok(ExitStatus::None)
    }

    pub fn interact_once(
        &mut self,
        uart: &dyn Uart,
        stdin: &mut Option<&mut (dyn ReadAsRawFd)>,
        stdout: &mut Option<&mut dyn Write>,
    ) -> Result<ExitStatus> {
        if let Some(deadline) = &self.deadline {
            if Instant::now() > *deadline {
                return Ok(ExitStatus::Timeout);
            }
        }
        // This _should_ really use unix `poll` in the conventional way
        // to learn when the console or uart file descriptors become ready,
        // but some UART backends will bury their implementation in libusb
        // and make discovering the file descriptor difficult or impossible.
        //
        // As a pragmatic implementation detail, we wait for the UART
        // for a short period of time and then service the console.
        //
        // TODO: as we write more backends, re-evaluate whether there is a
        // better way to approach waiting on the UART and keyboard.

        // Check for input on the uart.
        self.uart_read(uart, Duration::from_millis(10), stdout)?;
        if self
            .exit_success
            .as_ref()
            .map(|rx| rx.is_match(&self.buffer))
            == Some(true)
        {
            return Ok(ExitStatus::ExitSuccess);
        }
        if self
            .exit_failure
            .as_ref()
            .map(|rx| rx.is_match(&self.buffer))
            == Some(true)
        {
            return Ok(ExitStatus::ExitFailure);
        }
        self.process_input(uart, stdin)
    }

    pub fn captures(&self, status: ExitStatus) -> Option<Captures> {
        match status {
            ExitStatus::ExitSuccess => self
                .exit_success
                .as_ref()
                .map(|rx| rx.captures(&self.buffer))
                .flatten(),
            ExitStatus::ExitFailure => self
                .exit_failure
                .as_ref()
                .map(|rx| rx.captures(&self.buffer))
                .flatten(),
            _ => None,
        }
    }
}