#![forbid(unsafe_code)]
use smol::prelude::*;

use smol::{ unblock, Unblock, Timer };
use smol::lock::{ OnceCell, RwLock };
use std::fmt::Display;
use std::os::fd::AsRawFd;
use std::process::ExitCode;
use std::time::Duration;
use termios::Termios;

type Error = std::io::Error;
type Result<T> = std::result::Result<T, Error>;

struct Ivy {
  stdin: Unblock<std::io::Stdin>,
  stdout: Unblock<std::io::Stdout>,
  initial_termios: OnceCell<Termios>,
  width: RwLock<u64>,
  height: RwLock<u64>,
}

enum EscapeType {
  CSI,
  CSIPrivate,
}

impl EscapeType {
  fn intro(&self) -> &'static str {
    match self {
      EscapeType::CSI => "\x1b[",
      EscapeType::CSIPrivate => "\x1b[?",
    }
  }
}


fn main() -> ExitCode {
  smol::block_on(async {
    if let Err(e) = Ivy::new().await.run().await {
      println!("{:?}", e);
      ExitCode::FAILURE
    } else {
      ExitCode::SUCCESS
    }
  })
}


impl Ivy {
  async fn new() -> Self {
    Ivy {
      stdin: Unblock::new(std::io::stdin()),
      stdout: Unblock::new(std::io::stdout()),
      initial_termios: OnceCell::new(),
      width: RwLock::new(80),
      height: RwLock::new(24),
    }
  }

  async fn run(mut self) -> Result<()> {
    let mut error = None;

    error = error.or(self.init_termios().await.err());
    error = error.or(self.init_full_screen().await.err());

    error = error.or({
      for _ in 1 .. *self.height.read().await {
        self.stdout.write_all("\n~".as_bytes()).await?;
      }

      self.do_cursor_position(0, 0).await?;

      self.stdout.flush().await?;

      Ok(())
    }.err());

    Timer::after(Duration::from_millis(1000)).await;

    error = error.or(self.zap_full_screen().await.err());
    error = error.or(self.zap_termios().await.err());

    if let Some(error) = error {
      Err(error)
    } else {
      Ok(())
    }
  }

  async fn init_termios(&mut self) -> Result<()> {
    let _ = self.initial_termios.set(unblock(|| {
      let fd = std::io::stdin().as_raw_fd();
      Termios::from_fd(fd)
    }).await?).await;

    let mut termios = self.initial_termios.get().unwrap().clone();

    termios.c_lflag &= !(termios::ECHO
                         | termios::ECHONL
                         | termios::os::linux::ECHOCTL
                         | termios::ICANON);
    termios.c_lflag |= termios::ISIG;

    termios.c_cc[termios::VMIN] = 1;
    termios.c_cc[termios::VTIME] = 0;

    unblock(move || {
      let fd = std::io::stdin().as_raw_fd();
      termios::tcsetattr(fd, termios::TCSANOW, &mut termios)
    }).await?;

    Ok(())
  }

  async fn zap_termios(&mut self) -> Result<()> {
    let mut termios = self.initial_termios.get().unwrap().clone();

    unblock(move || {
      let fd = std::io::stdin().as_raw_fd();
      termios::tcsetattr(fd, termios::TCSANOW, &mut termios)
    }).await?;

    Ok(())
  }

  async fn init_full_screen(&mut self) -> Result<()> {
    self.do_start_alternate_screen().await?;
    self.do_cursor_position(0, 0).await?;

    let (width, height) = self.do_report_size().await?;
    *self.width.write().await = width;
    *self.height.write().await = height;

    Ok(())
  }

  async fn zap_full_screen(&mut self) -> Result<()> {
    self.do_end_alternate_screen().await?;
    self.stdout.flush().await?;

    Ok(())
  }

  async fn do_escape(&mut self, escape_type: EscapeType, code: &str,
                     parameters: &[impl Display])
      -> Result<()>
  {
    self.stdout.write_all(escape_type.intro().as_bytes()).await?;

    for (index, parameter) in parameters.iter().enumerate() {
      self.stdout.write_all(if index < parameters.len() - 1 {
        format!("{};", parameter)
      } else {
        format!("{}{}", parameter, code)
      }.as_bytes()).await?;
    }

    Ok(())
  }

  async fn read_report(&mut self, escape_type: EscapeType)
      -> Result<(char, Vec<u64>)>
  {
    let mut expected = escape_type.intro();

    while expected.len() > 0 {
      let mut buf = vec![0; 1];
      self.stdin.read_exact(&mut buf).await?;

      expected = &expected[1..];
    }

    let mut values = Vec::new();

    let mut number: u64 = 0;
    let mut in_number = false;
    let mut after_semicolon = false;

    let mut buf = vec![0; 1];
    self.stdin.read_exact(&mut buf).await?;

    loop {
      if let Ok(string) = std::str::from_utf8(&buf)
         && let Some(c) = string.chars().next()
      {
        if c.is_ascii_digit() {
          if in_number {
            number = number * 10
                     + <u32 as Into<u64>>::into(c.to_digit(10).unwrap());
          } else {
            number = c.to_digit(10).unwrap().into();

            in_number = true;
            after_semicolon = false;
          }
        } else if c == ';' {
          if in_number {
            values.push(number);

            in_number = false;
            after_semicolon = true;
          } else {
            break;
          }
        } else if c.is_ascii_alphabetic() {
          if in_number {
            values.push(number);
          } else if after_semicolon {
            break;
          }

          return Ok((c, values))
        } else {
          break;
        }
      } else {
        break;
      }

      self.stdin.read_exact(&mut buf).await?;
    }

    Err(std::io::Error::other("Invalid report from terminal."))
  }

  // xterm
  async fn do_start_alternate_screen(&mut self) -> Result<()> {
    self.do_escape(EscapeType::CSIPrivate, "h", &[1049]).await
  }

  // xterm
  async fn do_end_alternate_screen(&mut self) -> Result<()> {
    self.do_escape(EscapeType::CSIPrivate, "l", &[1049]).await
  }

  // vt220? vt100?
  async fn do_cursor_position(&mut self, x: u64, y: u64) -> Result<()> {
    self.do_escape(EscapeType::CSI, "H", &[y + 1, x + 1]).await
  }

  // dtterm? xterm
  async fn do_report_size(&mut self) -> Result<(u64, u64)> {
    self.do_escape(EscapeType::CSI, "t", &[18]).await?;
    self.stdout.flush().await?;
    let (code, values) = self.read_report(EscapeType::CSI).await?;
    if code == 't' && values.len() == 3 && values[0] == 8 {
      Ok((values[2], values[1]))
    } else {
      Err(std::io::Error::other("Couldn't read terminal size."))
    }
  }
}