use std::io::{self, Read, Write};
use std::sync::{Arc, Mutex};

// STDIN is file descriptor (fd) 0 on Linux and other UN*X-likes
pub const STDIN: i32 = 0;

// Key input types from the user
enum Key {
    Up,
    Down,
    Right,
    Left,
    Else(u8),
    Ignored,
}

/// Retrieve a single byte of input
///
/// Requires some setup beforehand (see beginning of repl())
fn getchar() -> Key {
    let mut b = [0; 1];
    io::stdout().lock().flush().unwrap();
    io::stdin().read_exact(&mut b).unwrap();

    // Might me an ASNI escape sequence
    if b[0] == 27 {
        io::stdin().read_exact(&mut b).unwrap();

        if b[0] == 91 {
            io::stdin().read_exact(&mut b).unwrap();

            match b[0] {
                // Arrow keys
                65 => return Key::Up,
                66 => return Key::Down,
                67 => return Key::Right,
                68 => return Key::Left,

                // Everything else
                _ => return Key::Ignored,
            }
        }

        return Key::Ignored;
    }

    Key::Else(b[0])
}

/// Handle user input at the repl prompt
///
/// This is required instead of io::stdin().read_line(), because certain
/// keys like `<tab>` and `<up>` have special functions (cycle through
/// autocomplete options, and history, respectively). It leverages
/// [getchar] to read each character as the user inputs it. This also
/// means special cases for handling backspace, newlines, etc. Assumes
/// that (ICANON and ECHO) are off. See the beginning of [crate::repl]
/// for more details.
pub fn getline(buffer: &mut Arc<Mutex<Vec<u8>>>, pos: &mut Arc<Mutex<usize>>) -> usize {
    // Loop over characters until there is a newline
    loop {
        let c = getchar();
        match c {
            Key::Up => {
                continue;
            }
            Key::Down => {
                continue;
            }
            Key::Right => {
                if *pos.lock().unwrap() >= buffer.lock().unwrap().len() {
                    continue;
                }
                print!("\x1b[1C");
                *pos.lock().unwrap() += 1;
            }
            Key::Left => {
                if *pos.lock().unwrap() == 0 {
                    continue;
                }
                print!("\u{8}");
                *pos.lock().unwrap() -= 1;
            }
            Key::Ignored => {
                continue;
            }
            Key::Else(c) => match c {
                // enter/return
                b'\n' => break,

                // tab
                b'\t' => {
                    *pos.lock().unwrap() += 1;
                    print!(" ");
                    buffer.lock().unwrap().push(b' ');
                }

                // ctrl-d
                4 => return 0,

                // backspace
                127 => {
                    if *pos.lock().unwrap() == 0 {
                        continue;
                    }
                    *pos.lock().unwrap() -= 1;

                    if *pos.lock().unwrap() == buffer.lock().unwrap().len() {
                        buffer.lock().unwrap().pop();
                        print!("\u{8} \u{8}");
                    } else {
                        buffer.lock().unwrap().remove(*pos.lock().unwrap());
                        print!(
                            "\u{8}{} ",
                            String::from_utf8_lossy(
                                &buffer.lock().unwrap()[*pos.lock().unwrap()..]
                            )
                        );
                        for _ in *pos.lock().unwrap()..buffer.lock().unwrap().len() + 1 {
                            print!("\u{8}");
                        }
                    }
                }

                // everything else
                _ => {
                    // Print out the character as the user is typing
                    print!("{}", c as char);

                    // Insert the character onto the buffer at whatever *pos.lock().unwrap()ition the cursor is at
                    buffer.lock().unwrap().insert(*pos.lock().unwrap(), c);

                    // Increment our *pos.lock().unwrap()ition
                    *pos.lock().unwrap() += 1;

                    // Reprint the end of the buffer if inserting at the front or middle
                    if *pos.lock().unwrap() != buffer.lock().unwrap().len() {
                        print!(
                            "{}",
                            String::from_utf8_lossy(
                                &buffer.lock().unwrap()[*pos.lock().unwrap()..]
                            )
                        );
                        for _ in *pos.lock().unwrap()..buffer.lock().unwrap().len() {
                            print!("\u{8}");
                        }
                    }
                }
            },
        }
    }

    *pos.lock().unwrap() = 0;
    println!();
    buffer.lock().unwrap().push(b'\n');
    buffer.lock().unwrap().len()
}