use nix::sys::signal::{kill, Signal};
use nix::unistd::Pid;
use std::env::current_dir;
use std::fs;
use std::io::{self, Read, Write};
use std::path::PathBuf;
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
#[derive(PartialEq)]
enum Key {
    Up,
    Down,
    Right,
    Left,
    Tab,
    ShiftTab,
    Ctrlc,
    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
    match b[0] {
        // Escape sequences
        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,

                    // Shift tab
                    90 => return Key::ShiftTab,

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

            return Key::Ignored;
        }

        // Tab
        9 => return Key::Tab,

        // ctrlc
        3 => return Key::Ctrlc,

        // Everything else
        _ => Key::Else(b[0]),
    }
}

/// Handles autocomplete functionality for file paths
///
/// Currently, dwvsh does not implement zsh's full autocomplete
/// ecosystem (though there are plans to). For now, this simply adds a
/// builtin way to get autocomplete suggestions for file paths via the
/// <tab> key.
fn autocomplete(
    buffer: &mut Arc<Mutex<Vec<u8>>>,
    index: usize,
    pwd: &PathBuf,
) -> Result<(String, usize), Box<dyn std::error::Error>> {
    let buffer = buffer.lock().unwrap();
    let word = match buffer.last() {
        Some(c) if *c == b' ' => "".to_string(),
        None => "".to_string(),
        _ => {
            let mut word: Vec<u8> = vec![];
            for c in buffer.iter().rev() {
                if *c == b' ' || *c == b'/' {
                    break;
                }
                word.push(*c);
            }
            word.reverse();
            String::from_utf8_lossy(&mut word).to_string()
        }
    };

    // Get a file listing
    let paths = fs::read_dir(&pwd)?;
    let paths = if word.is_empty() {
        paths
            .into_iter()
            .filter(|path| {
                !path
                    .as_ref()
                    .unwrap()
                    .file_name()
                    .to_string_lossy()
                    .starts_with(".")
            })
            .collect::<Vec<_>>()
    } else {
        paths
            .into_iter()
            .filter(|path| {
                path.as_ref()
                    .unwrap()
                    .file_name()
                    .to_string_lossy()
                    .starts_with(&word)
            })
            .collect::<Vec<_>>()
    };

    // Return nothing is paths is empty
    if paths.is_empty() {
        return Ok(("".to_string(), 0));
    }

    // Collect path into DirEntries
    let mut paths = paths
        .iter()
        .map(|path| path.as_ref().unwrap())
        .collect::<Vec<_>>();

    // Sort the paths
    paths.sort_by(|a, b| {
        a.file_name()
            .to_ascii_lowercase()
            .cmp(&b.file_name().to_ascii_lowercase())
    });

    // Output the file listing at index on the prompt
    // let path = paths[index].path();
    let path = paths[index].path();

    let path = if path.is_dir() {
        path.file_name().unwrap().to_str().unwrap().to_string() + "/"
    } else {
        path.file_name().unwrap().to_str().unwrap().to_string()
    };

    let path = if word.is_empty() {
        path
    } else {
        path[word.len()..].to_string()
    };

    print!("{}", path);

    Ok((path, paths.len()))
}

/// 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 {
    // Keep track of the last key
    let mut last: Option<Key> = None;

    // Keep track of index for autocomplete
    let mut pwd = current_dir().unwrap_or(PathBuf::from(env!("HOME")));
    let mut auindex = 0;
    let mut aulen = 0;

    // Keep track of the length of the last buffer from autcomplete()
    let mut length = 0;

    // 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::Tab => {
                if last == Some(Key::ShiftTab) {
                    auindex += 2;
                    if auindex >= length {
                        auindex = 0;
                    }
                }
                while aulen > 0 {
                    buffer.lock().unwrap().pop();
                    print!("\u{8} \u{8}");
                    *pos.lock().unwrap() -= 1;
                    aulen -= 1;
                }
                let (path, len) =
                    autocomplete(buffer, auindex, &pwd).unwrap_or(("".to_string(), 0));
                length = len;
                for c in path.into_bytes().iter() {
                    buffer.lock().unwrap().insert(*pos.lock().unwrap(), *c);
                    *pos.lock().unwrap() += 1;
                    aulen += 1;
                }
                auindex += 1;
                if auindex >= len {
                    auindex = 0;
                }
            }
            Key::ShiftTab => {
                if last == Some(Key::Tab) {
                    if auindex.checked_sub(2) == None {
                        auindex = length - 1;
                    } else {
                        auindex -= 2;
                    }
                }
                while aulen > 0 {
                    buffer.lock().unwrap().pop();
                    print!("\u{8} \u{8}");
                    *pos.lock().unwrap() -= 1;
                    aulen -= 1;
                }
                let (path, len) =
                    autocomplete(buffer, auindex, &pwd).unwrap_or(("".to_string(), 0));
                length = len;
                for c in path.into_bytes().iter() {
                    buffer.lock().unwrap().insert(*pos.lock().unwrap(), *c);
                    *pos.lock().unwrap() += 1;
                    aulen += 1;
                }
                auindex = if auindex == 0 { len - 1 } else { auindex - 1 };
            }
            Key::Ctrlc => {
                kill(Pid::from_raw(0 as i32), Signal::SIGINT).unwrap();
            }
            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}");
                        }
                    }

                    // Reset autocomplete variables
                    auindex = 0;
                    aulen = 0;
                }

                // everything else
                _ => {
                    let mut buffer = buffer.lock().unwrap();

                    // Print out the character as the user is typing
                    match buffer.last() {
                        Some(last) if *last == b'/' && c == b'/' => {
                            buffer.pop();
                            *pos.lock().unwrap() -= 1;
                        }
                        Some(_) => print!("{}", c as char),
                        None => print!("{}", c as char),
                    }

                    // Insert the character onto the buffer at whatever *pos.lock().unwrap()ition
                    // the cursor is at
                    buffer.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.len() {
                        print!(
                            "{}",
                            String::from_utf8_lossy(&buffer[*pos.lock().unwrap()..])
                        );
                        for _ in *pos.lock().unwrap()..buffer.len() {
                            print!("\u{8}");
                        }
                    }

                    // Update directory for autocomplete
                    let word = match buffer.last() {
                        Some(c) if *c == b' ' => "".to_string(),
                        None => "".to_string(),
                        _ => {
                            let mut word: Vec<u8> = vec![];
                            for c in buffer.iter().rev() {
                                if *c == b' ' {
                                    break;
                                }
                                word.push(*c);
                            }
                            word.reverse();
                            if word.starts_with(b"..")
                                && word.iter().filter(|c| *c == &b'/').count() == 1
                            {
                                word = vec![b'.', b'.']
                            }
                            loop {
                                match word.last() {
                                    Some(c) if *c == b'/' || *c == b'.' || *c == b'~' => {
                                        break;
                                    }
                                    Some(_) => {
                                        word.pop();
                                    }
                                    None => {
                                        break;
                                    }
                                }
                            }
                            String::from_utf8_lossy(&mut word).to_string()
                        }
                    };

                    // Check for the ~ character (used to represent $HOME)
                    let word = if word.is_empty() {
                        current_dir()
                            .unwrap_or(PathBuf::from(env!("HOME")))
                            .to_string_lossy()
                            .to_string()
                    } else if word.starts_with("~") {
                        let home = env!("HOME");
                        format!("{}{}", home, &word[1..]).to_string()
                    } else {
                        word
                    };

                    // Reset autocomplete variables
                    pwd = PathBuf::from(word);
                    auindex = 0;
                    aulen = 0;
                }
            },
        }

        // Update the last key
        last = Some(c);
    }

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