use std::sync::{Arc, Mutex};
use std::net::{TcpListener, TcpStream};
use std::thread;
use clap::Parser;
use std::io::Write;
use std::io::{self, BufRead};
use chrono::{DateTime, Utc};
use std::collections::BTreeMap;
use serde::{Serialize, Deserialize};
use std::fs::File;


/// Represent one single chat user and their network stuff
struct ChatUser {
    /// user id
    id: u64,

    /// Name of the chat user
    name: String,

    /// TCPStream socket object thingy
    socket: TcpStream,
}

impl ChatUser {
    pub fn new(id: u64, name: String, socket: TcpStream) -> Self {
        Self{id, name, socket}
    }
}

struct ChatServer {
    config: ConfigArgs,
    user_map: BTreeMap<u64, ChatUser>,
    user_id_counter: u64,
}

impl ChatServer {
    pub fn new(config: ConfigArgs) -> Self {
        Self{config, user_map: BTreeMap::new(), user_id_counter: 1}
    }

    pub fn get_user_count(&self) -> usize {
        self.user_map.len()
    }

    /// register a client by creating a ChatUser for it and assigning it a user id
    pub fn register(&mut self, name: String, socket: TcpStream) -> u64 {
        let chat_user = ChatUser::new(self.user_id_counter, name, socket);
        let client_id = chat_user.id;
        self.user_map.insert(chat_user.id, chat_user);
        self.user_id_counter += 1;

        client_id
    }

    pub fn deregister(&mut self, client_id: u64) -> Option<ChatUser> {
        self.user_map.remove(&client_id)
    }

    pub fn send_to_all(&mut self, msg: &str) -> Result<(), ChatError> {
        let now: DateTime<Utc> = Utc::now();
        let time_msg = format!("[{}] {}", now.format("%H:%M:%S"), msg);
        let mut broken_clients = vec![];
        for (user_id, user) in self.user_map.iter_mut() {
            if write!(user.socket, "{}\n", time_msg).is_err() {
                broken_clients.push((*user_id, user.name.clone()));
            }
        }

        // remove users from map
        for (user_id, _) in broken_clients.iter() {
            self.deregister(*user_id);
        }

        // send out the news
        for (_, name) in broken_clients.iter() {
            self.send_to_all(&format!("* {} has left the chat (broken pipe)", name))?;
        }

        Ok(())
    }

}

#[derive(Debug)]
enum ChatError {
    IOError(std::io::Error),
    MutexPoisonError(),
    Protocol(String),
}

impl From<std::io::Error> for ChatError {
    fn from(error: std::io::Error) -> Self {
        ChatError::IOError(error)
    }
}

impl <'a, T> From<std::sync::PoisonError<std::sync::MutexGuard<'a, T>>> for ChatError {
    fn from(_error: std::sync::PoisonError<std::sync::MutexGuard<'a, T>>) -> Self {
        ChatError::MutexPoisonError()
    }
}

fn handle_client(mut stream: TcpStream, server: Arc<Mutex<ChatServer>>, client_id: &mut Option<u64>) -> Result<(), ChatError> {
    let mut writer = stream.try_clone()?;
    let reader = io::BufReader::new(&mut stream);
    let mut lines = reader.lines();

    // greet and recv nick
    write!(writer, "Hello and welcome to RustChat!\nNick: ")?;
    let nick = lines.next().ok_or(ChatError::Protocol(String::from("Could not recv nickname")))??;
    // FIXME: check for nick name uniqueness

    // print joined msg and register at server
    server.lock()?.send_to_all(&format!("* {} has joined the chat", nick))?;
    let curr_users = server.lock()?.get_user_count();
    let users_in_room_msg = if curr_users == 1 { String::from("is 1 user") } else { format!("are {} users", curr_users) };
    write!(writer, "Welcome, {}! You can now start to chat! There {} in the room.\n", nick, users_in_room_msg)?;
    // server.lock()?.borrow_mut().push(ChatUser::new(nick.clone(), writer));
    *client_id = Some(server.lock()?.register(nick.clone(), writer));

    // read lines
    for line in lines {
        let msg_raw = line?;
        if msg_raw.is_empty() {
            continue;
        }
        let msg = format!("<{}> {}", nick, msg_raw);
        server.lock()?.send_to_all(&msg)?;
        println!("{}", msg);
    }
    Ok(())
}


fn run_thread(stream: TcpStream, server: Arc<Mutex<ChatServer>>) {
    let mut client_id = None;
    let quit_reason = match handle_client(stream, Arc::clone(&server), &mut client_id) {
        Ok(()) => String::from("Connection closed by user's choice"),
        Err(err) => format!("Client foobar't their thread: {:?}", err),
    };

    if let Some(client_id) = client_id {
        let mut srv = server.lock().unwrap();
        let name = srv.deregister(client_id).map(|client| client.name).unwrap_or("<unknown user>".into());
        let quit_msg = format!("* {} has left the chat ({})", name, quit_reason);
        println!("{}", quit_msg);
        srv.send_to_all(&quit_msg).unwrap();
    } else {
        println!("Client thread terminated before identifying themselves");
    }
}


/// Chatserver in RUST!
#[derive(Parser, Debug)]
#[clap(about, version, author)]
struct Args {
    /// Path to config file
    #[clap(short, long, default_value = "config.yaml")]
    config: String,

    /// IP address to bind to
    #[clap(long)]
    host: Option<String>,

    /// Port to run the server on
    #[clap(short, long)]
    port: Option<u16>,
}


#[derive(Debug, Serialize, Deserialize)]
struct ConfigArgs {
    host: String,
    port: u16,
    greeting_msg: String,
}

fn main() -> std::io::Result<()> {
    // argument parsing
    let args = Args::parse();

    // read config file
    let config_reader = File::open(args.config).expect("Could not open config file");
    let mut config: ConfigArgs = serde_yaml::from_reader(&config_reader).expect("Could not parse config file");

    if let Some(host) = args.host {
        config.host = host;
    }
    if let Some(port) = args.port {
        config.port = port;
    }
    let binding_host = format!("{}:{}", config.host, config.port);
    println!("Binding to {}", binding_host);

    let listener = TcpListener::bind(binding_host)?;
    let server = Arc::new(Mutex::new(ChatServer::new(config)));

    // accept connections and process them serially
    for stream in listener.incoming() {
        if let Ok(stream) = stream {
            let server_clone = Arc::clone(&server);
            thread::spawn(move || { run_thread(stream, server_clone); });
        }
    }
    Ok(())
}