pub mod general {
    use crate::config::ClientConfiguration;
    use async_channel::{Receiver, Sender};
    use futures::{stream::{SplitSink, SplitStream}, SinkExt, StreamExt};
    use tokio_util::{codec::Framed, sync::CancellationToken};
    use tokio::{net::UdpSocket, sync::{Mutex, mpsc}, io::{AsyncWriteExt, AsyncReadExt}, fs::File};
    use log::{error, info, warn};
    use aes_gcm::{
        aead::{Aead, AeadCore, KeyInit, OsRng},
        Aes256Gcm, Nonce};
    use base64::prelude::*;
    use std::{io::{Read, Write}, sync::Arc};
    use std::net::Ipv4Addr;
    
    use x25519_dalek::{PublicKey, StaticSecret};
    use crate::udp::{UDPVpnPacket, UDPVpnHandshake, UDPSerializable};

    use tun::{ AsyncDevice, DeviceReader, DeviceWriter, TunPacketCodec };

    pub trait ReadWrapper {
        async fn read(&mut self, buf: &mut Vec<u8>) -> Result<usize, ()>;
    }

    pub struct DevReader {
        pub dr: SplitStream<Framed<AsyncDevice, TunPacketCodec>>
    }

    // TODO: implement custom Error
    impl ReadWrapper for DevReader {
        async fn read(&mut self, buf: &mut Vec<u8>) -> Result<usize, ()> {
            if let Some(Ok(tb)) = self.dr.next().await {
                *buf = tb;
                return Ok(buf.len());
            }
            Err(())
        }
    }

    pub struct FdReader {
        pub br: File
    }

    impl ReadWrapper for FdReader {
        async fn read(&mut self, buf: &mut Vec<u8>) -> Result<usize, ()> {
            let r = self.br.read(buf).await;
            if let Ok(a) = r {
                return Ok(a);
            }
            Err(())
        }
    }

    pub trait WriteWrapper {
        async fn write(&mut self, msg: WriterMessage) -> Result<usize, String>;
    }

    pub enum WriterMessage {
        Plain(Vec<u8>),
        Gateway(Ipv4Addr)
    }

    pub struct DevWriter {
        pub dr: SplitSink<Framed<AsyncDevice, TunPacketCodec>, Vec<u8>>
    }

    // TODO: implement custom Error
    impl WriteWrapper for DevWriter {
        async fn write(&mut self, msg: WriterMessage) -> Result<usize, String> {
            match msg {
                WriterMessage::Plain(buf) => {
                    let l = buf.len();
                    return match self.dr.send(buf).await {
                        Ok(()) => Ok(l),
                        Err(e) => Err(e.to_string())
                    };
                },
                // this thing should be abolished later
                WriterMessage::Gateway(_addr) => {
                    Ok(0)
                }
            } 
        }
    }
    
    pub struct FdWriter {
        pub br: File
    }

    impl WriteWrapper for FdWriter {
        async fn write(&mut self, msg: WriterMessage) -> Result<usize, String> {
            match msg {
                WriterMessage::Plain(buf) => {
                    if let Ok(a) = self.br.write(&buf).await {
                        return Ok(a);
                    }
                    Err(String::new())
                },
                WriterMessage::Gateway(_addr) => {Ok(0)}
            }
        }
    }

    pub trait VpnClient {
        async fn start(&self);
    }
    
    pub struct CoreVpnClient<T, R> where T: ReadWrapper, R: WriteWrapper {
        pub client_config: ClientConfiguration,
        pub dev_reader: T,
        pub dev_writer: R,
        pub close_token: CancellationToken
    }

    impl<T: ReadWrapper + std::marker::Sync, R: WriteWrapper + std::marker::Sync> CoreVpnClient<T, R> {
         pub async fn start(&mut self, sock: UdpSocket) {
            info!("Starting client...");
    
            let dr_cancel: CancellationToken = CancellationToken::new();
            let sr_cancel: CancellationToken = CancellationToken::new();
        
            let sock_rec = Arc::new(sock);
            let sock_snd = sock_rec.clone();
        
            let (tx, mut rx) = mpsc::unbounded_channel::<Vec<u8>>();
            let (dx, mut mx) = mpsc::unbounded_channel::<Vec<u8>>();
        
            let cipher_shared: Arc<Mutex<Option<x25519_dalek::SharedSecret>>> = Arc::new(Mutex::new(None));
        
            let priv_key = BASE64_STANDARD.decode(&self.client_config.client.private_key).unwrap();
            
            let cipher_shared_clone = cipher_shared.clone();
        
            let pkey = BASE64_STANDARD.decode(&self.client_config.client.public_key).unwrap();
            let handshake = UDPVpnHandshake{ public_key: pkey, request_ip: self.client_config.client.address.parse::<Ipv4Addr>().unwrap() };
            let mut nz = 0;
            while nz < 25 {
                sock_snd.send(&handshake.serialize()).await.unwrap();
                nz += 1
            }
            //sock_snd.send(&handshake.serialize()).await.unwrap();
        
            let s_cipher = cipher_shared.clone();
    
            let _ = self.dev_writer.write(WriterMessage::Plain(handshake.serialize())).await;
    
            let mut buf = vec![0; 1400]; // mtu
            let mut buf1 = vec![0; 4096]; // should be changed to less bytes

            loop {
                tokio::select! {
                    _ = self.close_token.cancelled() => {
                        info!("Cancellation token has been thrown");
                        sr_cancel.cancel();
                        dr_cancel.cancel();
                        return;
                    }
                    rr = rx.recv() => {
                        if let Some(bytes) = rr {
                            info!("Write to tun. len={:?}", bytes.len());
                            
                            if let Err(e) = self.dev_writer.write(WriterMessage::Plain(bytes)).await {
                                error!("Writing error: {:?}", e);
                            }
                           /* if let Err(e) = self.dev_writer.flush().await {
                                error!("Flushing error: {:?}", e);
                            }*/
                        }
                    }
                    rr2 = mx.recv() => {
                        if let Some(bytes) = rr2 {
                            let s_c = s_cipher.lock().await;
                            
                            if s_c.is_some() {
                                let aes = Aes256Gcm::new(s_c.as_ref().unwrap().as_bytes().into());
                                let nonce = Aes256Gcm::generate_nonce(&mut OsRng);
                                let ciphered_data = aes.encrypt(&nonce, &bytes[..]);
                                
                                if let Ok(ciphered_d) = ciphered_data {
                                    let vpn_packet = UDPVpnPacket{ data: ciphered_d, nonce: nonce.to_vec()};
                                    let serialized_data = vpn_packet.serialize();
                                    info!("Write to socket");
                                    sock_snd.send(&serialized_data).await.unwrap();
                                } else {
                                    error!("Socket encryption failed.");
                                }
                            } else {
                                error!("There is no shared_secret in main loop");
                            }
                        }
                    }
                    rr = self.dev_reader.read(&mut buf) => {
                        if let Ok(n) = rr {
                            info!("Read from tun."); // hex::encode(&buf[..n])
                            dx.send(buf[..n].to_vec()).unwrap();
                        }
                    }
                    rr = sock_rec.recv(&mut buf1) => {
                        if let Ok(l) = rr {
                            info!("Read from socket");
                            let mut s_cipher = cipher_shared_clone.lock().await;
                            match buf1.first() {
                                Some(h) => {
                                    match h {
                                        0 => {
                                            let handshake = UDPVpnHandshake::deserialize(&(buf1[..l].to_vec()));
                                            let mut k = [0u8; 32];
                                            for (&x, p) in handshake.public_key.iter().zip(k.iter_mut()) {
                                                *p = x;
                                            }
                                            let mut k1 = [0u8; 32];
                                            for (&x, p) in priv_key.iter().zip(k1.iter_mut()) {
                                                *p = x;
                                            }
                                            *s_cipher = Some(StaticSecret::from(k1)
                                                .diffie_hellman(&PublicKey::from(k)));
                                        }, // handshake
                                        1 => {
                                            let wrapped_packet = UDPVpnPacket::deserialize(&(buf1[..l].to_vec()));
                                            if s_cipher.is_some() {
                                                let aes = Aes256Gcm::new(s_cipher.as_ref().unwrap().as_bytes().into());
                                                let nonce = Nonce::clone_from_slice(&wrapped_packet.nonce);
                                                match aes.decrypt(&nonce, &wrapped_packet.data[..]) {
                                                    Ok(decrypted) => { let _ = tx.send(decrypted); },
                                                    Err(error) => { error!("Decryption error! {:?}", error); }
                                                }
                                            } else {
                                                warn!("There is no static_secret");
                                            }
                                        }, // payload
                                        2 => { info!("Got keepalive packet"); },
                                        _ => { error!("Unexpected header value."); }
                                    }
                                },
                                None => { error!("There is no header."); }
                            }
                            drop(s_cipher);
                        }
                    }
                };
            }
        }
    }
}

pub mod android {
    #![cfg(target_os = "android")]
    use crate::client::general::{VpnClient, CoreVpnClient, FdReader, FdWriter};
    use crate::config::ClientConfiguration;
    use tokio_util::sync::CancellationToken;
    use std::os::fd::FromRawFd;
    use tokio::{net::UdpSocket, sync::{Mutex, mpsc}, io::{BufReader, BufWriter, AsyncWriteExt, AsyncReadExt}, fs::File};
    use log::{error, info, warn};

    pub struct AndroidClient {
        pub client_config: ClientConfiguration,
        pub fd: i32,
        pub close_token: CancellationToken
    }
    
    impl VpnClient for AndroidClient {
        async fn start(&self) {
            info!("FD: {:?}", &self.fd);
            let mut dev = unsafe { File::from_raw_fd(self.fd) };
            let mut dev1 = unsafe { File::from_raw_fd(self.fd) };
            let mut client = CoreVpnClient{client_config: self.client_config.clone(), dev_reader: FdReader{br: dev}, dev_writer: FdWriter{br: dev1}, close_token: self.close_token.clone()};
            info!("SSS: {:?}", &self.client_config.server.endpoint);
            let sock = UdpSocket::bind("0.0.0.0:0").await.unwrap();
            sock.connect(&self.client_config.server.endpoint).await.unwrap();
            client.start(sock).await;
        }
    }
}

pub mod desktop {
    use crate::client::general::{CoreVpnClient, DevReader, DevWriter, VpnClient};
    use crate::config::ClientConfiguration;
    use futures::{SinkExt, StreamExt};
    use log::info;
    use tokio::net::UdpSocket;
    use tokio::sync::Mutex;

    #[cfg(target_os = "linux")]
    use network_interface::{NetworkInterface, NetworkInterfaceConfig};

    use tun::{ Configuration, create_as_async };


    #[cfg(target_os = "linux")]
    fn configure_routes(endpoint_ip: &str, s_interface: Option<String>) {
        let interfaces = NetworkInterface::show().unwrap();
    
        let net_inter = interfaces.iter()
            .filter(|i| !i.addr.iter().any(|b| b.ip().to_string() == "127.0.0.1" || b.ip().to_string() == "::1") )
            .min_by(|x, y| x.index.cmp(&y.index))
            .unwrap();
    
        let inter_name = if s_interface.is_some() { s_interface.unwrap() } else { net_inter.name.clone() };
    
        info!("Main network interface: {:?}", inter_name);
    
        /*let mut ip_output = std::process::Command::new("sudo")
            .arg("ip")
            .arg("route")
            .arg("del")
            .arg("default")
            .output()
            .expect("Failed to delete default gateway.");
    
        if !ip_output.status.success() {
            error!("Failed to delete default gateway: {:?}", String::from_utf8_lossy(&ip_output.stderr));
        }*/
    
        let mut ip_output = std::process::Command::new("sudo")
            .arg("ip")
            .arg("-4")
            .arg("route")
            .arg("add")
            .arg("0.0.0.0/0")
            .arg("dev")
            .arg("tun0")
            .output()
            .expect("Failed to execute ip route command.");
    
        if !ip_output.status.success() {
            log::error!("Failed to route all traffic: {:?}", String::from_utf8_lossy(&ip_output.stderr));
        }
        // TODO: replace 192.168.0.1 with relative variable
        ip_output = std::process::Command::new("sudo")
            .arg("ip")
            .arg("route")
            .arg("add")
            .arg(endpoint_ip.to_owned()+"/32")
            .arg("via")
            .arg("192.168.0.1")
            .arg("dev")
            .arg(inter_name)
            .output()
            .expect("Failed to make exception for vpns endpoint.");
    
        if !ip_output.status.success() {
            log::error!("Failed to forward packets: {:?}", String::from_utf8_lossy(&ip_output.stderr));
        }
    }

    pub struct DesktopClient {
        pub client_config: ClientConfiguration,
        pub s_interface: Option<String>
    }
    
    impl VpnClient for DesktopClient {
        async fn start(&self) {
            info!("s_interface: {:?}", &self.s_interface);
            info!("client_address: {:?}", &self.client_config.client.address);
            let mut config = Configuration::default();
            config.address(&self.client_config.client.address)
                .netmask("255.255.255.255")
                .destination("10.66.66.1")
                .mtu(1400)
                .tun_name("tun0")
                .up();
        
            info!("SSS: {:?}", &self.client_config.server.endpoint);
            let sock = UdpSocket::bind(("0.0.0.0", 0)).await.unwrap();
            sock.connect(&self.client_config.server.endpoint).await.unwrap();

            let dev = create_as_async(&config).unwrap();
            let (mut dev_writer , mut dev_reader) = dev.into_framed().split();

            let mut client = CoreVpnClient{ client_config: self.client_config.clone(), dev_reader: DevReader{ dr: dev_reader }, dev_writer: DevWriter{dr: dev_writer }, close_token: tokio_util::sync::CancellationToken::new()};
           
            info!("Platform specific code");
           /* #[cfg(target_os = "linux")]
            {
                let s_a: std::net::SocketAddr = self.client_config.server.endpoint.parse().unwrap();
                configure_routes(&s_a.ip().to_string(), self.s_interface.clone());
            }*/
            
            client.start(sock).await;
        }
    }
}