use spin::RwLock;
use std::collections::HashMap;

use rand::prelude::*;
use rand::rngs::OsRng;

use x25519_dalek::PublicKey;
use x25519_dalek::StaticSecret;

use crate::noise;
use crate::messages;
use crate::types::*;
use crate::peer::Peer;

pub struct Device {
    pub sk : StaticSecret,               // static secret key
    pub pk : PublicKey,                  // static public key
    peers  : Vec<Peer>,                  // peer index  -> state
    pk_map : HashMap<[u8; 32], usize>,   // public key  -> peer index
    id_map : RwLock<HashMap<u32, usize>> // receive ids -> peer index
}

/* A mutable reference to the device needs to be held during configuration.
 * Wrapping the device in a RwLock enables peer config after "configuration time"
 */
impl Device {
    /// Initialize a new handshake state machine
    ///
    /// # Arguments
    ///
    /// * `sk` - x25519 scalar representing the local private key
    pub fn new(sk : StaticSecret) -> Device {
        Device {
            pk     : PublicKey::from(&sk),
            sk     : sk,
            peers  : vec![],
            pk_map : HashMap::new(),
            id_map : RwLock::new(HashMap::new())
        }
    }

    /// Add a new public key to the state machine
    /// To remove public keys, you must create a new machine instance
    ///
    /// # Arguments
    ///
    /// * `pk` - The public key to add
    pub fn add(&mut self, pk : PublicKey) -> Result<(), ConfigError> {
        // check that the pk is not added twice

        if let Some(_) = self.pk_map.get(pk.as_bytes()) {
            return Err(ConfigError::new("Duplicate public key"));
        };

        // check that the pk is not that of the device

        if *self.pk.as_bytes() == *pk.as_bytes() {
            return Err(ConfigError::new("Public key corresponds to secret key of interface"));
        }

        // map : pk -> new index

        let idx = self.peers.len();
        self.pk_map.insert(*pk.as_bytes(), idx);

        // map : new index -> peer

        self.peers.push(Peer::new(
            idx, pk, self.sk.diffie_hellman(&pk)
        ));

        Ok(())
    }

    /// Add a psk to the peer
    ///
    /// # Arguments
    ///
    /// * `pk` - The public key of the peer
    /// * `psk` - The psk to set / unset
    ///
    /// # Returns
    ///
    /// The call might fail if the public key is not found
    pub fn psk(&mut self, pk : PublicKey, psk : Option<Psk>) -> Result<(), ConfigError> {
        match self.pk_map.get(pk.as_bytes()) {
            Some(&idx) => {
                let peer = &mut self.peers[idx];
                peer.psk = match psk {
                    Some(v) => v,
                    None => [0u8; 32],
                };
                Ok(())
            },
            _ => Err(ConfigError::new("No such public key"))
        }
    }

    /// Release an id back to the pool
    ///
    /// # Arguments
    ///
    /// * `id` - The (sender) id to release
    pub fn release(&self, id : u32) {
        let mut m =self.id_map.write();
        debug_assert!(m.contains_key(&id), "Releasing id not allocated");
        m.remove(&id);
    }

    /// Begin a new handshake
    ///
    /// # Arguments
    ///
    /// * `pk` - Public key of peer to initiate handshake for
    pub fn begin(&self, pk : &PublicKey) -> Result<Vec<u8>, HandshakeError> {
        match self.pk_map.get(pk.as_bytes()) {
            None => Err(HandshakeError::UnknownPublicKey),
            Some(&idx) => {
                let peer = &self.peers[idx];
                let sender = self.allocate(idx);
                noise::create_initiation(self, peer, sender)
            }
        }
    }

    /// Process a handshake message.
    ///
    /// # Arguments
    ///
    /// * `msg` - Byte slice containing the message (untrusted input)
    pub fn process(&self, msg : &[u8]) -> Result<Output, HandshakeError> {
        match msg.get(0) {
            Some(&messages::TYPE_INITIATION) => {
                // consume the initiation
                let (peer, st) = noise::consume_initiation(self, msg)?;

                // allocate new index for response
                let sender = self.allocate(peer.idx);

                // create response (release id on error)
                noise::create_response(peer, sender, st).map_err(|e| {
                    self.release(sender);
                    e
                })
            },
            Some(&messages::TYPE_RESPONSE) =>
                noise::consume_response(self, msg),
            _ => Err(HandshakeError::InvalidMessageFormat)
        }
    }

    // Internal function
    //
    // Return the peer associated with the public key
    pub(crate) fn lookup_pk(&self, pk : &PublicKey) -> Result<&Peer, HandshakeError> {
        match self.pk_map.get(pk.as_bytes()) {
            Some(&idx) => Ok(&self.peers[idx]),
            _ => Err(HandshakeError::UnknownPublicKey)
        }
    }

    // Internal function
    //
    // Return the peer currently associated with the receiver identifier
    pub(crate) fn lookup_id(&self, id : u32) -> Result<&Peer, HandshakeError> {
        match self.id_map.read().get(&id) {
            Some(&idx) => Ok(&self.peers[idx]),
            _ => Err(HandshakeError::UnknownReceiverId)
        }
    }

    // Internal function
    //
    // Allocated a new receiver identifier for the peer index
    fn allocate(&self, idx : usize) -> u32 {
        let mut rng = OsRng::new().unwrap();

        loop {
            let id = rng.gen();

            // check membership with read lock
            if self.id_map.read().contains_key(&id) {
                continue
            }

            // take write lock and add index
            let mut m = self.id_map.write();
            if !m.contains_key(&id) {
                m.insert(id, idx);
                return id;
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use hex;
    use super::*;
    use messages::*;
    use std::convert::TryFrom;

    #[test]
    fn handshake() {
        // generate new keypairs

        let mut rng = OsRng::new().unwrap();

        let sk1 = StaticSecret::new(&mut rng);
        let pk1 = PublicKey::from(&sk1);

        let sk2 = StaticSecret::new(&mut rng);
        let pk2 = PublicKey::from(&sk2);

        // intialize devices on both ends

        let mut dev1 = Device::new(sk1);
        let mut dev2 = Device::new(sk2);

        dev1.add(pk2).unwrap();
        dev2.add(pk1).unwrap();

        // do a few handshakes

        for i in 0..10 {

            println!("handshake : {}", i);

            // create initiation

            let msg1 = dev1.begin(&pk2).unwrap();

            println!("msg1 = {}", hex::encode(&msg1[..]));
            println!("msg1 = {:?}", Initiation::try_from(&msg1[..]).unwrap());

            // process initiation and create response

            let (msg2, ks_r) = dev2.process(&msg1).unwrap();

            let ks_r = ks_r.unwrap();
            let msg2 = msg2.unwrap();

            println!("msg2 = {}", hex::encode(&msg2[..]));
            println!("msg2 = {:?}", Response::try_from(&msg2[..]).unwrap());

            assert!(!ks_r.confirmed, "Responders key-pair is confirmed");

            // process response and obtain confirmed key-pair

            let (msg3, ks_i) = dev1.process(&msg2).unwrap();
            let ks_i = ks_i.unwrap();

            assert!(msg3.is_none(), "Returned message after response");
            assert!(ks_i.confirmed, "Initiators key-pair is not confirmed");

            assert_eq!(ks_i.send, ks_r.recv, "KeyI.send != KeyR.recv");
            assert_eq!(ks_i.recv, ks_r.send, "KeyI.recv != KeyR.send");

            dev1.release(ks_i.send.id);
            dev2.release(ks_r.send.id);
        }
    }
}