// Copyright 2022-2023 - Nym Technologies SA <contact@nymtech.net>
// SPDX-License-Identifier: Apache-2.0

use crate::error::ClientCoreError;
use crate::init::types::RegistrationResult;
use futures::{SinkExt, StreamExt};
use log::{debug, info, trace, warn};
use nym_crypto::asymmetric::identity;
use nym_gateway_client::GatewayClient;
use nym_topology::{gateway, mix};
use nym_validator_client::client::IdentityKeyRef;
use nym_validator_client::UserAgent;
use rand::{seq::SliceRandom, Rng};
use std::{sync::Arc, time::Duration};
use tungstenite::Message;
use url::Url;

#[cfg(not(target_arch = "wasm32"))]
use tokio::net::TcpStream;
#[cfg(not(target_arch = "wasm32"))]
use tokio::time::sleep;
#[cfg(not(target_arch = "wasm32"))]
use tokio::time::Instant;
#[cfg(not(target_arch = "wasm32"))]
use tokio_tungstenite::connect_async;
#[cfg(not(target_arch = "wasm32"))]
use tokio_tungstenite::{MaybeTlsStream, WebSocketStream};

#[cfg(target_arch = "wasm32")]
use wasm_utils::websocket::JSWebsocket;
#[cfg(target_arch = "wasm32")]
use wasmtimer::std::Instant;
#[cfg(target_arch = "wasm32")]
use wasmtimer::tokio::sleep;

#[cfg(not(target_arch = "wasm32"))]
type WsConn = WebSocketStream<MaybeTlsStream<TcpStream>>;

#[cfg(target_arch = "wasm32")]
type WsConn = JSWebsocket;

const CONCURRENT_GATEWAYS_MEASURED: usize = 20;
const MEASUREMENTS: usize = 3;

#[cfg(not(target_arch = "wasm32"))]
const CONN_TIMEOUT: Duration = Duration::from_millis(1500);
const PING_TIMEOUT: Duration = Duration::from_millis(1000);

// The abstraction that some of these helpers use
pub trait ConnectableGateway {
    fn identity(&self) -> &identity::PublicKey;
    fn clients_address(&self) -> String;
    fn is_wss(&self) -> bool;
}

impl ConnectableGateway for gateway::LegacyNode {
    fn identity(&self) -> &identity::PublicKey {
        self.identity()
    }

    fn clients_address(&self) -> String {
        self.clients_address()
    }

    fn is_wss(&self) -> bool {
        self.clients_wss_port.is_some()
    }
}

struct GatewayWithLatency<'a, G: ConnectableGateway> {
    gateway: &'a G,
    latency: Duration,
}

impl<'a, G: ConnectableGateway> GatewayWithLatency<'a, G> {
    fn new(gateway: &'a G, latency: Duration) -> Self {
        GatewayWithLatency { gateway, latency }
    }
}

pub async fn current_gateways<R: Rng>(
    rng: &mut R,
    nym_apis: &[Url],
    user_agent: Option<UserAgent>,
) -> Result<Vec<gateway::LegacyNode>, ClientCoreError> {
    let nym_api = nym_apis
        .choose(rng)
        .ok_or(ClientCoreError::ListOfNymApisIsEmpty)?;
    let client = if let Some(user_agent) = user_agent {
        nym_validator_client::client::NymApiClient::new_with_user_agent(nym_api.clone(), user_agent)
    } else {
        nym_validator_client::client::NymApiClient::new(nym_api.clone())
    };

    log::debug!("Fetching list of gateways from: {nym_api}");

    let gateways = client.get_all_basic_entry_assigned_nodes(None).await?;
    log::debug!("Found {} gateways", gateways.len());
    log::trace!("Gateways: {:#?}", gateways);

    let valid_gateways = gateways
        .iter()
        .filter_map(|gateway| gateway.try_into().ok())
        .collect::<Vec<gateway::LegacyNode>>();
    log::debug!("After checking validity: {}", valid_gateways.len());
    log::trace!("Valid gateways: {:#?}", valid_gateways);

    log::info!("nym-api reports {} valid gateways", valid_gateways.len());

    Ok(valid_gateways)
}

pub async fn current_mixnodes<R: Rng>(
    rng: &mut R,
    nym_apis: &[Url],
) -> Result<Vec<mix::LegacyNode>, ClientCoreError> {
    let nym_api = nym_apis
        .choose(rng)
        .ok_or(ClientCoreError::ListOfNymApisIsEmpty)?;
    let client = nym_validator_client::client::NymApiClient::new(nym_api.clone());

    log::trace!("Fetching list of mixnodes from: {nym_api}");

    let mixnodes = client
        .get_all_basic_active_mixing_assigned_nodes(None)
        .await?;
    let valid_mixnodes = mixnodes
        .iter()
        .filter_map(|mixnode| mixnode.try_into().ok())
        .collect::<Vec<mix::LegacyNode>>();

    Ok(valid_mixnodes)
}

#[cfg(not(target_arch = "wasm32"))]
async fn connect(endpoint: &str) -> Result<WsConn, ClientCoreError> {
    match tokio::time::timeout(CONN_TIMEOUT, connect_async(endpoint)).await {
        Err(_elapsed) => Err(ClientCoreError::GatewayConnectionTimeout),
        Ok(Err(conn_failure)) => Err(conn_failure.into()),
        Ok(Ok((stream, _))) => Ok(stream),
    }
}

#[cfg(target_arch = "wasm32")]
async fn connect(endpoint: &str) -> Result<WsConn, ClientCoreError> {
    JSWebsocket::new(endpoint).map_err(|_| ClientCoreError::GatewayJsConnectionFailure)
}

async fn measure_latency<G>(gateway: &G) -> Result<GatewayWithLatency<G>, ClientCoreError>
where
    G: ConnectableGateway,
{
    let addr = gateway.clients_address();
    trace!(
        "establishing connection to {} ({addr})...",
        gateway.identity(),
    );
    let mut stream = connect(&addr).await?;

    let mut results = Vec::new();
    for _ in 0..MEASUREMENTS {
        let measurement_future = async {
            let ping_content = vec![1, 2, 3];
            let start = Instant::now();
            stream.send(Message::Ping(ping_content.clone())).await?;

            match stream.next().await {
                Some(Ok(Message::Pong(content))) => {
                    if content == ping_content {
                        let elapsed = Instant::now().duration_since(start);
                        trace!("current ping time: {elapsed:?}");
                        results.push(elapsed);
                    } else {
                        warn!("received a pong message with different content? wtf.")
                    }
                }
                Some(Ok(_)) => warn!("received a message that's not a pong!"),
                Some(Err(err)) => return Err(err.into()),
                None => return Err(ClientCoreError::GatewayConnectionAbruptlyClosed),
            }

            Ok::<(), ClientCoreError>(())
        };

        let timeout = sleep(PING_TIMEOUT);
        tokio::pin!(timeout);

        tokio::select! {
            _ = &mut timeout => {
                warn!("timed out while trying to perform measurement...")
            }
            res = measurement_future => res?,
        }
    }

    let count = results.len() as u64;
    if count == 0 {
        return Err(ClientCoreError::NoGatewayMeasurements {
            identity: gateway.identity().to_base58_string(),
        });
    }

    let sum: Duration = results.into_iter().sum();
    let avg = Duration::from_nanos(sum.as_nanos() as u64 / count);

    Ok(GatewayWithLatency::new(gateway, avg))
}

pub async fn choose_gateway_by_latency<'a, R: Rng, G: ConnectableGateway + Clone>(
    rng: &mut R,
    gateways: &[G],
    must_use_tls: bool,
) -> Result<G, ClientCoreError> {
    let gateways = filter_by_tls(gateways, must_use_tls)?;

    info!(
        "choosing gateway by latency, pinging {} gateways ...",
        gateways.len()
    );

    let gateways_with_latency = Arc::new(tokio::sync::Mutex::new(Vec::new()));
    futures::stream::iter(gateways)
        .for_each_concurrent(CONCURRENT_GATEWAYS_MEASURED, |gateway| async {
            let id = *gateway.identity();
            trace!("measuring latency to {id}...");
            match measure_latency(gateway).await {
                Ok(with_latency) => {
                    debug!("{id}: {:?}", with_latency.latency);
                    gateways_with_latency.lock().await.push(with_latency);
                }
                Err(err) => {
                    warn!("failed to measure {id}: {err}");
                }
            };
        })
        .await;

    let gateways_with_latency = gateways_with_latency.lock().await;
    let chosen = gateways_with_latency
        .choose_weighted(rng, |item| 1. / item.latency.as_secs_f32())
        .expect("invalid selection weight!");

    info!(
        "chose gateway {} with average latency of {:?}",
        chosen.gateway.identity(),
        chosen.latency
    );

    Ok(chosen.gateway.clone())
}

fn filter_by_tls<G: ConnectableGateway>(
    gateways: &[G],
    must_use_tls: bool,
) -> Result<Vec<&G>, ClientCoreError> {
    if must_use_tls {
        let filtered = gateways.iter().filter(|g| g.is_wss()).collect::<Vec<_>>();

        if filtered.is_empty() {
            return Err(ClientCoreError::NoWssGateways);
        }

        Ok(filtered)
    } else {
        Ok(gateways.iter().collect())
    }
}

pub(super) fn uniformly_random_gateway<R: Rng>(
    rng: &mut R,
    gateways: &[gateway::LegacyNode],
    must_use_tls: bool,
) -> Result<gateway::LegacyNode, ClientCoreError> {
    filter_by_tls(gateways, must_use_tls)?
        .choose(rng)
        .ok_or(ClientCoreError::NoGatewaysOnNetwork)
        .map(|&r| r.clone())
}

pub(super) fn get_specified_gateway(
    gateway_identity: IdentityKeyRef,
    gateways: &[gateway::LegacyNode],
    must_use_tls: bool,
) -> Result<gateway::LegacyNode, ClientCoreError> {
    log::debug!("Requesting specified gateway: {}", gateway_identity);
    let user_gateway = identity::PublicKey::from_base58_string(gateway_identity)
        .map_err(ClientCoreError::UnableToCreatePublicKeyFromGatewayId)?;

    let gateway = gateways
        .iter()
        .find(|gateway| gateway.identity_key == user_gateway)
        .ok_or_else(|| ClientCoreError::NoGatewayWithId(gateway_identity.to_string()))?;

    if must_use_tls && gateway.clients_wss_port.is_none() {
        return Err(ClientCoreError::UnsupportedWssProtocol {
            gateway: gateway_identity.to_string(),
        });
    }

    Ok(gateway.clone())
}

pub(super) async fn register_with_gateway(
    gateway_id: identity::PublicKey,
    gateway_listener: Url,
    our_identity: Arc<identity::KeyPair>,
) -> Result<RegistrationResult, ClientCoreError> {
    let mut gateway_client =
        GatewayClient::new_init(gateway_listener, gateway_id, our_identity.clone());

    gateway_client.establish_connection().await.map_err(|err| {
        log::warn!("Failed to establish connection with gateway!");
        ClientCoreError::GatewayClientError {
            gateway_id: gateway_id.to_base58_string(),
            source: err,
        }
    })?;
    let auth_response = gateway_client
        .perform_initial_authentication()
        .await
        .map_err(|err| {
            log::warn!("Failed to register with the gateway {gateway_id}: {err}");
            ClientCoreError::GatewayClientError {
                gateway_id: gateway_id.to_base58_string(),
                source: err,
            }
        })?;

    // this should NEVER happen, if it did, it means the function was misused,
    // because for any fresh **registration**, the derived key is always up to date
    if auth_response.requires_key_upgrade {
        return Err(ClientCoreError::UnexpectedKeyUpgrade {
            gateway_id: gateway_id.to_base58_string(),
        });
    }

    Ok(RegistrationResult {
        shared_keys: auth_response.initial_shared_key,
        authenticated_ephemeral_client: gateway_client,
    })
}