//! iroh transport scaffolding for every.channel.

use anyhow::{Context, Result};
use bytes::Bytes;
use ec_core::{StreamCatalogEntry, StreamControlAnnouncement};
use futures_lite::StreamExt;
use iroh::address_lookup::{
    DhtAddressLookup, DiscoveryEvent, DnsAddressLookup, MdnsAddressLookup, PkarrPublisher, UserData,
};
use iroh::endpoint::RelayMode;
use iroh::{
    address_lookup::memory::MemoryLookup, protocol::Router, Endpoint, EndpointAddr, PublicKey,
    SecretKey,
};
use iroh_gossip::{
    api::{Event, GossipReceiver, GossipSender},
    net::{Gossip, GOSSIP_ALPN},
    proto::TopicId,
};
use std::collections::BTreeMap;
use std::env;
use std::time::{Duration, Instant};

pub const ALPN_MOQ: &[u8] = b"every.channel/moq/0";
pub const DEFAULT_CATALOG_TOPIC: &str = "every.channel/catalog/v1";
pub const DEFAULT_CONTROL_TOPIC: &str = "every.channel/control/v1";
pub const MDNS_USER_DATA: &str = "every.channel";

#[derive(Debug, Clone)]
pub struct TokenBucket {
    capacity: u64,
    tokens: f64,
    refill_per_sec: f64,
    last_refill: Instant,
}

impl TokenBucket {
    pub fn new(capacity: u64, refill_per_sec: u64) -> Self {
        let capacity = capacity.max(1);
        let refill_per_sec = refill_per_sec.max(1) as f64;
        Self {
            capacity,
            tokens: capacity as f64,
            refill_per_sec,
            last_refill: Instant::now(),
        }
    }

    pub fn allow(&mut self, amount: u64) -> bool {
        self.refill();
        let amount = amount as f64;
        if amount <= self.tokens {
            self.tokens -= amount;
            true
        } else {
            false
        }
    }

    fn refill(&mut self) {
        let now = Instant::now();
        let elapsed = now.duration_since(self.last_refill).as_secs_f64();
        if elapsed <= 0.0 {
            return;
        }
        self.tokens = (self.tokens + elapsed * self.refill_per_sec).min(self.capacity as f64);
        self.last_refill = now;
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn token_bucket_allows_and_refills() {
        let mut bucket = TokenBucket::new(10, 10);
        assert!(bucket.allow(7));
        assert!(bucket.allow(3));
        assert!(!bucket.allow(1));

        // Force a refill without sleeping.
        bucket.last_refill = Instant::now() - Duration::from_secs(1);
        assert!(bucket.allow(1));
    }
}

#[derive(Debug, Clone, Copy, Default)]
pub struct DiscoveryConfig {
    pub dht: bool,
    pub mdns: bool,
    pub dns: bool,
}

impl DiscoveryConfig {
    pub fn from_env() -> Result<Self> {
        match env::var("EVERY_CHANNEL_IROH_DISCOVERY") {
            Ok(value) => Self::from_list(&value),
            Err(env::VarError::NotPresent) => Ok(Self::default()),
            Err(err) => Err(err.into()),
        }
    }

    pub fn from_list(value: &str) -> Result<Self> {
        let mut config = DiscoveryConfig::default();
        for raw in value.split(|c: char| c == ',' || c == ';' || c.is_whitespace()) {
            let token = raw.trim().to_ascii_lowercase();
            if token.is_empty() {
                continue;
            }
            match token.as_str() {
                "dht" => config.dht = true,
                "mdns" => config.mdns = true,
                "dns" => config.dns = true,
                "all" => {
                    config.dht = true;
                    config.mdns = true;
                    config.dns = true;
                }
                "none" | "off" => {
                    config = DiscoveryConfig::default();
                }
                _ => {
                    return Err(anyhow::anyhow!("unknown discovery mode: {token}"));
                }
            }
        }
        Ok(config)
    }
}

pub async fn build_endpoint(
    secret: Option<SecretKey>,
    discovery: DiscoveryConfig,
) -> Result<Endpoint> {
    let relay_mode = relay_mode_from_env().unwrap_or(RelayMode::Default);
    let mut builder = Endpoint::empty_builder(relay_mode);
    if let Some(secret) = secret {
        builder = builder.secret_key(secret);
    }
    if discovery.dns {
        builder = builder
            .address_lookup(PkarrPublisher::n0_dns())
            .address_lookup(DnsAddressLookup::n0_dns());
    }
    if discovery.dht {
        builder = builder.address_lookup(DhtAddressLookup::builder());
    }
    if discovery.mdns {
        builder = builder.address_lookup(MdnsAddressLookup::builder());
    }
    let endpoint = builder.bind().await?;
    endpoint.set_alpns(vec![ALPN_MOQ.to_vec()]);
    Ok(endpoint)
}

fn relay_mode_from_env() -> Result<RelayMode> {
    let value = match env::var("EVERY_CHANNEL_IROH_RELAY") {
        Ok(value) => value,
        Err(env::VarError::NotPresent) => return Ok(RelayMode::Default),
        Err(err) => return Err(err.into()),
    };
    match value.trim().to_ascii_lowercase().as_str() {
        "" | "default" => Ok(RelayMode::Default),
        "disabled" | "off" => Ok(RelayMode::Disabled),
        other => Err(anyhow::anyhow!("unknown relay mode: {other}")),
    }
}

pub async fn start_endpoint() -> Result<Endpoint> {
    let discovery = DiscoveryConfig::from_env()?;
    build_endpoint(None, discovery).await
}

pub fn catalog_topic() -> TopicId {
    let hash = blake3::hash(DEFAULT_CATALOG_TOPIC.as_bytes());
    TopicId::from_bytes(*hash.as_bytes())
}

pub fn control_topic() -> TopicId {
    let hash = blake3::hash(DEFAULT_CONTROL_TOPIC.as_bytes());
    TopicId::from_bytes(*hash.as_bytes())
}

pub fn parse_endpoint_addr(value: &str) -> Result<EndpointAddr> {
    let value = value.trim();
    if value.starts_with('{') {
        let addr =
            serde_json::from_str::<EndpointAddr>(value).context("invalid EndpointAddr json")?;
        return Ok(addr);
    }
    let id = value.parse::<PublicKey>().context("invalid endpoint id")?;
    Ok(EndpointAddr::new(id))
}

#[derive(Debug, Clone)]
pub struct MdnsDiscovery {
    mdns: MdnsAddressLookup,
    endpoint_id: PublicKey,
    user_data: Option<UserData>,
}

impl MdnsDiscovery {
    pub async fn start(
        endpoint: &Endpoint,
        user_data: Option<&str>,
        advertise: bool,
    ) -> Result<Self> {
        let mdns = MdnsAddressLookup::builder()
            .advertise(advertise)
            .build(endpoint.id())
            .context("mdns address lookup failed")?;
        endpoint.address_lookup().add(mdns.clone());

        let user_data = if let Some(value) = user_data {
            let data = UserData::try_from(value.to_string()).context("invalid mdns user data")?;
            endpoint.set_user_data_for_address_lookup(Some(data.clone()));
            Some(data)
        } else {
            None
        };

        Ok(Self {
            mdns,
            endpoint_id: endpoint.id(),
            user_data,
        })
    }

    pub async fn discover_peers(&self, timeout: Duration) -> Result<Vec<EndpointAddr>> {
        let mut stream = self.mdns.subscribe().await;
        let deadline = Instant::now() + timeout;
        let mut peers: BTreeMap<PublicKey, EndpointAddr> = BTreeMap::new();

        loop {
            let now = Instant::now();
            if now >= deadline {
                break;
            }
            let remaining = deadline - now;
            match tokio::time::timeout(remaining, stream.next()).await {
                Ok(Some(DiscoveryEvent::Discovered { endpoint_info, .. })) => {
                    if endpoint_info.endpoint_id == self.endpoint_id {
                        continue;
                    }
                    if let Some(expected) = self.user_data.as_ref() {
                        if endpoint_info.data.user_data() != Some(expected) {
                            continue;
                        }
                    }
                    let addr = EndpointAddr::from(endpoint_info);
                    peers.insert(addr.id, addr);
                }
                Ok(Some(DiscoveryEvent::Expired { .. })) => {}
                Ok(None) => break,
                Err(_) => break,
            }
        }

        Ok(peers.into_values().collect())
    }
}

#[derive(Debug)]
pub struct CatalogGossip {
    sender: GossipSender,
    receiver: GossipReceiver,
    _router: Router,
    _gossip: Gossip,
    _memory_lookup: MemoryLookup,
}

impl CatalogGossip {
    pub async fn join(endpoint: Endpoint, peers: &[String]) -> Result<Self> {
        let memory_lookup = MemoryLookup::new();
        endpoint.address_lookup().add(memory_lookup.clone());

        let gossip = Gossip::builder().spawn(endpoint.clone());
        let router = Router::builder(endpoint.clone())
            .accept(GOSSIP_ALPN, gossip.clone())
            .spawn();

        let peer_addrs = peers
            .iter()
            .map(|peer| parse_endpoint_addr(peer))
            .collect::<Result<Vec<_>, _>>()
            .context("failed to parse gossip peer addr")?;
        for peer in &peer_addrs {
            memory_lookup.add_endpoint_info(peer.clone());
        }
        let peer_ids = peer_addrs
            .iter()
            .map(|addr| addr.id)
            .collect::<Vec<PublicKey>>();

        // Allow local-only startup with no explicit bootstrap peers. In that mode we still
        // subscribe to the topic immediately and can add peers later.
        let topic = if peer_ids.is_empty() {
            gossip.subscribe(catalog_topic(), Vec::new()).await?
        } else {
            gossip.subscribe_and_join(catalog_topic(), peer_ids).await?
        };
        let (sender, receiver) = topic.split();

        Ok(Self {
            sender,
            receiver,
            _router: router,
            _gossip: gossip,
            _memory_lookup: memory_lookup,
        })
    }

    pub async fn announce(&mut self, entry: StreamCatalogEntry) -> Result<()> {
        let bytes = serde_json::to_vec(&entry)?;
        self.sender.broadcast(Bytes::from(bytes)).await?;
        Ok(())
    }

    pub async fn next_entry(&mut self) -> Result<Option<StreamCatalogEntry>> {
        while let Some(event) = self.receiver.try_next().await? {
            if let Event::Received(msg) = event {
                if let Ok(entry) = serde_json::from_slice::<StreamCatalogEntry>(&msg.content) {
                    return Ok(Some(entry));
                }
            }
        }
        Ok(None)
    }

    /// Add peers after the gossip topic has already been joined. This enables
    /// "nearby" discovery to continuously contribute new peers over time.
    pub fn add_peers(&self, peers: Vec<EndpointAddr>) {
        for peer in peers {
            self._memory_lookup.add_endpoint_info(peer);
        }
    }
}

#[derive(Debug)]
pub struct ControlGossip {
    sender: GossipSender,
    receiver: GossipReceiver,
    _router: Router,
    _gossip: Gossip,
    _memory_lookup: MemoryLookup,
}

impl ControlGossip {
    pub async fn join(endpoint: Endpoint, peers: &[String]) -> Result<Self> {
        let memory_lookup = MemoryLookup::new();
        endpoint.address_lookup().add(memory_lookup.clone());

        let gossip = Gossip::builder().spawn(endpoint.clone());
        let router = Router::builder(endpoint.clone())
            .accept(GOSSIP_ALPN, gossip.clone())
            .spawn();

        let peer_addrs = peers
            .iter()
            .map(|peer| parse_endpoint_addr(peer))
            .collect::<Result<Vec<_>, _>>()
            .context("failed to parse control peer addr")?;
        for peer in &peer_addrs {
            memory_lookup.add_endpoint_info(peer.clone());
        }
        let peer_ids = peer_addrs
            .iter()
            .map(|addr| addr.id)
            .collect::<Vec<PublicKey>>();

        // Allow local-only startup with no explicit bootstrap peers. In that mode we still
        // subscribe to the topic immediately and can add peers later.
        let topic = if peer_ids.is_empty() {
            gossip.subscribe(control_topic(), Vec::new()).await?
        } else {
            gossip.subscribe_and_join(control_topic(), peer_ids).await?
        };
        let (sender, receiver) = topic.split();

        Ok(Self {
            sender,
            receiver,
            _router: router,
            _gossip: gossip,
            _memory_lookup: memory_lookup,
        })
    }

    pub async fn announce(&mut self, announcement: StreamControlAnnouncement) -> Result<()> {
        let bytes = serde_json::to_vec(&announcement)?;
        self.sender.broadcast(Bytes::from(bytes)).await?;
        Ok(())
    }

    pub async fn next_announcement(&mut self) -> Result<Option<StreamControlAnnouncement>> {
        while let Some(event) = self.receiver.try_next().await? {
            if let Event::Received(msg) = event {
                if let Ok(announcement) =
                    serde_json::from_slice::<StreamControlAnnouncement>(&msg.content)
                {
                    return Ok(Some(announcement));
                }
            }
        }
        Ok(None)
    }

    pub fn add_peers(&self, peers: Vec<EndpointAddr>) {
        for peer in peers {
            self._memory_lookup.add_endpoint_info(peer);
        }
    }
}