binance-stream-handler 0.1.3

use ordered_float::OrderedFloat as OF;
use reqwest::Client;
use serde::Deserialize;
use std::collections::BTreeMap;
use tracing::{debug, error, info, trace, warn};

type Price = OF<f64>;
type Qty = f64;

#[allow(non_snake_case)]
#[derive(Debug, Deserialize, PartialEq)]
pub struct DepthUpdate {
    pub e: String,           // Event type: "depthUpdate"
    pub E: u64,              // Event time
    pub T: u64,              // Transaction time
    pub s: String,           // Symbol
    pub U: u64,              // First update ID in event
    pub u: u64,              // Final update ID in event
    pub pu: u64,             // Final update Id in last stream(ie `u` in last stream)
    pub b: Vec<[String; 2]>, // bids updates [price, qty]
    pub a: Vec<[String; 2]>, // asks updates
    pub channel_load: Option<usize>,
}

#[derive(Debug, Deserialize, PartialEq)]
pub struct CombinedDepthUpdate {
    // e.g. "adausdt@depth@100ms"
    pub stream: String,
    pub data: DepthUpdate,
}

#[derive(Debug, Clone)]
pub struct ResyncNeeded {
    pub symbol: String,
    pub expected_pu: Option<u64>, // what we expected (prev u)
    pub got_pu: u64,              // the pu we received
    pub got_U: u64,
    pub got_u: u64,               // the u we received
}

#[allow(non_snake_case)]
#[derive(Debug, Deserialize)]
pub struct DepthSnapshot {
    #[serde(rename = "lastUpdateId")]
    last_update_id: u64,
    E: u64,                 // event time (ms)
    T: u64,                 // transaction time (ms)
    bids: Vec<[String; 2]>, // [price, qty]
    asks: Vec<[String; 2]>,
}

#[derive(Debug)]
pub enum UpdateDecision<'a> {
    Drop,                   // ignore this event
    Apply(&'a DepthUpdate), // apply to book
    Resync(ResyncNeeded),   // trigger re-snapshot
}

/// A sorted Binance order book (bids descending by price, asks ascending).
///
/// Values are **absolute quantities** (Binance-style). `last_u` and `snapshot_id`
/// reflect the latest applied update and the initializing REST snapshot respectively.
///
/// Most users don't construct `OrderBook` directly—consume it via the
/// `watch::Receiver<OrderBook>` returned by [`generate_orderbooks`].
#[derive(Debug, Clone)]
pub struct OrderBook {
    pub symbol: String,
    // Sorted by price ascending (wrapped so it implements Ord)
    pub bids: BTreeMap<Price, Qty>,
    pub asks: BTreeMap<Price, Qty>,
    pub last_u: Option<u64>,
    pub snapshot_id: Option<u64>,
    pub depth: u16,
}

impl OrderBook {
    pub fn new(symbol: &str) -> Self {
        Self {
            symbol: symbol.to_ascii_uppercase(),
            bids: BTreeMap::new(),
            asks: BTreeMap::new(),
            last_u: None,
            snapshot_id: None,
            depth: 1000,
        }
    }

    pub async fn init_ob(symbol: &str) -> Result<OrderBook, Box<dyn std::error::Error>> {
        let mut ob = OrderBook::new(symbol);
        let snapshot = ob.get_depth_snapshot(ob.depth).await?;
        ob.from_snapshot(&snapshot);
        Ok(ob)
    }

    pub async fn resync_ob(&mut self) -> Result<(), Box<dyn std::error::Error>> {
        let new_snapshot = self.get_depth_snapshot(self.depth).await?;
        self.from_snapshot(&new_snapshot);
        Ok(())
    }

    pub async fn get_depth_snapshot(
        &self,
        limit: u16,
    ) -> Result<DepthSnapshot, Box<dyn std::error::Error>> {
        let sym = self.symbol.to_ascii_uppercase();
        let url = format!("https://fapi.binance.com/fapi/v1/depth?symbol={sym}&limit={limit}");

        let client = Client::builder()
            .user_agent("binance-stream-handler/0.1")
            .build()?;

        let resp = client.get(&url).send().await?;
        if !resp.status().is_success() {
            return Err(format!("Snapshot HTTP error: {}", resp.status()).into());
        }

        let snapshot: DepthSnapshot = resp.json().await?;

        Ok(snapshot)
    }

    /// Build a sorted book directly from a REST snapshot.
    pub fn from_snapshot(&mut self, snap: &DepthSnapshot) {
        self.bids.clear();
        self.asks.clear();

        self.snapshot_id = Some(snap.last_update_id);

        for [p, q] in &snap.bids {
            let (p, q) = (Self::parse_f64(p), Self::parse_f64(q));
            if q != 0.0 {
                self.bids.insert(OF(p), q);
            }
        }
        for [p, q] in &snap.asks {
            let (p, q) = (Self::parse_f64(p), Self::parse_f64(q));
            if q != 0.0 {
                self.asks.insert(OF(p), q);
            }
        }
    }

    /// Apply one WS depth update (absolute quantities)
    pub fn apply_update(&mut self, ev: &DepthUpdate) {
        // bids
        for [p, q] in &ev.b {
            let (p, q) = (Self::parse_f64(p), Self::parse_f64(q));
            if q == 0.0 {
                self.bids.remove(&OF(p));
            } else {
                self.bids.insert(OF(p), q);
            }
        }
        // asks
        for [p, q] in &ev.a {
            let (p, q) = (Self::parse_f64(p), Self::parse_f64(q));
            if q == 0.0 {
                self.asks.remove(&OF(p));
            } else {
                self.asks.insert(OF(p), q);
            }
        }
        self.last_u = Some(ev.u);
    }

    pub fn continuity_check<'a>(&mut self, du: &'a DepthUpdate) -> UpdateDecision<'a> {
        let snapshot_id = match self.snapshot_id {
            None => {
                self.last_u = None;
                return UpdateDecision::Resync(ResyncNeeded {
                    symbol: self.symbol.clone(),
                    expected_pu: None,
                    got_pu: du.pu,
                    got_U: du.U,
                    got_u: du.u,
                });
            }
            Some(s) => s,
        };

        match self.last_u {
            None => {
                if du.u < snapshot_id {
                    return UpdateDecision::Drop;
                }
            
                if du.U <= snapshot_id && snapshot_id <= du.u {
                    self.last_u = Some(du.u);
                    return UpdateDecision::Apply(du);
                }
            
                // du.U > snapshot_id => we missed the bridging update
                debug!(
                    "Missed updates after initialization for {}, snap_id: {} U: {} u: {}",
                    du.s, snapshot_id, du.U, du.u,
                );
                self.last_u = None;
                return UpdateDecision::Resync(ResyncNeeded {
                    symbol: self.symbol.clone(),
                    expected_pu: None,
                    got_pu: du.pu,
                    got_U: du.U,
                    got_u: du.u,
                });
            }

            Some(pu) => {
                if pu == du.pu {
                    self.last_u = Some(du.u);
                    return UpdateDecision::Apply(&du);
                } else if pu > du.pu {
                    return UpdateDecision::Drop;
                } else {
                    self.last_u = None;
                    return UpdateDecision::Resync(ResyncNeeded {
                        symbol: self.symbol.clone(),
                        expected_pu: Some(pu),
                        got_pu: du.pu,
                        got_U: du.U,
                        got_u: du.u,
                    });
                }
            }
        }
    }

    fn parse_f64(s: &str) -> f64 {
        // Binance sends clean numeric strings
        s.parse::<f64>().unwrap()
    }
}