Separated fetch

src/engine/fetch.rs

@@ -0,0 +1,80 @@
+use std::collections::HashMap;
+
+use pulse_wire::terminal::WatchListItem;
+use serde_json::Value;
+
+fn number(value: &Value, field: &str) -> Result<f64, String> {
+    let raw = value[field]
+        .as_str()
+        .ok_or_else(|| format!("asset context field {field} must be a string"))?;
+
+    raw.parse::<f64>()
+        .map_err(|error| format!("could not parse asset context field {field} ({raw}): {error}"))
+}
+
+pub async fn fetch_watch_list(symbols: &[&str]) -> Result<Vec<WatchListItem>, String> {
+    let response = hypersdk::hypercore::mainnet()
+        .meta_and_asset_ctxs(None)
+        .await
+        .map_err(|error| format!("Hyperliquid metaAndAssetCtxs request failed: {error}"))?;
+
+    let response = response
+        .as_array()
+        .ok_or("metaAndAssetCtxs response must be an array")?;
+
+    if response.len() != 2 {
+        return Err(format!(
+            "metaAndAssetCtxs response must contain meta and contexts, got {} entries",
+            response.len()
+        ));
+    }
+
+    let universe = response[0]["universe"]
+        .as_array()
+        .ok_or("metaAndAssetCtxs response is missing meta.universe")?;
+    let contexts = response[1]
+        .as_array()
+        .ok_or("metaAndAssetCtxs response contexts must be an array")?;
+
+    if universe.len() != contexts.len() {
+        return Err(format!(
+            "Hyperliquid returned {} instruments but {} contexts",
+            universe.len(),
+            contexts.len()
+        ));
+    }
+
+    let mut by_symbol = HashMap::with_capacity(universe.len());
+
+    for (meta, context) in universe.iter().zip(contexts) {
+        let symbol = meta["name"]
+            .as_str()
+            .ok_or("instrument metadata is missing a name")?;
+        let price = number(context, "markPx")?;
+        let previous_day_price = number(context, "prevDayPx")?;
+        let volume_24h = number(context, "dayNtlVlm")?;
+
+        if previous_day_price <= 0.0 {
+            return Err(format!("{symbol} has an invalid previous-day price"));
+        }
+
+        by_symbol.insert(
+            symbol,
+            WatchListItem {
+                symbol: symbol.to_owned(),
+                price,
+                trend: ((price / previous_day_price) - 1.0) * 100.0,
+                volume_24h,
+            },
+        );
+    }
+
+    symbols
+        .iter()
+        .map(|symbol| {
+            by_symbol
+                .remove(*symbol)
+                .ok_or_else(|| format!("{symbol} is not in the Hyperliquid perpetual universe"))
+        })
+        .collect()
+}