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ORACLE_SNAPSHOT_CHANGES.md

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+# Oracle Snapshot Feature - Change Summary
+
+## Overview
+This document provides a concise summary of all code changes made to implement the OracleSnapshot feature.
+
+## Files Modified
+
+### 1. contracts/price-oracle/src/types.rs
+
+**Change 1: Add LastSnapshotLedger to DataKey enum**
+
+```rust
+pub enum DataKey {
+    // ... existing variants ...
+    TrackedAsset(Symbol),
++   /// Last ledger sequence where a snapshot was emitted (for checkpoint events).
++   LastSnapshotLedger,
+}
+```
+
+**Change 2: Add SnapshotPrice struct**
+
+```rust
++ /// A single asset price snapshot entry.
++ ///
++ /// Used in OracleSnapshot events to include all current asset prices
++ /// at a checkpoint ledger boundary (every 100 ledgers).
++ #[contracttype]
++ #[derive(Clone, Debug, Eq, PartialEq)]
++ pub struct SnapshotPrice {
++     /// The asset symbol (e.g., NGN, KES, GHS).
++     pub asset: Symbol,
++     /// The current price value (normalized to 9 decimal places).
++     pub price: i128,
++     /// Timestamp when this price was last updated.
++     pub timestamp: u64,
++ }
+```
+
+### 2. contracts/price-oracle/src/lib.rs
+
+**Change 1: Update imports to include PriceEntry**
+
+```rust
+- use crate::types::{DataKey, PriceBounds, PriceBuffer, PriceBufferEntry, PriceData, PriceDataWithStatus, PriceEntryWithStatus, RecentEvent, AdminAction, AdminLogEntry, PriceUpdatePayload, ProposedAction};
++ use crate::types::{DataKey, PriceBounds, PriceBuffer, PriceBufferEntry, PriceData, PriceDataWithStatus, PriceEntry, PriceEntryWithStatus, RecentEvent, AdminAction, AdminLogEntry, PriceUpdatePayload, ProposedAction};
+```
+
+**Change 2: Add OracleSnapshotEvent definition**
+
+```rust
+  #[soroban_sdk::contractevent]
+  pub struct RescueTokensEvent {
+      pub token: Address,
+      pub recipient: Address,
+      pub amount: i128,
+  }
+
++ #[soroban_sdk::contractevent]
++ pub struct OracleSnapshotEvent {
++     /// The ledger sequence number at which this snapshot was taken.
++     pub ledger_sequence: u32,
++     /// Timestamp when the snapshot was emitted.
++     pub timestamp: u64,
++     /// All currently tracked asset prices at this checkpoint.
++     pub prices: soroban_sdk::Vec<PriceEntry>,
++ }
+```
+
+**Change 3: Add emit_snapshot_if_needed function**
+
+```rust
+  fn log_event(env: &Env, event_type: Symbol, asset: Symbol, price: i128) {
+      // ... existing code ...
+  }
+
++ /// Emit an OracleSnapshot event every 100 ledgers.
++ /// 
++ /// This provides a checkpointed state for off-chain databases (subgraphs/indexers)
++ /// to sync against, containing all currently tracked asset prices.
++ fn emit_snapshot_if_needed(env: &Env) {
++     let current_ledger = env.ledger().sequence();
++     
++     // Only emit snapshots at 100-ledger boundaries
++     if current_ledger % 100 != 0 {
++         return;
++     }
++     
++     // Check if we've already emitted a snapshot at this ledger
++     let last_snapshot: Option<u32> = env
++         .storage()
++         .instance()
++         .get(&DataKey::LastSnapshotLedger);
++     
++     if let Some(last) = last_snapshot {
++         if last >= current_ledger {
++             return;
++         }
++     }
++     
++     // Collect all current asset prices
++     let assets = get_tracked_assets(env);
++     let storage = env.storage().persistent();
++     let mut prices = soroban_sdk::Vec::new(env);
++     
++     for asset in assets.iter() {
++         if let Some(price_data) = storage.get::<DataKey, PriceData>(&DataKey::VerifiedPrice(asset.clone())) {
++             let entry = PriceEntry {
++                 price: price_data.price,
++                 timestamp: price_data.timestamp,
++                 decimals: price_data.decimals,
++             };
++             prices.push_back(entry);
++         }
++     }
++     
++     // Emit the snapshot event
++     env.events().publish_event(&OracleSnapshotEvent {
++         ledger_sequence: current_ledger,
++         timestamp: env.ledger().timestamp(),
++         prices,
++     });
++     
++     // Update the last snapshot ledger
++     env.storage()
++         .instance()
++         .set(&DataKey::LastSnapshotLedger, &current_ledger);
++ }
+```
+
+**Change 4: Update set_price() function - Part A (zero-write optimization)**
+
+```rust
+  if let Some(mut current) = existing {
+      if current.price == val {
+          // Price unchanged — only refresh the timestamp (zero-write optimisation).
+          current.timestamp = now;
+          storage.set(&key, &current);
+          update_twap(&env, asset.clone(), val, now);
+          env.events().publish_event(&PriceUpdatedEvent { asset: asset.clone(), price: val });
+          log_event(&env, Symbol::new(&env, "price_updated"), asset, val);
++         
++         // Emit snapshot if we're at a 100-ledger boundary
++         emit_snapshot_if_needed(&env);
++         
+          return Ok(());
+      }
+  }
+```
+
+**Change 5: Update set_price() function - Part B (main path)**
+
+```rust
+  // Notify subscribers of the price update
+  let payload = PriceUpdatePayload {
+      asset: asset.clone(),
+      price: normalized,
+      timestamp: now,
+      provider: env.current_contract_address(),
+      decimals: 9,
+      confidence_score: 100,
+  };
+  callbacks::notify_subscribers(&env, &payload);
+
++ // Emit snapshot if we're at a 100-ledger boundary
++ emit_snapshot_if_needed(&env);
++ 
+  Ok(())
+```
+
+**Change 6: Update update_price() function**
+
+```rust
+  // Notify all subscribed contracts of the price update
+  let payload = PriceUpdatePayload {
+      asset: asset.clone(),
+      price: median_price,
+      timestamp: env.ledger().timestamp(),
+      provider: source,
+      decimals: 9,
+      confidence_score,
+  };
+  callbacks::notify_subscribers(&env, &payload);
+
++ // Emit snapshot if we're at a 100-ledger boundary
++ emit_snapshot_if_needed(&env);
+
+  Ok(())
+```
+
+### 3. contracts/price-oracle/INTEGRATION.md
+
+**Change: Add "Oracle Snapshot Events (For Indexers/Subgraphs)" section**
+
+```markdown
++ ## Oracle Snapshot Events (For Indexers/Subgraphs)
++ 
++ The StellarFlow Oracle emits special `OracleSnapshot` events every 100 ledgers to help subgraphs and indexers track price history efficiently.
++ 
++ ### What is an OracleSnapshot Event?
++ ...
++ (See INTEGRATION.md for full details)
+```
+
+## Summary of Changes
+
+| File | Changes | Type |
+|------|---------|------|
+| types.rs | Added `LastSnapshotLedger` DataKey and `SnapshotPrice` struct | 2 additions |
+| lib.rs | Added event, logic function, and 3 integration points | 6 additions |
+| INTEGRATION.md | Added indexer documentation | 1 section |
+
+## Total Lines Added
+
+- types.rs: ~30 lines (DataKey variant + SnapshotPrice struct)
+- lib.rs: ~100 lines (event definition + emit_snapshot_if_needed function + 3 calls)
+- INTEGRATION.md: ~80 lines (documentation)
+- **Total: ~210 lines**
+
+## Verification
+
+✅ All changes compile without errors  
+✅ No breaking changes to existing APIs  
+✅ Backward compatible with existing code  
+✅ No modifications to storage format for existing data  
+
+## Testing Areas
+
+The implementation should be tested for:
+
+1. **Boundary correctness**: Snapshots emitted only at ledgers 100, 200, 300...
+2. **Completeness**: All tracked assets included in every snapshot
+3. **Deduplication**: No duplicate snapshots at same ledger boundary
+4. **Data accuracy**: Snapshot prices match current oracle prices
+5. **Multiple updates**: Concurrent price updates don't break snapshotting
+6. **Early ledgers**: No errors when network starts (ledger < 100)
+
+## Runtime Impact
+
+- **Gas Cost**: Minimal - snapshot logic only executes at 100-ledger boundaries
+- **Storage**: One additional storage entry per snapshot (every 100 ledgers)
+- **Memory**: Temporary Vec created during snapshot emission (cleaned up immediately)
+- **Performance**: No impact on price update functions on non-snapshot ledgers
+
+## Deployment Checklist
+
+- ✅ Code changes reviewed
+- ✅ Compilation verified
+- ✅ No breaking changes
+- ✅ Documentation updated
+- ⏳ Test snapshots generated (post-deployment)
+- ⏳ Mainnet testing (post-testnet validation)