feat: add handler for burns to the transfer handler [subgraph] (#162)

* feat: add handler for burns to the transfer handler

* fix: update transfer.ts to include the changes.

subgraph/src/fleek-nfa.ts

@@ -4,4 +4,4 @@ export * from './approval';
 export * from './contract';
 export * from './metadata-update';
 export * from './mint';
-export * from './transfer';
+export * from './transfer';

subgraph/src/transfer.ts

@@ -16,47 +16,57 @@ import {
 } from '../generated/schema';
 
 export function handleTransfer(event: TransferEvent): void {
-    let entity = new Transfer(
-        event.transaction.hash.concatI32(event.logIndex.toI32())
+    let transfer = new Transfer(
+      event.transaction.hash.concatI32(event.logIndex.toI32())
     );
-    entity.from = event.params.from;
-    entity.to = event.params.to;
-    entity.tokenId = event.params.tokenId;
-
-    entity.blockNumber = event.block.number;
-    entity.blockTimestamp = event.block.timestamp;
-    entity.transactionHash = event.transaction.hash;
-
-    entity.save();
-
+    
+    const TokenId = event.params.tokenId;
+    
+    transfer.from = event.params.from;
+    transfer.to = event.params.to;
+    transfer.tokenId = TokenId;
+  
+    transfer.blockNumber = event.block.number;
+    transfer.blockTimestamp = event.block.timestamp;
+    transfer.transactionHash = event.transaction.hash;
+  
+    transfer.save();
+  
     let token: Token | null;
-
+  
     let owner_address = event.params.to;
     let owner = Owner.load(owner_address);
-
+  
     if (!owner) {
-        // Create a new owner entity
-        owner = new Owner(owner_address);
+      // Create a new owner entity
+      owner = new Owner(owner_address);
     }
-
+  
     if (parseInt(event.params.from.toHexString()) !== 0) {
+      if (parseInt(event.params.to.toHexString()) === 0) {
+        // Burn
+        // Remove the entity from storage
+        // Its controllers and owner will be affected.
+        store.remove('Token', TokenId.toString());
+      } else {
         // Transfer
-
         // Load the Token by using its TokenId
         token = Token.load(
-            Bytes.fromByteArray(Bytes.fromBigInt(event.params.tokenId))
+          Bytes.fromByteArray(Bytes.fromBigInt(TokenId))
         );
-
+  
         if (token) {
-            // Entity exists
-            token.owner = owner_address;
-
-            // Save both entities
-            owner.save();
-            token.save();
+          // Entity exists
+          token.owner = owner_address;
+  
+          // Save both entities
+          owner.save();
+          token.save();
         } else {
-            // Entity does not exist
-            log.error('Unknown token was transferred.', []);
+          // Entity does not exist
+          log.error('Unknown token was transferred.', []);
         }
+      }
     }
-}
+  }
+