new: attempting to check with mapping for ERC721 tokens in Registry c…

…ontract, in runtime, when plasma token mapped event is received

root/src/mappings/registry.ts

@@ -1,6 +1,16 @@
+import { Address } from '@graphprotocol/graph-ts'
+
 import { TokenMapped } from '../../generated/Registry/Registry'
 import { TokenMapping } from '../../generated/schema'
 
+// Using contract address for creating instance of `Registry`
+// contract, to be used for checking whether token is ERC20/ ERC721
+import { registryAddress } from '../network'
+
+// This is the contract we're going to interact with when `TokenMapped` event is emitted
+// to check what kind of token it is
+import { Registry } from '../../generated/Registry/Registry'
+
 export function handlePlasmaTokenMapped(event: TokenMapped): void {
   let id = 'plasma-token-mapping-' + event.params.rootToken.toHexString()
 
@@ -11,6 +21,18 @@ export function handlePlasmaTokenMapped(event: TokenMapped): void {
 
   entity.rootToken = event.params.rootToken
   entity.childToken = event.params.childToken
+
+  // Attempting to check from `Registry` contract what kind of
+  // token it is.
+  //
+  // `tokenType` will be any of two possible values for Plasma Tokens
+  //
+  // 1. keccak256('ERC721') = 0x73ad2146b3d3a286642c794379d750360a2d53a3459a11b3e5d6cc900f55f44a
+  // 2. keccak256('ERC20') = 0x8ae85d849167ff996c04040c44924fd364217285e4cad818292c7ac37c0a345b
+  let registry = Registry.bind(Address.fromString(registryAddress))
+  entity.tokenType = registry.isERC721(event.params.rootToken) ? '0x73ad2146b3d3a286642c794379d750360a2d53a3459a11b3e5d6cc900f55f44a' : '0x8ae85d849167ff996c04040c44924fd364217285e4cad818292c7ac37c0a345b'
+
+  // Yes, this is plasma mapping handler, so it's a plasma bridge token
   entity.isPOS = false
 
   entity.timestamp = event.block.timestamp