subgraph mapping for Splice mints

splice_subgraph.ts

import { ERC721 as ERC721Contract } from '../generated/Splice/ERC721';
import { Bytes, ByteArray, ethereum } from '@graphprotocol/graph-ts';
import { Splice, Style } from '../generated/schema';
import { Minted, Splice as SpliceContract } from '../generated/Splice/Splice';

export function handleMinted(event: Minted): void {
  const tokenId = event.params.token_id.toString();
  const splice = new Splice(tokenId);

  const spliceContract = SpliceContract.bind(event.address);
  splice.metadata_url = spliceContract.tokenURI(event.params.token_id);

  splice.owner = event.transaction.from;
  splice.origin_hash = event.params.origin_hash;
  splice.minting_fee = event.transaction.value;

  //1st 4 byte = method keccak hash fragment
  const functionInput = event.transaction.input.subarray(4);

  //prepend a "tuple" prefix (function params are arrays, not tuples)
  const tuplePrefix = ByteArray.fromHexString(
    '0x0000000000000000000000000000000000000000000000000000000000000020'
  );

  const functionInputAsTuple = new Uint8Array(
    tuplePrefix.length + functionInput.length
  );

  functionInputAsTuple.set(tuplePrefix, 0);
  functionInputAsTuple.set(functionInput, tuplePrefix.length);

  const tupleInputBytes = Bytes.fromUint8Array(functionInputAsTuple);
  const decoded = ethereum.decode(
    '(address[],uint[],uint,bytes32[],bytes)',
    tupleInputBytes
  );

  const t = decoded.toTuple();
  const originAddresses = t[0].toAddressArray();
  const originTokenIds = t[1].toBigIntArray();
  splice.origin_collection = originAddresses[0];
  splice.origin_token_id = originTokenIds[0];
  const originContract = ERC721Contract.bind(originAddresses[0]);
  splice.origin_metadata_url = originContract.tokenURI(originTokenIds[0]);

  const style_id = event.params.style_token_id.toString();
  splice.style = style_id;
  const style = Style.load(style_id);
  if (style) {
    style.minted = style.minted + 1;
    style.save();
  }

  splice.save();
}