xo-stack/packages/primitives/src/transaction-graph.ts

import { Transaction } from './transaction.js';

import { binToHex, Output } from '@bitauth/libauth';

export interface UTXO extends Output {
  outpointTransactionHash: string;
  outpointIndex: number;
}

export class TransactionGraph {
  private transactions: Map<string, Transaction>;

  constructor() {
    this.transactions = new Map();
  }

  addTransaction(tx: Transaction) {
    this.transactions.set(tx.toHashHex(), tx);
  }

  removeTransaction(txHash: string) {
    this.transactions.delete(txHash);
  }

  removeDependentTransactions(txHash: string): string[] {
    const removedTxids: string[] = [];
    const toRemove: Set<string> = new Set([txHash]);

    const findDependents = (id: string) => {
      for (const [otherTxid, tx] of this.transactions) {
        if (
          tx
            .getInputs()
            .some((input) => binToHex(input.outpointTransactionHash) === id)
        ) {
          toRemove.add(otherTxid);
          findDependents(otherTxid);
        }
      }
    };

    findDependents(txHash);

    for (const id of toRemove) {
      if (this.transactions.has(id)) {
        this.transactions.delete(id);
        removedTxids.push(id);
      }
    }

    return removedTxids;
  }

  getTransaction(txHash: string): Transaction | undefined {
    return this.transactions.get(txHash);
  }

  getAllTransactions(): Transaction[] {
    return Array.from(this.transactions.values());
  }

  deriveUtxoState(): UTXO[] {
    const utxoMap = new Map<string, UTXO>();

    // First, add all outputs as potential UTXOs
    for (const tx of this.transactions.values()) {
      tx.getOutputs().forEach((output, outpointIndex) => {
        const txHashHex = tx.toHashHex();

        const utxo: UTXO = {
          outpointTransactionHash: txHashHex,
          outpointIndex,
          valueSatoshis: output.valueSatoshis,
          lockingBytecode: output.lockingBytecode,
        };
        utxoMap.set(`${txHashHex}:${outpointIndex}`, utxo);
      });
    }

    // Then, remove all spent outputs
    for (const tx of this.transactions.values()) {
      tx.getInputs().forEach((input) => {
        const outpointTransactionHashHex = binToHex(
          input.outpointTransactionHash
        );

        utxoMap.delete(`${outpointTransactionHashHex}:${input.outpointIndex}`);
      });
    }

    return Array.from(utxoMap.values());
  }

  isTransactionValid(tx: Transaction): boolean {
    const currentUtxos = this.deriveUtxoState();
    const utxoMap = new Map(
      currentUtxos.map((utxo) => [
        `${utxo.outpointTransactionHash}:${utxo.outpointIndex}`,
        utxo,
      ])
    );

    return tx.getInputs().every((input) => {
      const outpointTransactionHashHex = binToHex(
        input.outpointTransactionHash
      );
      return utxoMap.has(
        `${outpointTransactionHashHex}:${input.outpointIndex}`
      );
    });
  }

  getDependentTransactions(txHash: string): Transaction[] {
    return this.getAllTransactions().filter((tx) => {
      tx.getInputs().some((input) => {
        const outpointTransactionHashHex = binToHex(
          input.outpointTransactionHash
        );
        return outpointTransactionHashHex === txHash;
      });
    });
  }

  getBroadcastOrder(): Transaction[] {
    const visited = new Set<string>();
    const order: Transaction[] = [];

    const visit = (txid: string) => {
      if (visited.has(txid)) return;

      const tx = this.transactions.get(txid);
      if (!tx) return;

      visited.add(txid);

      // First, visit all transactions that this transaction depends on
      for (const input of tx.getInputs()) {
        const outpointTransactionHashHex = binToHex(
          input.outpointTransactionHash
        );
        visit(outpointTransactionHashHex);
      }

      order.push(tx);
    };

    // Start the topological sort from each transaction
    for (const tx of this.transactions.values()) {
      visit(tx.toHashHex());
    }

    return order;
  }

  getNextTransactionToBroadcast(): Transaction | undefined {
    // This is pretty inefficient in the sense we recompile the graph each time.
    // But I'm not sure if that would really have much real-world performance impact.
    return this.getBroadcastOrder()[0] ?? undefined;
  }
}