Solution to Encoded Blocks of transactions problem.

TransactionBlocks.js

/**
 * Get previous transactions from last transaction
 * @param last { Object }
 */
const getPrevTransactions = (last) => {
  let all = []
  all.push(last);

  if (last.previousBlock) {
    let hasPrev = true;
    while (hasPrev) {
      let lastIn = all[all.length - 1]; // get the last pushed transaction;
      // decode the prev tranx from the last given
      let prevTranx = JSON.parse(Buffer.from(lastIn.previousBlock, 'base64').toString())
      prevTranx.previousBlock ?
        all.push(prevTranx) : hasPrev = false;
    }
    all = [...new Set(all)].reverse() // remove duplicates if any and reverse transaction list
  }
  return all;
}

/**
 * get transaction by specified field
 * @param type { String } 
 * @param query { String }
 */
const getTransactionByAny = (transactions, by = '_id', query) => {
  const allowedFields = ['id', '_id', 'ref', 'txRef'];
  if (!allowedFields.includes(by)) {
    return 'query field not allowed'
  }
  by === 'id' ? by = '_id' : ''; // autocorrect user ( 🙂 )
  return transactions.find(tranx => tranx[`${by.trim()}`] === query);
}

/**
 * filter transactions by given field
 * @param transactions { Array }
 * @param by { String }
 * @param query { string }
 */
const filterTransactionsByAny = (transactions, by = 'amount', query = '100') => {
  const allowedFilters = ['address', 'amount', 'status', 'createdAt'];
  if (!allowedFilters.includes(by)) {
    return 'query field not allowed'
  }
  return transactions.filter(tranx => tranx[`${by.trim()}`] === query);
}

/**
 * get the sum of filtered transactions
 * @param filtered { Array }
 */
const sumFiltered = (filtered) => {
  return filtered.reduce((acc, curr) => curr.amount ? acc + Number(curr.amount) : acc + 0, 0);
}

// insert last transaction
const lastTranx = {}

const transactions = getPrevTransactions(lastTranx);
const filtered = filterTransactionsByAny(transactions, 'address', '1HSY7V2P488zb93ok9jWikmXwKCrQwcChC')
const tranx = getTransactionByAny(transactions, 'address', '1HSY7V2P488zb93ok9jWikmXwKCrQwcChC')
sumFiltered(filtered)