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Balance calculation
function recordTransaction(txn) {
// NON FUNCTIONING CODE
// Let 'friend' be the User's friend, the 'other' party in this Activity/Transaction
// Record the origin
var origin = friend.balance;
// Calculate friend balance
if(role == Activity.CREDITOR) {
friend.balance += txn.amount;
}
else if(role == Activity.DEBTOR) {
friend.balance -= txn.amount;
}
friend.balance = parseFloat(friend.balance.toFixed(2));
// Calculate sum totals
// Algorithm as follows:
// Sum total (sumFriendsOwe/sumIOwe) is the cumulative representation of debt/credit
// across all a User's friends. It is wrong to treat sumFriendsOwe/sumIOwe the same
// way as a single friend's balance, ie. one friend's credit does not cancel out
// another's debt. Each friend's credit/debit must be taken into account individually
// first, via the '.balance' field, then its effect factored into the sum totals.
//
// (1) In calculating the sum total, we first look at the current friend's balance
// and if the transaction is a credit or debit against him.
// If the balance is in credit, ie. positive, and the transaction is a credit,
// then we simply add the transaction amount towards the sum total, sumFriendsOwe.
// The same applies in the opposite direction, ie. a debit against a negative balance
// is simply added to sumIOwe.
//
// (2) The tricky bit arises when we cross zero, ie. a debt becomes credit and vice versa
// When crossing zero, if the transaction amount is larger than the existing balance,
// we need to first eliminate the balance on one side, then add the remainder to the other.
//
// Eg.
// Transaction type: Credit
// Transaction amount: 20
// Balance: -10
//
// (A) Eliminate the balance: sumIOwe -= 10 (making balance zero)
// (B) Add the remainder to the other side: sumFriendsOwe += (20-10) (making balance +10)
//
if(role == Activity.CREDITOR) {
if(origin >= 0) { // See above: (1)
this.sumFriendsOwe += txn.amount;
}
else if(origin < 0) {
// Here we take into account the case where the difference provided by
// txn.amount will cause a shift from credit to debt or vice versa.
// We first eliminate excess credit/debt, then add the remainder to the
// other side.
if(txn.amount > Math.abs(origin)) { // See above: (2)
this.sumFriendsOwe += txn.amount - Math.abs(origin);
this.sumIOwe -= Math.abs(origin);
}
else {
this.sumIOwe -= txn.amount;
}
}
}
else if(role == Activity.DEBTOR) {
if(origin <= 0) { // See above: (1)
this.sumIOwe += txn.amount;
}
else if(origin > 0) {
// Here we take into account the case where the difference provided by
// txn.amount will cause a shift from credit to debt or vice versa.
// We first eliminate excess credit/debt, then add the remainder to the
// other side.
if(txn.amount > origin) { // See above: (2)
this.sumFriendsOwe -= origin;
this.sumIOwe += txn.amount - Math.abs(origin);
}
else {
this.sumFriendsOwe -= txn.amount;
}
}
}
// Re-jigger the balances
friend.balance = Math.round(friend.balance * 100) / 100;
this.sumIOwe = Math.round(this.sumIOwe * 100) / 100;
this.sumFriendsOwe = Math.round(this.sumFriendsOwe * 100) / 100;
}
function voidTransaction() {
// NON FUNCTIONING CODE
// Let 'friend' be the User's friend, the 'other' party in this Activity/Transaction
// Undo the transaction
var origin = friend.balance;
if(role == Activity.CREDITOR) {
friend.balance -= txn.amount;
if(origin <= 0) {
this.sumIOwe += txn.amount;
}
else if(origin > 0) {
if(txn.amount > Math.abs(origin)) {
var balance = 0;
if(this.sumFriendsOwe >= Math.abs(origin)) {
this.sumFriendsOwe -= Math.abs(origin);
}
else {
balance = Math.abs(origin) - this.sumFriendsOwe;
}
this.sumIOwe += (txn.amount - Math.abs(origin)) + balance;
}
else {
this.sumFriendsOwe -= txn.amount;
}
}
}
else if(role == Activity.DEBTOR) {
friend.balance += txn.amount;
if(origin >= 0) {
this.sumFriendsOwe += txn.amount;
}
else if(origin < 0) {
if(txn.amount > Math.abs(origin)) {
var balance = 0;
if(this.sumIOwe >= Math.abs(origin)) {
this.sumIOwe -= Math.abs(origin);
}
else {
balance = Math.abs(origin) - this.sumIOwe;
}
this.sumFriendsOwe += (txn.amount - Math.abs(origin)) + balance;
}
else {
this.sumIOwe -= txn.amount;
}
}
}
// Re-jigger the balances
friend.balance = Math.round(friend.balance * 100) / 100;
this.sumIOwe = Math.round(this.sumIOwe * 100) / 100;
this.sumFriendsOwe = Math.round(this.sumFriendsOwe * 100) / 100;
}
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