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devcsrj/001_account_number.ts

Last active January 12, 2021 06:18
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Coding in Prose
Raw
001_account_number.ts
const num: number = 11111111;
Raw
002_account_number.ts
class AccountNumber {
private readonly value: number;
private constructor(value: number) {
this.value = value;
}
static from(value: number): AccountNumber {
if (lengthOf(value) != 10) 
throw new Error("Account number must be 10-digits");
return new AccountNumber(value);
}
}
Raw
003_account_number.ts
const num: AccountNumber = AccountNumber.from(11111111);
Raw
004_account_withdrawal.ts
const account: Account = ...;
account.withdraw(1000, "USD");
Raw
005_account_withdrawal.ts
class Account {
withdraw(amount: double, currency: string) {
// deduct funds
}
}
Raw
006_account_withdrawal.ts
const amount: Money = Money.of(1000, "USD");
const account: Account = …
account.withdraw(amount);
Raw
007_account_withdrawal.ts
class Account {
withdraw(amount: Money) {
// deduct funds
}
}
Raw
008_account_balance.ts
class Account {
private _balance: Money;
withdraw(amount: Money) {
if (amount.isNegative())
throw new Error("Can't withdraw a negative amount");
_balance = _balance.minus(amount);
}
get balance(): Money {
return _balance;
}
}
Raw
009_account_balance.ts
class Account {
private balance: Money;
...
Raw
010_account_balance.ts
class Account {
private readonly credits: Credit[];
private readonly debits: Debit[];
withdraw(amount: Money) {
if (amount.isNegative())
throw new Error("Can't withdraw a negative amount");
debits.push(new Debit(amount));
}
get balance(point: Timepoint): Money {
// Add all credits up to point in time
const totalCredit = credits
.filter(c => c.before(point))
.map(c => c.amount())
.reduce((sum, current) => sum.plus(current), Money.ZERO);
// Add all debits up to point in time
const totalDebits = debits
.filter(d => d.before(point))
.map(d => d.amount())
.reduce((sum, current) => sum.plus(current), Money.ZERO);
// the difference IS the balance
return totalDebits.minus(totalCredits);
}
}
Raw
011_account_balance.ts
const account: Account = ...;
const twoDaysAgo = new Timepoint(2020, 12, 15); // Dec 15, 2020
const balanceTwoDaysAgo: Money = account.balance(twoDaysAgo);
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