add js-fp3

js-fp3/domain/account.js

@@ -0,0 +1,72 @@
+import { ok, fail } from '../library/result.js';
+
+/**
+ * @typedef {Object} Account
+ * @property {string} id
+ * @property {import('./money.js').Money} balance
+ */
+
+/** @typedef {{ type: 'OpeningBalanceMustBeNonNegative' }} OpeningBalanceMustBeNonNegative */
+/** @typedef {{ type: 'AmountMustBePositive' }} AmountMustBePositive */
+/** @typedef {{ type: 'InsufficientBalance', balance: import('./money.js').Money, amount: import('./money.js').Money }} InsufficientBalance */
+/** @typedef {{ type: 'AccountNotFound', accountId: string }} AccountNotFound */
+
+/** @typedef {OpeningBalanceMustBeNonNegative | AmountMustBePositive | InsufficientBalance | AccountNotFound} AccountError */
+
+/**
+ * @type {OpeningBalanceMustBeNonNegative}
+ */
+export const openingBalanceMustBeNonNegative = { type: 'OpeningBalanceMustBeNonNegative' };
+
+/**
+ * @type {AmountMustBePositive}
+ */
+export const amountMustBePositive = { type: 'AmountMustBePositive' };
+
+/**
+ * @param {import('./money.js').Money} balance
+ * @param {import('./money.js').Money} amount
+ * @returns {InsufficientBalance}
+ */
+export const insufficientBalance = (balance, amount) => ({
+  type: 'InsufficientBalance',
+  balance,
+  amount,
+});
+
+/**
+ * @param {string} accountId
+ * @returns {AccountNotFound}
+ */
+export const accountNotFound = (accountId) => ({
+  type: 'AccountNotFound',
+  accountId,
+});
+
+/**
+ * @param {string} id
+ * @param {import('./money.js').Money} openingBalance
+ * @returns {import('../library/result.js').Result<Account, AccountError>}
+ */
+export const openAccount = (id, openingBalance) =>
+  openingBalance.amount < 0
+    ? fail(openingBalanceMustBeNonNegative)
+    : ok({ id, balance: openingBalance });
+
+/**
+ * @param {Account} account
+ * @param {import('./money.js').Money} amount
+ * @returns {import('../library/result.js').Result<Account, AccountError>}
+ */
+export const withdraw = (account, amount) => {
+  if (amount.amount <= 0) {
+    return fail(amountMustBePositive);
+  }
+  if (account.balance.amount < amount.amount) {
+    return fail(insufficientBalance(account.balance, amount));
+  }
+  return ok({
+    ...account,
+    balance: { amount: account.balance.amount - amount.amount },
+  });
+};

js-fp3/domain/money.js

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+/**
+ * @typedef {Object} Money
+ * @property {number} amount
+ */
+
+/**
+ * @param {number} amount
+ * @returns {Money}
+ */
+export const createMoney = (amount) => ({ amount });
+
+/**
+ * @param {Money} money
+ * @returns {string}
+ */
+export const formatMoney = (money) => money.amount.toFixed(2);