From b6c4f927532e4b241dfd335fa10757a941dc65f2 Mon Sep 17 00:00:00 2001
From: Andrej Dyck <43913051+andrej-dyck@users.noreply.github.com>
Date: Sat, 16 Dec 2023 16:20:14 +0100
Subject: [PATCH] add locale number parsing

---
 locale/index.ts             |  1 +
 locale/localeNumber.test.ts | 57 +++++++++++++++++++++++++++++++++++++
 locale/localeNumber.ts      | 40 ++++++++++++++++++++++++++
 tsconfig.json               |  4 +--
 4 files changed, 100 insertions(+), 2 deletions(-)
 create mode 100644 locale/index.ts
 create mode 100644 locale/localeNumber.test.ts
 create mode 100644 locale/localeNumber.ts

diff --git a/locale/index.ts b/locale/index.ts
new file mode 100644
index 0000000..28a66a4
--- /dev/null
+++ b/locale/index.ts
@@ -0,0 +1 @@
+export * from './localeNumber.js'
diff --git a/locale/localeNumber.test.ts b/locale/localeNumber.test.ts
new file mode 100644
index 0000000..88950e9
--- /dev/null
+++ b/locale/localeNumber.test.ts
@@ -0,0 +1,57 @@
+import { describe, expect, it, test } from 'vitest'
+import { localeNumber, Locale } from './localeNumber.js'
+
+describe('localeNumber', () => {
+
+  const numbers = [
+    0, 1, 1.1, -1, 0.5, -17.42, 2001, 2777227.19, 9007199254740991, -9007199254740991,
+  ]
+
+  test.each(numbers)('parses numbers in German format; %j', (number) => {
+    const locale = 'de-DE'
+    const formattedNumber = Intl.NumberFormat(locale).format(number)
+    expect(localeNumber(locale)(formattedNumber)).toBe(number)
+  })
+
+  test.each(numbers)('parses numbers in Invariant Country format; %j', (number) => {
+    const locale = 'us-US' as unknown as Locale
+    const formattedNumber = Intl.NumberFormat(locale).format(number)
+    expect(localeNumber(locale)(formattedNumber)).toBe(number)
+  })
+
+  test.each(numbers)('parses numbers in French format; %j', (number) => {
+    const locale = 'fr-FR' as unknown as Locale
+    const formattedNumber = Intl.NumberFormat(locale).format(number)
+    expect(localeNumber(locale)(formattedNumber)).toBe(number)
+  })
+
+  test.each(numbers)('parses numbers in Switzerland format; %j', (number) => {
+    const locale = 'de-CH' as unknown as Locale
+    const formattedNumber = Intl.NumberFormat(locale).format(number)
+    expect(localeNumber(locale)(formattedNumber)).toBe(number)
+  })
+
+  test.each(numbers)('parses numbers in Kyrgyzstan format; %j', (number) => {
+    const locale = 'ky-KG' as unknown as Locale
+    const formattedNumber = Intl.NumberFormat(locale).format(number)
+    expect(localeNumber(locale)(formattedNumber)).toBe(number)
+  })
+
+  test.each(numbers)('parses numbers in Estonia format; %j', (number) => {
+    const locale = 'et-EE' as unknown as Locale
+    const formattedNumber = Intl.NumberFormat(locale).format(number)
+    expect(localeNumber(locale)(formattedNumber)).toBe(number)
+  })
+
+  it.each([
+    '1 000 172,3', '1,000,172.30',
+  ])('is undefined when number is formatted in a different locale; %j', (value) => {
+    expect(localeNumber('de-DE')(value)).toBeUndefined()
+  })
+
+  it.each([
+    '', 'NaN', 'Infinity', 'null', 'abc',
+  ])('is undefined for non-numbers; %j', (value) => {
+    expect(localeNumber('de-DE')(value)).toBeUndefined()
+  })
+})
diff --git a/locale/localeNumber.ts b/locale/localeNumber.ts
new file mode 100644
index 0000000..dc3f149
--- /dev/null
+++ b/locale/localeNumber.ts
@@ -0,0 +1,40 @@
+/* eslint-disable @typescript-eslint/no-non-null-assertion */
+
+export type Locale = string // todo: ideally 'de-DE' | 'us-US' | 'fr-FR' | ...
+
+/**
+ * Parses number formatted as a local string (must still consist of 0-9 digits)
+ * using Intl.NumberFormat(locale) to determine decimal and group separators
+ */
+export const localeNumber = (locale: Locale) => (number: string): number | undefined => {
+  if (number.length === 0) return undefined
+
+  const { decimal, group, minusSign } = cachedSeparators(locale)
+  const parsed = Number(
+    number.replace(minusSign, '-').replaceAll(group, '').replaceAll(decimal, '.')
+  )
+  return Number.isFinite(parsed) ? parsed : undefined
+}
+
+/*
+ * Example:
+ *   const germanNumber = localeNumber('de-DE')
+ *   const n = germanNumber('-2.777.227,19') // -> -2777227.19
+ */
+
+type LocaleSeparators = { locale: Locale, decimal: string, group: string, minusSign: string }
+
+const localeSeparators = (locale: Locale): LocaleSeparators => {
+  const parts = new Intl.NumberFormat(locale).formatToParts(-10000.1)
+  return {
+    locale,
+    decimal: parts.find(p => p.type === 'decimal')!.value,
+    group: parts.find(p => p.type === 'group')!.value,
+    minusSign: parts.find(p => p.type === 'minusSign')!.value,
+  }
+}
+
+const cachedSeparators = (locale: Locale): LocaleSeparators =>
+  separators.get(locale) ?? separators.set(locale, localeSeparators(locale)).get(locale)!
+
+const separators = new Map<Locale, LocaleSeparators>()
diff --git a/tsconfig.json b/tsconfig.json
index 7188578..c9f8ce2 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -6,7 +6,7 @@
     /* Base Options */
     "esModuleInterop": true,
     "skipLibCheck": true,
-    "target": "ESNext",
+    "target": "ES2022",
     "allowJs": true,
     "resolveJsonModule": true,
     "moduleDetection": "force",
@@ -27,7 +27,7 @@
     "strictNullChecks": true,
 
     /* Libs */
-    "lib": ["ESNext"],
+    "lib": ["ES2022"],
     "types": ["node", "./json/index.d.ts"],
 
     "outDir": "./dist"