From ba085eee0809ac58b2ca3382076ba83263d89e5c Mon Sep 17 00:00:00 2001
From: Alexander Lichter <manniL@gmx.net>
Date: Mon, 19 Aug 2019 01:00:45 +0200
Subject: [PATCH 1/2] feat: add numbers to words

---
 src/numbersToWords.js       | 64 +++++++++++++++++++++++++++++++++++++
 test/numbersToWords.test.js | 22 +++++++++++++
 2 files changed, 86 insertions(+)
 create mode 100644 src/numbersToWords.js
 create mode 100644 test/numbersToWords.test.js

diff --git a/src/numbersToWords.js b/src/numbersToWords.js
new file mode 100644
index 0000000..2699786
--- /dev/null
+++ b/src/numbersToWords.js
@@ -0,0 +1,64 @@
+// https://stackoverflow.com/a/30524915/3975480
+
+const arr = x => Array.from(x)
+const num = x => Number(x) || 0
+const isEmpty = xs => xs.length === 0
+const take = n => xs => xs.slice(0, n)
+const drop = n => xs => xs.slice(n)
+const reverse = xs => xs.slice(0).reverse()
+const pipe = f => g => x => g(f(x))
+const not = x => !x
+const chunk = n => xs => isEmpty(xs) ? [] : [take(n)(xs), ...chunk(n)(drop(n)(xs))]
+
+const a = [
+  '', 'one', 'two', 'three', 'four',
+  'five', 'six', 'seven', 'eight', 'nine',
+  'ten', 'eleven', 'twelve', 'thirteen', 'fourteen',
+  'fifteen', 'sixteen', 'seventeen', 'eighteen', 'nineteen'
+]
+
+const onesWithZero = ['zero', ...a.slice(1)]
+
+const b = [
+  '', '', 'twenty', 'thirty', 'forty',
+  'fifty', 'sixty', 'seventy', 'eighty', 'ninety'
+]
+const g = [
+  '', 'thousand', 'million', 'billion', 'trillion', 'quadrillion',
+  'quintillion', 'sextillion', 'septillion', 'octillion', 'nonillion'
+]
+
+export const encode = n => numToWords(String(n)).trim()
+export const decode = str => Number(str.split(' ').map(numberExpression => numberExpression === 'point' ? '.' : onesWithZero.findIndex(matched => matched === numberExpression.toLowerCase())).join(''))
+
+// numToWords :: (Number a, String a) => a -> String
+const numToWords = n => {
+  if (n === '0') {
+    return onesWithZero[0]
+  }
+
+  const isDecimal = n.match(/(.*)\.(.*)/)
+
+  if (isDecimal) {
+    const [, beforePoint, afterPoint] = isDecimal
+    return numToWords(beforePoint) + 'point ' + afterPoint.split('').map(numToWords).join('')
+  }
+
+  // this part is really nasty still
+  // it might edit this again later to show how Monoids could fix this up
+  const makeGroup = ([ones, tens, huns]) => [
+    num(huns) === 0 ? '' : a[huns] + ' hundred ',
+    num(ones) === 0 ? b[tens] : (b[tens] && b[tens] + '-') || '',
+    a[tens + ones] || a[ones]
+  ].join('')
+
+  // "thousands" constructor; no real good names for this, i guess
+  const thousand = (group, i) => group === '' ? group : `${group} ${g[i]}`
+
+  return pipe(reverse)(chunk(3))(arr(n))
+    .map(makeGroup)
+    .map(thousand)
+    .filter(pipe(isEmpty)(not))
+    .reverse()
+    .join(' ')
+}
diff --git a/test/numbersToWords.test.js b/test/numbersToWords.test.js
new file mode 100644
index 0000000..02bc90e
--- /dev/null
+++ b/test/numbersToWords.test.js
@@ -0,0 +1,22 @@
+import { decode, encode } from 'numbersToWords'
+
+const resultPairs = [
+  [1.234562343, 'one point two three four five six two three four three'],
+  [1, 'one']
+]
+
+describe('encoding', () => {
+  test('default', () => {
+    resultPairs.forEach(([input, output]) => {
+      expect(encode(input)).toBe(output)
+    })
+  })
+})
+
+describe('decoding', () => {
+  test('default', () => {
+    resultPairs.forEach(([output, input]) => {
+      expect(decode(input)).toBe(output)
+    })
+  })
+})

From bd28841dc0bd43bbff35439ca7a3ba8e76e15314 Mon Sep 17 00:00:00 2001
From: Alexander Lichter <manniL@gmx.net>
Date: Mon, 19 Aug 2019 01:16:32 +0200
Subject: [PATCH 2/2] fix: issues with zero in number string

---
 src/numbersToWords.js       | 2 +-
 test/numbersToWords.test.js | 6 ++++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/numbersToWords.js b/src/numbersToWords.js
index 2699786..3438cb4 100644
--- a/src/numbersToWords.js
+++ b/src/numbersToWords.js
@@ -34,7 +34,7 @@ export const decode = str => Number(str.split(' ').map(numberExpression => numbe
 // numToWords :: (Number a, String a) => a -> String
 const numToWords = n => {
   if (n === '0') {
-    return onesWithZero[0]
+    return `${onesWithZero[0]} `
   }
 
   const isDecimal = n.match(/(.*)\.(.*)/)
diff --git a/test/numbersToWords.test.js b/test/numbersToWords.test.js
index 02bc90e..d454452 100644
--- a/test/numbersToWords.test.js
+++ b/test/numbersToWords.test.js
@@ -1,8 +1,10 @@
 import { decode, encode } from 'numbersToWords'
 
 const resultPairs = [
-  [1.234562343, 'one point two three four five six two three four three'],
-  [1, 'one']
+  [1.2345678901, 'one point two three four five six seven eight nine zero one'],
+  [1, 'one'],
+  [3.012001, 'three point zero one two zero zero one'],
+  [0, 'zero']
 ]
 
 describe('encoding', () => {