Discussion on: Daily Challenge #217 - SMS w/ an Old Phone

const sendMessage = (msg) => {
  const keys = ['1', '2', '3', '4', '5', '6', '7', '8', '9', '*', '0', '#']
  const letters = ['.,?!', 'abc', 'def', 'ghi', 'jkl', 'mno', 'pqrs', 'tuv', 'wxyz', '-+=']
  const letterKeyMap = {}
  letters.forEach((ls, i) => ls.split('').forEach((l, r) => letterKeyMap[l] = [i, r + 1]))
  const isLowerCase = (c) => c.toLowerCase() === c

  let caseUp = false
  let lastKey
  return msg.split('').map((c, i, a) => {
    let caseChange = ''
    let key = ''
    let extra = ''
    if (c === ' ') { // Space
      key = '0'
    } else if (keys.indexOf(c) >= 0) { // Number
      key = keys[keys.indexOf(c)]
      extra = `-`
    } else { // Letter
      if (caseUp && isLowerCase(c) || !caseUp && !isLowerCase(c)) {
        caseChange = '#'
        caseUp = !isLowerCase(c)
      }
      const [ki, repeat] = letterKeyMap[c.toLowerCase()]
      key = keys[ki]
      extra = key.repeat(repeat - 1)
    }
    const addSpace = key === lastKey && caseChange === '' ? ' ' : ''
    const res = `${addSpace}${caseChange}${key}${extra}`
    lastKey = res[res.length - 1]
    return res
  }).join('')
}

const test = (msg, expected) => {
  const result = sendMessage(msg)
  console.log(`${result.localeCompare(expected) === 0} ${msg} ${result} === ${expected}`)
}

test('Def Con 1!', '#3#33 3330#222#666 6601-1111')
test('hey', '4433999')
test('one two three', '666 6633089666084477733 33')
test('Hello World!', '#44#33555 5556660#9#66677755531111')
test('Hi dev.to!  Fun times.', '#44#44403 338881866611110 0#333#88660844463377771')