// Helpers

function appendElement(parentElement, tag) {
  element = document.createElement(tag)
  parentElement.appendChild(element)
  return element
}
  
function appendText(parentElement, text) {
  element = document.createTextNode(text)
  parentElement.appendChild(element)
  return element
}

// Only suggest sharps for the moment
tonalities = ['C', 'C♯', 'D', 'D♯', 'E', 'F', 'F♯', 'G', 'G♯', 'A', 'A♯', 'B']

function getRoot(c) {
  if (c.indexOf('♯') > -1 || c.indexOf('♭') > -1) {
    return c.substring(0, 2)
  } else {
    return c[0]
  }
}

function getShift(t1, t2) {
  return tonalities.indexOf(getRoot(t2)) - tonalities.indexOf(getRoot(t1))
}

function applyShift(t1, s) {
  let root = getRoot(t1)
  let mode = t1.substring(root.length)
  root = tonalities[(tonalities.indexOf(root) + s + tonalities.length) % tonalities.length]
  return `${root}${mode}`
}


const node = document.querySelector('[data-tonality]')
let tonality = node.dataset.tonality
mode = tonality[tonality.length - 1] == 'm' ? 'm' : ''

label = appendElement(node, 'label')
label['className'] = 'g-Chords__Tonality'
label.onchange = (e) => {
  const shift = getShift(tonality, e.target.value)
  tonality = e.target.value
  document.querySelectorAll('.g-Chords__Chord').forEach(chord => {
    if (chord.innerText !== '%') {
      chord.innerText = applyShift(chord.innerText, shift)
    }
  })
}

appendText(label, 'Tonalité :')

select = appendElement(label, 'select')
select['name'] = 'tonality'
tonalities.forEach(t => {
  option = appendElement(select, 'option')
  option['value'] = t
  if (tonality == `${t}${mode}`) {
    option['selected'] = true
  }
  appendText(option, `${t}${mode}`)
})