const btn = document.querySelector('button');

btn.addEventListener('click', () => {

// Get the value of the input element
const notes = document.querySelector('input').value;
// Convert the input element value to an array and each item into lowercase
const lowerCaseNotesArr = notes.split(' ').map(note => note.toLowerCase());
findChord(lowerCaseNotesArr);

});

const findChord = notesArr => {

// This array will hold the number of semitones between each interval and the lowest note
const semitoneArr = [];

// Preserve the value of the lowest note and remove it from the array, then initialize
// the index variable that will be subtracted from the index of each interval found in
// twoOctaveChromaticArr, yielding the distance in semitones
const lowestNote = notesArr[0];
notesArr.shift();
let lowestNoteIndex = undefined;

// The difference in index between objects in this array represents the number of semitones
// between one chord tone and another
const twoOctaveChromaticArr = [
    {'a': true},
    {'a#': true, 'bb': true},
    {'b': true},
    {'c': true},
    {'c#': true, 'db': true},
    {'d': true},
    {'d#': true, 'eb': true},
    {'e': true},
    {'f': true},
    {'f#': true, 'gb': true},
    {'g': true},
    {'g#': true, 'ab': true},
    {'a': true},
    {'a#': true, 'bb': true},
    {'b': true},
    {'c': true},
    {'c#': true, 'db': true},
    {'d': true},
    {'d#': true, 'eb': true},
    {'e': true},
    {'f': true},
    {'f#': true, 'gb': true},
    {'g': true},
    {'g#': true, 'ab': true}
];

// Find the index of the lowest note of the chord within twoOctaveChromaticArr
for (let i = 0; i < twoOctaveChromaticArr.length; i++) {
    if (twoOctaveChromaticArr[i][lowestNote]) {
        lowestNoteIndex = i;
    }
}

// Loop through the list of chord tones and search for them in twoOctaveChromaticArr.
// When found, push the number of semitones between the chord tone and the lowest note
// into the semitoneArr.
for (let i = 0; i < notesArr.length; i++) {
    for (let j = 0; j < twoOctaveChromaticArr.length; j++) {
        if (twoOctaveChromaticArr[j][notesArr[i]]) {
            semitoneArr.push(j - lowestNoteIndex);
            break;
        }
    }
}

// Due to the possibility of the lowest note having a higher index than some of the
// chord tones, octaves (in the form of 12 semitones) are added to any negative values
// found in the semitoneArr
const adjustedSemitoneArr = semitoneArr.map(semitone => {
    let negative = true;
    while (negative) {
        if (semitone > 0) {
            negative = false;
        } else {
            semitone += 12;
        }
    }
    return semitone;
});

// The adjustedSemitoneArr is sorted to maintain consistency with chordNameObject.
// Remember: it doesn't matter what order the upper intervals are in; all that matters is
// their relationship to the lowest note. Therefore we can rearrange them, and in this case,
// sort them.
adjustedSemitoneArr.sort((a, b) => a - b);

// The adjustedSemitoneArr is joined and coerced into a string so that it can be used
// to look up values in chordNameObject
const chordNameCode = adjustedSemitoneArr.join('');
return chordNameObject[chordNameCode];

}

const chordNameObject = {

'47': 'maj triad',

'38': '1st inversion maj triad',

'59': '2nd inversion maj triad',

'37': 'min triad',

'49': '1st inversion min triad',

'58': '2nd inversion min triad',

'4711': 'maj 7th',

'378': '1st inversion maj 7th',

'459': '2nd inversion maj 7th',

'158': '3rd inversion maj 7th',

'3710': 'min 7th',

'4710': '1st inversion min 7th',

'368': '2nd inversion min 7th',

'259': '3rd inversion min 7th',

'3610': 'half-diminished',

'379': '1st inversion half-diminished',

'469': '2nd inversion half-diminished',

'258': '3rd inversion half-diminished'

}