Introduce some basic chord progressions

[braaar]

We want to have some kind of harmonic logic in the app so that you can get chords that fit together harmonically.

In the harmonic style of 18th century european musicians, chords are grouped into their harmonic functions with a number from 1 to 7.

Function	Extension	Notes
I		The root (tonic)
II
III
IV		Subdominant
V		Dominant
VI
VII

In the C major scale, these chords are

• I: C major
• II: D minor
• III: E minor
• IV: F major
• V: G major
• VI: A minor
• VII: B dim

We want to write a function that will take some numbers and translate them into actual chords

const fourChords = {
  chords: [1, 5, 6, 4],
  mode: "major"
}
const keyCenter = "C";

writeChordProgression(fourChords, keyCenter); // returns [ "C", "G", "Am", "F"]

We can use this function alongside a large catalogue of chord progressions to get a random chord progression from the selection. If you grab two progressions you now have an A and B part you can alternate between.

getRandomProgression("C", "major"); // returns [ "C", "G", "Am", "F"]
getRandomProgression("C", "major"); // returns [ "C", "F", "G", "F"]

[braaar]

Four chords can get a bit tiring in the long run, so we probably want to add more chord progressions. We can write them in this format. We will store these in a large object or array directly in the source code for now (no need to add complexity and hosting costs by adding a database at this stage)

fourChordsMinor: { 
  chords: [1, 6, 3, 7]
  mode: "minor"
}

[braaar]

I think we can bring rhythm/time into this at a later point. For now let's assume that every chord has the same duration or an undefined duration that the user can figure out for themselves.

[braaar]

Let's get some 12 bar blues progressions!