Circle of Fifths in Swift: Notes for Key

circlefifths.swift

import Foundation

// randomly thinking about how you might use circle of fifths to return notes in any given musical Key
enum KeySignature:String {
    case A, B, C, CSharp = "C♯",D, E, F, G, AFlat = "A♭", BFlat = "B♭", CFlat = "C♭", DFlat = "D♭", EFlat = "E♭", GFlat = "G♭"
    case Am, Bm, Cm, Dm, Em, Fm, Gm, FSharpm = "F♯m", CSharpm = "C♯m", GSharpm = "G♯m", EFlatm = "E♭m", BFlatm = "B♭m", AFlatm = "A♭m", ASharpm = "A♯m"
    func major() -> KeySignature {
        switch self {
        case .Am:
           return KeySignature.C
        case .Em:
            return KeySignature.G
        case .Bm:
            let b = KeySignature.D
            return b
        case .FSharpm:
            return KeySignature.A
        case .CSharpm:
            return KeySignature.E
        case .GSharpm:
            return KeySignature.B
        case .EFlatm:
            return KeySignature.GFlat
        case .BFlatm:
            return KeySignature.DFlat
        case .Fm:
            return KeySignature.AFlat
        case .Cm:
            return KeySignature.EFlat
        case .Gm:
            return KeySignature.BFlat
        case .Dm:
            return KeySignature.F
        case .AFlatm:
            return KeySignature.CFlat
        case .ASharpm:
            return KeySignature.CSharp
        default:
            return self
        }
        
    }
    
    func notesForKey() -> [String] {
        var k = ["C","D","E","F","G","A","B"]
        let key = self.major()
        if key.rawValue == "F" || key.rawValue.characters.last == "♭" {
            repeat {
                k = [String](k.suffix(4) + k.prefix(3))
                k[3] = k[3] + "♭"
            }
                while key.rawValue != k[0]
        }
        else {
            while key.rawValue != k[0] {
                k = [String](k.suffix(3) + k.prefix(4))
                k[6] = k[6] + "♯"
            }
        }
        // Fixes ordering for relative minors
        var ind = 0
        for i in k.enumerated() {
            if i.element.first == self.rawValue.first {
                ind = i.offset
            }
        }
        let arraySlice = k[k.index(k.startIndex, offsetBy: ind)..<k.endIndex] + k[k.startIndex..<k.index(k.startIndex, offsetBy: ind)]
        
        return Array(arraySlice)
    }
    
}


KeySignature.E.notesForKey() // ["E", "F♯", "G♯", "A", "B", "C♯", "D♯"]
KeySignature.BFlatm.notesForKey() // ["B♭", "C", "D♭", "E♭", "F", "G♭", "A♭"]