Improved performance of chords creation for a specific key by creating functions instead of creating them on init (#52)

* improved performance on chords creation for key by creating functions that only create the necessary

* fixed unit-tests

* converted functions to computed properties

Author: SebastianBoldt

Sources/Tonic/Key.swift

@@ -15,12 +15,6 @@ public struct Key: Equatable {
     /// A note set containing all the notes in the key
     public let noteSet: NoteSet
 
-    /// All the traditional triads representable root, third, and fifth from each note in the key
-    public let primaryTriads: [Chord]
-
-    /// All chords that fit in the key
-    public let chords: [Chord]
-
     /// Initialize the key
     /// - Parameters:
     ///   - root: The primary note class of the key, also known as the tonic
@@ -36,7 +30,36 @@ public struct Key: Equatable {
             }
         }
         noteSet = NoteSet(notes: r)
+    }
+
+    /// The type of accidental to use in this key
+    public var preferredAccidental: Accidental {
+        if root.accidental == .sharp {
+            return .sharp
+        }
+        if root.accidental == .flat {
+            return .flat
+        }
+
+        let naturalKeysWithFlats: [Key] = [.F, .d, .g, .c, .f]
+        if naturalKeysWithFlats.contains(self) {
+            return .flat
+        }
+        return .sharp
+    }
 
+    /// All chords that fit in the key
+    public var chords: [Chord] {
+        let table = ChordTable.shared
+        var chords: [Chord] = []
+        for (_, chord) in table.chords where chord.noteClassSet.isSubset(of: noteSet.noteClassSet) {
+            chords.append(Chord(chord.root, type: chord.type))
+        }
+        return chords
+    }
+
+    /// All the traditional triads representable root, third, and fifth from each note in the key
+    public var primaryTriads: [Chord] {
         let table = ChordTable.shared
 
         var chords: [Chord] = []
@@ -53,25 +76,7 @@ public struct Key: Equatable {
 
         let primaryTriadsStartingWithC = primaryTriads.sorted(by: { $0.root.letter < $1.root.letter })
         let rootPosition = primaryTriadsStartingWithC.firstIndex(where: { $0.root == root }) ?? 0
-        self.primaryTriads = Array(primaryTriadsStartingWithC.rotatingLeft(positions: rootPosition))
-
-        self.chords = chords
-    }
-
-    /// The type of accidental to use in this key
-    public var preferredAccidental: Accidental {
-        if root.accidental == .sharp {
-            return .sharp
-        }
-        if root.accidental == .flat {
-            return .flat
-        }
-
-        let naturalKeysWithFlats: [Key] = [.F, .d, .g, .c, .f]
-        if naturalKeysWithFlats.contains(self) {
-            return .flat
-        }
-        return .sharp
+        return Array(primaryTriadsStartingWithC.rotatingLeft(positions: rootPosition))
     }
 }