create ER diagram, refactor to conform to diagram, simplify session management

WorkoutsPlus/Models/WorkoutItem.swift

@@ -41,9 +41,10 @@ final class WorkoutItem: Nameable, Positionable {
 		var position: Int = 0
 		var set: [WorkoutItem] = []
 		
-		var exercise: Exercise? 	   //	Do Push-up 	| Run Marathon
-		var reps: Int												   // 8 times 				| 1 time
-		var value: Double?							   // With 10 				| 42,187
+		// Exercise has to be optional to allow Rest and Set to be a WorkoutItem (without being an Exercise).
+		var exerciseData: Exercise? 	   //	Do Push-up 	| Run Marathon
+		var plannedReps: Int												   // 8 times 				| 1 time
+		var plannedValue: Double							    // With 10 				| 42,187
 		var metric: ExerciseMetric? // kg (weight) | km (distance)
 		
 		enum WorkoutItemType: Codable {
@@ -53,15 +54,15 @@ final class WorkoutItem: Nameable, Positionable {
 		}
 		
 		init(_ exercise: Exercise) {
-				self.exercise = exercise
+				self.exerciseData = exercise
 				self.workoutItemType = .exercise
 				
 				// Push-up
 				self.name = exercise.name
 				// 8x
-				self.reps = 1
+				self.plannedReps = 1
 				// 0
-				self.value = 0
+				self.plannedValue = 0
 				// kg
 				self.metric = exercise.metric
 		}
@@ -69,7 +70,8 @@ final class WorkoutItem: Nameable, Positionable {
 		init(set: [WorkoutItem] = []) {
 				self.workoutItemType = .set
 				self.name = "Set"
-				self.reps = 3
+				self.plannedReps = 3
+				self.plannedValue = 0
 				set.forEach(addChild)
 		}
 		
@@ -82,8 +84,8 @@ final class WorkoutItem: Nameable, Positionable {
 		init(rest: Double) {
 				self.workoutItemType = .rest
 				self.name = "Rest"
-				self.reps = 1
-				self.value = rest
+				self.plannedReps = 1
+				self.plannedValue = rest
 				self.metric = .time
 		}
 }