Switch TimelineItems to use an OrderedDictionary

Shared/Extensions/OrderedDictionary.swift

@@ -0,0 +1,64 @@
+//
+//  OrderedDictionary.swift
+//  SwiftDataStructures
+//
+//  Created by Tim Ekl on 6/2/14.
+//  Copyright (c) 2014 Tim Ekl. Available under MIT License. See LICENSE.md.
+//
+
+import Foundation
+
+struct OrderedDictionary<Tk: Hashable, Tv> {
+	var keys: Array<Tk> = []
+	var values: Dictionary<Tk,Tv> = [:]
+	
+	var count: Int {
+		assert(keys.count == values.count, "Keys and values array out of sync")
+		return self.keys.count;
+	}
+	
+	// Explicitly define an empty initializer to prevent the default memberwise initializer from being generated
+	init() {}
+	
+	subscript(index: Int) -> Tv? {
+		get {
+			let key = self.keys[index]
+			return self.values[key]
+		}
+		set(newValue) {
+			let key = self.keys[index]
+			if (newValue != nil) {
+				self.values[key] = newValue
+			} else {
+				self.values[key] = nil
+				self.keys.remove(at: index)
+			}
+		}
+	}
+	
+	subscript(key: Tk) -> Tv? {
+		get {
+			return self.values[key]
+		}
+		set(newValue) {
+			if newValue == nil {
+				self.values[key] = nil
+				self.keys = self.keys.filter {$0 != key}
+			} else {
+				let oldValue = self.values.updateValue(newValue!, forKey: key)
+				if oldValue == nil {
+					self.keys.append(key)
+				}
+			}
+		}
+	}
+	
+	var description: String {
+		var result = "{\n"
+		for i in 0..<self.count {
+			result += "[\(i)]: \(self.keys[i]) => \(String(describing: self[i]))\n"
+		}
+		result += "}"
+		return result
+	}
+}