Improve history, resume videos, mark watched videos (fixes #42)

Model/Watch.swift

@@ -0,0 +1,47 @@
+import CoreData
+import Defaults
+import Foundation
+
+@objc(Watch)
+final class Watch: NSManagedObject, Identifiable {
+    @Default(.watchedThreshold) private var watchedThreshold
+}
+
+extension Watch {
+    @nonobjc class func fetchRequest() -> NSFetchRequest<Watch> {
+        NSFetchRequest<Watch>(entityName: "Watch")
+    }
+
+    @NSManaged var videoID: String
+    @NSManaged var videoDuration: Double
+
+    @NSManaged var watchedAt: Date?
+    @NSManaged var stoppedAt: Double
+
+    var progress: Double {
+        guard videoDuration.isFinite, !videoDuration.isZero else {
+            return 0
+        }
+
+        let progress = (stoppedAt / videoDuration) * 100
+        return min(max(progress, 0), 100)
+    }
+
+    var finished: Bool {
+        progress >= Double(watchedThreshold)
+    }
+
+    var watchedAtString: String? {
+        guard let watchedAt = watchedAt else {
+            return nil
+        }
+
+        if watchedAt.timeIntervalSinceNow < 5 {
+            return "just now"
+        }
+
+        let formatter = RelativeDateTimeFormatter()
+        formatter.unitsStyle = .full
+        return formatter.localizedString(for: watchedAt, relativeTo: Date())
+    }
+}