Restructure model

Model/Accounts/InstancesModel.swift

@@ -0,0 +1,47 @@
+import Defaults
+import Foundation
+
+final class InstancesModel: ObservableObject {
+    var all: [Instance] {
+        Defaults[.instances]
+    }
+
+    var lastUsed: Instance? {
+        guard let id = Defaults[.lastInstanceID] else {
+            return nil
+        }
+
+        return InstancesModel.find(id)
+    }
+
+    static func find(_ id: Instance.ID?) -> Instance? {
+        guard id != nil else {
+            return nil
+        }
+
+        return Defaults[.instances].first { $0.id == id }
+    }
+
+    static func accounts(_ id: Instance.ID?) -> [Account] {
+        Defaults[.accounts].filter { $0.instanceID == id }
+    }
+
+    static func add(app: VideosApp, name: String, url: String) -> Instance {
+        let instance = Instance(app: app, id: UUID().uuidString, name: name, url: url)
+        Defaults[.instances].append(instance)
+
+        return instance
+    }
+
+    static func remove(_ instance: Instance) {
+        let accounts = InstancesModel.accounts(instance.id)
+        if let index = Defaults[.instances].firstIndex(where: { $0.id == instance.id }) {
+            Defaults[.instances].remove(at: index)
+            accounts.forEach { AccountsModel.remove($0) }
+        }
+    }
+
+    static func setLastAccount(_ account: Account?) {
+        Defaults[.lastAccountID] = account?.id
+    }
+}