New account selection menu

Shared/Navigation/AccountsViewModel.swift

@@ -0,0 +1,36 @@
+import Foundation
+
+final class AccountsViewModel: ObservableObject {
+    typealias AreInIncreasingOrder = (Account, Account) -> Bool
+
+    var accounts: [Account] { AccountsModel.shared.all }
+
+    var sortedAccounts: [Account] {
+        accounts.sorted { lhs, rhs in
+            let predicates: [AreInIncreasingOrder] = [
+                { ($0.app ?? .local).rawValue < ($1.app ?? .local).rawValue },
+                { $0.urlHost < $1.urlHost },
+                { $0.description < $1.description }
+            ]
+
+            for predicate in predicates {
+                if !predicate(lhs, rhs), !predicate(rhs, lhs) {
+                    continue
+                }
+
+                return predicate(lhs, rhs)
+            }
+
+            return false
+        }
+    }
+
+    var publicAccount: Account? { AccountsModel.shared.publicAccount }
+    var currentAccount: Account? { AccountsModel.shared.current }
+
+    var instances: [Instance] { InstancesModel.shared.all }
+
+    func accountsOfInstance(_ instance: Instance) -> [Account] {
+        accounts.filter { $0.instance.apiURL == instance.apiURL }.sorted { $0.name < $1.name }
+    }
+}