refactor and cleanup [skip ci]

submodules/Postbox/Sources/PreferencesView.swift

@@ -0,0 +1,59 @@
+import Foundation
+
+final class MutablePreferencesView: MutablePostboxView {
+    fileprivate let keys: Set<ValueBoxKey>
+    fileprivate var values: [ValueBoxKey: PreferencesEntry]
+    
+    init(postbox: Postbox, keys: Set<ValueBoxKey>) {
+        self.keys = keys
+        var values: [ValueBoxKey: PreferencesEntry] = [:]
+        for key in keys {
+            if let value = postbox.preferencesTable.get(key: key) {
+                values[key] = value
+            }
+        }
+        self.values = values
+    }
+    
+    func replay(postbox: Postbox, transaction: PostboxTransaction) -> Bool {
+        var updated = false
+        for operation in transaction.currentPreferencesOperations {
+            switch operation {
+                case let .update(key, value):
+                    if self.keys.contains(key) {
+                        let currentValue = self.values[key]
+                        var updatedValue = false
+                        if let value = value, let currentValue = currentValue {
+                            if !value.isEqual(to: currentValue) {
+                                updatedValue = true
+                            }
+                        } else if (value != nil) != (currentValue != nil) {
+                            updatedValue = true
+                        }
+                        if updatedValue {
+                            if let value = value {
+                                self.values[key] = value
+                            } else {
+                                self.values.removeValue(forKey: key)
+                            }
+                            updated = true
+                        }
+                    }
+            }
+        }
+        
+        return updated
+    }
+    
+    func immutableView() -> PostboxView {
+        return PreferencesView(self)
+    }
+}
+
+public final class PreferencesView: PostboxView {
+    public let values: [ValueBoxKey: PreferencesEntry]
+    
+    init(_ view: MutablePreferencesView) {
+        self.values = view.values
+    }
+}