refactor and cleanup [skip ci]

submodules/Postbox/Sources/SynchronizePeerReadStatesView.swift

@@ -0,0 +1,46 @@
+import Foundation
+
+final class MutableSynchronizePeerReadStatesView {
+    var operations: [PeerId: PeerReadStateSynchronizationOperation]
+    
+    init(operations: [PeerId: PeerReadStateSynchronizationOperation]) {
+        self.operations = operations
+    }
+    
+    func refreshDueToExternalTransaction(fetchSynchronizePeerReadStateOperations: () -> [PeerId: PeerReadStateSynchronizationOperation]) -> Bool {
+        let operations = fetchSynchronizePeerReadStateOperations()
+        if self.operations != operations {
+            self.operations = operations
+            return true
+        } else {
+            return false
+        }
+    }
+    
+    func replay(_ updatedOperations: [PeerId: PeerReadStateSynchronizationOperation?]) -> Bool {
+        var updated = false
+        for (peerId, operation) in updatedOperations {
+            if let operation = operation {
+                if self.operations[peerId] == nil || self.operations[peerId]! != operation {
+                    self.operations[peerId] = operation
+                    updated = true
+                }
+            } else {
+                if let _ = self.operations[peerId] {
+                    let _ = self.operations.removeValue(forKey: peerId)
+                    updated = true
+                }
+            }
+        }
+        
+        return updated
+    }
+}
+
+public final class SynchronizePeerReadStatesView {
+    public let operations: [PeerId: PeerReadStateSynchronizationOperation]
+    
+    init(_ mutableView: MutableSynchronizePeerReadStatesView) {
+        self.operations = mutableView.operations
+    }
+}