Implement the LiveObject.canApplyOperation method

Based on [1] at 2b5651e. Development approach as described in 4494033.

[1] ably/specification#343

Author: lawrence-forooghian

Sources/AblyLiveObjects/Internal/LiveObjectMutableState.swift

@@ -1,3 +1,5 @@
+internal import AblyPlugin
+
 /// This is the equivalent of the `LiveObject` abstract class described in RTLO.
 ///
 /// ``DefaultLiveCounter`` and ``DefaultLiveMap`` include it by composition.
@@ -8,4 +10,27 @@ internal struct LiveObjectMutableState {
     internal var siteTimeserials: [String: String] = [:]
     // RTLO3c
     internal var createOperationIsMerged = false
+
+    /// Indicates whether an operation described by an `ObjectMessage` should be applied or discarded, per RTLO4a.
+    internal func canApplyOperation(from objectMessage: InboundObjectMessage, logger: Logger) -> Bool {
+        // RTLO4a3: Both ObjectMessage.serial and ObjectMessage.siteCode must be non-empty strings
+        guard let serial = objectMessage.serial, !serial.isEmpty,
+              let siteCode = objectMessage.siteCode, !siteCode.isEmpty
+        else {
+            // RTLO4a3: Otherwise, log a warning that the object operation message has invalid serial values
+            logger.log("Object operation message has invalid serial values: serial=\(objectMessage.serial ?? "nil"), siteCode=\(objectMessage.siteCode ?? "nil")", level: .warn)
+            return false
+        }
+
+        // RTLO4a4: Get the siteSerial value stored for this LiveObject in the siteTimeserials map using the key ObjectMessage.siteCode
+        let siteSerial = siteTimeserials[siteCode]
+
+        // RTLO4a5: If the siteSerial for this LiveObject is null or an empty string, return true
+        guard let siteSerial, !siteSerial.isEmpty else {
+            return true
+        }
+
+        // RTLO4a6: If the siteSerial for this LiveObject is not an empty string, return true if ObjectMessage.serial is greater than siteSerial when compared lexicographically
+        return serial > siteSerial
+    }
 }

Tests/AblyLiveObjectsTests/LiveObjectMutableStateTests.swift

@@ -0,0 +1,116 @@
+import Ably
+@testable import AblyLiveObjects
+import AblyPlugin
+import Testing
+
+/// Tests for `LiveObjectMutableState`.
+struct LiveObjectMutableStateTests {
+    /// Tests for `LiveObjectMutableState.canApplyOperation`, covering RTLO4 specification points.
+    struct CanApplyOperationTests {
+        /// Test case data for canApplyOperation tests
+        struct TestCase {
+            let description: String
+            let objectMessageSerial: String?
+            let objectMessageSiteCode: String?
+            let siteTimeserials: [String: String]
+            let expectedResult: Bool
+        }
+
+        // @spec RTLO4a3
+        // @spec RTLO4a4
+        // @spec RTLO4a5
+        // @spec RTLO4a6
+        @Test(arguments: [
+            // RTLO4a3: Both ObjectMessage.serial and ObjectMessage.siteCode must be non-empty strings
+            TestCase(
+                description: "serial is nil, siteCode is valid - should return false",
+                objectMessageSerial: nil,
+                objectMessageSiteCode: "site1",
+                siteTimeserials: [:],
+                expectedResult: false,
+            ),
+            TestCase(
+                description: "serial is empty string, siteCode is valid - should return false",
+                objectMessageSerial: "",
+                objectMessageSiteCode: "site1",
+                siteTimeserials: [:],
+                expectedResult: false,
+            ),
+            TestCase(
+                description: "serial is valid, siteCode is nil - should return false",
+                objectMessageSerial: "serial1",
+                objectMessageSiteCode: nil,
+                siteTimeserials: [:],
+                expectedResult: false,
+            ),
+            TestCase(
+                description: "serial is valid, siteCode is empty string - should return false",
+                objectMessageSerial: "serial1",
+                objectMessageSiteCode: "",
+                siteTimeserials: [:],
+                expectedResult: false,
+            ),
+            TestCase(
+                description: "both serial and siteCode are invalid - should return false",
+                objectMessageSerial: nil,
+                objectMessageSiteCode: "",
+                siteTimeserials: [:],
+                expectedResult: false,
+            ),
+
+            // RTLO4a5: If the siteSerial for this LiveObject is null or an empty string, return true
+            TestCase(
+                description: "siteSerial is nil (siteCode doesn't exist) - should return true",
+                objectMessageSerial: "serial2",
+                objectMessageSiteCode: "site1",
+                siteTimeserials: ["site2": "serial1"], // i.e. only has an entry for a different siteCode
+                expectedResult: true,
+            ),
+            TestCase(
+                description: "siteSerial is empty string - should return true",
+                objectMessageSerial: "serial2",
+                objectMessageSiteCode: "site1",
+                siteTimeserials: ["site1": "", "site2": "serial1"],
+                expectedResult: true,
+            ),
+
+            // RTLO4a6: If the siteSerial for this LiveObject is not an empty string, return true if ObjectMessage.serial is greater than siteSerial when compared lexicographically
+            TestCase(
+                description: "serial is greater than siteSerial lexicographically - should return true",
+                objectMessageSerial: "serial2",
+                objectMessageSiteCode: "site1",
+                siteTimeserials: ["site1": "serial1"],
+                expectedResult: true,
+            ),
+            TestCase(
+                description: "serial is less than siteSerial lexicographically - should return false",
+                objectMessageSerial: "serial1",
+                objectMessageSiteCode: "site1",
+                siteTimeserials: ["site1": "serial2"],
+                expectedResult: false,
+            ),
+            TestCase(
+                description: "serial equals siteSerial - should return false",
+                objectMessageSerial: "serial1",
+                objectMessageSiteCode: "site1",
+                siteTimeserials: ["site1": "serial1"],
+                expectedResult: false,
+            ),
+        ])
+        func canApplyOperation(testCase: TestCase) {
+            let state = LiveObjectMutableState(
+                objectID: "test:object@123",
+                siteTimeserials: testCase.siteTimeserials,
+            )
+            let objectMessage = TestFactories.inboundObjectMessage(
+                serial: testCase.objectMessageSerial,
+                siteCode: testCase.objectMessageSiteCode,
+            )
+            let logger = TestLogger()
+
+            let result = state.canApplyOperation(from: objectMessage, logger: logger)
+
+            #expect(result == testCase.expectedResult, "Expected \(testCase.expectedResult) for case: \(testCase.description)")
+        }
+    }
+}