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Implement the LiveObject.canApplyOperation method
Based on [1] at 29276a5. Development approach as described in cb427d8. [1] ably/specification#343
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‎Sources/AblyLiveObjects/Internal/LiveObjectMutableState.swift‎

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internal import AblyPlugin
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/// This is the equivalent of the `LiveObject` abstract class described in RTLO.
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///
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/// ``DefaultLiveCounter`` and ``DefaultLiveMap`` include it by composition.
@@ -8,4 +10,41 @@ internal struct LiveObjectMutableState {
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internal var siteTimeserials: [String: String] = [:]
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// RTLO3c
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internal var createOperationIsMerged = false
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/// Represents parameters of an operation that `canApplyOperation` has decided can be applied to a `LiveObject`.
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///
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/// The key thing is that it offers a non-nil `serial` and `siteCode`, which will be needed when subsequently performing the operation.
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internal struct ApplicableOperation: Equatable {
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internal let objectMessageSerial: String
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internal let objectMessageSiteCode: String
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}
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/// Indicates whether an operation described by an `ObjectMessage` should be applied or discarded, per RTLO4a.
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///
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/// Instead of returning a `Bool`, in the case where the operation can be applied it returns a non-nil `ApplicableOperation` (whose non-nil `serial` and `siteCode` will be needed as part of subsequently performing this operation).
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internal func canApplyOperation(objectMessageSerial: String?, objectMessageSiteCode: String?, logger: Logger) -> ApplicableOperation? {
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// RTLO4a3: Both ObjectMessage.serial and ObjectMessage.siteCode must be non-empty strings
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guard let serial = objectMessageSerial, !serial.isEmpty,
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let siteCode = objectMessageSiteCode, !siteCode.isEmpty
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else {
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// RTLO4a3: Otherwise, log a warning that the object operation message has invalid serial values
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logger.log("Object operation message has invalid serial values: serial=\(objectMessageSerial ?? "nil"), siteCode=\(objectMessageSiteCode ?? "nil")", level: .warn)
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return nil
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}
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// RTLO4a4: Get the siteSerial value stored for this LiveObject in the siteTimeserials map using the key ObjectMessage.siteCode
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let siteSerial = siteTimeserials[siteCode]
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// RTLO4a5: If the siteSerial for this LiveObject is null or an empty string, return true
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guard let siteSerial, !siteSerial.isEmpty else {
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return ApplicableOperation(objectMessageSerial: serial, objectMessageSiteCode: siteCode)
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}
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// RTLO4a6: If the siteSerial for this LiveObject is not an empty string, return true if ObjectMessage.serial is greater than siteSerial when compared lexicographically
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if serial > siteSerial {
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return ApplicableOperation(objectMessageSerial: serial, objectMessageSiteCode: siteCode)
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}
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return nil
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}
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}

‎Tests/AblyLiveObjectsTests/LiveObjectMutableStateTests.swift‎

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

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