JsonLogicKMP

Kotlin multiplatform JsonLogic expressions evaluation engine. Targets iOS and JVM (also Android). The JsonLogic format is designed to allow you to share rules (logic) between front-end and back-end code.

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Gradle build system

repositories {
    mavenCentral()
}

dependencies {
    // JVM & Android targets
    implementation "pl.allegro.mobile:json-logic-core-jvm:1.0.0"
    implementation "pl.allegro.mobile:json-logic-operations-stdlib-jvm:1.0.0"
    // KMP target
    implementation "pl.allegro.mobile:json-logic-core:1.0.0"
    implementation "pl.allegro.mobile:json-logic-operations-stdlib:1.0.0"
}

Swift Package Manager

The Swift Package Manager is a tool for automating the distribution of Swift code and is integrated into the swift compiler.

Once you have your Swift package set up, adding Alamofire as a dependency is as easy as adding it to the dependencies value of your Package.swift.

dependencies: [
    .package(url: "https://github.com/allegro/json-logic-kmp", .exact("1.0.0"))
]

CocoaPods

To integrate JsonLogicKMP with your Xcode project using CocoaPods, specify it in your Podfile:

pod 'JsonLogicKMP'

How to initialize the engine?

Logic evalautor is initialized by simply building it. All of the json-logic standard operations are added by default.

Log operation is an exception which requires a callback function to log values. It's added by special function addLogger().

Initialization in Kotlin:

val jsonLogicLoggingCallback: (Any?) -> Unit = { Log.d("JsonLogicEngine-log: $it") }

fun buildJsonLogicEngineWithLogger(): JsonLogicEngine {
    return JsonLogicEngine
        .Builder()
        .addLogger(jsonLogicLoggingCallback)
        .build()    
}

and Swift:

    let logger = Logger(subsystem: "JsonLogicKMP", category: "JsonLogic")
    let jsonLogicLoggingCallback: (Any?) -> Void = {
        guard let message = $0 else { return }
        logger.debug("\(String(describing: message), privacy: .private)")
    }
    
    func buildJsonLogicEngineWithLogger(): JsonLogicEngine = JsonLogicKMP.JsonLogicEngineBuilder()
        .addLogger(loggingCallback: jsonLogicLoggingCallback)
        .build()

To expand the possibilities of the engnine add our additional standard library with more Kotlin based operators. To do it use OperationsProvider and its ready-to-use operations sets.

On Kotlin target:

fun buildJsonLogicEngineWithStandardOperations(): JsonLogicEngine {
    return JsonLogicEngine
        .Builder()
        .addStandardOperations(OperationsProvider.standardOperations)
        .addFunctionalOperations(OperationsProvider.functionalOperations)
        .build()
}

and Swift one:

    func buildJsonLogicEngineWithLogger(): JsonLogicEngine {
        return JsonLogicKMP.JsonLogicEngineBuilder()
            .addStandardOperations(operations: OperationsProvider.shared.standardOperations)
            .addFunctionalOperations(operations: OperationsProvider.shared.functionalOperations)
            .build()
    }

Json logic expressions evaluation

Logic expressions are represented by maps where key is operation name and value is arguments. User might provide some additional input using data parameter.

Example of expression evaluation in Kotlin is shown below:

fun evaluateAdditionOperation(): JsonLogicResult {
    val logicEngine = JsonLogicEngine.Builder().build()
    val expression = mapOf("+" to listOf(1, mapOf("var" to "second")))
    val data = mapOf("second" to 2)
    
    return logicEngine.evaluate(expression, data)
}

and in Swift:

func evaluateAdditionOperation() -> JsonLogicResult {
    let engine = JsonLogicKMP.JsonLogicEngineBuilder().build()
    let logicExpression: [String: Any] = ["+": [1, ["var": "second"]]]
    let logicData: [String: Any] = ["second": 2]
        
    return engine.evaluate(expression: logicExpression, data: logicData)
}

Expressions evaluation results are type of JsonLogicResult. It indicates if evaluation is successful or what kind of error occured.

Custom operations

There is a possibility to create more json logic operations with simple api available in operations-api module.

Using gradle just add proper dependency and write your own logic:

repositories {
    mavenCentral()
}

dependencies {
    // JVM & Android targets
    implementation "pl.allegro.mobile:json-logic-operations-api-jvm:1.0.0"
    // KMP target
    implementation "pl.allegro.mobile:json-logic-operations-api:1.0.0"
}

For simple operation that doesn't evaluate any json logic expressions internally, use StandardLogicOperation interface:

object Size : StandardLogicOperation {
    override fun evaluateLogic(expression: Any?, data: Any?): Any? = (expression as? List<*>)?.size
}

For more complex operations use FunctionalLogicOperation interface:

object Find : FunctionalLogicOperation, EvaluatingUnwrapper {
    override fun evaluateLogic(expression: Any?, data: Any?, evaluator: LogicEvaluator): Any? {
        return expression.asList.let { expressionValues ->
            val inputData = unwrapDataByEvaluation(expressionValues, data, evaluator)
            val predicateOperation = expressionValues.getMappingOperationOrNull()

            predicateOperation?.let {
                inputData?.find { evaluator.evaluateLogic(predicateOperation, it) == true }
            }
        }
    }
}

Main difference between these two is that functional operations has access to some LogicEvaluator instance. It allows them to evaluate expressions internally.

To add custom operations in Kotlin implementation use:

fun initializeJsonLogicEngineWithCustomOperations(): JsonLogicEngine {
    return JsonLogicEngine
        .Builder()
        .addStandardOperation(operationName = "size", operation = Size)
        .addFunctionalOperation(operationName = "find", operation = Find)
        .build()
}

or in Swift:

func initializeJsonLogicEngineWithCustomOperations() -> JsonLogicEngine {
    return JsonLogicKMP.JsonLogicEngineBuilder()
        .addStandardOperation(operationName: "size", operation: Size.shared)
        .addFunctionalOperation(operationName: "find", operation: Find.shared)
        .build()
}

Contribution

If you have any idea on how to improve this project just submit a pull request. Provide some description about changes and examples. When your PR is approved by 2 reviewers it is ready to merge!

License

JsonLogicKMP is published under Apache License 2.0.