Implement Logger.kt (#11)

build.gradle.kts

@@ -58,9 +58,9 @@ dependencies {
     api("org.apache.commons:commons-math3:3.6.1")
 
     // This dependency is used internally, and not exposed to consumers on their own compile classpath.
-    implementation("com.google.guava:guava:31.1-jre")
     implementation("net.swiftzer.semver:semver:1.3.0")
     implementation("com.goncalossilva:murmurhash:0.4.0")
+    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.6.0")
 }
 
 // Apply a specific Java toolchain to ease working on different environments.
@@ -80,3 +80,18 @@ tasks.named<Test>("test") {
         showStandardStreams = true
     }
 }
+
+// TODO: Remove excludes when Instance.kt is ready
+sourceSets {
+    main {
+        kotlin {
+            exclude("com/featurevisor/sdk/Instance.kt")
+            exclude("com/featurevisor/sdk/InstanceOptions.kt")
+        }
+    }
+    test {
+        kotlin {
+            exclude("com/featurevisor/sdk/InstanceTest.kt")
+        }
+    }
+}

src/main/kotlin/com/featurevisor/sdk/Logger.kt

@@ -0,0 +1,52 @@
+package com.featurevisor.sdk
+
+import com.featurevisor.sdk.LogLevel.*
+
+typealias LogMessage = String
+typealias LogDetails = Map<String, Any>
+typealias LogHandler = (level: LogLevel, message: LogMessage, details: LogDetails?) -> Unit
+
+enum class LogLevel(val value: String) {
+    ERROR("error"),
+    WARN("warn"),
+    INFO("info"),
+    DEBUG("debug")
+}
+
+class Logger(
+    private var levels: List<LogLevel>,
+    private val handle: LogHandler,
+) {
+
+    companion object {
+        private val defaultLogLevels: List<LogLevel> = listOf(ERROR, WARN)
+        private val defaultLogHandler: LogHandler = { level, message, _ ->
+            println("[${level.value}] $message")
+        }
+
+        fun createLogger(levels: List<LogLevel> = defaultLogLevels, handle: LogHandler = defaultLogHandler): Logger =
+            Logger(levels, handle)
+    }
+
+    fun setLevels(levels: List<LogLevel>) {
+        this.levels = levels
+    }
+
+    fun debug(message: LogMessage, details: LogDetails? = null) =
+        log(DEBUG, message, details)
+
+    fun info(message: LogMessage, details: LogDetails? = null) =
+        log(INFO, message, details)
+
+    fun warn(message: LogMessage, details: LogDetails? = null) =
+        log(WARN, message, details)
+
+    fun error(message: LogMessage, details: LogDetails? = null) =
+        log(ERROR, message, details)
+
+    private fun log(level: LogLevel, message: LogMessage, details: LogDetails? = null) {
+        if (level in levels) {
+            handle(level, message, details)
+        }
+    }
+}

src/test/kotlin/com/featurevisor/sdk/LoggerTest.kt

@@ -0,0 +1,108 @@
+package com.featurevisor.sdk
+
+import com.featurevisor.sdk.LogLevel.DEBUG
+import com.featurevisor.sdk.LogLevel.ERROR
+import com.featurevisor.sdk.LogLevel.INFO
+import com.featurevisor.sdk.LogLevel.WARN
+import io.mockk.every
+import io.mockk.mockk
+import io.mockk.verify
+import org.junit.jupiter.api.Test
+
+class LoggerTest {
+
+    private val mockLogMessage = "test message"
+    private val mockLogDetails: Map<String, Any> = emptyMap()
+    private val mockLogHandler: LogHandler = mockk {
+        every { this@mockk(any(), any(), any()) } answers { nothing }
+    }
+
+    private val systemUnderTest = Logger.createLogger(
+        handle = mockLogHandler,
+    )
+
+    @Test
+    fun `log DEBUG message when level DEBUG is set`() {
+        systemUnderTest.setLevels(listOf(DEBUG))
+
+        systemUnderTest.debug(
+            message = mockLogMessage,
+            details = mockLogDetails,
+        )
+
+        verify(exactly = 1) {
+            mockLogHandler(DEBUG, mockLogMessage, mockLogDetails)
+        }
+    }
+
+    @Test
+    fun `log INFO message when level INFO is set`() {
+        systemUnderTest.setLevels(listOf(INFO))
+
+        systemUnderTest.info(
+            message = mockLogMessage,
+            details = mockLogDetails,
+        )
+
+        verify(exactly = 1) {
+            mockLogHandler(INFO, mockLogMessage, mockLogDetails)
+        }
+    }
+
+    @Test
+    fun `log WARN message when level WARN is set`() {
+        systemUnderTest.setLevels(listOf(WARN))
+
+        systemUnderTest.warn(
+            message = mockLogMessage,
+            details = mockLogDetails,
+        )
+
+        verify(exactly = 1) {
+            mockLogHandler(WARN, mockLogMessage, mockLogDetails)
+        }
+    }
+
+    @Test
+    fun `log ERROR message when level ERROR is set`() {
+        systemUnderTest.setLevels(listOf(ERROR))
+
+        systemUnderTest.error(
+            message = mockLogMessage,
+            details = mockLogDetails,
+        )
+
+        verify(exactly = 1) {
+            mockLogHandler(ERROR, mockLogMessage, mockLogDetails)
+        }
+    }
+
+    @Test
+    fun `do not log any message when not set in log levels`() {
+        systemUnderTest.setLevels(listOf())
+
+        systemUnderTest.info(
+            message = mockLogMessage,
+            details = mockLogDetails,
+        )
+        systemUnderTest.warn(
+            message = mockLogMessage,
+            details = mockLogDetails,
+        )
+        systemUnderTest.debug(
+            message = mockLogMessage,
+            details = mockLogDetails,
+        )
+        systemUnderTest.error(
+            message = mockLogMessage,
+            details = mockLogDetails,
+        )
+
+        verify(exactly = 0) {
+            mockLogHandler(INFO, any(), any())
+            mockLogHandler(WARN, any(), any())
+            mockLogHandler(DEBUG, any(), any())
+            mockLogHandler(ERROR, any(), any())
+        }
+    }
+}