feat(retrofit): Add JsonFallback annotation and addEnumAdapter extension function for adding fallback to enums

config/libs.toml

@@ -83,6 +83,7 @@ junit4 = { module = "junit:junit", version.ref = "junit4" }
 junit5-api = { module = "org.junit.jupiter:junit-jupiter-engine", version.ref = "junit5" }
 junit5-engine = { module = "org.junit.jupiter:junit-jupiter-engine", version.ref = "junit5" }
 moshi = { module = "com.squareup.moshi:moshi", version.ref = "moshi" }
+moshi-adapters = { module = "com.squareup.moshi:moshi-adapters", version.ref = "moshi" }
 okhttp = { module = "com.squareup.okhttp3:okhttp", version.ref = "okhttp" }
 okhttp-mockWebServer = { module = "com.squareup.okhttp3:mockwebserver", version.ref = "okhttp" }
 orgJson = { module = "org.json:json", version.ref = "orgJson" }

retrofit/README.MD

@@ -116,6 +116,28 @@ moshiBuilder.add(JavaTimeMoshiAdapter)
 Moshi adapter for converting java.time's `Instant`, `LocalTime`, `LocalDate`, `LocalDateTime` and `ZonedDateTime` to ISO String
 for JSON serialization.
 
+## Enum json fallback
+
+Annotation `@JsonFallback` for adding fallback value to enum.
+Enum class can be added via `Moshi.Builder` with extension function `addEnumAdapter`.
+
+```kotlin
+@JsonClass(generateAdapter = false)
+enum class Level {
+   @Json(name = "low")
+   LOW,
+
+   @Json(name = "medium")
+   MEDIUM,
+
+   @Json(name = "high")
+   HIGH,
+
+   @JsonFallback
+   OTHER;
+}
+```
+
 ## OKHttp Cache manager
 
 (Only on Android projects)

retrofit/build.gradle.kts

@@ -44,6 +44,7 @@ kotlin {
          dependencies {
             api(libs.okhttp)
             api(libs.moshi)
+            api(libs.moshi.adapters)
             api(libs.retrofit)
 
             implementation(projects.core)

retrofit/src/jvmCommon/kotlin/si/inova/kotlinova/retrofit/moshi/JsonFallback.kt

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2023 INOVA IT d.o.o.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation
+ * files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy,
+ * modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software
+ *  is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ *  OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ *   BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ *   OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package si.inova.kotlinova.retrofit.moshi
+
+import com.squareup.moshi.JsonAdapter
+import com.squareup.moshi.Moshi
+import com.squareup.moshi.adapters.EnumJsonAdapter
+
+/**
+ * Annotation for adding fallback value to enum.
+ *
+ * Enum class can be added via [Moshi.Builder] with extension function [addEnumAdapter].
+ *
+ * Usage:
+ *
+ * ```kotlin
+ * @JsonClass(generateAdapter = false)
+ * enum class Level {
+ *    @Json(name = "low")
+ *    LOW,
+ *
+ *    @Json(name = "medium")
+ *    MEDIUM,
+ *
+ *    @Json(name = "high")
+ *    HIGH,
+ *
+ *    @JsonFallback
+ *    OTHER;
+ * }
+ * ```
+ */
+annotation class JsonFallback
+
+inline fun <reified T : Enum<T>> Moshi.Builder.addEnumAdapter(): Moshi.Builder =
+   with(T::class.java) { add(this, createEnumAdapter()) }
+
+fun <T : Enum<T>> Class<T>.createEnumAdapter(): JsonAdapter<T> {
+   var default: T? = null
+
+   enumConstants?.forEach { enumConstant ->
+      if (getField(enumConstant.name).isAnnotationPresent(JsonFallback::class.java)) {
+         check(default == null) { "Multiple entries annotated with @${JsonFallback::class.simpleName} on $name" }
+         default = enumConstant
+      }
+   }
+
+   requireNotNull(default) { "No entry annotated with @${JsonFallback::class.simpleName} on $name" }
+
+   return EnumJsonAdapter.create(this).withUnknownFallback(default)
+}