Implement plugin state (closes #603) (#622)

plugin-api/build.gradle.kts

@@ -1,5 +1,7 @@
 import com.vanniktech.maven.publish.SonatypeHost
 
+val jacksonVersion = "2.19.1"
+
 plugins {
     kotlin("jvm")
     `java-library`
@@ -11,6 +13,10 @@ group = "org.gameyfin"
 dependencies {
     // PF4J (shared)
     api("org.pf4j:pf4j:${rootProject.extra["pf4jVersion"]}")
+
+    // JSON serialization
+    compileOnly("com.fasterxml.jackson.core:jackson-databind:$jacksonVersion")
+    implementation("com.fasterxml.jackson.module:jackson-module-kotlin:$jacksonVersion")
 }
 
 mavenPublishing {

plugin-api/src/main/kotlin/org/gameyfin/pluginapi/core/wrapper/GameyfinPlugin.kt

@@ -1,7 +1,14 @@
 package org.gameyfin.pluginapi.core.wrapper
 
+import com.fasterxml.jackson.databind.ObjectMapper
+import com.fasterxml.jackson.module.kotlin.KotlinModule
 import org.pf4j.Plugin
 import org.pf4j.PluginWrapper
+import java.nio.file.Files
+import java.nio.file.Path
+import kotlin.io.path.createFile
+import kotlin.io.path.exists
+import kotlin.io.path.fileSize
 
 /**
  * Abstract base class for all Gameyfin plugins.
@@ -25,20 +32,17 @@ abstract class GameyfinPlugin(wrapper: PluginWrapper) : Plugin(wrapper) {
          * Supported logo file formats.
          */
         val SUPPORTED_LOGO_FORMATS: List<String> = listOf("png", "jpg", "jpeg", "gif", "svg", "webp")
-
-        /**
-         * Reference to the current plugin instance.
-         */
-        lateinit var plugin: GameyfinPlugin
-            private set
     }
 
     /**
-     * Initializes the plugin and sets the static plugin reference.
+     * State file for the plugin, used to persist plugin-specific state.
      */
-    init {
-        plugin = this
-    }
+    val stateFile: Path = Path.of("${wrapper.pluginId}.state.json")
+
+    /**
+     * JSON serializer for serializing and deserializing plugin state.
+     */
+    val objectMapper: ObjectMapper = ObjectMapper().registerModule(KotlinModule.Builder().build())
 
     /**
      * Checks if the plugin contains a logo file in any supported format.
@@ -73,4 +77,18 @@ abstract class GameyfinPlugin(wrapper: PluginWrapper) : Plugin(wrapper) {
 
         return null
     }
+
+    inline fun <reified T> loadState(): T? {
+        if (!stateFile.exists() || stateFile.fileSize() == 0L) return null
+        return Files.newBufferedReader(stateFile).use {
+            objectMapper.readValue(it.readText(), T::class.java)
+        }
+    }
+
+    inline fun <reified T> saveState(state: T) {
+        if (!stateFile.exists()) stateFile.createFile()
+        Files.newBufferedWriter(stateFile).use {
+            it.write(objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(state))
+        }
+    }
 }