1 files changed, 105 insertions, 0 deletions
diff --git a/src/Utilities/ServiceLocator.kt b/src/Utilities/ServiceLocator.kt
new file mode 100644
index 00000000..bc04238f
--- /dev/null
+++ b/src/Utilities/ServiceLocator.kt
@@ -0,0 +1,105 @@
+package org.jetbrains.dokka.Utilities
+
+import org.jetbrains.dokka.DokkaGenerator
+import java.io.File
+import java.util.*
+import java.util.jar.JarFile
+import java.util.zip.ZipEntry
+
+data class ServiceDescriptor(val name: String, val category: String, val description: String?, val className: String)
+
+class ServiceLookupException(message: String) : Exception(message)
+
+public object ServiceLocator {
+    public fun <T : Any> lookup(clazz: Class<T>, category: String, implementationName: String, conf: DokkaGenerator): T {
+        val descriptor = lookupDescriptor(category, implementationName)
+        val loadedClass = javaClass.classLoader.loadClass(descriptor.className)
+        val constructor = loadedClass.constructors
+                .filter { it.parameterTypes.isEmpty() || (it.parameterTypes.size() == 1 && conf.javaClass.isInstance(it.parameterTypes[0])) }
+                .sortedByDescending { it.parameterTypes.size() }
+                .firstOrNull() ?: throw ServiceLookupException("Class ${descriptor.className} has no corresponding constructor")
+
+        val implementationRawType: Any = if (constructor.parameterTypes.isEmpty()) constructor.newInstance() else constructor.newInstance(constructor)
+
+        if (!clazz.isInstance(implementationRawType)) {
+            throw ServiceLookupException("Class ${descriptor.className} is not a subtype of ${clazz.name}")
+        }
+
+        @Suppress("UNCHECKED_CAST")
+        return implementationRawType as T
+    }
+
+    public fun <T> lookupClass(clazz: Class<T>, category: String, implementationName: String): Class<T> = lookupDescriptor(category, implementationName).className.let { className ->
+        javaClass.classLoader.loadClass(className).let { loaded ->
+            if (!clazz.isAssignableFrom(loaded)) {
+                throw ServiceLookupException("Class $className is not a subtype of ${clazz.name}")
+            }
+
+            @Suppress("UNCHECKED_CAST")
+            val casted = loaded as Class<T>
+
+            casted
+        }
+    }
+
+    private fun lookupDescriptor(category: String, implementationName: String): ServiceDescriptor {
+        val properties = javaClass.classLoader.getResourceAsStream("dokka/$category/$implementationName.properties")?.use { stream ->
+            Properties().let { properties ->
+                properties.load(stream)
+                properties
+            }
+        } ?: throw ServiceLookupException("No implementation with name $implementationName found in category $category")
+
+        val className = properties["class"]?.toString() ?: throw ServiceLookupException("Implementation $implementationName has no class configured")
+
+        return ServiceDescriptor(implementationName, category, properties["description"]?.toString(), className)
+    }
+
+    fun allServices(category: String): List<ServiceDescriptor> = javaClass.classLoader.getResourceAsStream("dokka/$category")?.use { stream ->
+        val entries = this.javaClass.classLoader.getResources("dokka/$category")?.toList() ?: emptyList()
+
+        entries.flatMap {
+            when (it.protocol) {
+                "file" -> File(it.file).listFiles()?.filter { it.extension == "properties" }?.map { lookupDescriptor(category, it.nameWithoutExtension) } ?: emptyList()
+                "jar" -> {
+                    val file = JarFile(it.file.removePrefix("file:").substringBefore("!"))
+                    try {
+                        val jarPath = it.file.substringAfterLast("!").removePrefix("/")
+                        file.entries()
+                                .asSequence()
+                                .filter { entry -> !entry.isDirectory && entry.path == jarPath && entry.extension == "properties" }
+                                .map { entry ->
+                                    lookupDescriptor(category, entry.fileName.substringBeforeLast("."))
+                                }.toList()
+                    } finally {
+                        file.close()
+                    }
+                }
+                else -> emptyList<ServiceDescriptor>()
+            }
+        }
+    } ?: emptyList()
+}
+
+public inline fun <reified T : Any> ServiceLocator.lookup(category: String, implementationName: String, conf: DokkaGenerator): T = lookup(javaClass<T>(), category, implementationName, conf)
+public inline fun <reified T : Any> ServiceLocator.lookupClass(category: String, implementationName: String): Class<T> = lookupClass(javaClass<T>(), category, implementationName)
+public inline fun <reified T : Any> ServiceLocator.lookupOrNull(category: String, implementationName: String, conf: DokkaGenerator): T? = try {
+    lookup(javaClass<T>(), category, implementationName, conf)
+} catch (any: Throwable) {
+    null
+}
+
+fun main(args: Array<String>) {
+    ServiceLocator.allServices("format").forEach {
+        println(it)
+    }
+}
+
+private val ZipEntry.fileName: String
+    get() = name.substringAfterLast("/", name)
+
+private val ZipEntry.path: String
+    get() = name.substringBeforeLast("/", "").removePrefix("/")
+
+private val ZipEntry.extension: String?
+    get() = fileName.let { fn -> if ("." in fn) fn.substringAfterLast(".") else null }