game item to load its own image if needed; common resource pool to assist that

src/net/torvald/terrarum/CommonResourcePool.kt

@@ -0,0 +1,64 @@
+package net.torvald.terrarum
+
+import com.badlogic.gdx.utils.Disposable
+import com.badlogic.gdx.utils.Queue
+
+/**
+ * Created by minjaesong on 2019-03-10.
+ */
+object CommonResourcePool {
+
+    private val loadingList = Queue<Pair<Pair<String, Class<*>>, () -> Disposable>>()
+    private val pool = HashMap<String, Disposable>()
+    //private val typesMap = HashMap<String, Class<*>>()
+    private var loadCounter = -1 // using counters so that the loading can be done on separate thread (gg if the asset requires GL context to be loaded)
+    val loaded: Boolean
+        get() = loadCounter == 0
+
+    fun <T> addToLoadingList(identifier: String, type: Class<T>, loadFunction: () -> Disposable) {
+        loadingList.addFirst(identifier to type to loadFunction)
+
+        if (loadCounter == -1)
+            loadCounter = 1
+        else
+            loadCounter += 1
+    }
+
+    /**
+     * You are supposed to call this function only once.
+     */
+    fun loadAll() {
+        if (loaded) throw IllegalStateException("Assets are already loaded and shipped out :p")
+
+        while (!loadingList.isEmpty) {
+            val (k, loadfun) = loadingList.removeFirst()
+            val (name, type) = k
+
+            if (pool.containsKey(name)) {
+                throw IllegalArgumentException("Assets with identifier '$name' already exists.")
+            }
+
+            //typesMap[name] = type
+            pool[name] = loadfun.invoke()
+
+            loadCounter -= 1
+        }
+    }
+
+    operator fun get(identifier: String): Disposable {
+        val obj = pool[identifier]!!
+
+        return obj
+    }
+
+    fun dispose() {
+        pool.forEach { _, u ->
+            try {
+                u.dispose()
+            }
+            catch (e: Throwable) {
+                e.printStackTrace()
+            }
+        }
+    }
+}