From 425527ddb252737b98bad2e7eb4dc4a059816b99 Mon Sep 17 00:00:00 2001
From: Marc Baloup <marc.baloup@laposte.net>
Date: Sun, 8 Aug 2021 12:56:36 +0200
Subject: [PATCH] Wrapper for lazy loaded values

---
 .../java/fr/pandacube/lib/core/util/Lazy.java | 48 +++++++++++++++++
 .../lib/core/util/LazyOrException.java        | 52 +++++++++++++++++++
 2 files changed, 100 insertions(+)
 create mode 100644 Core/src/main/java/fr/pandacube/lib/core/util/Lazy.java
 create mode 100644 Core/src/main/java/fr/pandacube/lib/core/util/LazyOrException.java

diff --git a/Core/src/main/java/fr/pandacube/lib/core/util/Lazy.java b/Core/src/main/java/fr/pandacube/lib/core/util/Lazy.java
new file mode 100644
index 0000000..a50373a
--- /dev/null
+++ b/Core/src/main/java/fr/pandacube/lib/core/util/Lazy.java
@@ -0,0 +1,48 @@
+package fr.pandacube.lib.core.util;
+
+import java.util.Objects;
+import java.util.function.Supplier;
+
+/**
+ * Represents a lazy loaded value.
+ * 
+ * The value will be computed using the Supplier provided in the
+ * constructor, only the first time the {@link #get()} method is
+ * called.
+ *
+ * @param <T> the type of the enclosed value.
+ */
+public class Lazy<T> implements Supplier<T> {
+	
+	private T cachedValue;
+	private final Supplier<T> supplier;
+	private boolean cached = false;
+	
+	public Lazy(Supplier<T> s) {
+		supplier = Objects.requireNonNull(s);
+	}
+	
+	/**
+	 * Get the wrapped value, from cache or from the provider if it is not yet cached.
+	 * 
+	 * If the provider throws an exception, it will be redirected to the caller as is, and no value will be cached (the next call to this method will
+	 * execute the supplier again).
+	 */
+	@Override
+	public synchronized T get() {
+		if (!cached) // check outside synchronized method to reduce useless synchronization if value is already cached
+			set(supplier.get());
+		return cachedValue;
+	}
+	
+	public synchronized void reset() {
+		cached = false;
+		cachedValue = null;
+	}
+	
+	public synchronized void set(T value) {
+		cachedValue = value;
+		cached = true;
+	}
+
+}
diff --git a/Core/src/main/java/fr/pandacube/lib/core/util/LazyOrException.java b/Core/src/main/java/fr/pandacube/lib/core/util/LazyOrException.java
new file mode 100644
index 0000000..e9bf467
--- /dev/null
+++ b/Core/src/main/java/fr/pandacube/lib/core/util/LazyOrException.java
@@ -0,0 +1,52 @@
+package fr.pandacube.lib.core.util;
+
+import java.util.Objects;
+
+/**
+ * Represents a lazy loaded value.
+ * 
+ * The value will be computed using the Supplier provided in the
+ * constructor, only the first time the {@link #get()} method is
+ * called.
+ *
+ * @param <T> the type of the enclosed value.
+ */
+public class LazyOrException<T> {
+	
+	private T cachedValue;
+	private final SupplierException<T> supplier;
+	private boolean cached = false;
+	
+	public LazyOrException(SupplierException<T> s) {
+		supplier = Objects.requireNonNull(s);
+	}
+	
+	/**
+	 * Get the wrapped value, from cache or from the provider if it is not yet cached.
+	 * 
+	 * If the provider throws an exception, it will be redirected to the caller as is, and no value will be cached (the next call to this method will
+	 * execute the supplier again).
+	 */
+	public synchronized T get() throws Exception {
+		if (!cached) // check outside synchronized method to reduce useless synchronization if value is already cached
+			set(supplier.get());
+		return cachedValue;
+	}
+	
+	public synchronized void reset() {
+		cached = false;
+		cachedValue = null;
+	}
+	
+	public synchronized void set(T value) {
+		cachedValue = value;
+		cached = true;
+	}
+	
+	
+	@FunctionalInterface
+	public interface SupplierException<T> {
+		public T get() throws Exception;
+	}
+
+}