core: Add PotentialAnnotation helper to store different annotation possibilities (none, type, insance).

1 files changed, 241 insertions, 0 deletions

diff --git a/sangria-core/src/main/java/com/tavianator/sangria/core/PotentialAnnotation.java b/sangria-core/src/main/java/com/tavianator/sangria/core/PotentialAnnotation.java
new file mode 100644
index 0000000..302e5e1
--- /dev/null
+++ b/sangria-core/src/main/java/com/tavianator/sangria/core/PotentialAnnotation.java
@@ -0,0 +1,241 @@
+/****************************************************************************
+ * Sangria                                                                  *
+ * Copyright (C) 2014 Tavian Barnes <tavianator@tavianator.com>             *
+ *                                                                          *
+ * Licensed under the Apache License, Version 2.0 (the "License");          *
+ * you may not use this file except in compliance with the License.         *
+ * You may obtain a copy of the License at                                  *
+ *                                                                          *
+ * http://www.apache.org/licenses/LICENSE-2.0                               *
+ *                                                                          *
+ * Unless required by applicable law or agreed to in writing, software      *
+ * distributed under the License is distributed on an "AS IS" BASIS,        *
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. *
+ * See the License for the specific language governing permissions and      *
+ * limitations under the License.                                           *
+ ****************************************************************************/
+
+package com.tavianator.sangria.core;
+
+import java.lang.annotation.Annotation;
+import java.util.*;
+
+import com.google.inject.CreationException;
+import com.google.inject.Key;
+import com.google.inject.TypeLiteral;
+import com.google.inject.spi.Message;
+
+/**
+ * A record of stored annotations, perfect for builders with {@code annotatedWith()} methods.
+ *
+ * @author Tavian Barnes (tavianator@tavianator.com)
+ * @version 1.1
+ * @since 1.1
+ */
+public abstract class PotentialAnnotation {
+    /**
+     * A visitor interface to examine a {@link PotentialAnnotation}'s annotation, if it exists.
+     *
+     * @param <T> The type to return.
+     * @author Tavian Barnes (tavianator@tavianator.com)
+     * @version 1.1
+     * @since 1.1
+     */
+    public interface Visitor<T> {
+        /**
+         * Called when there is no annotation.
+         *
+         * @return Any value.
+         */
+        T visitNoAnnotation();
+
+        /**
+         * Called when an annotation type is stored.
+         *
+         * @param annotationType The annotation type.
+         * @return Any value.
+         */
+        T visitAnnotationType(Class<? extends Annotation> annotationType);
+
+        /**
+         * Called when an annotation instance is stored.
+         *
+         * @param annotation The annotation instance.
+         * @return Any value.
+         */
+        T visitAnnotationInstance(Annotation annotation);
+    }
+
+    private static final PotentialAnnotation NONE = new NoAnnotation();
+
+    /**
+     * @return A {@link PotentialAnnotation} with no annotation.
+     */
+    public static PotentialAnnotation none() {
+        return NONE;
+    }
+
+    private PotentialAnnotation() {
+    }
+
+    /**
+     * Add an annotation.
+     *
+     * @param annotationType The annotation type to add.
+     * @return A new {@link PotentialAnnotation} associated with the given annotation type.
+     * @throws CreationException If an annotation is already present.
+     */
+    public PotentialAnnotation annotatedWith(Class<? extends Annotation> annotationType) {
+        throw annotationAlreadyPresent();
+    }
+
+    /**
+     * Add an annotation.
+     *
+     * @param annotation The annotation instance to add.
+     * @return A new {@link PotentialAnnotation} associated with the given annotation instance.
+     * @throws CreationException If an annotation is already present.
+     */
+    public PotentialAnnotation annotatedWith(Annotation annotation) {
+        throw annotationAlreadyPresent();
+    }
+
+    private CreationException annotationAlreadyPresent() {
+        Message message = new Message("An annotation was already present");
+        return new CreationException(Collections.singletonList(message));
+    }
+
+    /**
+     * @return Whether an annotation is present.
+     */
+    public abstract boolean hasAnnotation();
+
+    /**
+     * Create a {@link Key} with the given type and the stored annotation.
+     *
+     * @param type The type of the key to create.
+     * @param <T>  The type of the key to create.
+     * @return A {@link Key}.
+     */
+    public <T> Key<T> getKey(Class<T> type) {
+        return getKey(TypeLiteral.get(type));
+    }
+
+    /**
+     * Create a {@link Key} with the given type and the stored annotation.
+     *
+     * @param type The type of the key to create.
+     * @param <T>  The type of the key to create.
+     * @return A {@link Key}.
+     */
+    public abstract <T> Key<T> getKey(TypeLiteral<T> type);
+
+    /**
+     * Accept a {@link Visitor}.
+     *
+     * @param visitor The visitor to accept.
+     * @param <T> The type for the visitor to return.
+     * @return The value produced by the visitor.
+     */
+    public abstract <T> T accept(Visitor<T> visitor);
+
+    @Override
+    public abstract String toString();
+
+    /**
+     * Implementation of {@link #none()}.
+     */
+    private static class NoAnnotation extends PotentialAnnotation {
+        @Override
+        public PotentialAnnotation annotatedWith(Class<? extends Annotation> annotationType) {
+            return new AnnotationType(annotationType);
+        }
+
+        @Override
+        public PotentialAnnotation annotatedWith(Annotation annotation) {
+            return new AnnotationInstance(annotation);
+        }
+
+        @Override
+        public boolean hasAnnotation() {
+            return false;
+        }
+
+        @Override
+        public <T> Key<T> getKey(TypeLiteral<T> type) {
+            return Key.get(type);
+        }
+
+        @Override
+        public <T> T accept(Visitor<T> visitor) {
+            return visitor.visitNoAnnotation();
+        }
+
+        @Override
+        public String toString() {
+            return "[no annotation]";
+        }
+    }
+
+    /**
+     * Implementation of {@link #annotatedWith(Class)}.
+     */
+    private static class AnnotationType extends PotentialAnnotation {
+        private final Class<? extends Annotation> annotationType;
+
+        AnnotationType(Class<? extends Annotation> annotationType) {
+            this.annotationType = annotationType;
+        }
+
+        @Override
+        public boolean hasAnnotation() {
+            return true;
+        }
+
+        @Override
+        public <T> Key<T> getKey(TypeLiteral<T> type) {
+            return Key.get(type, annotationType);
+        }
+
+        @Override
+        public <T> T accept(Visitor<T> visitor) {
+            return visitor.visitAnnotationType(annotationType);
+        }
+
+        @Override
+        public String toString() {
+            return "@" + annotationType.getCanonicalName();
+        }
+    }
+
+    /**
+     * Implementation of {@link #annotatedWith(Annotation)}.
+     */
+    private static class AnnotationInstance extends PotentialAnnotation {
+        private final Annotation annotation;
+
+        AnnotationInstance(Annotation annotation) {
+            this.annotation = annotation;
+        }
+
+        @Override
+        public boolean hasAnnotation() {
+            return true;
+        }
+
+        @Override
+        public <T> Key<T> getKey(TypeLiteral<T> type) {
+            return Key.get(type, annotation);
+        }
+
+        @Override
+        public <T> T accept(Visitor<T> visitor) {
+            return visitor.visitAnnotationInstance(annotation);
+        }
+
+        @Override
+        public String toString() {
+            return annotation.toString();
+        }
+    }
+}