GUACAMOLE-728: Define EnumGuacamoleProperty for convenience and maintainability.

guacamole-ext/src/main/java/org/apache/guacamole/properties/EnumGuacamoleProperty.java

@@ -0,0 +1,254 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.guacamole.properties;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+import java.lang.reflect.Field;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import org.apache.guacamole.GuacamoleException;
+import org.apache.guacamole.GuacamoleServerException;
+
+/**
+ * A GuacamoleProperty whose possible values are defined by an enum. Possible
+ * values may be defined either through providing an explicit mapping or
+ * through annotating the enum constant definitions with the
+ * {@link PropertyValue} annotation.
+ *
+ * @param <T>
+ *     The enum which defines the possible values of this property.
+ */
+public abstract class EnumGuacamoleProperty<T extends Enum<T>> implements GuacamoleProperty<T> {
+
+    /**
+     * Defines the string value which should be accepted and parsed into the
+     * annotated enum constant.
+     */
+    @Retention(RetentionPolicy.RUNTIME)
+    @Target(ElementType.FIELD)
+    public static @interface PropertyValue {
+
+        /**
+         * Returns the String value that should produce the annotated enum
+         * constant when parsed.
+         *
+         * @return
+         *     The String value that should produce the annotated enum constant
+         *     when parsed.
+         */
+        String value();
+
+    }
+
+    /**
+     * Mapping of valid property values to the corresponding enum constants
+     * that those values parse to.
+     */
+    private final Map<String, T> valueMapping;
+
+    /**
+     * Produces a mapping of Guacamole property value to corresponding enum
+     * constant. All enum constants annotated with {@link PropertyValue} are
+     * included in the resulting Map.
+     *
+     * @param <T>
+     *     The enum for which a value mapping is being produced.
+     *
+     * @param enumClass
+     *     The Class of the enum for which a value mapping is being produced.
+     *
+     * @return
+     *     A new Map which associates the Guacamole property string values of
+     *     enum constants (as defined by {@link PropertyValue} annotations)
+     *     with their corresponding enum constants.
+     */
+    private static <T extends Enum<T>> Map<String, T> getValueMapping(Class<T> enumClass) {
+
+        T[] values = enumClass.getEnumConstants();
+        Map<String, T> valueMapping = new HashMap<>(values.length);
+
+        for (T value : values) {
+
+            // Retrieve Field which corresponds to the current enum constant
+            Field field;
+            try {
+                field = enumClass.getDeclaredField(value.name());
+            }
+            catch (NoSuchFieldException e) {
+                // This SHOULD be impossible
+                throw new IllegalStateException("Fields of enum do not "
+                        + "match declared values.", e);
+            }
+
+            // Map enum constant only if PropertyValue annotation is present
+            PropertyValue valueAnnotation = field.getAnnotation(PropertyValue.class);
+            if (valueAnnotation != null)
+                valueMapping.put(valueAnnotation.value(), value);
+
+        }
+
+        return valueMapping;
+
+    }
+
+    /**
+     * Produces a new Map having the given key/value pairs. Each key MUST be a
+     * String, and each value MUST be an enum constant belonging to the given
+     * enum.
+     *
+     * @param <T>
+     *     The enum whose constants may be used as values within the Map.
+     *
+     * @param key
+     *     The key of the first key/value pair to include within the Map.
+     *
+     * @param value
+     *     The value of the first key/value pair to include within the Map.
+     *
+     * @param additional
+     *     Any additional key/value pairs to be included beyond the first. This
+     *     array must be even in length, where each even element is a String
+     *     key and each odd element is the enum constant value to be associated
+     *     with the key immediately preceding it.
+     *
+     * @return
+     *     A new Map having each of the given key/value pairs.
+     *
+     * @throws IllegalArgumentException
+     *     If any provided key is not a String, if any provided value is not
+     *     an enum constant from the given enum type, or if the length of
+     *     {@code additional} is not even.
+     */
+    @SuppressWarnings("unchecked") // We check this ourselves with instanceof and getDeclaringClass()
+    private static <T extends Enum<T>> Map<String, T> mapOf(String key, T value,
+            Object... additional) throws IllegalArgumentException {
+
+        // Verify length of additional pairs is even
+        if (additional.length % 2 != 0)
+            throw new IllegalArgumentException("Array of additional key/value pairs must be even in length.");
+
+        // Add first type-checked pair
+        Map<String, T> valueMapping = new HashMap<>(1 + additional.length);
+        valueMapping.put(key, value);
+
+        Class<T> enumClass = value.getDeclaringClass();
+
+        // Add remaining, unchecked pairs
+        for (int i = 0; i < additional.length; i += 2) {
+
+            // Verify that unchecked keys are indeed Strings
+            Object additionalKey = additional[i];
+            if (!(additionalKey instanceof String))
+                throw new IllegalArgumentException("Keys of additional key/value pairs must be strings.");
+
+            // Verify that unchecked values are indeed constants defined by the
+            // expected enum
+            Object additionalValue = additional[i + 1];
+            if (!(additionalValue instanceof Enum) || enumClass != ((Enum) additionalValue).getDeclaringClass())
+                throw new IllegalArgumentException("Values of additional key/value pairs must be enum constants of the correct type.");
+
+            valueMapping.put((String) additionalKey, (T) additionalValue);
+
+        }
+
+        return valueMapping;
+
+    }
+
+    /**
+     * Creates a new EnumGuacamoleProperty which parses String property values
+     * into corresponding enum constants as defined by the given Map.
+     *
+     * @param valueMapping
+     *     A Map which maps all legal String values to their corresponding enum
+     *     constants.
+     */
+    public EnumGuacamoleProperty(Map<String, T> valueMapping) {
+        this.valueMapping = valueMapping;
+    }
+
+    /**
+     * Creates a new EnumGuacamoleProperty which parses String property values
+     * into corresponding enum constants as defined by the
+     * {@link PropertyValue} annotations associated with those constants.
+     *
+     * @param enumClass
+     *     The enum whose annotated constants should be used as legal values of
+     *     this property.
+     */
+    public EnumGuacamoleProperty(Class<T> enumClass) {
+        this(getValueMapping(enumClass));
+    }
+
+    /**
+     * Creates a new EnumGuacamoleProperty which parses the given String
+     * property values into the given corresponding enum constants.
+     *
+     * @param key
+     *     The first String value to accept as a legal value of this property.
+     *
+     * @param value
+     *     The enum constant that {@code key} should be parsed into.
+     *
+     * @param additional
+     *     Any additional key/value pairs to be included beyond the first. This
+     *     array must be even in length, where each even element is a String
+     *     key and each odd element is the enum constant value to be associated
+     *     with the key immediately preceding it.
+     *
+     * @throws IllegalArgumentException
+     *     If any provided key is not a String, if any provided value is not
+     *     an enum constant from the given enum type, or if the length of
+     *     {@code additional} is not even.
+     */
+    public EnumGuacamoleProperty(String key, T value, Object... additional)
+            throws IllegalArgumentException {
+        this(mapOf(key, value, additional));
+    }
+
+    @Override
+    public T parseValue(String value) throws GuacamoleException {
+
+        // Simply pass through null values
+        if (value == null)
+            return null;
+
+        // Translate values based on explicit string/constant mapping
+        T parsedValue = valueMapping.get(value);
+        if (parsedValue != null)
+            return parsedValue;
+
+        // Produce human-readable error if no matching constant is found
+        List<String> legalValues = new ArrayList<>(valueMapping.keySet());
+        Collections.sort(legalValues);
+
+        throw new GuacamoleServerException(String.format("\"%s\" is not a "
+                + "valid value for property \"%s\". Valid values are: \"%s\"",
+                value, getName(), String.join("\", \"", legalValues)));
+
+    }
+
+}