java/org/eclipse/lsp4j/jsonrpc/json/adapters/EnumTypeAdapter.java

/******************************************************************************
 * Copyright (c) 2016-2017 TypeFox and others.
 * 
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 * 
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 ******************************************************************************/
package org.eclipse.lsp4j.jsonrpc.json.adapters;

import java.io.IOException;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;

import com.google.gson.Gson;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonToken;
import com.google.gson.stream.JsonWriter;

/**
 * A custom type adapter for enums that uses integer values.
 */
public class EnumTypeAdapter<T extends Enum<T>> extends TypeAdapter<T> {
	
	public static class Factory implements TypeAdapterFactory {

		@Override
		@SuppressWarnings({ "unchecked", "rawtypes" })
		public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> typeToken) {
			Class<?> rawType = typeToken.getRawType();
			if (!Enum.class.isAssignableFrom(rawType) || rawType == Enum.class)
				return null;
			if (!rawType.isEnum())
				rawType = rawType.getSuperclass();
			try {
				return new EnumTypeAdapter(rawType);
			} catch (IllegalAccessException e) {
				throw new RuntimeException(e);
			}
		}
		
	}
	
	private static String VALUE_FIELD_NAME = "value";
	
	private final Map<String, T> nameToConstant = new HashMap<>();
	private final Map<Integer, T> valueToConstant = new HashMap<>();
	private final Map<T, Integer> constantToValue = new HashMap<>();
	
	EnumTypeAdapter(Class<T> classOfT) throws IllegalAccessException {
		try {
			Field valueField = classOfT.getDeclaredField(VALUE_FIELD_NAME);
			if (valueField.getType() != int.class && valueField.getType() != Integer.class)
				throw new IllegalArgumentException("The field 'value' must contain an integer value.");
			valueField.setAccessible(true);
			for (T constant : classOfT.getEnumConstants()) {
				nameToConstant.put(constant.name(), constant);
				Integer constValue = (Integer) valueField.get(constant);
				valueToConstant.put(constValue, constant);
				constantToValue.put(constant, constValue);
			}
		} catch (NoSuchFieldException e) {
			for (T constant : classOfT.getEnumConstants()) {
				nameToConstant.put(constant.name(), constant);
				int constValue = constant.ordinal();
				valueToConstant.put(constValue, constant);
				constantToValue.put(constant, constValue);
			}
		}
	}
	
	@Override
	public T read(JsonReader in) throws IOException {
		JsonToken peek = in.peek();
		if (peek == JsonToken.NULL) {
			in.nextNull();
			return null;
		} else if (peek == JsonToken.NUMBER) {
			return valueToConstant.get(in.nextInt());
		} else {
			String string = in.nextString();
			try {
				return valueToConstant.get(Integer.parseInt(string));
			} catch (NumberFormatException e) {
				return nameToConstant.get(string);
			}
		}
	}

	@Override
	public void write(JsonWriter out, T value) throws IOException {
		if (value != null)
			out.value(constantToValue.get(value));
		else
			out.value((String) null);
	}

}