/*
 * Copyright 2011 Google Inc.
 * 
 * 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.google.web.bindery.requestfactory.vm.impl;

import com.google.gwt.dev.util.StringKey;
import com.google.gwt.user.server.Base64Utils;

import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * Utility class for encoding RequestFactory operation ids.
 */
public class OperationKey extends StringKey {
  /**
   * The expected length of values returned from {@link #hash(String)}.
   */
  public static final int HASH_LENGTH = 28;

  static {
    assert HASH_LENGTH == hash("").length();
  }

  /**
   * Compute a base64-encoded SHA1 hash of the input string's UTF8
   * representation. The result is a {@value #HASH_LENGTH}-character sequence.
   */
  public static String hash(String raw) {
    try {
      MessageDigest md = MessageDigest.getInstance("SHA1");
      byte[] data = md.digest(raw.getBytes(StandardCharsets.UTF_8));
      return Base64Utils.toBase64(data);
    } catch (NoSuchAlgorithmException e) {
      throw new RuntimeException("No SHA1 algorithm", e);
    }
  }

  static String stripReturnType(String descriptor) {
    assert descriptor.contains(")") : descriptor + " does not look like a method descriptor";
    return descriptor.substring(0, descriptor.lastIndexOf(')')) + ")V";
  }

  private static String key(String requestContextBinaryName, String methodName, String descriptor) {
    String raw = requestContextBinaryName + "::" + methodName + stripReturnType(descriptor);
    return raw.length() >= HASH_LENGTH ? hash(raw) : raw;
  }

  public OperationKey(String encoded) {
    super(encoded);
    assert encoded.length() == HASH_LENGTH : "Expecting only " + HASH_LENGTH
        + " characters, received " + encoded.length();
  }

  public OperationKey(String requestContextBinaryName, String methodName, String descriptor) {
    super(key(requestContextBinaryName, methodName, descriptor));
  }
}
