/**
 * Copyright (C) 2006 Google Inc.
 *
 * <p>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
 *
 * <p>http://www.apache.org/licenses/LICENSE-2.0
 *
 * <p>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 play.inject;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Set;
import java.util.HashSet;

/**
 * Provides access to the calling line of code.
 * https://github.com/google/guice/blob/3.0/core/src/com/google/inject/internal/util/SourceProvider.java
 *
 * @author crazybob@google.com (Bob Lee)
 */
public final class SourceProvider {

  /** Indicates that the source is unknown. */
  public static final Object UNKNOWN_SOURCE = "[unknown source]";

  private final Set<String> classNamesToSkip;

  public static final SourceProvider DEFAULT_INSTANCE =
      new SourceProvider(Collections.singleton(SourceProvider.class.getName()));

  private SourceProvider(Collection<String> classesToSkip) {
    this.classNamesToSkip = Collections.unmodifiableSet(new HashSet<String>(classesToSkip));
  }

  /**
   * Returns a new instance that also skips {@code moreClassesToSkip}.
   *
   * @param moreClassesToSkip a list of classes to skip in from source provider.
   * @return the source provider skipping {@code moreClassesToSkip}.
   */
  public SourceProvider plusSkippedClasses(Class... moreClassesToSkip) {
    Set<String> toSkip = new HashSet<String>(classNamesToSkip);
    toSkip.addAll(asStrings(moreClassesToSkip));
    return new SourceProvider(toSkip);
  }

  /** Returns the class names as Strings */
  private static List<String> asStrings(Class... classes) {
    List<String> strings = new ArrayList<String>();
    for (Class c : classes) {
      strings.add(c.getName());
    }
    return strings;
  }

  /**
   * Returns the calling line of code. The selected line is the nearest to the top of the stack that
   * is not skipped.
   *
   * @return a stack trace element containing the caller.
   */
  public StackTraceElement get() {
    for (final StackTraceElement element : new Throwable().getStackTrace()) {
      String className = element.getClassName();
      if (!classNamesToSkip.contains(className)) {
        return element;
      }
    }
    throw new AssertionError();
  }
}
