// Protocol Buffers - Google's data interchange format
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package com.google.protobuf.util;

import static com.google.common.base.Preconditions.checkArgument;

import com.google.common.primitives.Ints;
import com.google.protobuf.Descriptors.Descriptor;
import com.google.protobuf.Descriptors.FieldDescriptor;
import com.google.protobuf.FieldMask;
import com.google.protobuf.Internal;
import com.google.protobuf.Message;

import java.util.Arrays;

/**
 * Utility helper functions to work with {@link com.google.protobuf.FieldMask}.
 */
public class FieldMaskUtil {
  private static final String FIELD_PATH_SEPARATOR = ",";
  private static final String FIELD_PATH_SEPARATOR_REGEX = ",";
  private static final String FIELD_SEPARATOR_REGEX = "\\.";
  
  private FieldMaskUtil() {}

  /**
   * Converts a FieldMask to a string.
   */
  public static String toString(FieldMask fieldMask) {
    // TODO(xiaofeng): Consider using com.google.common.base.Joiner here instead.
    StringBuilder result = new StringBuilder();
    boolean first = true;
    for (String value : fieldMask.getPathsList()) {
      if (value.isEmpty()) {
        // Ignore empty paths.
        continue;
      }
      if (first) {
        first = false;
      } else {
        result.append(FIELD_PATH_SEPARATOR);
      }
      result.append(value);
    }
    return result.toString();
  }

  /**
   * Parses from a string to a FieldMask.
   */
  public static FieldMask fromString(String value) {
    // TODO(xiaofeng): Consider using com.google.common.base.Splitter here instead.
    return fromStringList(
        null, Arrays.asList(value.split(FIELD_PATH_SEPARATOR_REGEX)));
  }

  /**
   * Parses from a string to a FieldMask and validates all field paths.
   * 
   * @throws IllegalArgumentException if any of the field path is invalid.
   */
  public static FieldMask fromString(Class<? extends Message> type, String value) {
    // TODO(xiaofeng): Consider using com.google.common.base.Splitter here instead.
    return fromStringList(
        type, Arrays.asList(value.split(FIELD_PATH_SEPARATOR_REGEX)));
  }

  /**
   * Constructs a FieldMask for a list of field paths in a certain type.
   *
   * @throws IllegalArgumentException if any of the field path is not valid.
   */
  // TODO(xiaofeng): Consider renaming fromStrings()
  public static FieldMask fromStringList(
      Class<? extends Message> type, Iterable<String> paths) {
    FieldMask.Builder builder = FieldMask.newBuilder();
    for (String path : paths) {
      if (path.isEmpty()) {
        // Ignore empty field paths.
        continue;
      }
      if (type != null && !isValid(type, path)) {
        throw new IllegalArgumentException(
            path + " is not a valid path for " + type);
      }
      builder.addPaths(path);
    }
    return builder.build();
  }

  /**
   * Constructs a FieldMask from the passed field numbers.
   *
   * @throws IllegalArgumentException if any of the fields are invalid for the message.
   */
  public static FieldMask fromFieldNumbers(Class<? extends Message> type, int... fieldNumbers) {
    return fromFieldNumbers(type, Ints.asList(fieldNumbers));
  }

  /**
   * Constructs a FieldMask from the passed field numbers.
   *
   * @throws IllegalArgumentException if any of the fields are invalid for the message.
   */
  public static FieldMask fromFieldNumbers(
      Class<? extends Message> type, Iterable<Integer> fieldNumbers) {
    Descriptor descriptor = Internal.getDefaultInstance(type).getDescriptorForType();

    FieldMask.Builder builder = FieldMask.newBuilder();
    for (Integer fieldNumber : fieldNumbers) {
      FieldDescriptor field = descriptor.findFieldByNumber(fieldNumber);
      checkArgument(
          field != null,
          String.format("%s is not a valid field number for %s.", fieldNumber, type));
      builder.addPaths(field.getName());
    }
    return builder.build();
  }

  /**
   * Checks whether paths in a given fields mask are valid.
   */
  public static boolean isValid(Class<? extends Message> type, FieldMask fieldMask) {
    Descriptor descriptor =
        Internal.getDefaultInstance(type).getDescriptorForType();
    
    return isValid(descriptor, fieldMask);
  }
  
  /**
   * Checks whether paths in a given fields mask are valid.
   */
  public static boolean isValid(Descriptor descriptor, FieldMask fieldMask) {
    for (String path : fieldMask.getPathsList()) {
      if (!isValid(descriptor, path)) {
        return false;
      }
    }
    return true;
  }

  /**
   * Checks whether a given field path is valid.
   */
  public static boolean isValid(Class<? extends Message> type, String path) {
    Descriptor descriptor =
        Internal.getDefaultInstance(type).getDescriptorForType();
    
    return isValid(descriptor, path);
  }

  /**
   * Checks whether paths in a given fields mask are valid.
   */
  public static boolean isValid(Descriptor descriptor, String path) {
    String[] parts = path.split(FIELD_SEPARATOR_REGEX);
    if (parts.length == 0) {
      return false;
    }
    for (String name : parts) {
      if (descriptor == null) {
        return false;
      }
      FieldDescriptor field = descriptor.findFieldByName(name);
      if (field == null) {
        return false;
      }
      if (!field.isRepeated()
          && field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
        descriptor = field.getMessageType();
      } else {
        descriptor = null;
      }
    }
    return true;
  }
  
  /**
   * Converts a FieldMask to its canonical form. In the canonical form of a
   * FieldMask, all field paths are sorted alphabetically and redundant field
   * paths are moved.
   */
  public static FieldMask normalize(FieldMask mask) {
    return new FieldMaskTree(mask).toFieldMask();
  }

  /**
   * Creates a union of two or more FieldMasks.
   */
  public static FieldMask union(
      FieldMask firstMask, FieldMask secondMask, FieldMask... otherMasks) {
    FieldMaskTree maskTree = new FieldMaskTree(firstMask).mergeFromFieldMask(secondMask);
    for (FieldMask mask : otherMasks) {
      maskTree.mergeFromFieldMask(mask);
    }
    return maskTree.toFieldMask();
  }

  /**
   * Calculates the intersection of two FieldMasks.
   */
  public static FieldMask intersection(FieldMask mask1, FieldMask mask2) {
    FieldMaskTree tree = new FieldMaskTree(mask1);
    FieldMaskTree result = new FieldMaskTree();
    for (String path : mask2.getPathsList()) {
      tree.intersectFieldPath(path, result);
    }
    return result.toFieldMask();
  }

  /**
   * Options to customize merging behavior.
   */
  public static final class MergeOptions {
    private boolean replaceMessageFields = false;
    private boolean replaceRepeatedFields = false;
    // TODO(b/28277137): change the default behavior to always replace primitive fields after
    // fixing all failing TAP tests.
    private boolean replacePrimitiveFields = false;

    /**
     * Whether to replace message fields (i.e., discard existing content in
     * destination message fields) when merging.
     * Default behavior is to merge the source message field into the
     * destination message field.
     */ 
    public boolean replaceMessageFields() {
      return replaceMessageFields;
    }

    /**
     * Whether to replace repeated fields (i.e., discard existing content in
     * destination repeated fields) when merging.
     * Default behavior is to append elements from source repeated field to the
     * destination repeated field.
     */
    public boolean replaceRepeatedFields() {
      return replaceRepeatedFields;
    }

    /**
     * Whether to replace primitive (non-repeated and non-message) fields in
     * destination message fields with the source primitive fields (i.e., if the
     * field is set in the source, the value is copied to the
     * destination; if the field is unset in the source, the field is cleared
     * from the destination) when merging.
     *
     * <p>Default behavior is to always set the value of the source primitive
     * field to the destination primitive field, and if the source field is
     * unset, the default value of the source field is copied to the
     * destination.
     */
    public boolean replacePrimitiveFields() {
      return replacePrimitiveFields;
    }

    public void setReplaceMessageFields(boolean value) {
      replaceMessageFields = value;
    }

    public void setReplaceRepeatedFields(boolean value) {
      replaceRepeatedFields = value;
    }

    public void setReplacePrimitiveFields(boolean value) {
      replacePrimitiveFields = value;
    }
  }

  /**
   * Merges fields specified by a FieldMask from one message to another with the
   * specified merge options.
   */
  public static void merge(FieldMask mask, Message source,
      Message.Builder destination, MergeOptions options) {
    new FieldMaskTree(mask).merge(source, destination, options);
  }

  /**
   * Merges fields specified by a FieldMask from one message to another.
   */
  public static void merge(FieldMask mask, Message source,
      Message.Builder destination) {
    merge(mask, source, destination, new MergeOptions());
  }
}