// Copyright 2014 The Bazel Authors. All rights reserved.
//
// 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.devtools.build.lib.vfs;

import com.google.common.collect.ImmutableSet;

import java.util.Objects;

import javax.annotation.Nullable;

/**
 * An immutable set of modified source files. The scope of these files is context-dependent; in some
 * uses this may mean information about all files in the client, while in other uses this may mean
 * information about some specific subset of files. {@link #EVERYTHING_MODIFIED} can be used to
 * indicate that all files of interest have been modified.
 */
public final class ModifiedFileSet {

  public static final ModifiedFileSet EVERYTHING_MODIFIED = new ModifiedFileSet(null);
  public static final ModifiedFileSet NOTHING_MODIFIED = new ModifiedFileSet(
      ImmutableSet.<PathFragment>of());

  @Nullable private final ImmutableSet<PathFragment> modified;

  /**
   * Whether all files of interest should be treated as potentially modified.
   */
  public boolean treatEverythingAsModified() {
    return modified == null;
  }

  /**
   * The set of files of interest that were modified.
   *
   * @throws IllegalStateException if {@link #treatEverythingAsModified} returns true.
   */
  public ImmutableSet<PathFragment> modifiedSourceFiles() {
    if (treatEverythingAsModified()) {
      throw new IllegalStateException();
    }
    return modified;
  }

  @Override
  public boolean equals(Object o) {
    if (!(o instanceof ModifiedFileSet)) {
      return false;
    }
    ModifiedFileSet other = (ModifiedFileSet) o;
    return Objects.equals(modified, other.modified);
  }

  @Override
  public int hashCode() {
    return Objects.hashCode(modified);
  }

  @Override
  public String toString() {
    if (this == EVERYTHING_MODIFIED) {
      return "EVERYTHING_MODIFIED";
    } else if (this == NOTHING_MODIFIED) {
      return "NOTHING_MODIFIED";
    } else {
      return modified.toString();
    }
  }

  private ModifiedFileSet(ImmutableSet<PathFragment> modified) {
    this.modified = modified;
  }

  /**
   * The builder for {@link ModifiedFileSet}.
   */
  public static class Builder {
    private final ImmutableSet.Builder<PathFragment> setBuilder =
        ImmutableSet.<PathFragment>builder();

    public ModifiedFileSet build() {
      ImmutableSet<PathFragment> modified = setBuilder.build();
      return modified.isEmpty() ? NOTHING_MODIFIED : new ModifiedFileSet(modified);
    }

    public Builder modify(PathFragment pathFragment) {
      setBuilder.add(pathFragment);
      return this;
    }

    public Builder modifyAll(Iterable<PathFragment> pathFragments) {
      setBuilder.addAll(pathFragments);
      return this;
    }
  }

  public static Builder builder() {
    return new Builder();
  }

  public static ModifiedFileSet union(ModifiedFileSet mfs1, ModifiedFileSet mfs2) {
    if (mfs1.treatEverythingAsModified() || mfs2.treatEverythingAsModified()) {
      return ModifiedFileSet.EVERYTHING_MODIFIED;
    }
    if (mfs1.equals(ModifiedFileSet.NOTHING_MODIFIED)) {
      return mfs2;
    }
    if (mfs2.equals(ModifiedFileSet.NOTHING_MODIFIED)) {
      return mfs1;
    }
    return ModifiedFileSet.builder()
        .modifyAll(mfs1.modifiedSourceFiles())
        .modifyAll(mfs2.modifiedSourceFiles())
        .build();
  }
}