/src/com/facebook/buck/io/MorePaths.java

/*
 * Copyright 2013-present Facebook, 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.facebook.buck.io;

import com.facebook.buck.util.HumanReadableException;
import com.facebook.buck.util.environment.Platform;
import com.google.common.base.Function;
import com.google.common.base.Preconditions;
import com.google.common.collect.FluentIterable;
import com.google.common.collect.ImmutableSet;
import com.google.common.io.ByteSource;

import java.io.IOException;
import java.io.InputStream;
import java.nio.file.FileSystem;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Optional;

import javax.annotation.Nullable;

/**
 * Common functions that are done with a {@link Path}. If a function is going to take a
 * {@link ProjectFilesystem}, then it should be in {@link MoreProjectFilesystems} instead.
 */
public class MorePaths {

  /** Utility class: do not instantiate. */
  private MorePaths() {}

  public static final Path EMPTY_PATH = Paths.get("");

  public static String pathWithUnixSeparators(String path) {
    return pathWithUnixSeparators(Paths.get(path));
  }

  public static String pathWithUnixSeparators(Path path) {
    return path.toString().replace('\\', '/');
  }

  public static String pathWithWindowsSeparators(Path path) {
    return path.toString().replace('/', '\\');
  }

  public static String pathWithPlatformSeparators(String path) {
    return pathWithPlatformSeparators(Paths.get(path));
  }

  public static String pathWithPlatformSeparators(Path path) {
    if (Platform.detect() == Platform.WINDOWS) {
      return pathWithWindowsSeparators(path);
    } else {
      return pathWithUnixSeparators(path);
    }
  }

  public static String pathWithUnixSeparatorsAndTrailingSlash(Path path) {
    return pathWithUnixSeparators(path) + "/";
  }

  public static Path getParentOrEmpty(Path path) {
    Path parent = path.getParent();
    if (parent == null) {
      parent = EMPTY_PATH;
    }
    return parent;
  }

  /**
   * Get the path of a file relative to a base directory.
   *
   * @param path must reference a file, not a directory.
   * @param baseDir must reference a directory that is relative to a common directory with the path.
   *     may be null if referencing the same directory as the path.
   * @return the relative path of path from the directory baseDir.
   */
  public static Path getRelativePath(Path path, @Nullable Path baseDir) {
    if (baseDir == null) {
      // This allows callers to use this method with "file.parent()" for files from the project
      // root dir.
      baseDir = EMPTY_PATH;
    }
    Preconditions.checkArgument(!path.isAbsolute(),
        "Path must be relative: %s.", path);
    Preconditions.checkArgument(!baseDir.isAbsolute(),
        "Path must be relative: %s.", baseDir);
    return relativize(baseDir, path);
  }

  /**
   * Get a relative path from path1 to path2, first normalizing each path.
   *
   * This method is a workaround for JDK-6925169 (Path.relativize
   * returns incorrect result if path contains "." or "..").
   */
  public static Path relativize(Path path1, Path path2) {
    Preconditions.checkArgument(
        path1.isAbsolute() == path2.isAbsolute(),
        "Both paths must be absolute or both paths must be relative. (%s is %s, %s is %s)",
        path1,
        path1.isAbsolute() ? "absolute" : "relative",
        path2,
        path2.isAbsolute() ? "absolute" : "relative");

    path1 = normalize(path1);
    path2 = normalize(path2);

    // On Windows, if path1 is "" then Path.relativize returns ../path2 instead of path2 or ./path2
    if (EMPTY_PATH.equals(path1)) {
      return path2;
    }
    return path1.relativize(path2);
  }

  /**
   * Get a path without unnecessary path parts.
   *
   * This method is a workaround for JDK-8037945 (Paths.get("").normalize() throws
   * ArrayIndexOutOfBoundsException).
   */
  public static Path normalize(Path path) {
    if (!EMPTY_PATH.equals(path)) {
      path = path.normalize();
    }
    return path;
  }

  /**
   * Creates a symlink at {@code pathToProjectRoot.resolve(pathToDesiredLinkUnderProjectRoot)} that
   * points to {@code pathToProjectRoot.resolve(pathToExistingFileUnderProjectRoot)} using a
   * relative symlink. Both params must be relative to the project root.
   *
   * @param pathToDesiredLinkUnderProjectRoot must reference a file, not a directory.
   * @param pathToExistingFileUnderProjectRoot must reference a file, not a directory.
   * @return the relative path from the new symlink that was created to the existing file.
   */
  public static Path createRelativeSymlink(
      Path pathToDesiredLinkUnderProjectRoot,
      Path pathToExistingFileUnderProjectRoot,
      Path pathToProjectRoot) throws IOException {
    Path target = getRelativePath(
        pathToExistingFileUnderProjectRoot,
        pathToDesiredLinkUnderProjectRoot.getParent());
    Files.createSymbolicLink(pathToProjectRoot.resolve(pathToDesiredLinkUnderProjectRoot), target);
    return target;
  }

  /**
   * Filters out {@link Path} objects from {@code paths} that aren't a subpath of {@code root} and
   * returns a set of paths relative to {@code root}.
   */
  public static ImmutableSet<Path> filterForSubpaths(Iterable<Path> paths, final Path root) {
    final Path normalizedRoot = root.toAbsolutePath().normalize();
    return FluentIterable.from(paths)
        .filter(input -> {
          if (input.isAbsolute()) {
            return input.normalize().startsWith(normalizedRoot);
          } else {
            return true;
          }
        })
        .transform(input -> {
          if (input.isAbsolute()) {
            return relativize(normalizedRoot, input);
          } else {
            return input;
          }
        })
        .toSet();
  }

  /**
   * Expands "~/foo" into "/home/zuck/foo". Returns regular paths unmodified.
   */
  public static Path expandHomeDir(Path path) {
    if (!path.startsWith("~")) {
      return path;
    }
    Path homePath = path.getFileSystem().getPath(System.getProperty("user.home"));
    if (path.equals(path.getFileSystem().getPath("~"))) {
      return homePath;
    }
    return homePath.resolve(path.subpath(1, path.getNameCount()));
  }

  public static ByteSource asByteSource(final Path path) {
    return new ByteSource() {
      @Override
      public InputStream openStream() throws IOException {
        return Files.newInputStream(path);
      }
    };
  }

  public static String getFileExtension(Path path) {
    String name = path.getFileName().toString();
    int index = name.lastIndexOf('.');
    return index == -1 ? "" : name.substring(index + 1);
  }

  public static String getNameWithoutExtension(Path file) {
    String name = file.getFileName().toString();
    int index = name.lastIndexOf('.');
    return index == -1 ? name : name.substring(0, index);
  }


  public static String stripPathPrefixAndExtension(Path fileName, String prefix) {
    String nameWithoutExtension = getNameWithoutExtension(fileName);

    if (!nameWithoutExtension.startsWith(prefix) ||
        nameWithoutExtension.length() < prefix.length()) {
      throw new HumanReadableException(
          "Invalid prefix on filename in path %s (file %s) - expecting %s",
          fileName,
          nameWithoutExtension,
          prefix);
    }

    return nameWithoutExtension.substring(
        prefix.length(),
        nameWithoutExtension.length());
  }

  public static Optional<Path> stripPrefix(Path p, Path prefix) {
    if (prefix.getNameCount() > p.getNameCount()) {
      return Optional.empty();
    }
    for (int i = 0; i < prefix.getNameCount(); ++i) {
      if (!prefix.getName(i).equals(p.getName(i))) {
        return Optional.empty();
      }
    }
    return Optional.of(p.subpath(prefix.getNameCount(), p.getNameCount()));
  }

  public static Function<String, Path> toPathFn(final FileSystem fileSystem) {
    return input -> fileSystem.getPath(input);
  }

  private static Path dropPathPart(Path p, int i) {
    if (i == 0) {
      return p.subpath(1, p.getNameCount());
    } else if (i == p.getNameCount() - 1) {
      return p.subpath(0, p.getNameCount() - 1);
    } else {
      return p.subpath(0, i).resolve(p.subpath(i + 1, p.getNameCount()));
    }
  }

  /**
   * Drop any "." parts (useless).  Do keep ".." parts; don't normalize them away.
   *
   * Note that while Path objects provide a {@link Path#normalize()} method for eliminating
   * redundant parts of paths like in {@code foo/a/../b/c}, changing its internal parts
   * (and actually using the filesystem), we don't use those methods to clean up the incoming paths;
   * we only strip empty parts, and those consisting only of {@code .} because doing so maps
   * exactly-same paths together, and can't influence where it may point to, whereas {@code ..} and
   * symbolic links might.
   */
  public static Path fixPath(Path p) {
    int i = 0;
    while (i < p.getNameCount()) {
      if (p.getName(i).toString().equals(".")) {
        p = dropPathPart(p, i);
      } else {
        i++;
      }
    }
    return p;
  }

  /**
   * Drop the cache in Path object.
   *
   * Path's implementation class {@code UnixPath}, will lazily initialize a String representation
   * and store it in the object when {@code #toString()} is called for the first time. This doubles
   * the memory requirement for the Path object.
   *
   * This hack constructs a new path, dropping the cached toString value.
   *
   * Due to the nature of what this function does, it's very sensitive to the implementation. Any
   * calls to {@code #toString()} on the returned object would also recreate the cached string
   * value.
   */
  public static Path dropInternalCaches(Path p) {
    return p.getFileSystem().getPath(p.toString());
  }
}