// Copyright 2014 Google Inc. 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.unix;

/**
 * <p>Equivalent to UNIX's "struct stat", a FileStatus instance contains
 * various bits of metadata about a directory entry.
 *
 * <p>The Java SDK provides access to some but not all of the information
 * available via the stat(2) and lstat(2) syscalls, but often requires that
 * multiple calls be made to obtain it.  By reifying stat buffers as Java
 * objects and providing a wrapper around the stat/lstat calls, we give client
 * applications access to the richer file metadata and enable a reduction in
 * the number of system calls, which is critical for high-performance tools.
 *
 * <p>This class is optimized for memory usage.  Operations that are not yet
 * required for any client are intentionally unimplemented to save space.
 * Currently, we only support these fields: st_mode, st_size, st_atime,
 * st_atimensec, st_mtime, st_mtimensec, st_ctime, st_ctimensec, st_dev, st_ino.
 * Methods that require other fields throw UnsupportedOperationException.
 */
public class FileStatus {

  private final int st_mode;
  private final int st_atime; // (unsigned)
  private final int st_atimensec; // (unsigned)
  private final int st_mtime; // (unsigned)
  private final int st_mtimensec; // (unsigned)
  private final int st_ctime; // (unsigned)
  private final int st_ctimensec; // (unsigned)
  private final long st_size;
  private final int st_dev;
  private final long st_ino;

  /**
   * Constructs a FileStatus instance.  (Called only from JNI code.)
   */
  protected FileStatus(int st_mode, int st_atime, int st_atimensec, int st_mtime, int st_mtimensec,
                       int st_ctime, int st_ctimensec, long st_size, int st_dev, long st_ino) {
    this.st_mode = st_mode;
    this.st_atime = st_atime;
    this.st_atimensec = st_atimensec;
    this.st_mtime = st_mtime;
    this.st_mtimensec = st_mtimensec;
    this.st_ctime = st_ctime;
    this.st_ctimensec = st_ctimensec;
    this.st_size = st_size;
    this.st_dev = st_dev;
    this.st_ino = st_ino;
  }

  /**
   * Returns the device number of this inode.
   */
  public int getDeviceNumber() {
    return st_dev;
  }

  /**
   * Returns the number of this inode.  Inode numbers are (usually) unique for
   * a given device.
   */
  public long getInodeNumber() {
    return st_ino;
  }

  /**
   * Returns true iff this file is a regular file.
   */
  public boolean isRegularFile() {
    return (st_mode & S_IFMT) == S_IFREG;
  }

  /**
   * Returns true iff this file is a directory.
   */
  public boolean isDirectory() {
    return (st_mode & S_IFMT) == S_IFDIR;
  }

  /**
   * Returns true iff this file is a symbolic link.
   */
  public boolean isSymbolicLink() {
    return (st_mode & S_IFMT) == S_IFLNK;
  }

  /**
   * Returns true iff this file is a character device.
   */
  public boolean isCharacterDevice() {
    return (st_mode & S_IFMT) == S_IFCHR;
  }

  /**
   * Returns true iff this file is a block device.
   */
  public boolean isBlockDevice() {
    return (st_mode & S_IFMT) == S_IFBLK;
  }

  /**
   * Returns true iff this file is a FIFO.
   */
  public boolean isFIFO() {
    return (st_mode & S_IFMT) == S_IFIFO;
  }

  /**
   * Returns true iff this file is a UNIX-domain socket.
   */
  public boolean isSocket() {
    return (st_mode & S_IFMT) == S_IFSOCK;
  }

  /**
   * Returns true iff this file has its "set UID" bit set.
   */
  public boolean isSetUserId() {
    return (st_mode & S_ISUID) != 0;
  }

  /**
   * Returns true iff this file has its "set GID" bit set.
   */
  public boolean isSetGroupId() {
    return (st_mode & S_ISGID) != 0;
  }

  /**
   * Returns true iff this file has its "sticky" bit set.  See UNIX manuals for
   * explanation.
   */
  public boolean isSticky() {
    return (st_mode & S_ISVTX) != 0;
  }

  /**
   * Returns the user/group/other permissions part of the mode bits (i.e.
   * st_mode masked with 0777), interpreted according to longstanding UNIX
   * tradition.
   */
  public int getPermissions() {
    return st_mode & S_IRWXA;
  }

  /**
   * Returns the total size, in bytes, of this file.
   */
  public long getSize() {
    return st_size;
  }

  /**
   * Returns the last access time of this file (seconds since UNIX epoch).
   */
  public long getLastAccessTime() {
    return unsignedIntToLong(st_atime);
  }

  /**
   * Returns the fractional part of the last access time of this file (nanoseconds).
   */
  public long getFractionalLastAccessTime() {
    return unsignedIntToLong(st_atimensec);
  }

  /**
   * Returns the last modified time of this file (seconds since UNIX epoch).
   */
  public long getLastModifiedTime() {
    return unsignedIntToLong(st_mtime);
  }

  /**
   * Returns the fractional part of the last modified time of this file (nanoseconds).
   */
  public long getFractionalLastModifiedTime() {
    return unsignedIntToLong(st_mtimensec);
  }

  /**
   * Returns the last change time of this file (seconds since UNIX epoch).
   */
  public long getLastChangeTime() {
    return unsignedIntToLong(st_ctime);
  }

  /**
   * Returns the fractional part of the last change time of this file (nanoseconds).
   */
  public long getFractionalLastChangeTime() {
    return unsignedIntToLong(st_ctimensec);
  }

  ////////////////////////////////////////////////////////////////////////

  @Override
  public String toString() {
    return String.format("FileStatus(mode=0%06o,size=%d,mtime=%d)",
                         st_mode, st_size, st_mtime);
  }

  @Override
  public int hashCode() {
    return st_mode;
  }

  ////////////////////////////////////////////////////////////////////////
  // Platform-specific details. These fields are public so that they can
  // be used from other packages. See POSIX and/or Linux manuals for details.
  //
  // These need to be kept in sync with the native code and system call
  // interface.  (The unit tests ensure that.)  Of course, this decoding could
  // be done in the JNI code to ensure maximum portability, but (a) we don't
  // expect we'll need that any time soon, and (b) that would require eager
  // rather than on-demand bitmunging of all attributes.  In any case, it's not
  // part of the interface so it can be easily changed later if necessary.

  public static final int S_IFMT =   0170000; // mask: filetype bitfields
  public static final int S_IFSOCK = 0140000; // socket
  public static final int S_IFLNK =  0120000; // symbolic link
  public static final int S_IFREG =  0100000; // regular file
  public static final int S_IFBLK =  0060000; // block device
  public static final int S_IFDIR =  0040000; // directory
  public static final int S_IFCHR =  0020000; // character device
  public static final int S_IFIFO =  0010000; // fifo
  public static final int S_ISUID =  0004000; // set UID bit
  public static final int S_ISGID =  0002000; // set GID bit (see below)
  public static final int S_ISVTX =  0001000; // sticky bit (see below)
  public static final int S_IRWXA =  00777; // mask: all permissions
  public static final int S_IRWXU =  00700; // mask: file owner permissions
  public static final int S_IRUSR =  00400; // owner has read permission
  public static final int S_IWUSR =  00200; // owner has write permission
  public static final int S_IXUSR =  00100; // owner has execute permission
  public static final int S_IRWXG =  00070; // mask: group permissions
  public static final int S_IRGRP =  00040; // group has read permission
  public static final int S_IWGRP =  00020; // group has write permission
  public static final int S_IXGRP =  00010; // group has execute permission
  public static final int S_IRWXO =  00007; // mask: other permissions
  public static final int S_IROTH =  00004; // others have read permission
  public static final int S_IWOTH =  00002; // others have write permisson
  public static final int S_IXOTH =  00001; // others have execute permission

  public static final int S_IEXEC =  00111; // owner, group, world execute

  static long unsignedIntToLong(int i) {
    return (i & 0x7FFFFFFF) - (long) (i & 0x80000000);
  }

}