pkg/analyzer/lib/src/util/absolute_path.dart

// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

library analyzer.src.util.absolute_path;

/// The class for manipulating absolute, normalized paths.
class AbsolutePathContext {
  static const int _COLON = 0x3A;
  static const int _LOWER_A = 0x61;
  static const int _LOWER_Z = 0x7A;
  static const int _UPPER_A = 0x41;
  static const int _UPPER_Z = 0x5A;

  final bool _isWindows;
  String separator;
  int _separatorChar;
  String _singlePeriodComponent;
  String _doublePeriodComponent;
  String _singlePeriodEnding;
  String _doublePeriodEnding;

  AbsolutePathContext(this._isWindows) {
    separator = _isWindows ? r'\' : '/';
    _separatorChar = separator.codeUnitAt(0);
    _singlePeriodComponent = separator + '.' + separator;
    _doublePeriodComponent = separator + '..' + separator;
    _singlePeriodEnding = separator + '.';
    _doublePeriodEnding = separator + '..';
  }

  /// Append the given relative [suffix] to the given absolute [parent].
  ///
  ///     context.append('/path/to', 'foo'); // -> '/path/to/foo'
  ///
  /// The given [suffix] cannot be an absolute path or use `..`.
  String append(String parent, String suffix) {
    return '$parent$separator$suffix';
  }

  /// Return the part of the absolute [path] after the last separator on the
  /// context's platform.
  ///
  ///     context.basename('/path/to/foo.dart'); // -> 'foo.dart'
  ///     context.basename('/path/to');          // -> 'to'
  ///     context.basename('/path');             // -> 'path'
  ///     context.basename('/');                 // -> ''
  String basename(String path) {
    int index = path.lastIndexOf(separator);
    return path.substring(index + 1);
  }

  /// Return the part of the absolute [path] before the last separator.
  ///
  ///     context.dirname('/path/to/foo.dart'); // -> '/path/to'
  ///     context.dirname('/path/to');          // -> '/path'
  ///     context.dirname(r'/path');            // -> '/'
  ///     context.dirname(r'/');                // -> '/'
  ///     context.dirname(r'C:\path');          // -> 'C:\'
  ///     context.dirname(r'C:\');              // -> 'C:\'
  String dirname(String path) {
    int firstIndex = path.indexOf(separator);
    int lastIndex = path.lastIndexOf(separator);
    return lastIndex == firstIndex
        ? path.substring(0, firstIndex + 1)
        : path.substring(0, lastIndex);
  }

  /// Return `true` if the given [path] is valid.
  ///
  ///     context.isNormalized('/foo/bar');        // -> true
  ///     context.isNormalized('/foo/bar/../baz'); // -> false
  bool isValid(String path) {
    return _isAbsolute(path) && _isNormalized(path);
  }

  /// Return `true` if [child] is a path beneath [parent], and `false`
  /// otherwise. Both the [child] and [parent] paths must be absolute paths.
  ///
  ///     context.isWithin('/root/path', '/root/path/a'); // -> true
  ///     context.isWithin('/root/path', '/root/other');  // -> false
  ///     context.isWithin('/root/path', '/root/path');   // -> false
  bool isWithin(String parent, String child) {
    int parentLength = parent.length;
    int childLength = child.length;
    if (parentLength >= childLength) {
      return false;
    }
    if (child.codeUnitAt(parentLength) != _separatorChar) {
      return false;
    }
    return _startsWithUnsafe(child, parent);
  }

  /// Split [path] into its components using [separator].
  ///
  ///     context.split('/path/to/foo'); // -> ['', 'path', 'to', 'foo']
  List<String> split(String path) {
    return path.split(separator);
  }

  /// If the given [child] is within the given [parent], then return the
  /// relative path from [parent] to [child]. Otherwise return `null`. Both
  /// the [child] and [parent] paths must be absolute paths.
  ///
  ///     context.relative('/root/path', '/root/path/a/b.dart'); // -> 'a/b.dart'
  ///     context.relative('/root/path', '/root/other.dart');    // -> null
  String suffix(String parent, String child) {
    String parentPrefix = parent + separator;
    if (child.startsWith(parentPrefix)) {
      return child.substring(parentPrefix.length);
    }
    return null;
  }

  /// Return `true` if the given [path] is absolute.
  ///
  ///     _isAbsolute('/foo/bar');   // -> true
  ///     _isAbsolute('/');          // -> true
  ///     _isAbsolute('foo/bar');    // -> false
  ///     _isAbsolute('C:\foo\bar'); // -> true
  ///     _isAbsolute('C:\');        // -> true
  ///     _isAbsolute('foo\bar');    // -> false
  bool _isAbsolute(String path) {
    if (_isWindows) {
      return path.length >= 3 &&
          _isAlphabetic(path.codeUnitAt(0)) &&
          path.codeUnitAt(1) == _COLON &&
          path.codeUnitAt(2) == _separatorChar;
    } else {
      return path.isNotEmpty && path.codeUnitAt(0) == _separatorChar;
    }
  }

  /// Return `true` if the given absolute [path] is normalized.
  ///
  ///     _isNormalized('/foo/bar');        // -> true
  ///     _isNormalized('/foo/..bar');      // -> true
  ///     _isNormalized('/foo/bar..');      // -> true
  ///     _isNormalized('/');               // -> true
  ///     _isNormalized('/foo/bar/../baz'); // -> false
  ///     _isNormalized('/foo/bar/..');     // -> false
  bool _isNormalized(String path) {
    return !path.contains(_singlePeriodComponent) &&
        !path.contains(_doublePeriodComponent) &&
        !path.endsWith(_singlePeriodEnding) &&
        !path.endsWith(_doublePeriodEnding);
  }

  /// Returns whether [char] is the code for an ASCII letter (uppercase or
  /// lowercase).
  static bool _isAlphabetic(int char) {
    return char >= _UPPER_A && char <= _UPPER_Z ||
        char >= _LOWER_A && char <= _LOWER_Z;
  }

  /// Return `true` if [str] starts with the given [prefix].
  ///
  /// The check is done from the end of [prefix], because absolute paths
  /// usually have the same prefix, e.g. the user's home directory.
  static bool _startsWithUnsafe(String str, String prefix) {
    int len = prefix.length;
    for (int i = len - 1; i >= 0; i--) {
      if (str.codeUnitAt(i) != prefix.codeUnitAt(i)) {
        return false;
      }
    }
    return true;
  }
}