Refactor pkg/path.

pkg/path/lib/src/context.dart

Index: pkg/path/lib/src/context.dart
diff --git a/pkg/path/lib/src/context.dart b/pkg/path/lib/src/context.dart
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+++ b/pkg/path/lib/src/context.dart
@@ -0,0 +1,492 @@
+// Copyright (c) 2013, 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 path.context;
+
+import 'style.dart';
+import 'parsed_path.dart';
+import 'path_exception.dart';
+import '../path.dart' as p;
+
+/// An instantiable class for manipulating paths. Unlike the top-level
+/// functions, this lets you explicitly select what platform the paths will use.
+class Context {
+  /// Creates a new path context for the given style and current directory.
+  ///
+  /// If [style] is omitted, it uses the host operating system's path style. If
+  /// only [current] is omitted, it defaults ".". If *both* [style] and
+  /// [current] are omitted, [current] defaults to the real current working
+  /// directory.
+  ///
+  /// On the browser, [style] defaults to [Style.url] and [current] defaults to
+  /// the current URL.
+  factory Context({Style style, String current}) {
+    if (current == null) {
+      if (style == null) {
+        current = p.current;
+      } else {
+        current = ".";
+      }
+    }
+
+    if (style == null) style = Style.platform;
+
+    return new Context._(style, current);
+  }
+
+  Context._(this.style, this.current);
+
+  /// The style of path that this context works with.
+  final Style style;
+
+  /// The current directory that relative paths will be relative to.
+  final String current;
+
+  /// Gets the path separator for the context's [style]. On Mac and Linux,
+  /// this is `/`. On Windows, it's `\`.
+  String get separator => style.separator;
+
+  /// Creates a new path by appending the given path parts to [current].
+  /// Equivalent to [join()] with [current] as the first argument. Example:
+  ///
+  ///     var context = new Context(current: '/root');
+  ///     context.absolute('path', 'to', 'foo'); // -> '/root/path/to/foo'
+  ///
+  /// If [current] isn't absolute, this won't return an absolute path.
+  String absolute(String part1, [String part2, String part3, String part4,
+              String part5, String part6, String part7]) {
+    return join(current, part1, part2, part3, part4, part5, part6, part7);
+  }
+
+  /// Gets the part of [path] after the last separator on the context's
+  /// platform.
+  ///
+  ///     context.basename('path/to/foo.dart'); // -> 'foo.dart'
+  ///     context.basename('path/to');          // -> 'to'
+  ///
+  /// Trailing separators are ignored.
+  ///
+  ///     context.basename('path/to/'); // -> 'to'
+  String basename(String path) => _parse(path).basename;
+
+  /// Gets the part of [path] after the last separator on the context's
+  /// platform, and without any trailing file extension.
+  ///
+  ///     context.basenameWithoutExtension('path/to/foo.dart'); // -> 'foo'
+  ///
+  /// Trailing separators are ignored.
+  ///
+  ///     context.basenameWithoutExtension('path/to/foo.dart/'); // -> 'foo'
+  String basenameWithoutExtension(String path) =>
+    _parse(path).basenameWithoutExtension;
+
+  /// Gets the part of [path] before the last separator.
+  ///
+  ///     context.dirname('path/to/foo.dart'); // -> 'path/to'
+  ///     context.dirname('path/to');          // -> 'path'
+  ///
+  /// Trailing separators are ignored.
+  ///
+  ///     context.dirname('path/to/'); // -> 'path'
+  String dirname(String path) {
+    var parsed = _parse(path);
+    parsed.removeTrailingSeparators();
+    if (parsed.parts.isEmpty) return parsed.root == null ? '.' : parsed.root;
+    if (parsed.parts.length == 1) {
+      return parsed.root == null ? '.' : parsed.root;
+    }
+    parsed.parts.removeLast();
+    parsed.separators.removeLast();
+    parsed.removeTrailingSeparators();
+    return parsed.toString();
+  }
+
+  /// Gets the file extension of [path]: the portion of [basename] from the last
+  /// `.` to the end (including the `.` itself).
+  ///
+  ///     context.extension('path/to/foo.dart'); // -> '.dart'
+  ///     context.extension('path/to/foo'); // -> ''
+  ///     context.extension('path.to/foo'); // -> ''
+  ///     context.extension('path/to/foo.dart.js'); // -> '.js'
+  ///
+  /// If the file name starts with a `.`, then it is not considered an
+  /// extension:
+  ///
+  ///     context.extension('~/.bashrc');    // -> ''
+  ///     context.extension('~/.notes.txt'); // -> '.txt'
+  String extension(String path) => _parse(path).extension;
+
+  // TODO(nweiz): add a UNC example for Windows once issue 7323 is fixed.
+  /// Returns the root of [path] if it's absolute, or an empty string if it's
+  /// relative.
+  ///
+  ///     // Unix
+  ///     context.rootPrefix('path/to/foo'); // -> ''
+  ///     context.rootPrefix('/path/to/foo'); // -> '/'
+  ///
+  ///     // Windows
+  ///     context.rootPrefix(r'path\to\foo'); // -> ''
+  ///     context.rootPrefix(r'C:\path\to\foo'); // -> r'C:\'
+  ///
+  ///     // URL
+  ///     context.rootPrefix('path/to/foo'); // -> ''
+  ///     context.rootPrefix('http://dartlang.org/path/to/foo');
+  ///       // -> 'http://dartlang.org'
+  String rootPrefix(String path) {
+    var root = _parse(path).root;
+    return root == null ? '' : root;
+  }
+
+  /// Returns `true` if [path] is an absolute path and `false` if it is a
+  /// relative path.
+  ///
+  /// On POSIX systems, absolute paths start with a `/` (forward slash). On
+  /// Windows, an absolute path starts with `\\`, or a drive letter followed by
+  /// `:/` or `:\`. For URLs, absolute paths either start with a protocol and
+  /// optional hostname (e.g. `http://dartlang.org`, `file://`) or with a `/`.
+  ///
+  /// URLs that start with `/` are known as "root-relative", since they're
+  /// relative to the root of the current URL. Since root-relative paths are
+  /// still absolute in every other sense, [isAbsolute] will return true for
+  /// them. They can be detected using [isRootRelative].
+  bool isAbsolute(String path) => _parse(path).isAbsolute;
+
+  /// Returns `true` if [path] is a relative path and `false` if it is absolute.
+  /// On POSIX systems, absolute paths start with a `/` (forward slash). On
+  /// Windows, an absolute path starts with `\\`, or a drive letter followed by
+  /// `:/` or `:\`.
+  bool isRelative(String path) => !this.isAbsolute(path);
+
+  /// Returns `true` if [path] is a root-relative path and `false` if it's not.
+  ///
+  /// URLs that start with `/` are known as "root-relative", since they're
+  /// relative to the root of the current URL. Since root-relative paths are
+  /// still absolute in every other sense, [isAbsolute] will return true for
+  /// them. They can be detected using [isRootRelative].
+  ///
+  /// No POSIX and Windows paths are root-relative.
+  bool isRootRelative(String path) => _parse(path).isRootRelative;
+
+  /// Joins the given path parts into a single path. Example:
+  ///
+  ///     context.join('path', 'to', 'foo'); // -> 'path/to/foo'
+  ///
+  /// If any part ends in a path separator, then a redundant separator will not
+  /// be added:
+  ///
+  ///     context.join('path/', 'to', 'foo'); // -> 'path/to/foo
+  ///
+  /// If a part is an absolute path, then anything before that will be ignored:
+  ///
+  ///     context.join('path', '/to', 'foo'); // -> '/to/foo'
+  ///
+  String join(String part1, [String part2, String part3, String part4,
+              String part5, String part6, String part7, String part8]) {
+    var parts = [part1, part2, part3, part4, part5, part6, part7, part8];
+    _validateArgList("join", parts);
+    return joinAll(parts.where((part) => part != null));
+  }
+
+  /// Joins the given path parts into a single path. Example:
+  ///
+  ///     context.joinAll(['path', 'to', 'foo']); // -> 'path/to/foo'
+  ///
+  /// If any part ends in a path separator, then a redundant separator will not
+  /// be added:
+  ///
+  ///     context.joinAll(['path/', 'to', 'foo']); // -> 'path/to/foo
+  ///
+  /// If a part is an absolute path, then anything before that will be ignored:
+  ///
+  ///     context.joinAll(['path', '/to', 'foo']); // -> '/to/foo'
+  ///
+  /// For a fixed number of parts, [join] is usually terser.
+  String joinAll(Iterable<String> parts) {
+    var buffer = new StringBuffer();
+    var needsSeparator = false;
+    var isAbsoluteAndNotRootRelative = false;
+
+    for (var part in parts.where((part) => part != '')) {
+      if (this.isRootRelative(part) && isAbsoluteAndNotRootRelative) {
+        // If the new part is root-relative, it preserves the previous root but
+        // replaces the path after it.
+        var parsed = _parse(part);
+        parsed.root = this.rootPrefix(buffer.toString());
+        if (parsed.root.contains(style.needsSeparatorPattern)) {
+          parsed.separators[0] = style.separator;
+        }
+        buffer.clear();
+        buffer.write(parsed.toString());
+      } else if (this.isAbsolute(part)) {
+        isAbsoluteAndNotRootRelative = !this.isRootRelative(part);
+        // An absolute path discards everything before it.
+        buffer.clear();
+        buffer.write(part);
+      } else {
+        if (part.length > 0 && part[0].contains(style.separatorPattern)) {
+          // The part starts with a separator, so we don't need to add one.
+        } else if (needsSeparator) {
+          buffer.write(separator);
+        }
+
+        buffer.write(part);
+      }
+
+      // Unless this part ends with a separator, we'll need to add one before
+      // the next part.
+      needsSeparator = part.contains(style.needsSeparatorPattern);
+    }
+
+    return buffer.toString();
+  }
+
+  // TODO(nweiz): add a UNC example for Windows once issue 7323 is fixed.
+  /// Splits [path] into its components using the current platform's
+  /// [separator]. Example:
+  ///
+  ///     context.split('path/to/foo'); // -> ['path', 'to', 'foo']
+  ///
+  /// The path will *not* be normalized before splitting.
+  ///
+  ///     context.split('path/../foo'); // -> ['path', '..', 'foo']
+  ///
+  /// If [path] is absolute, the root directory will be the first element in the
+  /// array. Example:
+  ///
+  ///     // Unix
+  ///     context.split('/path/to/foo'); // -> ['/', 'path', 'to', 'foo']
+  ///
+  ///     // Windows
+  ///     context.split(r'C:\path\to\foo'); // -> [r'C:\', 'path', 'to', 'foo']
+  List<String> split(String path) {
+    var parsed = _parse(path);
+    // Filter out empty parts that exist due to multiple separators in a row.
+    parsed.parts = parsed.parts.where((part) => !part.isEmpty)
+                               .toList();
+    if (parsed.root != null) parsed.parts.insert(0, parsed.root);
+    return parsed.parts;
+  }
+
+  /// Normalizes [path], simplifying it by handling `..`, and `.`, and
+  /// removing redundant path separators whenever possible.
+  ///
+  ///     context.normalize('path/./to/..//file.text'); // -> 'path/file.txt'
+  String normalize(String path) {
+    var parsed = _parse(path);
+    parsed.normalize();
+    return parsed.toString();
+  }
+
+  /// Attempts to convert [path] to an equivalent relative path relative to
+  /// [root].
+  ///
+  ///     var context = new Context(current: '/root/path');
+  ///     context.relative('/root/path/a/b.dart'); // -> 'a/b.dart'
+  ///     context.relative('/root/other.dart'); // -> '../other.dart'
+  ///
+  /// If the [from] argument is passed, [path] is made relative to that instead.
+  ///
+  ///     context.relative('/root/path/a/b.dart',
+  ///         from: '/root/path'); // -> 'a/b.dart'
+  ///     context.relative('/root/other.dart',
+  ///         from: '/root/path'); // -> '../other.dart'
+  ///
+  /// If [path] and/or [from] are relative paths, they are assumed to be
+  /// relative to [current].
+  ///
+  /// Since there is no relative path from one drive letter to another on
+  /// Windows, this will return an absolute path in that case.
+  ///
+  ///     context.relative(r'D:\other', from: r'C:\other'); // -> 'D:\other'
+  ///
+  /// This will also return an absolute path if an absolute [path] is passed to
+  /// a context with a relative path for [current].
+  ///
+  ///     var context = new Context(r'some/relative/path');
+  ///     context.relative(r'/absolute/path'); // -> '/absolute/path'
+  ///
+  /// If [root] is relative, it may be impossible to determine a path from
+  /// [from] to [path]. For example, if [root] and [path] are "." and [from] is
+  /// "/", no path can be determined. In this case, a [PathException] will be
+  /// thrown.
+  String relative(String path, {String from}) {
+    from = from == null ? current : this.join(current, from);
+
+    // We can't determine the path from a relative path to an absolute path.
+    if (this.isRelative(from) && this.isAbsolute(path)) {
+      return this.normalize(path);
+    }
+
+    // If the given path is relative, resolve it relative to the context's
+    // current directory.
+    if (this.isRelative(path) || this.isRootRelative(path)) {
+      path = this.absolute(path);
+    }
+
+    // If the path is still relative and `from` is absolute, we're unable to
+    // find a path from `from` to `path`.
+    if (this.isRelative(path) && this.isAbsolute(from)) {
+      throw new PathException('Unable to find a path to "$path" from "$from".');
+    }
+
+    var fromParsed = _parse(from)..normalize();
+    var pathParsed = _parse(path)..normalize();
+
+    if (fromParsed.parts.length > 0 && fromParsed.parts[0] == '.') {
+      return pathParsed.toString();
+    }
+
+    // If the root prefixes don't match (for example, different drive letters
+    // on Windows), then there is no relative path, so just return the absolute
+    // one. In Windows, drive letters are case-insenstive and we allow
+    // calculation of relative paths, even if a path has not been normalized.
+    if (fromParsed.root != pathParsed.root &&
+        ((fromParsed.root ==  null || pathParsed.root == null) ||
+          fromParsed.root.toLowerCase().replaceAll('/', '\\') !=
+          pathParsed.root.toLowerCase().replaceAll('/', '\\'))) {
+      return pathParsed.toString();
+    }
+
+    // Strip off their common prefix.
+    while (fromParsed.parts.length > 0 && pathParsed.parts.length > 0 &&
+           fromParsed.parts[0] == pathParsed.parts[0]) {
+      fromParsed.parts.removeAt(0);
+      fromParsed.separators.removeAt(1);
+      pathParsed.parts.removeAt(0);
+      pathParsed.separators.removeAt(1);
+    }
+
+    // If there are any directories left in the from path, we need to walk up
+    // out of them. If a directory left in the from path is '..', it cannot
+    // be cancelled by adding a '..'.
+    if (fromParsed.parts.length > 0 && fromParsed.parts[0] == '..') {
+      throw new PathException('Unable to find a path to "$path" from "$from".');
+    }
+    pathParsed.parts.insertAll(0,
+        new List.filled(fromParsed.parts.length, '..'));
+    pathParsed.separators[0] = '';
+    pathParsed.separators.insertAll(1,
+        new List.filled(fromParsed.parts.length, style.separator));
+
+    // Corner case: the paths completely collapsed.
+    if (pathParsed.parts.length == 0) return '.';
+
+    // Corner case: path was '.' and some '..' directories were added in front.
+    // Don't add a final '/.' in that case.
+    if (pathParsed.parts.length > 1 && pathParsed.parts.last == '.') {
+      pathParsed.parts.removeLast();
+      pathParsed.separators..removeLast()..removeLast()..add('');
+    }
+
+    // Make it relative.
+    pathParsed.root = '';
+    pathParsed.removeTrailingSeparators();
+
+    return pathParsed.toString();
+  }
+
+  /// Returns `true` if [child] is a path beneath `parent`, and `false`
+  /// otherwise.
+  ///
+  ///     path.isWithin('/root/path', '/root/path/a'); // -> true
+  ///     path.isWithin('/root/path', '/root/other'); // -> false
+  ///     path.isWithin('/root/path', '/root/path'); // -> false
+  bool isWithin(String parent, String child) {
+    var relative;
+    try {
+      relative = this.relative(child, from: parent);
+    } on PathException catch (_) {
+      // If no relative path from [parent] to [child] is found, [child]
+      // definitely isn't a child of [parent].
+      return false;
+    }
+
+    var parts = this.split(relative);
+    return this.isRelative(relative) && parts.first != '..' &&
+        parts.first != '.';
+  }
+
+  /// Removes a trailing extension from the last part of [path].
+  ///
+  ///     context.withoutExtension('path/to/foo.dart'); // -> 'path/to/foo'
+  String withoutExtension(String path) {
+    var parsed = _parse(path);
+
+    for (var i = parsed.parts.length - 1; i >= 0; i--) {
+      if (!parsed.parts[i].isEmpty) {
+        parsed.parts[i] = parsed.basenameWithoutExtension;
+        break;
+      }
+    }
+
+    return parsed.toString();
+  }
+
+  /// Returns the path represented by [uri].
+  ///
+  /// For POSIX and Windows styles, [uri] must be a `file:` URI. For the URL
+  /// style, this will just convert [uri] to a string.
+  ///
+  ///     // POSIX
+  ///     context.fromUri(Uri.parse('file:///path/to/foo'))
+  ///       // -> '/path/to/foo'
+  ///
+  ///     // Windows
+  ///     context.fromUri(Uri.parse('file:///C:/path/to/foo'))
+  ///       // -> r'C:\path\to\foo'
+  ///
+  ///     // URL
+  ///     context.fromUri(Uri.parse('http://dartlang.org/path/to/foo'))
+  ///       // -> 'http://dartlang.org/path/to/foo'
+  String fromUri(Uri uri) => style.pathFromUri(uri);
+
+  /// Returns the URI that represents [path].
+  ///
+  /// For POSIX and Windows styles, this will return a `file:` URI. For the URL
+  /// style, this will just convert [path] to a [Uri].
+  ///
+  ///     // POSIX
+  ///     context.toUri('/path/to/foo')
+  ///       // -> Uri.parse('file:///path/to/foo')
+  ///
+  ///     // Windows
+  ///     context.toUri(r'C:\path\to\foo')
+  ///       // -> Uri.parse('file:///C:/path/to/foo')
+  ///
+  ///     // URL
+  ///     context.toUri('http://dartlang.org/path/to/foo')
+  ///       // -> Uri.parse('http://dartlang.org/path/to/foo')
+  Uri toUri(String path) {
+    if (isRelative(path)) {
+      return style.relativePathToUri(path);
+    } else {
+      return style.absolutePathToUri(join(current, path));
+    }
+  }
+
+  ParsedPath _parse(String path) => new ParsedPath.parse(path, style);
+}
+
+/// Validates that there are no non-null arguments following a null one and
+/// throws an appropriate [ArgumentError] on failure.
+_validateArgList(String method, List<String> args) {
+  for (var i = 1; i < args.length; i++) {
+    // Ignore nulls hanging off the end.
+    if (args[i] == null || args[i - 1] != null) continue;
+
+    var numArgs;
+    for (numArgs = args.length; numArgs >= 1; numArgs--) {
+      if (args[numArgs - 1] != null) break;
+    }
+
+    // Show the arguments.
+    var message = new StringBuffer();
+    message.write("$method(");
+    message.write(args.take(numArgs)
+        .map((arg) => arg == null ? "null" : '"$arg"')
+        .join(", "));
+    message.write("): part ${i - 1} was null, but part $i was not.");
+    throw new ArgumentError(message.toString());
+  }
+}