// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.


// Package path implements utility routines for manipulating slash-separated
// paths.
//
// The path package should only be used for paths separated by forward
// slashes, such as the paths in URLs. This package does not deal with
// Windows paths with drive letters or backslashes; to manipulate
// operating system paths, use the path/filepath package.
package path

// A lazybuf is a lazily constructed path buffer.
// It supports append, reading previously appended bytes,
// and retrieving the final string. It does not allocate a buffer
// to hold the output until that output diverges from s.
type lazybuf struct {
	s   string
	buf []byte
	w   int
}

func ( *lazybuf) ( int) byte {
	if .buf != nil {
		return .buf[]
	}
	return .s[]
}

func ( *lazybuf) ( byte) {
	if .buf == nil {
		if .w < len(.s) && .s[.w] ==  {
			.w++
			return
		}
		.buf = make([]byte, len(.s))
		copy(.buf, .s[:.w])
	}
	.buf[.w] = 
	.w++
}

func ( *lazybuf) () string {
	if .buf == nil {
		return .s[:.w]
	}
	return string(.buf[:.w])
}

// Clean returns the shortest path name equivalent to path
// by purely lexical processing. It applies the following rules
// iteratively until no further processing can be done:
//
//  1. Replace multiple slashes with a single slash.
//  2. Eliminate each . path name element (the current directory).
//  3. Eliminate each inner .. path name element (the parent directory)
//     along with the non-.. element that precedes it.
//  4. Eliminate .. elements that begin a rooted path:
//     that is, replace "/.." by "/" at the beginning of a path.
//
// The returned path ends in a slash only if it is the root "/".
//
// If the result of this process is an empty string, Clean
// returns the string ".".
//
// See also Rob Pike, “Lexical File Names in Plan 9 or
// Getting Dot-Dot Right,”
// https://9p.io/sys/doc/lexnames.html
func ( string) string {
	if  == "" {
		return "."
	}

	 := [0] == '/'
	 := len()

	// Invariants:
	//	reading from path; r is index of next byte to process.
	//	writing to buf; w is index of next byte to write.
	//	dotdot is index in buf where .. must stop, either because
	//		it is the leading slash or it is a leading ../../.. prefix.
	 := lazybuf{s: }
	,  := 0, 0
	if  {
		.append('/')
		,  = 1, 1
	}

	for  <  {
		switch {
		case [] == '/':
			// empty path element
			++
		case [] == '.' && (+1 ==  || [+1] == '/'):
			// . element
			++
		case [] == '.' && [+1] == '.' && (+2 ==  || [+2] == '/'):
			// .. element: remove to last /
			 += 2
			switch {
			case .w > :
				// can backtrack
				.w--
				for .w >  && .index(.w) != '/' {
					.w--
				}
			case !:
				// cannot backtrack, but not rooted, so append .. element.
				if .w > 0 {
					.append('/')
				}
				.append('.')
				.append('.')
				 = .w
			}
		default:
			// real path element.
			// add slash if needed
			if  && .w != 1 || ! && .w != 0 {
				.append('/')
			}
			// copy element
			for ;  <  && [] != '/'; ++ {
				.append([])
			}
		}
	}

	// Turn empty string into "."
	if .w == 0 {
		return "."
	}

	return .string()
}

// lastSlash(s) is strings.LastIndex(s, "/") but we can't import strings.
func ( string) int {
	 := len() - 1
	for  >= 0 && [] != '/' {
		--
	}
	return 
}

// Split splits path immediately following the final slash,
// separating it into a directory and file name component.
// If there is no slash in path, Split returns an empty dir and
// file set to path.
// The returned values have the property that path = dir+file.
func ( string) (,  string) {
	 := lastSlash()
	return [:+1], [+1:]
}

// Join joins any number of path elements into a single path,
// separating them with slashes. Empty elements are ignored.
// The result is Cleaned. However, if the argument list is
// empty or all its elements are empty, Join returns
// an empty string.
func ( ...string) string {
	 := 0
	for ,  := range  {
		 += len()
	}
	if  == 0 {
		return ""
	}
	 := make([]byte, 0, +len()-1)
	for ,  := range  {
		if len() > 0 ||  != "" {
			if len() > 0 {
				 = append(, '/')
			}
			 = append(, ...)
		}
	}
	return Clean(string())
}

// Ext returns the file name extension used by path.
// The extension is the suffix beginning at the final dot
// in the final slash-separated element of path;
// it is empty if there is no dot.
func ( string) string {
	for  := len() - 1;  >= 0 && [] != '/'; -- {
		if [] == '.' {
			return [:]
		}
	}
	return ""
}

// Base returns the last element of path.
// Trailing slashes are removed before extracting the last element.
// If the path is empty, Base returns ".".
// If the path consists entirely of slashes, Base returns "/".
func ( string) string {
	if  == "" {
		return "."
	}
	// Strip trailing slashes.
	for len() > 0 && [len()-1] == '/' {
		 = [0 : len()-1]
	}
	// Find the last element
	if  := lastSlash();  >= 0 {
		 = [+1:]
	}
	// If empty now, it had only slashes.
	if  == "" {
		return "/"
	}
	return 
}

// IsAbs reports whether the path is absolute.
func ( string) bool {
	return len() > 0 && [0] == '/'
}

// Dir returns all but the last element of path, typically the path's directory.
// After dropping the final element using Split, the path is Cleaned and trailing
// slashes are removed.
// If the path is empty, Dir returns ".".
// If the path consists entirely of slashes followed by non-slash bytes, Dir
// returns a single slash. In any other case, the returned path does not end in a
// slash.
func ( string) string {
	,  := Split()
	return Clean()
}