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// Copyright 2010 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 filepath

import (
        "strings"
)

func isSlash(c uint8) bool {
        return c == '\\' || c == '/'
}

// IsAbs returns true if the path is absolute.
func IsAbs(path string) (b bool) {
        v := VolumeName(path)
        if v == "" {
                return false
        }
        path = path[len(v):]
        if path == "" {
                return false
        }
        return isSlash(path[0])
}

// VolumeName returns leading volume name.  
// Given "C:\foo\bar" it returns "C:" under windows.
// Given "\\host\share\foo" it returns "\\host\share".
// On other platforms it returns "".
func VolumeName(path string) (v string) {
        if len(path) < 2 {
                return ""
        }
        // with drive letter
        c := path[0]
        if path[1] == ':' &&
                ('0' <= c && c <= '9' || 'a' <= c && c <= 'z' ||
                        'A' <= c && c <= 'Z') {
                return path[:2]
        }
        // is it UNC
        if l := len(path); l >= 5 && isSlash(path[0]) && isSlash(path[1]) &&
                !isSlash(path[2]) && path[2] != '.' {
                // first, leading `\\` and next shouldn't be `\`. its server name.
                for n := 3; n < l-1; n++ {
                        // second, next '\' shouldn't be repeated.
                        if isSlash(path[n]) {
                                n++
                                // third, following something characters. its share name.
                                if !isSlash(path[n]) {
                                        if path[n] == '.' {
                                                break
                                        }
                                        for ; n < l; n++ {
                                                if isSlash(path[n]) {
                                                        break
                                                }
                                        }
                                        return path[:n]
                                }
                                break
                        }
                }
        }
        return ""
}

// HasPrefix tests whether the path p begins with prefix.
// It ignores case while comparing.
func HasPrefix(p, prefix string) bool {
        if strings.HasPrefix(p, prefix) {
                return true
        }
        return strings.HasPrefix(strings.ToLower(p), strings.ToLower(prefix))
}