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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.

// Windows environment variables.

package syscall

import (
        "unicode/utf16"
        "unsafe"
)

func Getenv(key string) (value string, found bool) {
        b := make([]uint16, 100)
        n, e := GetEnvironmentVariable(StringToUTF16Ptr(key), &b[0], uint32(len(b)))
        if n == 0 && e == ERROR_ENVVAR_NOT_FOUND {
                return "", false
        }
        if n > uint32(len(b)) {
                b = make([]uint16, n)
                n, e = GetEnvironmentVariable(StringToUTF16Ptr(key), &b[0], uint32(len(b)))
                if n > uint32(len(b)) {
                        n = 0
                }
        }
        if n == 0 {
                return "", false
        }
        return string(utf16.Decode(b[0:n])), true
}

func Setenv(key, value string) error {
        var v *uint16
        if len(value) > 0 {
                v = StringToUTF16Ptr(value)
        }
        e := SetEnvironmentVariable(StringToUTF16Ptr(key), v)
        if e != nil {
                return e
        }
        return nil
}

func Clearenv() {
        for _, s := range Environ() {
                // Environment variables can begin with =
                // so start looking for the separator = at j=1.
                // http://blogs.msdn.com/b/oldnewthing/archive/2010/05/06/10008132.aspx
                for j := 1; j < len(s); j++ {
                        if s[j] == '=' {
                                Setenv(s[0:j], "")
                                break
                        }
                }
        }
}

func Environ() []string {
        s, e := GetEnvironmentStrings()
        if e != nil {
                return nil
        }
        defer FreeEnvironmentStrings(s)
        r := make([]string, 0, 50) // Empty with room to grow.
        for from, i, p := 0, 0, (*[1 << 24]uint16)(unsafe.Pointer(s)); true; i++ {
                if p[i] == 0 {
                        // empty string marks the end
                        if i <= from {
                                break
                        }
                        r = append(r, string(utf16.Decode(p[from:i])))
                        from = i + 1
                }
        }
        return r
}