// SPDX-License-Identifier: Apache-2.0
//
// Copyright The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//go:build windows

package registry

import (
	"io"

	"golang.org/x/sys/windows"
)

// decodeUTF16String decodes the unterminated UTF16 string b up to the first NUL.
// A trailing odd byte is ignored. scratch holds the code units; it is returned
// with any growth so the caller can reuse it for the next string. The returned
// string does not reference b.
func decodeUTF16String(b []byte, scratch []uint16) (string, []uint16) {
	scratch = scratch[:0]

	for i := 0; i+1 < len(b); i += 2 {
		scratch = append(scratch, bo.Uint16(b[i:]))
	}

	return windows.UTF16ToString(scratch), scratch
}

// readUTF16String Reads a null-terminated UTF16 string at the current offset.
func readUTF16String(r io.Reader) (string, error) {
	b := make([]byte, 2)
	out := make([]uint16, 0, 100)

	for {
		// A short read at the end of the buffer is an error, not a code unit.
		if _, err := io.ReadFull(r, b); err != nil {
			return "", err
		}

		if b[0] == 0 && b[1] == 0 {
			return windows.UTF16ToString(out), nil
		}

		out = append(out, bo.Uint16(b))
	}
}