// Copyright 2011 Miek Gieben. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package dns

import (
	"crypto/sha1"
	"hash"
	"io"
	"strings"
)

type saltWireFmt struct {
	Salt string `dns:"size-hex"`
}

// HashName hashes a string (label) according to RFC 5155. It returns the hashed string.
func HashName(label string, ha uint8, iter uint16, salt string) string {
	saltwire := new(saltWireFmt)
	saltwire.Salt = salt
	wire := make([]byte, DefaultMsgSize)
	n, err := PackStruct(saltwire, wire, 0)
	if err != nil {
		return ""
	}
	wire = wire[:n]
	name := make([]byte, 255)
	off, err := PackDomainName(strings.ToLower(label), name, 0, nil, false)
	if err != nil {
		return ""
	}
	name = name[:off]
	var s hash.Hash
	switch ha {
	case SHA1:
		s = sha1.New()
	default:
		return ""
	}

	// k = 0
	name = append(name, wire...)
	io.WriteString(s, string(name))
	nsec3 := s.Sum(nil)
	// k > 0
	for k := uint16(0); k < iter; k++ {
		s.Reset()
		nsec3 = append(nsec3, wire...)
		io.WriteString(s, string(nsec3))
		nsec3 = s.Sum(nil)
	}
	return unpackBase32(nsec3)
}