// Copyright 2017 Baliance. All rights reserved.
//
// Use of this source code is governed by the terms of the Affero GNU General
// Public License version 3.0 as published by the Free Software Foundation and
// appearing in the file LICENSE included in the packaging of this file. A
// commercial license can be purchased by contacting sales@baliance.com.

package spreadsheet

import (
	"fmt"
)

// PasswordHash returns the password hash for a workbook using the modified
// spreadsheetML password hash that is compatible with Excel.
func PasswordHash(s string) string {
	hash := uint16(0)
	if len(s) > 0 {
		for i := len(s) - 1; i >= 0; i-- {
			c := s[i]
			hash = ((hash >> 14) & 0x01) | ((hash << 1) & 0x7fff)
			hash ^= uint16(c)
		}
		hash = ((hash >> 14) & 0x01) | ((hash << 1) & 0x7fff)
		hash ^= uint16(len(s))
		hash ^= (0x8000 | ('N' << 8) | 'K')
	}
	return fmt.Sprintf("%04X", uint64(hash))
}