/*
 *  ====================================================================
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 * ====================================================================
 */

package org.apache.poi.xssf.usermodel.helpers;

import java.security.SecureRandom;
import java.util.Arrays;

import javax.xml.bind.DatatypeConverter;
import javax.xml.namespace.QName;

import org.apache.poi.poifs.crypt.CryptoFunctions;
import org.apache.poi.poifs.crypt.HashAlgorithm;
import org.apache.xmlbeans.XmlCursor;
import org.apache.xmlbeans.XmlObject;

public class XSSFPaswordHelper {
    /**
     * Sets the XORed or hashed password 
     *
     * @param xobj the xmlbeans object which contains the password attributes
     * @param password the password, if null, the password attributes will be removed
     * @param hashAlgo the hash algorithm, if null the password will be XORed
     * @param prefix the prefix of the password attributes, may be null
     */
    public static void setPassword(XmlObject xobj, String password, HashAlgorithm hashAlgo, String prefix) {
        XmlCursor cur = xobj.newCursor();

        if (password == null) {
            cur.removeAttribute(getAttrName(prefix, "password"));
            cur.removeAttribute(getAttrName(prefix, "algorithmName"));
            cur.removeAttribute(getAttrName(prefix, "hashValue"));
            cur.removeAttribute(getAttrName(prefix, "saltValue"));
            cur.removeAttribute(getAttrName(prefix, "spinCount"));
            return;
        } 
        
        cur.toFirstContentToken();
        if (hashAlgo == null) {
            int hash = CryptoFunctions.createXorVerifier1(password);
            cur.insertAttributeWithValue(getAttrName(prefix, "password"), Integer.toHexString(hash).toUpperCase());
        } else {
            SecureRandom random = new SecureRandom(); 
            byte salt[] = random.generateSeed(16);
    
            // Iterations specifies the number of times the hashing function shall be iteratively run (using each
            // iteration's result as the input for the next iteration).
            int spinCount = 100000;

            // Implementation Notes List:
            // --> In this third stage, the reversed byte order legacy hash from the second stage shall
            //     be converted to Unicode hex string representation
            byte hash[] = CryptoFunctions.hashPassword(password, hashAlgo, salt, spinCount, false);
            
            cur.insertAttributeWithValue(getAttrName(prefix, "algorithmName"), hashAlgo.jceId); 
            cur.insertAttributeWithValue(getAttrName(prefix, "hashValue"), DatatypeConverter.printBase64Binary(hash));
            cur.insertAttributeWithValue(getAttrName(prefix, "saltValue"), DatatypeConverter.printBase64Binary(salt));
            cur.insertAttributeWithValue(getAttrName(prefix, "spinCount"), ""+spinCount);
        }
        cur.dispose();
    }

    /**
     * Validates the password, i.e.
     * calculates the hash of the given password and compares it against the stored hash
     *
     * @param xobj the xmlbeans object which contains the password attributes
     * @param password the password, if null the method will always return false,
     *  even if there's no password set
     * @param prefix the prefix of the password attributes, may be null
     * 
     * @return true, if the hashes match
     */
    public static boolean validatePassword(XmlObject xobj, String password, String prefix) {
        // TODO: is "velvetSweatshop" the default password?
        if (password == null) return false;
        
        XmlCursor cur = xobj.newCursor();
        String xorHashVal = cur.getAttributeText(getAttrName(prefix, "password"));
        String algoName = cur.getAttributeText(getAttrName(prefix, "algorithmName"));
        String hashVal = cur.getAttributeText(getAttrName(prefix, "hashValue"));
        String saltVal = cur.getAttributeText(getAttrName(prefix, "saltValue"));
        String spinCount = cur.getAttributeText(getAttrName(prefix, "spinCount"));
        cur.dispose();

        if (xorHashVal != null) {
            int hash1 = Integer.parseInt(xorHashVal, 16);
            int hash2 = CryptoFunctions.createXorVerifier1(password);
            return hash1 == hash2;
        } else {
            if (hashVal == null || algoName == null || saltVal == null || spinCount == null) {
                return false;
            }
            
            byte hash1[] = DatatypeConverter.parseBase64Binary(hashVal);
            HashAlgorithm hashAlgo = HashAlgorithm.fromString(algoName);
            byte salt[] = DatatypeConverter.parseBase64Binary(saltVal);
            int spinCnt = Integer.parseInt(spinCount);
            byte hash2[] = CryptoFunctions.hashPassword(password, hashAlgo, salt, spinCnt, false);
            return Arrays.equals(hash1, hash2);
        }
    }
    
    
    private static QName getAttrName(String prefix, String name) {
        if (prefix == null || "".equals(prefix)) {
            return new QName(name);
        } else {
            return new QName(prefix+Character.toUpperCase(name.charAt(0))+name.substring(1));
        }
    }
}
