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      1 /*
      2  * Copyright (C) 2017 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package android.service.autofill;
     18 
     19 import static android.view.autofill.Helper.sDebug;
     20 
     21 import android.annotation.NonNull;
     22 import android.annotation.TestApi;
     23 import android.os.Parcel;
     24 import android.os.Parcelable;
     25 import android.util.Log;
     26 import android.view.autofill.AutofillId;
     27 
     28 import com.android.internal.util.Preconditions;
     29 
     30 import java.util.Arrays;
     31 
     32 /**
     33  * Validator that returns {@code true} if the number created by concatenating all given fields
     34  * pass a Luhn algorithm checksum. All non-digits are ignored.
     35  *
     36  * <p>See {@link SaveInfo.Builder#setValidator(Validator)} for examples.
     37  */
     38 public final class LuhnChecksumValidator extends InternalValidator implements Validator,
     39         Parcelable {
     40     private static final String TAG = "LuhnChecksumValidator";
     41 
     42     private final AutofillId[] mIds;
     43 
     44     /**
     45       * Default constructor.
     46       *
     47       * @param ids id of fields that comprises the number to be checked.
     48       */
     49     public LuhnChecksumValidator(@NonNull AutofillId... ids) {
     50         mIds = Preconditions.checkArrayElementsNotNull(ids, "ids");
     51     }
     52 
     53     /**
     54      * Checks if the Luhn checksum is valid.
     55      *
     56      * @param number The number including the checksum
     57      */
     58     private static boolean isLuhnChecksumValid(@NonNull String number) {
     59         int sum = 0;
     60         boolean isDoubled = false;
     61 
     62         for (int i = number.length() - 1; i >= 0; i--) {
     63             final int digit = number.charAt(i) - '0';
     64             if (digit < 0 || digit > 9) {
     65                 // Ignore non-digits
     66                 continue;
     67             }
     68 
     69             int addend;
     70             if (isDoubled) {
     71                 addend = digit * 2;
     72                 if (addend > 9) {
     73                     addend -= 9;
     74                 }
     75             } else {
     76                 addend = digit;
     77             }
     78             sum += addend;
     79             isDoubled = !isDoubled;
     80         }
     81 
     82         return sum % 10 == 0;
     83     }
     84 
     85     /** @hide */
     86     @Override
     87     @TestApi
     88     public boolean isValid(@NonNull ValueFinder finder) {
     89         if (mIds == null || mIds.length == 0) return false;
     90 
     91         final StringBuilder builder = new StringBuilder();
     92         for (AutofillId id : mIds) {
     93             final String partialNumber = finder.findByAutofillId(id);
     94             if (partialNumber == null) {
     95                 if (sDebug) Log.d(TAG, "No partial number for id " + id);
     96                 return false;
     97             }
     98             builder.append(partialNumber);
     99         }
    100 
    101         final String number = builder.toString();
    102         boolean valid = isLuhnChecksumValid(number);
    103         if (sDebug) Log.d(TAG, "isValid(" + number.length() + " chars): " + valid);
    104         return valid;
    105     }
    106 
    107     @Override
    108     public String toString() {
    109         if (!sDebug) return super.toString();
    110 
    111         return "LuhnChecksumValidator: [ids=" + Arrays.toString(mIds) + "]";
    112     }
    113 
    114     /////////////////////////////////////
    115     // Parcelable "contract" methods. //
    116     /////////////////////////////////////
    117     @Override
    118     public int describeContents() {
    119         return 0;
    120     }
    121 
    122     @Override
    123     public void writeToParcel(Parcel parcel, int flags) {
    124         parcel.writeParcelableArray(mIds, flags);
    125     }
    126 
    127     public static final Parcelable.Creator<LuhnChecksumValidator> CREATOR =
    128             new Parcelable.Creator<LuhnChecksumValidator>() {
    129         @Override
    130         public LuhnChecksumValidator createFromParcel(Parcel parcel) {
    131             return new LuhnChecksumValidator(parcel.readParcelableArray(null, AutofillId.class));
    132         }
    133 
    134         @Override
    135         public LuhnChecksumValidator[] newArray(int size) {
    136             return new LuhnChecksumValidator[size];
    137         }
    138     };
    139 }
    140