Revert converting CardUtils to Kotlin

stripe/src/main/java/com/stripe/android/CardUtils.java

@@ -0,0 +1,156 @@
+package com.stripe.android;
+
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
+
+import com.stripe.android.model.Card;
+
+import static com.stripe.android.model.Card.CardBrand;
+
+/**
+ * Utility class for functions to do with cards.
+ */
+public final class CardUtils {
+
+    private static final int LENGTH_COMMON_CARD = 16;
+    private static final int LENGTH_AMERICAN_EXPRESS = 15;
+    private static final int LENGTH_DINERS_CLUB = 14;
+
+    private CardUtils() {}
+
+    /**
+     * Returns a {@link CardBrand} corresponding to a partial card number,
+     * or {@link Card.CardBrand#UNKNOWN} if the card brand can't be determined from the input value.
+     *
+     * @param cardNumber a credit card number or partial card number
+     * @return the {@link Card.CardBrand} corresponding to that number,
+     * or {@link CardBrand#UNKNOWN} if it can't be determined
+     */
+    @NonNull
+    @Card.CardBrand
+    public static String getPossibleCardType(@Nullable String cardNumber) {
+        return getPossibleCardType(cardNumber, true);
+    }
+
+    /**
+     * Checks the input string to see whether or not it is a valid card number, possibly
+     * with groupings separated by spaces or hyphens.
+     *
+     * @param cardNumber a String that may or may not represent a valid card number
+     * @return {@code true} if and only if the input value is a valid card number
+     */
+    public static boolean isValidCardNumber(@Nullable String cardNumber) {
+        String normalizedNumber = StripeTextUtils.removeSpacesAndHyphens(cardNumber);
+        return isValidLuhnNumber(normalizedNumber) && isValidCardLength(normalizedNumber);
+    }
+
+    /**
+     * Checks the input string to see whether or not it is a valid Luhn number.
+     *
+     * @param cardNumber a String that may or may not represent a valid Luhn number
+     * @return {@code true} if and only if the input value is a valid Luhn number
+     */
+    static boolean isValidLuhnNumber(@Nullable String cardNumber) {
+        if (cardNumber == null) {
+            return false;
+        }
+
+        boolean isOdd = true;
+        int sum = 0;
+
+        for (int index = cardNumber.length() - 1; index >= 0; index--) {
+            char c = cardNumber.charAt(index);
+            if (!Character.isDigit(c)) {
+                return false;
+            }
+
+            int digitInteger = Character.getNumericValue(c);
+            isOdd = !isOdd;
+
+            if (isOdd) {
+                digitInteger *= 2;
+            }
+
+            if (digitInteger > 9) {
+                digitInteger -= 9;
+            }
+
+            sum += digitInteger;
+        }
+
+        return sum % 10 == 0;
+    }
+
+    /**
+     * Checks to see whether the input number is of the correct length, after determining its brand.
+     * This function does not perform a Luhn check.
+     *
+     * @param cardNumber the card number with no spaces or dashes
+     * @return {@code true} if the card number is of known type and the correct length
+     */
+    static boolean isValidCardLength(@Nullable String cardNumber) {
+        return cardNumber != null && isValidCardLength(cardNumber,
+                getPossibleCardType(cardNumber, false));
+    }
+
+    /**
+     * Checks to see whether the input number is of the correct length, given the assumed brand of
+     * the card. This function does not perform a Luhn check.
+     *
+     * @param cardNumber the card number with no spaces or dashes
+     * @param cardBrand a {@link Card.CardBrand} used to get the correct size
+     * @return {@code true} if the card number is the correct length for the assumed brand
+     */
+    static boolean isValidCardLength(
+            @Nullable String cardNumber,
+            @NonNull @CardBrand String cardBrand) {
+        if (cardNumber == null || CardBrand.UNKNOWN.equals(cardBrand)) {
+            return false;
+        }
+
+        final int length = cardNumber.length();
+        switch (cardBrand) {
+            case Card.CardBrand.AMERICAN_EXPRESS: {
+                return length == LENGTH_AMERICAN_EXPRESS;
+            }
+            case CardBrand.DINERS_CLUB: {
+                return length == LENGTH_DINERS_CLUB;
+            }
+            default: {
+                return length == LENGTH_COMMON_CARD;
+            }
+        }
+    }
+
+    @NonNull
+    @CardBrand
+    private static String getPossibleCardType(@Nullable String cardNumber,
+                                              boolean shouldNormalize) {
+        if (StripeTextUtils.isBlank(cardNumber)) {
+            return Card.CardBrand.UNKNOWN;
+        }
+
+        String spacelessCardNumber = cardNumber;
+        if (shouldNormalize) {
+            spacelessCardNumber = StripeTextUtils.removeSpacesAndHyphens(cardNumber);
+        }
+
+        if (StripeTextUtils.hasAnyPrefix(spacelessCardNumber, Card.PREFIXES_AMERICAN_EXPRESS)) {
+            return CardBrand.AMERICAN_EXPRESS;
+        } else if (StripeTextUtils.hasAnyPrefix(spacelessCardNumber, Card.PREFIXES_DISCOVER)) {
+            return Card.CardBrand.DISCOVER;
+        } else if (StripeTextUtils.hasAnyPrefix(spacelessCardNumber, Card.PREFIXES_JCB)) {
+            return Card.CardBrand.JCB;
+        } else if (StripeTextUtils.hasAnyPrefix(spacelessCardNumber, Card.PREFIXES_DINERS_CLUB)) {
+            return Card.CardBrand.DINERS_CLUB;
+        } else if (StripeTextUtils.hasAnyPrefix(spacelessCardNumber, Card.PREFIXES_VISA)) {
+            return CardBrand.VISA;
+        } else if (StripeTextUtils.hasAnyPrefix(spacelessCardNumber, Card.PREFIXES_MASTERCARD)) {
+            return CardBrand.MASTERCARD;
+        } else if (StripeTextUtils.hasAnyPrefix(spacelessCardNumber, Card.PREFIXES_UNIONPAY)) {
+            return Card.CardBrand.UNIONPAY;
+        } else {
+            return Card.CardBrand.UNKNOWN;
+        }
+    }
+}