Format Credit Card Number with Android TextWatcher

package org.o7planning.textwatchercreditcardexample;

import java.util.Arrays;

public enum CreditCardType {
    // 4
    VISA("Visa", "icon_visa",
            13, 19,
            new int[]{4},
            new int[]{4,4,4,4,4}
    ),
    // 4026, 417500, 4405, 4508, 4844, 4913, 4917
    VISA_ELECTRON("Visa Electron", "icon_visa_electron",
            16, 16,
            new int[]{4026, 417500, 4405, 4508, 4844, 4913, 4917},
            new int[]{4,4,4,4}
    ),
    // 34, 37
    AMERICAN_EXPRESS("American Express", "icon_american_express",
            15, 15,
            new int[]{34, 37},
            new int[]{4,6,5}
    ),
    // 51‑55, 222100‑272099
    MASTERCARD("MasterCard", "icon_mastercard",
            16, 16,
            concat(intRange(51,55), intRange(222100,272099)),
            new int[]{4,4,4,4}
    ),
    // 6011, 622126‑622925, 644‑649, 65
    DISCOVER("MasterCard", "icon_mastercard",
            16, 16,
            append(concat(intRange(622126,622925), intRange(644,649)),6011,65),
            new int[]{4,4,4,4}
    ),
    // 3528‑3589
    JCB("JCB", "icon_jcb",
            16, 16,
             intRange(3528,3589),
            new int[]{4,4,4,4}
    ),
    // 1
    UATP("UATP", "icon_uatp",
            15, 15,
            new int[]{1},
            new int[]{4,5,6}
    ),
    // 5019
    DANKORT("Dankort", "icon_dankort",
            16, 16,
            new int[]{5019},
            new int[]{4,4,4,4}
    );

    public static final int[] DEFAULT_BLOCK_LENGTHS = new int[] {4, 4, 4, 4, 4};
    public static final int DEFAULT_MAX_LENGTH = 4 * 5 ;

    private String[] prefixs;
    private int[] blockLengths;
    private String name;
    // Name of Image in "drawable" folder.
    private String imageResourceName;

    private int minLength;
    private int maxLength;

    CreditCardType(String name, String imageResourceName,
                    int minLength, int maxLength,
                    int[] intPrefixs, int[] blockLengths)  {
        this.name = name;
        this.imageResourceName = imageResourceName;
        if(intPrefixs!= null)  {
            this.prefixs = new String[intPrefixs.length];
            for(int i=0;i< intPrefixs.length;i++) {
                this.prefixs[i] = String.valueOf(intPrefixs[i]);
            }
        }
        this.minLength = minLength;
        this.maxLength = maxLength;
        this.blockLengths = blockLengths;
    }

    public String getName() {
        return name;
    }

    public int getMinLength() {
        return minLength;
    }

    public int getMaxLength() {
        return maxLength;
    }
    public String[] getPrefixs()  {
        return this.prefixs;
    }

    public int[] getBlockLengths()  {
        return this.blockLengths;
    }

    public String getImageResourceName()  {
        return this.imageResourceName;
    }

    private static int[] intRange(int from, int to)  {
        int length = to - from + 1;
        int[] ret = new int[length];
        for(int i= from; i < to + 1; i++) {
            ret[i-from] = i;
        }
        return ret;
    }

    private static int[] concat(int[] first, int[] second)  {
        int[] both = Arrays.copyOf(first, first.length + second.length);
        System.arraycopy(second, 0, both, first.length, second.length);
        return both;
    }

    private static int[] append(int[] first, int ... value)  {
        if(value == null || value.length == 0)  {
            return first;
        }
        int[] both = Arrays.copyOf(first, first.length + value.length);

        for(int i = 0; i < value.length; i++) {
            both[first.length + i] = value[i];
        }
        return both;
    }

    public static CreditCardType detect(String creditCardNumber)  {
        if(creditCardNumber == null || creditCardNumber.isEmpty())  {
            return null;
        }
        CreditCardType found = null;
        int max = 0;
        for(CreditCardType type: CreditCardType.values()) {
            for(String prefix : type.prefixs) {
                if(creditCardNumber.startsWith(prefix) && prefix.length() > max) {
                    found = type;
                    max = prefix.length();
                }
            }
        }
        return found;
    }

}

package org.o7planning.textwatchercreditcardexample;

import android.graphics.drawable.Drawable;
import android.text.Editable;
import android.text.TextWatcher;
import android.util.Log;
import android.widget.EditText;

public class CreditCardNumberTextWatcher implements TextWatcher {

    private static final String LOG_TAG = "AndroidExample";
    public static final char SEPARATOR = '-';

    private EditText editText;

    private int after;
    private String beforeString;

    public CreditCardNumberTextWatcher(EditText editText) {
        this.editText = editText;
    }

    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {
        this.after = after;
        this.beforeString = s.toString();
        Log.e(LOG_TAG, "@@beforeTextChanged s=" + s
                + " . start="+ start+" . after=" + after+" . count="+ count);
    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
        Log.e(LOG_TAG, "@@onTextChanged s=" + s
                + " . start="+ start+" . before=" + before+" . count="+ count);
        String newText = s.toString();

        String textPrefix = newText.substring(0, start);
        String textInserted = newText.substring(start, start + this.after);
        String textSuffix = newText.substring(start + this.after);
        String textBeforeCursor = textPrefix + textInserted;

        // User delete the SEPARATOR.
        if(this.after == 0 && count == 0 && beforeString.charAt(start) == SEPARATOR)  {
            if(start > 0)  {
                textPrefix = textPrefix.substring(0, textPrefix.length() -1);
            }
        }

        // Non-digit
        String regex = "[^\\d]";

        String textPrefixClean = textPrefix.replaceAll(regex, "");
        String textInsertedClean = textInserted.replaceAll(regex, "");
        String textSuffixClean = textSuffix.replaceAll(regex, "");
        String textBeforeCursorClean = textPrefixClean + textInsertedClean;

        // creditCardNumber
        String newTextClean = textPrefixClean + textInsertedClean + textSuffixClean;

        CreditCardType creditCardType = this.showDetectedCreditCardImage(newTextClean);

        int[] blockLengths = CreditCardType.DEFAULT_BLOCK_LENGTHS; // {4,4,4,4,4}
        int minLength = 0;
        int maxLength = CreditCardType.DEFAULT_MAX_LENGTH; // 4*5

        if(creditCardType != null)  {
            blockLengths = creditCardType.getBlockLengths();
            minLength = creditCardType.getMinLength();
            maxLength = creditCardType.getMaxLength();
        }
        Log.i(LOG_TAG, "newTextClean= " + newTextClean);


        int[] separatorIndexs = new int[blockLengths.length];
        for(int i=0; i < separatorIndexs.length; i++) {
            if(i==0)  {
                separatorIndexs[i] = blockLengths[i];
            } else {
                separatorIndexs[i] = blockLengths[i] + separatorIndexs[i-1];
            }
        }
        Log.i(LOG_TAG, "blockLengths= " + this.toString(blockLengths));
        Log.i(LOG_TAG, "separatorIndexs= " +  this.toString(separatorIndexs));

        int cursorPosition = start + this.after - textBeforeCursor.length() + textBeforeCursorClean.length();

        StringBuilder sb = new StringBuilder();
        int separatorCount = 0;
        int cursorPositionDelta = 0;
        int LOOP_MAX = Math.min(newTextClean.length(), maxLength);

        for(int i = 0; i < LOOP_MAX; i++) {
            sb.append(newTextClean.charAt(i));

            if(this.contains(separatorIndexs,i + 1) && i < LOOP_MAX - 1) {
                sb.append(SEPARATOR);
                separatorCount++;
                if(i < cursorPosition) {
                    cursorPositionDelta++;
                }
            }
        }
        cursorPosition= cursorPosition + cursorPositionDelta;

        String textFormatted = sb.toString();
        if(cursorPosition > textFormatted.length()) {
            cursorPosition =  textFormatted.length();
        }

        this.editText.removeTextChangedListener(this);
        this.editText.setText(textFormatted);
        this.editText.addTextChangedListener(this);
        this.editText.setSelection(cursorPosition);
    }

    @Override
    public void afterTextChanged(Editable s) {

    }

    private String toString(int[] array)  {
        StringBuilder sb= new StringBuilder();
        for(int i=0;i< array.length;i++) {
            if(i == 0) {
                sb.append("[").append(array[i]);
            } else {
                sb.append(", ").append(array[i]);
            }
        }
        sb.append("]");
        return sb.toString();
    }

    private boolean contains(int[] values, int value)  {
        for(int i=0;i<values.length;i++) {
            if(values[i] == value) {
                return true;
            }
        }
        return false;
    }


    private CreditCardType showDetectedCreditCardImage(String creditCardNumber)  {
        CreditCardType type = CreditCardType.detect(creditCardNumber);

        if(type != null)  {
            Drawable icon = ResourceUtils.getDrawableByName(this.editText.getContext(), type.getImageResourceName());
            this.editText.setCompoundDrawablesWithIntrinsicBounds(null, null, icon, null);
        } else {
            Drawable icon = ResourceUtils.getDrawableByName(this.editText.getContext(), "icon_none");
            this.editText.setCompoundDrawablesWithIntrinsicBounds(null, null, icon, null);
        }
        return type;
    }
}

package org.o7planning.textwatchercreditcardexample;

import android.content.Context;
import android.content.res.Resources;
import android.graphics.drawable.Drawable;

public class ResourceUtils {

    public static Drawable getDrawableByName(Context context, String resourceName)  {
        Resources resources = context.getResources();
        final int resourceId = resources.getIdentifier(resourceName, "drawable",
                context.getPackageName());
        return resources.getDrawable(resourceId);
    }
}

package org.o7planning.textwatchercreditcardexample;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.text.TextWatcher;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

    private EditText editTextCreditCardNumber;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        this.editTextCreditCardNumber = (EditText) this.findViewById(R.id.editText_creditCardNumber);

        TextWatcher textWatcher = new CreditCardNumberTextWatcher(this.editTextCreditCardNumber);
        this.editTextCreditCardNumber.addTextChangedListener(textWatcher);
    }
}