public abstract class PhoneCallReceiver extends BroadcastReceiver {
private static int lastState = TelephonyManager.CALL_STATE_IDLE;
private static Date callStartTime;
private static boolean isIncoming;
private static String savedNumber;

@Override
public void onReceive(Context context, Intent intent) {
    if (intent.getAction().equals("android.intent.action.NEW_OUTGOING_CALL")) {
        savedNumber = intent.getExtras().getString("android.intent.extra.PHONE_NUMBER");
    }
    else{
        String stateStr = intent.getExtras().getString(TelephonyManager.EXTRA_STATE);
        String number = intent.getExtras().getString(TelephonyManager.EXTRA_INCOMING_NUMBER);



        int state = 0;
        if(stateStr.equals(TelephonyManager.EXTRA_STATE_IDLE)){
            state = TelephonyManager.CALL_STATE_IDLE;
        }
        else if(stateStr.equals(TelephonyManager.EXTRA_STATE_OFFHOOK)){
            state = TelephonyManager.CALL_STATE_OFFHOOK;
        }
        else if(stateStr.equals(TelephonyManager.EXTRA_STATE_RINGING)){
            state = TelephonyManager.CALL_STATE_RINGING;
        }
        onCallStateChanged(context, state, number);
    }
}

protected void onIncomingCallStarted(Context ctx, String number, Date start){}

protected void onOutgoingCallStarted(Context ctx, String number, Date start){}

protected void onIncomingCallEnded(Context ctx, String number, Date start, Date end){}

protected void onOutgoingCallEnded(Context ctx, String number, Date start, Date end){}

protected void onMissedCall(Context ctx, String number, Date start){}

public void onCallStateChanged(Context context, int state, String number) {
    if(lastState == state){
        return;
    }
    switch (state) {
        case TelephonyManager.CALL_STATE_RINGING:
            isIncoming = true;
            callStartTime = new Date();
            savedNumber = number;
            onIncomingCallStarted(context, number, callStartTime);
            break;

        case TelephonyManager.CALL_STATE_OFFHOOK:
            if(lastState != TelephonyManager.CALL_STATE_RINGING){
                isIncoming = false;
                callStartTime = new Date();
                onOutgoingCallStarted(context, savedNumber, callStartTime);
            }
            break;

        case TelephonyManager.CALL_STATE_IDLE:
            if(lastState == TelephonyManager.CALL_STATE_RINGING){
                onMissedCall(context, savedNumber, callStartTime);
            }
            else if(isIncoming){
                onIncomingCallEnded(context, savedNumber, callStartTime, new Date());
            }
            else{
                onOutgoingCallEnded(context, savedNumber, callStartTime, new Date());
            }
            break;
    }
    lastState = state;
}

public class CallReciever extends PhoneCallReceiver {
DatabaseHelper databaseHelper ;
 @Override
protected void onIncomingCallEnded(final Context ctx, final String number, Date start, Date end) {
        SharedPreferences preferencesUnknown = PreferenceManager.getDefaultSharedPreferences(ctx);
        final SharedPreferences.Editor editorUnknown = preferencesUnknown.edit();
        boolean checkedUnknown = preferencesUnknown.getBoolean("checkedunknown", false);
        if (checkedUnknown) {
            boolean isUnknown = contactExists(ctx, number);
            if (isUnknown == false) {
                AlertDialog.Builder alerDialog = new AlertDialog.Builder(ctx);
                alerDialog.setIcon(R.drawable.calllogo);
                alerDialog.setTitle(number);
                alerDialog.setMessage("Save this number ?");
                alerDialog.setCancelable(false);
                alerDialog.setPositiveButton("YES", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        Intent intent = new Intent(ctx, CategoryPhoneActivity.class);
                        intent.putExtra("Phone", number);
                        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                        ctx.startActivity(intent);
                    }
                });
                alerDialog.setNegativeButton("NO", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.cancel();
                    }
                });
                AlertDialog aldialog = alerDialog.create();
                aldialog.setCanceledOnTouchOutside(false);
                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                    aldialog.getWindow().setType(WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY); } else {
                    aldialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
                }
                aldialog.show(); } else {
                Toast.makeText(ctx, "Number is already saved", Toast.LENGTH_SHORT).show(); }
        }else{
            AlertDialog.Builder alerDialog = new AlertDialog.Builder(ctx);
            alerDialog.setTitle(number);
            alerDialog.setMessage("Save this number ?");
            alerDialog.setPositiveButton("YES", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    Intent intent = new Intent(ctx, CategoryPhoneActivity.class);
                    intent.putExtra("Phone", number);
                    intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                    ctx.startActivity(intent);
                }
            });
            AlertDialog aldialog = alerDialog.create();
            aldialog.setCanceledOnTouchOutside(false);
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                aldialog.getWindow().setType(WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY); } else {
                aldialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
            }
            aldialog.show(); }
    }

private void requestCallLogPermission() {
    if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.READ_CALL_LOG)){
        new AlertDialog.Builder(this).setTitle("Permission Needed")
                .setMessage("This permission is needed by App to work properly !")
                .setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        ActivityCompat.requestPermissions(MainActivity.this, new String[] {Manifest.permission.READ_CALL_LOG},
                                CALL_LOG_PERMISSION);
                    }
                }).setCancelable(false)
                .create().show();
    }else {
        ActivityCompat.requestPermissions(this, new String[] {Manifest.permission.READ_CALL_LOG},
                CALL_LOG_PERMISSION);
    }
}


@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    switch(requestCode){
        case MY_PERMISSIONS_REQUEST_READ_PHONE_STATE:
            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED){

            }else {
                return;
            }
        case CALL_LOG_PERMISSION:
            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                Toast.makeText(this, "Call Log Permission Granted !", Toast.LENGTH_SHORT).show();
            }
    }
}