CardLockRepository.java

package com.example.taccardi.zak;

import android.support.annotation.NonNull;
import io.reactivex.Observable;

/**
 * Use this class to lock (prevent charges to it) or unlock (allow charges) a card.
 */
interface CardLockRepository {

    /**
     * @return emits updates about a card is locked with the the specified id.
     * This will also emit whether the card is currently locked or unlocked as its first
     * emission upon initial subscription
     */
    Observable<LockedStatus> updates(@NonNull CardId cardId);

    /**
     * @return emits the errors that may occur when an attempt to lock or unlock a card fails
     */
    Observable<CardLockUpdateError> errors(@NonNull CardId cardId);

    /**
     * Lock or unlock a card.
     *
     * @param lockOrUnlock specify {@link LockedStatus#LOCKED} to lock the card,
     *                     or {@link LockedStatus#NOT_LOCKED} to unlocked
     * @see {@link #updates(CardId)} for updates when this call succeeds
     * @see {@link #errors(CardId)} for updates when this call fails
     */
    void lockOrUnlockCard(@NonNull CardId cardId, LockedStatus lockOrUnlock);
}

/**
 * Whether or not a card is locked, or not locked.
 */
enum LockedStatus {
    /**
     * Card has been locked, and CANNOT be used for payment.
     */
    LOCKED,
    /**
     * Card has been unlocked, and CANT be used for payment.
     */
    NOT_LOCKED
}

/**
 * The errors that can occur from when attempting to lock or unlock a card.
 */
final class CardLockUpdateError {
    //details about error
}

/**
 * Unique identifier for a card.
 */
final class CardId {
    //...
}