/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.nfc.cardemulation;

import android.annotation.NonNull;
import android.annotation.RequiresPermission;
import android.annotation.SdkConstant;
import android.annotation.SdkConstant.SdkConstantType;
import android.app.Activity;
import android.app.ActivityThread;
import android.content.ComponentName;
import android.content.Context;
import android.content.pm.IPackageManager;
import android.content.pm.PackageManager;
import android.nfc.INfcCardEmulation;
import android.nfc.NfcAdapter;
import android.os.RemoteException;
import android.provider.Settings;
import android.provider.Settings.SettingNotFoundException;
import android.util.Log;

import java.util.HashMap;
import java.util.List;
import java.util.regex.Pattern;

/**
 * This class can be used to query the state of
 * NFC card emulation services.
 *
 * For a general introduction into NFC card emulation,
 * please read the <a href="{@docRoot}guide/topics/connectivity/nfc/hce.html">
 * NFC card emulation developer guide</a>.</p>
 *
 * <p class="note">Use of this class requires the
 * {@link PackageManager#FEATURE_NFC_HOST_CARD_EMULATION} to be present
 * on the device.
 */
public final class CardEmulation {
    private static final Pattern AID_PATTERN = Pattern.compile("[0-9A-Fa-f]{10,32}\\*?\\#?");
    static final String TAG = "CardEmulation";

    /**
     * Activity action: ask the user to change the default
     * card emulation service for a certain category. This will
     * show a dialog that asks the user whether he wants to
     * replace the current default service with the service
     * identified with the ComponentName specified in
     * {@link #EXTRA_SERVICE_COMPONENT}, for the category
     * specified in {@link #EXTRA_CATEGORY}
     */
    @SdkConstant(SdkConstantType.ACTIVITY_INTENT_ACTION)
    public static final String ACTION_CHANGE_DEFAULT =
            "android.nfc.cardemulation.action.ACTION_CHANGE_DEFAULT";

    /**
     * The category extra for {@link #ACTION_CHANGE_DEFAULT}.
     *
     * @see #ACTION_CHANGE_DEFAULT
     */
    public static final String EXTRA_CATEGORY = "category";

    /**
     * The service {@link ComponentName} object passed in as an
     * extra for {@link #ACTION_CHANGE_DEFAULT}.
     *
     * @see #ACTION_CHANGE_DEFAULT
     */
    public static final String EXTRA_SERVICE_COMPONENT = "component";

    /**
     * Category used for NFC payment services.
     */
    public static final String CATEGORY_PAYMENT = "payment";

    /**
     * Category that can be used for all other card emulation
     * services.
     */
    public static final String CATEGORY_OTHER = "other";

    /**
     * Return value for {@link #getSelectionModeForCategory(String)}.
     *
     * <p>In this mode, the user has set a default service for this
     *    category.
     *
     * <p>When using ISO-DEP card emulation with {@link HostApduService}
     *    or {@link OffHostApduService}, if a remote NFC device selects
     *    any of the Application IDs (AIDs)
     *    that the default service has registered in this category,
     *    that service will automatically be bound to to handle
     *    the transaction.
     */
    public static final int SELECTION_MODE_PREFER_DEFAULT = 0;

    /**
     * Return value for {@link #getSelectionModeForCategory(String)}.
     *
     * <p>In this mode, when using ISO-DEP card emulation with {@link HostApduService}
     *    or {@link OffHostApduService}, whenever an Application ID (AID) of this category
     *    is selected, the user is asked which service he wants to use to handle
     *    the transaction, even if there is only one matching service.
     */
    public static final int SELECTION_MODE_ALWAYS_ASK = 1;

    /**
     * Return value for {@link #getSelectionModeForCategory(String)}.
     *
     * <p>In this mode, when using ISO-DEP card emulation with {@link HostApduService}
     *    or {@link OffHostApduService}, the user will only be asked to select a service
     *    if the Application ID (AID) selected by the reader has been registered by multiple
     *    services. If there is only one service that has registered for the AID,
     *    that service will be invoked directly.
     */
    public static final int SELECTION_MODE_ASK_IF_CONFLICT = 2;

    static boolean sIsInitialized = false;
    static HashMap<Context, CardEmulation> sCardEmus = new HashMap<Context, CardEmulation>();
    static INfcCardEmulation sService;

    final Context mContext;

    private CardEmulation(Context context, INfcCardEmulation service) {
        mContext = context.getApplicationContext();
        sService = service;
    }

    /**
     * Helper to get an instance of this class.
     *
     * @param adapter A reference to an NfcAdapter object.
     * @return
     */
    public static synchronized CardEmulation getInstance(NfcAdapter adapter) {
        if (adapter == null) throw new NullPointerException("NfcAdapter is null");
        Context context = adapter.getContext();
        if (context == null) {
            Log.e(TAG, "NfcAdapter context is null.");
            throw new UnsupportedOperationException();
        }
        if (!sIsInitialized) {
            IPackageManager pm = ActivityThread.getPackageManager();
            if (pm == null) {
                Log.e(TAG, "Cannot get PackageManager");
                throw new UnsupportedOperationException();
            }
            try {
                if (!pm.hasSystemFeature(PackageManager.FEATURE_NFC_HOST_CARD_EMULATION, 0)) {
                    Log.e(TAG, "This device does not support card emulation");
                    throw new UnsupportedOperationException();
                }
            } catch (RemoteException e) {
                Log.e(TAG, "PackageManager query failed.");
                throw new UnsupportedOperationException();
            }
            sIsInitialized = true;
        }
        CardEmulation manager = sCardEmus.get(context);
        if (manager == null) {
            // Get card emu service
            INfcCardEmulation service = adapter.getCardEmulationService();
            if (service == null) {
                Log.e(TAG, "This device does not implement the INfcCardEmulation interface.");
                throw new UnsupportedOperationException();
            }
            manager = new CardEmulation(context, service);
            sCardEmus.put(context, manager);
        }
        return manager;
    }

    /**
     * Allows an application to query whether a service is currently
     * the default service to handle a card emulation category.
     *
     * <p>Note that if {@link #getSelectionModeForCategory(String)}
     * returns {@link #SELECTION_MODE_ALWAYS_ASK} or {@link #SELECTION_MODE_ASK_IF_CONFLICT},
     * this method will always return false. That is because in these
     * selection modes a default can't be set at the category level. For categories where
     * the selection mode is {@link #SELECTION_MODE_ALWAYS_ASK} or
     * {@link #SELECTION_MODE_ASK_IF_CONFLICT}, use
     * {@link #isDefaultServiceForAid(ComponentName, String)} to determine whether a service
     * is the default for a specific AID.
     *
     * @param service The ComponentName of the service
     * @param category The category
     * @return whether service is currently the default service for the category.
     *
     * <p class="note">Requires the {@link android.Manifest.permission#NFC} permission.
     */
    public boolean isDefaultServiceForCategory(ComponentName service, String category) {
        try {
            return sService.isDefaultServiceForCategory(mContext.getUserId(), service, category);
        } catch (RemoteException e) {
            // Try one more time
            recoverService();
            if (sService == null) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return false;
            }
            try {
                return sService.isDefaultServiceForCategory(mContext.getUserId(), service,
                        category);
            } catch (RemoteException ee) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return false;
            }
        }
    }

    /**
     *
     * Allows an application to query whether a service is currently
     * the default handler for a specified ISO7816-4 Application ID.
     *
     * @param service The ComponentName of the service
     * @param aid The ISO7816-4 Application ID
     * @return whether the service is the default handler for the specified AID
     *
     * <p class="note">Requires the {@link android.Manifest.permission#NFC} permission.
     */
    public boolean isDefaultServiceForAid(ComponentName service, String aid) {
        try {
            return sService.isDefaultServiceForAid(mContext.getUserId(), service, aid);
        } catch (RemoteException e) {
            // Try one more time
            recoverService();
            if (sService == null) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return false;
            }
            try {
                return sService.isDefaultServiceForAid(mContext.getUserId(), service, aid);
            } catch (RemoteException ee) {
                Log.e(TAG, "Failed to reach CardEmulationService.");
                return false;
            }
        }
    }

    /**
     * Returns whether the user has allowed AIDs registered in the
     * specified category to be handled by a service that is preferred
     * by the foreground application, instead of by a pre-configured default.
     *
     * Foreground applications can set such preferences using the
     * {@link #setPreferredService(Activity, ComponentName)} method.
     *
     * @param category The category, e.g. {@link #CATEGORY_PAYMENT}
     * @return whether AIDs in the category can be handled by a service
     *         specified by the foreground app.
     */
    public boolean categoryAllowsForegroundPreference(String category) {
        if (CATEGORY_PAYMENT.equals(category)) {
            boolean preferForeground = false;
            try {
                preferForeground = Settings.Secure.getInt(mContext.getContentResolver(),
                        Settings.Secure.NFC_PAYMENT_FOREGROUND) != 0;
            } catch (SettingNotFoundException e) {
            }
            return preferForeground;
        } else {
            // Allowed for all other categories
            return true;
        }
    }

    /**
     * Returns the service selection mode for the passed in category.
     * Valid return values are:
     * <p>{@link #SELECTION_MODE_PREFER_DEFAULT} the user has requested a default
     *    service for this category, which will be preferred.
     * <p>{@link #SELECTION_MODE_ALWAYS_ASK} the user has requested to be asked
     *    every time what service he would like to use in this category.
     * <p>{@link #SELECTION_MODE_ASK_IF_CONFLICT} the user will only be asked
     *    to pick a service if there is a conflict.
     * @param category The category, for example {@link #CATEGORY_PAYMENT}
     * @return the selection mode for the passed in category
     */
    public int getSelectionModeForCategory(String category) {
        if (CATEGORY_PAYMENT.equals(category)) {
            String defaultComponent = Settings.Secure.getString(mContext.getContentResolver(),
                    Settings.Secure.NFC_PAYMENT_DEFAULT_COMPONENT);
            if (defaultComponent != null) {
                return SELECTION_MODE_PREFER_DEFAULT;
            } else {
                return SELECTION_MODE_ALWAYS_ASK;
            }
        } else {
            return SELECTION_MODE_ASK_IF_CONFLICT;
        }
    }

    /**
     * Registers a list of AIDs for a specific category for the
     * specified service.
     *
     * <p>If a list of AIDs for that category was previously
     * registered for this service (either statically
     * through the manifest, or dynamically by using this API),
     * that list of AIDs will be replaced with this one.
     *
     * <p>Note that you can only register AIDs for a service that
     * is running under the same UID as the caller of this API. Typically
     * this means you need to call this from the same
     * package as the service itself, though UIDs can also
     * be shared between packages using shared UIDs.
     *
     * @param service The component name of the service
     * @param category The category of AIDs to be registered
     * @param aids A list containing the AIDs to be registered
     * @return whether the registration was successful.
     */
    public boolean registerAidsForService(ComponentName service, String category,
            List<String> aids) {
        AidGroup aidGroup = new AidGroup(aids, category);
        try {
            return sService.registerAidGroupForService(mContext.getUserId(), service, aidGroup);
        } catch (RemoteException e) {
            // Try one more time
            recoverService();
            if (sService == null) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return false;
            }
            try {
                return sService.registerAidGroupForService(mContext.getUserId(), service,
                        aidGroup);
            } catch (RemoteException ee) {
                Log.e(TAG, "Failed to reach CardEmulationService.");
                return false;
            }
        }
    }

    /**
     * Unsets the off-host Secure Element for the given service.
     *
     * <p>Note that this will only remove Secure Element that was dynamically
     * set using the {@link #setOffHostForService(ComponentName, String)}
     * and resets it to a value that was statically assigned using manifest.
     *
     * <p>Note that you can only unset off-host SE for a service that
     * is running under the same UID as the caller of this API. Typically
     * this means you need to call this from the same
     * package as the service itself, though UIDs can also
     * be shared between packages using shared UIDs.
     *
     * @param service The component name of the service
     * @return whether the registration was successful.
     */
    @RequiresPermission(android.Manifest.permission.NFC)
    @NonNull
    public boolean unsetOffHostForService(@NonNull ComponentName service) {
        NfcAdapter adapter = NfcAdapter.getDefaultAdapter(mContext);
        if (adapter == null) {
            return false;
        }

        try {
            return sService.unsetOffHostForService(mContext.getUserId(), service);
        } catch (RemoteException e) {
            // Try one more time
            recoverService();
            if (sService == null) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return false;
            }
            try {
                return sService.unsetOffHostForService(mContext.getUserId(), service);
            } catch (RemoteException ee) {
                Log.e(TAG, "Failed to reach CardEmulationService.");
                return false;
            }
        }
    }

    /**
     * Sets the off-host Secure Element for the given service.
     *
     * <p>If off-host SE was initially set (either statically
     * through the manifest, or dynamically by using this API),
     * it will be replaced with this one. All AIDs registered by
     * this service will be re-routed to this Secure Element if
     * successful. AIDs that was statically assigned using manifest
     * will re-route to off-host SE that stated in manifest after NFC
     * toggle.
     *
     * <p>Note that you can only set off-host SE for a service that
     * is running under the same UID as the caller of this API. Typically
     * this means you need to call this from the same
     * package as the service itself, though UIDs can also
     * be shared between packages using shared UIDs.
     *
     * <p>Registeration will be successful only if the Secure Element
     * exists on the device.
     *
     * @param service The component name of the service
     * @param offHostSecureElement Secure Element to register the AID to. Only accept strings with
     *                             prefix SIM or prefix eSE.
     *                             Ref: GSMA TS.26 - NFC Handset Requirements
     *                             TS26_NFC_REQ_069: For UICC, Secure Element Name SHALL be
     *                                               SIM[smartcard slot]
     *                                               (e.g. SIM/SIM1, SIM2… SIMn).
     *                             TS26_NFC_REQ_070: For embedded SE, Secure Element Name SHALL be
     *                                               eSE[number]
     *                                               (e.g. eSE/eSE1, eSE2, etc.).
     * @return whether the registration was successful.
     */
    @RequiresPermission(android.Manifest.permission.NFC)
    @NonNull
    public boolean setOffHostForService(@NonNull ComponentName service,
            @NonNull String offHostSecureElement) {
        boolean validSecureElement = false;

        NfcAdapter adapter = NfcAdapter.getDefaultAdapter(mContext);
        if (adapter == null || offHostSecureElement == null) {
            return false;
        }

        List<String> validSE = adapter.getSupportedOffHostSecureElements();
        if ((offHostSecureElement.startsWith("eSE") && !validSE.contains("eSE"))
                || (offHostSecureElement.startsWith("SIM") && !validSE.contains("SIM"))) {
            return false;
        }

        if (!offHostSecureElement.startsWith("eSE") && !offHostSecureElement.startsWith("SIM")) {
            return false;
        }

        if (offHostSecureElement.equals("eSE")) {
            offHostSecureElement = "eSE1";
        } else if (offHostSecureElement.equals("SIM")) {
            offHostSecureElement = "SIM1";
        }

        try {
            return sService.setOffHostForService(mContext.getUserId(), service,
                offHostSecureElement);
        } catch (RemoteException e) {
            // Try one more time
            recoverService();
            if (sService == null) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return false;
            }
            try {
                return sService.setOffHostForService(mContext.getUserId(), service,
                        offHostSecureElement);
            } catch (RemoteException ee) {
                Log.e(TAG, "Failed to reach CardEmulationService.");
                return false;
            }
        }
    }

    /**
     * Retrieves the currently registered AIDs for the specified
     * category for a service.
     *
     * <p>Note that this will only return AIDs that were dynamically
     * registered using {@link #registerAidsForService(ComponentName, String, List)}
     * method. It will *not* return AIDs that were statically registered
     * in the manifest.
     *
     * @param service The component name of the service
     * @param category The category for which the AIDs were registered,
     *                 e.g. {@link #CATEGORY_PAYMENT}
     * @return The list of AIDs registered for this category, or null if it couldn't be found.
     */
    public List<String> getAidsForService(ComponentName service, String category) {
        try {
            AidGroup group =  sService.getAidGroupForService(mContext.getUserId(), service,
                    category);
            return (group != null ? group.getAids() : null);
        } catch (RemoteException e) {
            recoverService();
            if (sService == null) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return null;
            }
            try {
                AidGroup group = sService.getAidGroupForService(mContext.getUserId(), service,
                        category);
                return (group != null ? group.getAids() : null);
            } catch (RemoteException ee) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return null;
            }
        }
    }

    /**
     * Removes a previously registered list of AIDs for the specified category for the
     * service provided.
     *
     * <p>Note that this will only remove AIDs that were dynamically
     * registered using the {@link #registerAidsForService(ComponentName, String, List)}
     * method. It will *not* remove AIDs that were statically registered in
     * the manifest. If dynamically registered AIDs are removed using
     * this method, and a statically registered AID group for the same category
     * exists in the manifest, the static AID group will become active again.
     *
     * @param service The component name of the service
     * @param category The category of the AIDs to be removed, e.g. {@link #CATEGORY_PAYMENT}
     * @return whether the group was successfully removed.
     */
    public boolean removeAidsForService(ComponentName service, String category) {
        try {
            return sService.removeAidGroupForService(mContext.getUserId(), service, category);
        } catch (RemoteException e) {
            // Try one more time
            recoverService();
            if (sService == null) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return false;
            }
            try {
                return sService.removeAidGroupForService(mContext.getUserId(), service, category);
            } catch (RemoteException ee) {
                Log.e(TAG, "Failed to reach CardEmulationService.");
                return false;
            }
        }
    }

    /**
     * Allows a foreground application to specify which card emulation service
     * should be preferred while a specific Activity is in the foreground.
     *
     * <p>The specified Activity must currently be in resumed state. A good
     * paradigm is to call this method in your {@link Activity#onResume}, and to call
     * {@link #unsetPreferredService(Activity)} in your {@link Activity#onPause}.
     *
     * <p>This method call will fail in two specific scenarios:
     * <ul>
     * <li> If the service registers one or more AIDs in the {@link #CATEGORY_PAYMENT}
     * category, but the user has indicated that foreground apps are not allowed
     * to override the default payment service.
     * <li> If the service registers one or more AIDs in the {@link #CATEGORY_OTHER}
     * category that are also handled by the default payment service, and the
     * user has indicated that foreground apps are not allowed to override the
     * default payment service.
     * </ul>
     *
     * <p> Use {@link #categoryAllowsForegroundPreference(String)} to determine
     * whether foreground apps can override the default payment service.
     *
     * <p>Note that this preference is not persisted by the OS, and hence must be
     * called every time the Activity is resumed.
     *
     * @param activity The activity which prefers this service to be invoked
     * @param service The service to be preferred while this activity is in the foreground
     * @return whether the registration was successful
     */
    public boolean setPreferredService(Activity activity, ComponentName service) {
        // Verify the activity is in the foreground before calling into NfcService
        if (activity == null || service == null) {
            throw new NullPointerException("activity or service or category is null");
        }
        if (!activity.isResumed()) {
            throw new IllegalArgumentException("Activity must be resumed.");
        }
        try {
            return sService.setPreferredService(service);
        } catch (RemoteException e) {
            // Try one more time
            recoverService();
            if (sService == null) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return false;
            }
            try {
                return sService.setPreferredService(service);
            } catch (RemoteException ee) {
                Log.e(TAG, "Failed to reach CardEmulationService.");
                return false;
            }
        }
    }

    /**
     * Unsets the preferred service for the specified Activity.
     *
     * <p>Note that the specified Activity must still be in resumed
     * state at the time of this call. A good place to call this method
     * is in your {@link Activity#onPause} implementation.
     *
     * @param activity The activity which the service was registered for
     * @return true when successful
     */
    public boolean unsetPreferredService(Activity activity) {
        if (activity == null) {
            throw new NullPointerException("activity is null");
        }
        if (!activity.isResumed()) {
            throw new IllegalArgumentException("Activity must be resumed.");
        }
        try {
            return sService.unsetPreferredService();
        } catch (RemoteException e) {
            // Try one more time
            recoverService();
            if (sService == null) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return false;
            }
            try {
                return sService.unsetPreferredService();
            } catch (RemoteException ee) {
                Log.e(TAG, "Failed to reach CardEmulationService.");
                return false;
            }
        }
    }

    /**
     * Some devices may allow an application to register all
     * AIDs that starts with a certain prefix, e.g.
     * "A000000004*" to register all MasterCard AIDs.
     *
     * Use this method to determine whether this device
     * supports registering AID prefixes.
     *
     * @return whether AID prefix registering is supported on this device.
     */
    public boolean supportsAidPrefixRegistration() {
        try {
            return sService.supportsAidPrefixRegistration();
        } catch (RemoteException e) {
            recoverService();
            if (sService == null) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return false;
            }
            try {
                return sService.supportsAidPrefixRegistration();
            } catch (RemoteException ee) {
                Log.e(TAG, "Failed to reach CardEmulationService.");
                return false;
            }
        }
    }

    /**
     * @hide
     */
    public boolean setDefaultServiceForCategory(ComponentName service, String category) {
        try {
            return sService.setDefaultServiceForCategory(mContext.getUserId(), service, category);
        } catch (RemoteException e) {
            // Try one more time
            recoverService();
            if (sService == null) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return false;
            }
            try {
                return sService.setDefaultServiceForCategory(mContext.getUserId(), service,
                        category);
            } catch (RemoteException ee) {
                Log.e(TAG, "Failed to reach CardEmulationService.");
                return false;
            }
        }
    }

    /**
     * @hide
     */
    public boolean setDefaultForNextTap(ComponentName service) {
        try {
            return sService.setDefaultForNextTap(mContext.getUserId(), service);
        } catch (RemoteException e) {
            // Try one more time
            recoverService();
            if (sService == null) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return false;
            }
            try {
                return sService.setDefaultForNextTap(mContext.getUserId(), service);
            } catch (RemoteException ee) {
                Log.e(TAG, "Failed to reach CardEmulationService.");
                return false;
            }
        }
    }

    /**
     * @hide
     */
    public List<ApduServiceInfo> getServices(String category) {
        try {
            return sService.getServices(mContext.getUserId(), category);
        } catch (RemoteException e) {
            // Try one more time
            recoverService();
            if (sService == null) {
                Log.e(TAG, "Failed to recover CardEmulationService.");
                return null;
            }
            try {
                return sService.getServices(mContext.getUserId(), category);
            } catch (RemoteException ee) {
                Log.e(TAG, "Failed to reach CardEmulationService.");
                return null;
            }
        }
    }

    /**
     * A valid AID according to ISO/IEC 7816-4:
     * <ul>
     * <li>Has >= 5 bytes and <=16 bytes (>=10 hex chars and <= 32 hex chars)
     * <li>Consist of only hex characters
     * <li>Additionally, we allow an asterisk at the end, to indicate
     *     a prefix
     * <li>Additinally we allow an (#) at symbol at the end, to indicate
     *     a subset
     * </ul>
     *
     * @hide
     */
    public static boolean isValidAid(String aid) {
        if (aid == null)
            return false;

        // If a prefix/subset AID, the total length must be odd (even # of AID chars + '*')
        if ((aid.endsWith("*") || aid.endsWith("#")) && ((aid.length() % 2) == 0)) {
            Log.e(TAG, "AID " + aid + " is not a valid AID.");
            return false;
        }

        // If not a prefix/subset AID, the total length must be even (even # of AID chars)
        if ((!(aid.endsWith("*") || aid.endsWith("#"))) && ((aid.length() % 2) != 0)) {
            Log.e(TAG, "AID " + aid + " is not a valid AID.");
            return false;
        }

        // Verify hex characters
        if (!AID_PATTERN.matcher(aid).matches()) {
            Log.e(TAG, "AID " + aid + " is not a valid AID.");
            return false;
        }

        return true;
    }

    void recoverService() {
        NfcAdapter adapter = NfcAdapter.getDefaultAdapter(mContext);
        sService = adapter.getCardEmulationService();
    }

}