[remoting android] Refactor OAuthTokenFetcher for reusability

remoting/android/java/src/org/chromium/chromoting/OAuthTokenFetcher.java

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-package org.chromium.chromoting;
-
-import android.app.Activity;
-import android.os.AsyncTask;
-
-import com.google.android.gms.auth.GoogleAuthException;
-import com.google.android.gms.auth.GoogleAuthUtil;
-import com.google.android.gms.auth.UserRecoverableAuthException;
-
-import java.io.IOException;
-
-/**
- * This helper class fetches an OAuth token on a separate thread, and properly handles the various
- * error-conditions that can occur (such as, starting an Activity to prompt user for input).
- */
-public class OAuthTokenFetcher {
-    /**
-     * Callback interface to receive the token, or an error notification. These will be called
-     * on the application's main thread. Note that if a user-recoverable error occurs, neither of
-     * these callback will be triggered. Instead, a new Activity will be launched, and the calling
-     * Activity must override
-     * {@link android.app.Activity#onActivityResult} and handle the result code
-     * {@link REQUEST_CODE_RECOVER_FROM_OAUTH_ERROR} to re-attempt or cancel fetching the token.
-     */
-    public interface Callback {
-        /** Called when a token is obtained. */
-        void onTokenFetched(String token);
-
-        /**
-         * Called if an unrecoverable error prevents fetching a token.
-         * @param errorResource String resource of error-message to be displayed.
-         */
-        void onError(int errorResource);
-    }
-
-    /** Request code used for starting the OAuth recovery activity. */
-    public static final int REQUEST_CODE_RECOVER_FROM_OAUTH_ERROR = 100;
-
-    /** Scopes at which the authentication token we request will be valid. */
-    private static final String TOKEN_SCOPE = "oauth2:https://www.googleapis.com/auth/chromoting "
-            + "https://www.googleapis.com/auth/googletalk";
-
-    /**
-     * Reference to the main activity. Used for running tasks on the main thread, and for
-     * starting other activities to handle user-recoverable errors.
-     */
-    private Activity mActivity;
-
-    /** Account name (e-mail) for which the token will be fetched. */
-    private String mAccountName;
-
-    private Callback mCallback;
-
-    public OAuthTokenFetcher(Activity activity, String accountName, Callback callback) {
-        mActivity = activity;
-        mAccountName = accountName;
-        mCallback = callback;
-    }
-
-    /** Begins fetching a token. Should be called on the main thread. */
-    public void fetch() {
-        fetchImpl(null);
-    }
-
-    /**
-     * Begins fetching a token, clearing an existing token from the cache. Should be called on the
-     * main thread.
-     * @param expiredToken A previously-fetched token which has expired.
-     */
-    public void clearAndFetch(String expiredToken) {
-        fetchImpl(expiredToken);
-    }
-
-    private void fetchImpl(final String expiredToken) {
-        new AsyncTask<Void, Void, Void>() {
-            @Override
-            protected Void doInBackground(Void... params) {
-                try {
-                    if (expiredToken != null) {
-                        GoogleAuthUtil.clearToken(mActivity, expiredToken);
-                    }
-
-                    // This method is deprecated but its replacement is not yet available.
-                    // TODO(lambroslambrou): Fix this by replacing |mAccountName| with an instance
-                    // of android.accounts.Account.
-                    String token = GoogleAuthUtil.getToken(mActivity, mAccountName, TOKEN_SCOPE);
-                    handleTokenReceived(token);
-                } catch (IOException ioException) {
-                    handleError(R.string.error_network_error);
-                } catch (UserRecoverableAuthException recoverableException) {
-                    handleRecoverableException(recoverableException);
-                } catch (GoogleAuthException fatalException) {
-                    handleError(R.string.error_unexpected);
-                }
-                return null;
-            }
-        }.execute();
-    }
-
-    private void handleTokenReceived(final String token) {
-        mActivity.runOnUiThread(new Runnable() {
-            @Override
-            public void run() {
-                mCallback.onTokenFetched(token);
-            }
-        });
-    }
-
-    private void handleError(final int error) {
-        mActivity.runOnUiThread(new Runnable() {
-            @Override
-            public void run() {
-                mCallback.onError(error);
-            }
-        });
-    }
-
-    private void handleRecoverableException(final UserRecoverableAuthException exception) {
-        mActivity.runOnUiThread(new Runnable() {
-            @Override
-            public void run() {
-                mActivity.startActivityForResult(exception.getIntent(),
-                        REQUEST_CODE_RECOVER_FROM_OAUTH_ERROR);
-            }
-        });
-    }
-}