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/*
* Copyright 2010 Facebook
*
* 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.
*/

#import "Facebook.h"
#import "FBLoginDialog.h"
#import "FBRequest.h"
#import "FBError.h"
#import "FBSessionManualTokenCachingStrategy.h"
#import "JSON.h"
#import "FBSession+Internal.h"
#import "FBUtility.h"

static NSString* kDialogBaseURL = @"https://m." FB_BASE_URL "/dialog/";
static NSString* kGraphBaseURL = @"https://graph." FB_BASE_URL "/";
static NSString* kRestserverBaseURL = @"https://api." FB_BASE_URL "/method/";

static NSString* kFBAppAuthURLScheme = @"fbauth";
static NSString* kFBAppAuthURLPath = @"authorize";
static NSString* kRedirectURL = @"fbconnect://success";

static NSString* kLogin = @"oauth";
static NSString* kApprequests = @"apprequests";
static NSString* kSDKVersion = @"2";

// If the last time we extended the access token was more than 24 hours ago
// we try to refresh the access token again.
static const int kTokenExtendThreshold = 24;

static NSString *requestFinishedKeyPath = @"state";
static void *finishedContext = @"finishedContext";
static void *tokenContext = @"tokenContext";

// the following const strings name properties for which KVO is manually handled
static NSString *const FBaccessTokenPropertyName = @"accessToken";
static NSString *const FBexpirationDatePropertyName = @"expirationDate";

///////////////////////////////////////////////////////////////////////////////////////////////////

@interface Facebook () <FBRequestDelegate>

// private properties
@property(nonatomic, copy) NSString* appId;
// session and tokenCaching object implement login logic and token state in Facebook class
@property(nonatomic, readwrite, retain) FBSession *session;
@property(nonatomic) BOOL hasUpdatedAccessToken;
@property(nonatomic, retain) FBSessionManualTokenCachingStrategy *tokenCaching;

@end

///////////////////////////////////////////////////////////////////////////////////////////////////

@implementation Facebook

@synthesize sessionDelegate = _sessionDelegate,
            urlSchemeSuffix = _urlSchemeSuffix,
            appId = _appId,
            session = _session,
            hasUpdatedAccessToken = _hasUpdatedAccessToken,
            tokenCaching = _tokenCaching;

///////////////////////////////////////////////////////////////////////////////////////////////////
// private


- (id)initWithAppId:(NSString *)appId
        andDelegate:(id<FBSessionDelegate>)delegate {
    self = [self initWithAppId:appId urlSchemeSuffix:nil andDelegate:delegate];
    return self;
}

/**
* Initialize the Facebook object with application ID.
*
* @param appId the facebook app id
* @param urlSchemeSuffix
* urlSchemeSuffix is a string of lowercase letters that is
* appended to the base URL scheme used for Facebook Login. For example,
* if your facebook ID is "350685531728" and you set urlSchemeSuffix to
* "abcd", the Facebook app will expect your application to bind to
* the following URL scheme: "fb350685531728abcd".
* This is useful if your have multiple iOS applications that
* share a single Facebook application id (for example, if you
* have a free and a paid version on the same app) and you want
* to use Facebook Login with both apps. Giving both apps different
* urlSchemeSuffix values will allow the Facebook app to disambiguate
* their URL schemes and always redirect the user back to the
* correct app, even if both the free and the app is installed
* on the device.
* urlSchemeSuffix is supported on version 3.4.1 and above of the Facebook
* app. If the user has an older version of the Facebook app
* installed and your app uses urlSchemeSuffix parameter, the SDK will
* proceed as if the Facebook app isn't installed on the device
* and redirect the user to Safari.
* @param delegate the FBSessionDelegate
*/
- (id)initWithAppId:(NSString *)appId
    urlSchemeSuffix:(NSString *)urlSchemeSuffix
        andDelegate:(id<FBSessionDelegate>)delegate {
    
    self = [super init];
    if (self) {
        _requests = [[NSMutableSet alloc] init];
        _lastAccessTokenUpdate = [[NSDate distantPast] retain];
        _frictionlessRequestSettings = [[FBFrictionlessRequestSettings alloc] init];
        _tokenCaching = [[FBSessionManualTokenCachingStrategy alloc] init];
        self.appId = appId;
        self.sessionDelegate = delegate;
        self.urlSchemeSuffix = urlSchemeSuffix;
        
        // observe tokenCaching properties so we can forward KVO
        [self.tokenCaching addObserver:self
                            forKeyPath:FBaccessTokenPropertyName
                               options:NSKeyValueObservingOptionPrior
                               context:tokenContext];
        [self.tokenCaching addObserver:self
                            forKeyPath:FBexpirationDatePropertyName
                               options:NSKeyValueObservingOptionPrior
                               context:tokenContext];
    }
    return self;
}

/**
* Override NSObject : free the space
*/
- (void)dealloc {
    [_session release];
    [_tokenCaching release];
    for (FBRequest* _request in _requests) {
        [_request removeObserver:self forKeyPath:requestFinishedKeyPath];
    }
    [_lastAccessTokenUpdate release];
    [_requests release];
    [_fbDialog release];
    [_appId release];
    [_urlSchemeSuffix release];
    [_frictionlessRequestSettings release];
    [super dealloc];
}

- (void)invalidateSession {
    
    [self.session close];
    [self.tokenCaching clearToken];
    
    [FBSession deleteFacebookCookies];
    
    // setting to nil also terminates any active request for whitelist
    [_frictionlessRequestSettings updateRecipientCacheWithRecipients:nil];
}

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
- (void)observeFinishedContextValueForKeyPath:(NSString *)keyPath
                                     ofObject:(id)object
                                       change:(NSDictionary *)change {
    FBRequest* _request = (FBRequest*)object;
    FBRequestState requestState = [_request state];
    if (requestState == kFBRequestStateComplete) {
        if ([_request sessionDidExpire]) {
            [self invalidateSession];
            if ([self.sessionDelegate respondsToSelector:@selector(fbSessionInvalidated)]) {
                [self.sessionDelegate fbSessionInvalidated];
            }
        }
        [_request removeObserver:self forKeyPath:requestFinishedKeyPath];
        [_requests removeObject:_request];
    }
    
}
#pragma GCC diagnostic pop

- (void)observeTokenContextValueForKeyPath:(NSString *)keyPath
                                    change:(NSDictionary *)change {
    // here we are forwarding KVO notifications from an inner object
    if ([change objectForKey:NSKeyValueChangeNotificationIsPriorKey]) {
        [self willChangeValueForKey:keyPath];
    } else {
        [self didChangeValueForKey:keyPath];
    }
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    // dispatch for various observe cases
    if (context == finishedContext) {
        [self observeFinishedContextValueForKeyPath:keyPath
                                           ofObject:object
                                             change:change];
    } else if (context == tokenContext) {
        [self observeTokenContextValueForKeyPath:keyPath
                                             change:change];
    } else {
        [super observeValueForKeyPath:keyPath
                             ofObject:object
                               change:change
                              context:context];
    }
}

/**
* A private function for getting the app's base url.
*/
- (NSString *)getOwnBaseUrl {
    return [NSString stringWithFormat:@"fb%@%@://authorize",
            _appId,
            _urlSchemeSuffix ? _urlSchemeSuffix : @""];
}

/**
* A function for parsing URL parameters.
*/
- (NSDictionary*)parseURLParams:(NSString *)query {
NSArray *pairs = [query componentsSeparatedByString:@"&"];
NSMutableDictionary *params = [[[NSMutableDictionary alloc] init] autorelease];
for (NSString *pair in pairs) {
NSArray *kv = [pair componentsSeparatedByString:@"="];
NSString *val =
        [[kv objectAtIndex:1]
         stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
        
[params setObject:val forKey:[kv objectAtIndex:0]];
}
    return params;
}

- (void)updateSessionIfTokenUpdated {
    if (self.hasUpdatedAccessToken) {
        self.hasUpdatedAccessToken = NO;

        // invalidate current session and create a new one with the same permissions
        NSArray *permissions = self.session.permissions;
        [self.session close];
        self.session = [[[FBSession alloc] initWithAppID:_appId
                                             permissions:permissions
                                         urlSchemeSuffix:_urlSchemeSuffix
                                      tokenCacheStrategy:self.tokenCaching]
                           autorelease];
    
        // get the session into a valid state
        [self.session openWithCompletionHandler:nil];
    }
}

///////////////////////////////////////////////////////////////////////////////////////////////////
//public

/**
* Starts a dialog which prompts the user to log in to Facebook and grant
* the requested permissions to the application.
*
* If the device supports multitasking, we use fast app switching to show
* the dialog in the Facebook app or, if the Facebook app isn't installed,
* in Safari (this enables Facebook Login by allowing multiple apps on
* the device to share the same user session).
* When the user grants or denies the permissions, the app that
* showed the dialog (the Facebook app or Safari) redirects back to
* the calling application, passing in the URL the access token
* and/or any other parameters the Facebook backend includes in
* the result (such as an error code if an error occurs).
*
* See http://developers.facebook.com/docs/authentication/ for more details.
*
* Also note that requests may be made to the API without calling
* authorize() first, in which case only public information is returned.
*
* @param permissions
* A list of permission required for this application: e.g.
* "read_stream", "publish_stream", or "offline_access". see
* http://developers.facebook.com/docs/authentication/permissions
* This parameter should not be null -- if you do not require any
* permissions, then pass in an empty String array.
* @param delegate
* Callback interface for notifying the calling application when
* the user has logged in.
*/
- (void)authorize:(NSArray *)permissions {
    
    // if we already have a session, git rid of it
    [self.session close];
    self.session = nil;
    [self.tokenCaching clearToken];
    
    self.session = [[[FBSession alloc] initWithAppID:_appId
                                        permissions:permissions
                                    urlSchemeSuffix:_urlSchemeSuffix
                                 tokenCacheStrategy:self.tokenCaching]
                    autorelease];
    
    [self.session openWithCompletionHandler:^(FBSession *session, FBSessionState status, NSError *error) {
        switch (status) {
            case FBSessionStateOpen:
                // call the legacy session delegate
                [self fbDialogLogin:session.accessToken expirationDate:session.expirationDate];
                break;
            case FBSessionStateClosedLoginFailed:
                { // prefer to keep decls near to their use
                    
                    // unpack the error code and reason in order to compute cancel bool
                    NSString *errorCode = [[error userInfo] objectForKey:FBErrorLoginFailedOriginalErrorCode];
                    NSString *errorReason = [[error userInfo] objectForKey:FBErrorLoginFailedReason];
                    BOOL userDidCancel = !errorCode && (!errorReason ||
                                                        [errorReason isEqualToString:FBErrorLoginFailedReasonInlineCancelledValue]);
                    
                    // call the legacy session delegate
                    [self fbDialogNotLogin:userDidCancel];
                }
                break;
            // presently extension, log-out and invalidation are being implemented in the Facebook class
            default:
                break; // so we do nothing in response to those state transitions
        }
    }];
 }

-(NSString*)accessToken {
    return self.tokenCaching.accessToken;
}

-(void)setAccessToken:(NSString *)accessToken {
    self.tokenCaching.accessToken = accessToken;
    self.hasUpdatedAccessToken = YES;
}

-(NSDate*)expirationDate {
    return self.tokenCaching.expirationDate;
    self.hasUpdatedAccessToken = YES;
}

-(void)setExpirationDate:(NSDate *)expirationDate {
    self.tokenCaching.expirationDate = expirationDate;
}

/**
* Attempt to extend the access token.
*
* Access tokens typically expire within 30-60 days. When the user uses the
* app, the app should periodically try to obtain a new access token. Once an
* access token has expired, the app can no longer renew it. The app then has
* to ask the user to re-authorize it to obtain a new access token.
*
* To ensure your app always has a fresh access token for active users, it's
* recommended that you call extendAccessTokenIfNeeded in your application's
* applicationDidBecomeActive: UIApplicationDelegate method.
*/
- (void)extendAccessToken {
    if (_isExtendingAccessToken) {
        return;
    }
    _isExtendingAccessToken = YES;
    NSMutableDictionary* params = [NSMutableDictionary dictionaryWithObjectsAndKeys:
                                   @"auth.extendSSOAccessToken", @"method",
                                   nil];
    [self requestWithParams:params andDelegate:self];
}

/**
* Calls extendAccessToken if shouldExtendAccessToken returns YES.
*/
- (void)extendAccessTokenIfNeeded {
    if ([self shouldExtendAccessToken]) {
        [self extendAccessToken];
    }
}

/**
* Returns YES if the last time a new token was obtained was over 24 hours ago.
*/
- (BOOL)shouldExtendAccessToken {
    if ([self isSessionValid]){
        NSCalendar *calendar = [[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar] autorelease];
        NSDateComponents *components = [calendar components:NSHourCalendarUnit
                                                   fromDate:_lastAccessTokenUpdate
                                                     toDate:[NSDate date]
                                                    options:0];
        
        if (components.hour >= kTokenExtendThreshold) {
            return YES;
        }
    }
    return NO;
}

/**
* This function processes the URL the Facebook application or Safari used to
* open your application during a Facebook Login flow.
*
* You MUST call this function in your UIApplicationDelegate's handleOpenURL
* method (see
* http://developer.apple.com/library/ios/#documentation/uikit/reference/UIApplicationDelegate_Protocol/Reference/Reference.html
* for more info).
*
* This will ensure that the authorization process will proceed smoothly once the
* Facebook application or Safari redirects back to your application.
*
* @param URL the URL that was passed to the application delegate's handleOpenURL method.
*
* @return YES if the URL starts with 'fb[app_id]://authorize and hence was handled
* by SDK, NO otherwise.
*/
- (BOOL)handleOpenURL:(NSURL *)url {
    return [self.session handleOpenURL:url];
}

/**
* Invalidate the current user session by removing the access token in
* memory and clearing the browser cookie.
*
* Note that this method dosen't unauthorize the application --
* it just removes the access token. To unauthorize the application,
* the user must remove the app in the app settings page under the privacy
* settings screen on facebook.com.
*/
- (void)logout {
    [self invalidateSession];
    
    if ([self.sessionDelegate respondsToSelector:@selector(fbDidLogout)]) {
        [self.sessionDelegate fbDidLogout];
    }
}

/**
* Invalidate the current user session by removing the access token in
* memory and clearing the browser cookie.
*
* @deprecated Use of a single session delegate, set at app init, is preferred
*/
- (void)logout:(id<FBSessionDelegate>)delegate {
    [self logout];
    // preserve deprecated callback behavior, but leave cached delegate intact
    // avoid calling twice if the passed and cached delegates are the same
    if (delegate != self.sessionDelegate &&
        [delegate respondsToSelector:@selector(fbDidLogout)]) {
        [delegate fbDidLogout];
    }
}

/**
* Make a request to Facebook's REST API with the given
* parameters. One of the parameter keys must be "method" and its value
* should be a valid REST server API method.
*
* See http://developers.facebook.com/docs/reference/rest/
*
* @param parameters
* Key-value pairs of parameters to the request. Refer to the
* documentation: one of the parameters must be "method".
* @param delegate
* Callback interface for notifying the calling application when
* the request has received response
* @return FBRequest*
* Returns a pointer to the FBRequest object.
*/
- (FBRequest*)requestWithParams:(NSMutableDictionary *)params
                    andDelegate:(id <FBRequestDelegate>)delegate {
    if ([params objectForKey:@"method"] == nil) {
        NSLog(@"API Method must be specified");
        return nil;
    }
    
    NSString * methodName = [params objectForKey:@"method"];
    [params removeObjectForKey:@"method"];
    
    return [self requestWithMethodName:methodName
                             andParams:params
                         andHttpMethod:@"GET"
                           andDelegate:delegate];
}

/**
* Make a request to Facebook's REST API with the given method name and
* parameters.
*
* See http://developers.facebook.com/docs/reference/rest/
*
*
* @param methodName
* a valid REST server API method.
* @param parameters
* Key-value pairs of parameters to the request. Refer to the
* documentation: one of the parameters must be "method". To upload
* a file, you should specify the httpMethod to be "POST" and the
* “params” you passed in should contain a value of the type
* (UIImage *) or (NSData *) which contains the content that you
* want to upload
* @param delegate
* Callback interface for notifying the calling application when
* the request has received response
* @return FBRequest*
* Returns a pointer to the FBRequest object.
*/
- (FBRequest*)requestWithMethodName:(NSString *)methodName
                          andParams:(NSMutableDictionary *)params
                      andHttpMethod:(NSString *)httpMethod
                        andDelegate:(id <FBRequestDelegate>)delegate {
    [self updateSessionIfTokenUpdated];
    [self extendAccessTokenIfNeeded];

    FBRequest *request = [[FBRequest alloc] initWithSession:self.session
                                                 restMethod:methodName
                                                 parameters:params
                                                 HTTPMethod:httpMethod];
    [request setDelegate:delegate];
    [request startWithCompletionHandler:nil];

    return request;
}

/**
* Make a request to the Facebook Graph API without any parameters.
*
* See http://developers.facebook.com/docs/api
*
* @param graphPath
* Path to resource in the Facebook graph, e.g., to fetch data
* about the currently logged authenticated user, provide "me",
* which will fetch http://graph.facebook.com/me
* @param delegate
* Callback interface for notifying the calling application when
* the request has received response
* @return FBRequest*
* Returns a pointer to the FBRequest object.
*/
- (FBRequest*)requestWithGraphPath:(NSString *)graphPath
                       andDelegate:(id <FBRequestDelegate>)delegate {
    
    return [self requestWithGraphPath:graphPath
                            andParams:[NSMutableDictionary dictionary]
                        andHttpMethod:@"GET"
                          andDelegate:delegate];
}

/**
* Make a request to the Facebook Graph API with the given string
* parameters using an HTTP GET (default method).
*
* See http://developers.facebook.com/docs/api
*
*
* @param graphPath
* Path to resource in the Facebook graph, e.g., to fetch data
* about the currently logged authenticated user, provide "me",
* which will fetch http://graph.facebook.com/me
* @param parameters
* key-value string parameters, e.g. the path "search" with
* parameters "q" : "facebook" would produce a query for the
* following graph resource:
* https://graph.facebook.com/search?q=facebook
* @param delegate
* Callback interface for notifying the calling application when
* the request has received response
* @return FBRequest*
* Returns a pointer to the FBRequest object.
*/
- (FBRequest*)requestWithGraphPath:(NSString *)graphPath
                         andParams:(NSMutableDictionary *)params
                       andDelegate:(id <FBRequestDelegate>)delegate {
    
    return [self requestWithGraphPath:graphPath
                            andParams:params
                        andHttpMethod:@"GET"
                          andDelegate:delegate];
}

/**
* Make a request to the Facebook Graph API with the given
* HTTP method and string parameters. Note that binary data parameters
* (e.g. pictures) are not yet supported by this helper function.
*
* See http://developers.facebook.com/docs/api
*
*
* @param graphPath
* Path to resource in the Facebook graph, e.g., to fetch data
* about the currently logged authenticated user, provide "me",
* which will fetch http://graph.facebook.com/me
* @param parameters
* key-value string parameters, e.g. the path "search" with
* parameters {"q" : "facebook"} would produce a query for the
* following graph resource:
* https://graph.facebook.com/search?q=facebook
* To upload a file, you should specify the httpMethod to be
* "POST" and the “params” you passed in should contain a value
* of the type (UIImage *) or (NSData *) which contains the
* content that you want to upload
* @param httpMethod
* http verb, e.g. "GET", "POST", "DELETE"
* @param delegate
* Callback interface for notifying the calling application when
* the request has received response
* @return FBRequest*
* Returns a pointer to the FBRequest object.
*/
- (FBRequest*)requestWithGraphPath:(NSString *)graphPath
                         andParams:(NSMutableDictionary *)params
                     andHttpMethod:(NSString *)httpMethod
                       andDelegate:(id <FBRequestDelegate>)delegate {
    [self updateSessionIfTokenUpdated];
    [self extendAccessTokenIfNeeded];

    FBRequest *request = [[FBRequest alloc] initWithSession:self.session
                                                  graphPath:graphPath
                                                 parameters:params
                                                 HTTPMethod:httpMethod];
    [request setDelegate:delegate];
    [request startWithCompletionHandler:nil];

    return request;
}

/**
* Generate a UI dialog for the request action.
*
* @param action
* String representation of the desired method: e.g. "login",
* "feed", ...
* @param delegate
* Callback interface to notify the calling application when the
* dialog has completed.
*/
- (void)dialog:(NSString *)action
   andDelegate:(id<FBDialogDelegate>)delegate {
    NSMutableDictionary * params = [NSMutableDictionary dictionary];
    [self dialog:action andParams:params andDelegate:delegate];
}

/**
* Generate a UI dialog for the request action with the provided parameters.
*
* @param action
* String representation of the desired method: e.g. "login",
* "feed", ...
* @param parameters
* key-value string parameters
* @param delegate
* Callback interface to notify the calling application when the
* dialog has completed.
*/
- (void)dialog:(NSString *)action
     andParams:(NSMutableDictionary *)params
   andDelegate:(id <FBDialogDelegate>)delegate {
    
    [_fbDialog release];
    
    NSString *dialogURL = [kDialogBaseURL stringByAppendingString:action];
    [params setObject:@"touch" forKey:@"display"];
    [params setObject:kSDKVersion forKey:@"sdk"];
    [params setObject:kRedirectURL forKey:@"redirect_uri"];
    
    if ([action isEqualToString:kLogin]) {
        [params setObject:@"user_agent" forKey:@"type"];
        _fbDialog = [[FBLoginDialog alloc] initWithURL:dialogURL loginParams:params delegate:self];
    } else {
        [params setObject:_appId forKey:@"app_id"];
        if ([self isSessionValid]) {
            [params setValue:[self.accessToken stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding]
                      forKey:@"access_token"];
            [self extendAccessTokenIfNeeded];
        }
        
        // by default we show dialogs, frictionless cases may have a hidden view
        BOOL invisible = NO;
        
        // frictionless handling for application requests
        if ([action isEqualToString:kApprequests]) {
            // if frictionless requests are enabled
            if (self.isFrictionlessRequestsEnabled) {
                // 1. show the "Don't show this again for these friends" checkbox
                // 2. if the developer is sending a targeted request, then skip the loading screen
                [params setValue:@"1" forKey:@"frictionless"];
                // 3. request the frictionless recipient list encoded in the success url
                [params setValue:@"1" forKey:@"get_frictionless_recipients"];
            }
            
            // set invisible if all recipients are enabled for frictionless requests
            id fbid = [params objectForKey:@"to"];
            if (fbid != nil) {
                // if value parses as a json array expression get the list that way
                SBJsonParser *parser = [[[SBJsonParser alloc] init] autorelease];
                id fbids = [parser objectWithString:fbid];
                if (![fbids isKindOfClass:[NSArray class]]) {
                    // otherwise seperate by commas (handles the singleton case too)
                    fbids = [fbid componentsSeparatedByString:@","];
                }
                invisible = [self isFrictionlessEnabledForRecipients:fbids];
            }
        }
        
        _fbDialog = [[FBDialog alloc] initWithURL:dialogURL
                                           params:params
                                  isViewInvisible:invisible
                             frictionlessSettings:_frictionlessRequestSettings
                                         delegate:delegate];
    }
    
    [_fbDialog show];
}

- (BOOL)isFrictionlessRequestsEnabled {
    return _frictionlessRequestSettings.enabled;
}

- (void)enableFrictionlessRequests {
    [_frictionlessRequestSettings enableWithFacebook:self];
}

- (void)reloadFrictionlessRecipientCache {
    [_frictionlessRequestSettings reloadRecipientCacheWithFacebook:self];
}

- (BOOL)isFrictionlessEnabledForRecipient:(NSString*)fbid {
    return [_frictionlessRequestSettings isFrictionlessEnabledForRecipient:fbid];
}

- (BOOL)isFrictionlessEnabledForRecipients:(NSArray*)fbids {
    return [_frictionlessRequestSettings isFrictionlessEnabledForRecipients:fbids];
}

/**
* @return boolean - whether this object has an non-expired session token
*/
- (BOOL)isSessionValid {
    return (self.accessToken != nil && self.expirationDate != nil
            && NSOrderedDescending == [self.expirationDate compare:[NSDate date]]);
    
}

///////////////////////////////////////////////////////////////////////////////////////////////////
//FBLoginDialogDelegate

/**
* Set the authToken and expirationDate after login succeed
*/
- (void)fbDialogLogin:(NSString *)token expirationDate:(NSDate *)expirationDate {
    [_lastAccessTokenUpdate release];
    _lastAccessTokenUpdate = [[NSDate date] retain];
    [self reloadFrictionlessRecipientCache];
    if ([self.sessionDelegate respondsToSelector:@selector(fbDidLogin)]) {
        [self.sessionDelegate fbDidLogin];
    }
}

/**
* Did not login call the not login delegate
*/
- (void)fbDialogNotLogin:(BOOL)cancelled {
    if ([self.sessionDelegate respondsToSelector:@selector(fbDidNotLogin:)]) {
        [self.sessionDelegate fbDidNotLogin:cancelled];
    }
}

#pragma mark - FBRequestDelegate Methods
// These delegate methods are only called for requests that extendAccessToken initiated

- (void)request:(FBRequest *)request didFailWithError:(NSError *)error {
    _isExtendingAccessToken = NO;
}

- (void)request:(FBRequest *)request didLoad:(id)result {
    _isExtendingAccessToken = NO;
    NSString* accessToken = [result objectForKey:@"access_token"];
    NSString* expTime = [result objectForKey:@"expires_at"];
    
    if (accessToken == nil || expTime == nil) {
        return;
    }
    
    self.accessToken = accessToken;
    
    NSTimeInterval timeInterval = [expTime doubleValue];
    NSDate *expirationDate = [NSDate distantFuture];
    if (timeInterval != 0) {
        expirationDate = [NSDate dateWithTimeIntervalSince1970:timeInterval];
    }
    self.expirationDate = expirationDate;
    [_lastAccessTokenUpdate release];
    _lastAccessTokenUpdate = [[NSDate date] retain];
    
    [self updateSessionIfTokenUpdated];
    
    if ([self.sessionDelegate respondsToSelector:@selector(fbDidExtendToken:expiresAt:)]) {
        [self.sessionDelegate fbDidExtendToken:accessToken expiresAt:expirationDate];
    }
}

- (void)request:(FBRequest *)request didLoadRawResponse:(NSData *)data {
}

- (void)request:(FBRequest *)request didReceiveResponse:(NSURLResponse *)response{
}

- (void)requestLoading:(FBRequest *)request{
}

+ (BOOL)automaticallyNotifiesObserversForKey:(NSString *)key {
    // these properties must manually notify for KVO
    if ([key isEqualToString:FBaccessTokenPropertyName] ||
        [key isEqualToString:FBexpirationDatePropertyName]) {
        return NO;
    } else {
        return [super automaticallyNotifiesObserversForKey:key];
    }
}

@end
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