main.m

#import <UIKit/UIKit.h>
#import "LegacyAppDelegate.h"
@import Firebase;

// Helper function for consistent user assignment
static uint32_t fnv1aHash(NSString *str) {
    uint32_t hash = 2166136261u;
    for (NSInteger i = 0; i < str.length; i++) {
        hash ^= (uint32_t)[str characterAtIndex:i];
        hash *= 16777619u;
    }
    return hash;
}

static BOOL shouldUseNewVersion(float percentage) {
    NSString *identifier = [[[UIDevice currentDevice] identifierForVendor] UUIDString];
    uint32_t hash = fnv1aHash(identifier);
    float normalizedValue = (float)hash / (float)UINT32_MAX;
    return normalizedValue < (percentage / 100.0f);
}

int main(int argc, char * argv[]) {
#ifdef DEBUG
    @autoreleasepool {
        @try {
            // Initialize Firebase
            [FIRApp configure];
            
            // Set up Remote Config with default value
            FIRRemoteConfig *config = [FIRRemoteConfig remoteConfig];
            [config setDefaults:@{@"new_version_rollout_percentage": @1.0}];
            
            // Create semaphore for sync config fetch
            dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
            __block BOOL useNewVersion = NO;
            
            // Fetch config
            [config fetchWithCompletionHandler:^(FIRRemoteConfigFetchStatus status, NSError *error) {
                if (status == FIRRemoteConfigFetchStatusSuccess) {
                    [config activateWithCompletion:^(BOOL changed, NSError *error) {
                        float percentage = [config[@"new_version_rollout_percentage"].numberValue floatValue];
                        useNewVersion = shouldUseNewVersion(percentage);
                        dispatch_semaphore_signal(semaphore);
                    }];
                } else {
                    useNewVersion = shouldUseNewVersion(1.0f); // Default to 1%
                    dispatch_semaphore_signal(semaphore);
                }
            }];
            
            // Wait with timeout
            dispatch_semaphore_wait(semaphore, dispatch_time(DISPATCH_TIME_NOW, 3 * NSEC_PER_SEC));
            
            if (useNewVersion) {
                return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
            } else {
                return UIApplicationMain(argc, argv, nil, NSStringFromClass([LegacyAppDelegate class]));
            }
                
        } @catch (NSException *exception) {
            NSLog(@"[weatherbug main] Caught exception. name: %@; reason: %@\n %@", 
                  exception.name, exception.reason, [exception callStackSymbols]);
            NSLog(@"[weatherbug main] Caught exception: %@", exception);
            @throw;
        } @catch (...) {
            dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
                @throw;
            });
        }
    }
#else
    @autoreleasepool {
        [FIRApp configure];
        FIRRemoteConfig *config = [FIRRemoteConfig remoteConfig];
        float percentage = [config[@"new_version_rollout_percentage"].numberValue floatValue];
        BOOL useNewVersion = shouldUseNewVersion(percentage);
        
        return UIApplicationMain(argc, argv, nil, 
            NSStringFromClass(useNewVersion ? [AppDelegate class] : [LegacyAppDelegate class]));
    }
#endif
}