- (BHToken *)block_hookWithMode:(BlockHookMode)mode
                     usingBlock:(id)block

NSObject *z = NSObject.new;
int(^block)(int x, int y) = ^int(int x, int y) {
    int result = x + y;
    NSLog(@"%d + %d = %d, z is a NSObject: %@", x, y, result, z);
    return result;
};
    
BHToken *token = [block block_hookWithMode:BlockHookModeDead|BlockHookModeBefore|BlockHookModeInstead|BlockHookModeAfter usingBlock:^(BHInvocation *invocation, int x, int y) {
    int ret = 0;
    [invocation getReturnValue:&ret];
    switch (invocation.mode) {
        case BlockHookModeBefore:
            // BHInvocation has to be the first arg.
            NSLog(@"hook before block! invocation:%@", invocation);
            break;
        case BlockHookModeInstead:
            [invocation invokeOriginalBlock];
            NSLog(@"let me see original result: %d", ret);
            // change the block imp and result
            ret = x * y;
            [invocation setReturnValue:&ret];
            NSLog(@"hook instead: '+' -> '*'");
            break;
        case BlockHookModeAfter:
            // print args and result
            NSLog(@"hook after block! %d * %d = %d", x, y, ret);
            break;
        case BlockHookModeDead:
            // BHInvocation is the only arg.
            NSLog(@"block dead! token:%@", invocation.token);
            break;
        default:
            break;
    }
}];
    
NSLog(@"hooked block");
int ret = block(3, 5);
NSLog(@"hooked result:%d", ret);
// remove token.
[token remove];
NSLog(@"remove tokens, original block");
ret = block(3, 5);
NSLog(@"original result:%d", ret);

NSObject *testArg = [NSObject new];
NSObject *testArg1 = [NSObject new];
    
NSObject *(^testblock)(NSObject *) = ^(NSObject *a) {
    return [NSObject new];
};
    
[testblock block_interceptor:^(BHInvocation *invocation, IntercepterCompletion  _Nonnull completion) {
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        NSObject * __unsafe_unretained arg;
        [invocation getArgument:&arg atIndex:1];
        NSLog(@"Original argument:%@", arg);
        [invocation setArgument:(void *)&testArg1 atIndex:1];
        completion();
    });
}];
    
testblock(testArg);