Recursive desribeOparandOnStack

CalcBrain.m

+(NSString *)describeOperandOnStack:(NSMutableArray *)stack withRootOperation:(NSString *)rootOperation {
    NSString *result = @"";
    
    id topOfStack = [stack lastObject];
    if (topOfStack) [stack removeLastObject];
    
    if ([topOfStack isKindOfClass:[NSNumber class]]) {
        result = [NSString stringWithFormat:@"%@", topOfStack];
    } else if ([topOfStack isKindOfClass:[NSString class]]) {
        NSString* operation = topOfStack;
        BOOL noParenthesesNeededForSure = !rootOperation || [self isSingleOperandOperation:rootOperation];
        
        if ([operation isEqualToString:@"+"]) {
            NSString *format = @"(%@ + %@)";
            if (noParenthesesNeededForSure || [@"+" isEqualToString:rootOperation] ) {
                format = @"%@ + %@";
            }
            
            result = [NSString stringWithFormat:format, [self describeOperandOnStack:stack withRootOperation:@"+"], [self describeOperandOnStack:stack withRootOperation:@"+"]];
        } else if ([operation isEqualToString:@"*"]) {
            NSString *format = @"(%@ * %@)";
            if (noParenthesesNeededForSure || [@"+" isEqualToString:rootOperation] || [@"-" isEqualToString:rootOperation]) {
                format = @"%@ * %@";
            }
            
            result = [NSString stringWithFormat:format, [self describeOperandOnStack:stack withRootOperation:@"*"], [self describeOperandOnStack:stack withRootOperation:@"*"]];
        } else if ([operation isEqualToString:@"-"]) {
            NSString *format = @"(%@ - %@)";
            if (noParenthesesNeededForSure) {
                format = @"%@ - %@";
            }

            NSString* subtrahend = [self describeOperandOnStack:stack withRootOperation:@"-"];
            result = [NSString stringWithFormat:format, [self describeOperandOnStack:stack withRootOperation:@"-"], subtrahend];
        } else if ([operation isEqualToString:@"/"]) {
            NSString *format = @"(%@ / %@)";
            if (noParenthesesNeededForSure || [@"+" isEqualToString:rootOperation] || [@"-" isEqualToString:rootOperation]) {
                format = @"%@ / %@";
            }
            
            NSString* divisor = [self describeOperandOnStack:stack withRootOperation:@"/"];
            if (divisor) result = [NSString stringWithFormat:format, [self describeOperandOnStack:stack withRootOperation:@"/"], divisor];
        } else if ([operation isEqualToString:@"sin"]) {
            result = [NSString stringWithFormat:@"sin(%@)", [self describeOperandOnStack:stack withRootOperation:@"sin"]];
        } else if ([operation isEqualToString:@"cos"]) {
            result = [NSString stringWithFormat:@"cos(%@)", [self describeOperandOnStack:stack withRootOperation:@"cos"]];
        } else if ([operation isEqualToString:@"sqrt"]) {
            result = [NSString stringWithFormat:@"sqrt(%@)", [self describeOperandOnStack:stack withRootOperation:@"sqrt"]];
        } else {
            result = operation;
        }
    }
    
    if ([stack count] != 0 && !rootOperation) {
        return [NSString stringWithFormat:@"%@, %@", [self describeOperandOnStack:stack withRootOperation:nil], result];
    } else {
        return result;
    }
}