struct Counter {
    count: u32,
}

impl Counter {
    fn new() -> Counter {
        Counter { count: 0 }
    }
}

impl Iterator for Counter {
    type Item = u32;

    fn next(&mut self) -> Option<Self::Item> {
        self.count += 1;
        if self.count < 6 {
            Some(self.count)
        } else {
            None
        }
    }
}

/// Adds one to the number given.
///
/// # Examples
///
/// ```
/// let five = 5;
///
/// assert_eq!(6, wasm_test::add_one(5));
/// ```
#[no_mangle]
pub extern "C" fn add_one(a: u32) -> u32 {
    a + 1
}

/// Test iterator function in wasm
///
/// # Examples
///
/// ```
/// assert_eq!(18, wasm_test::iterators());
/// ```
#[no_mangle]
pub extern "C" fn iterators() -> u32 {
    Counter::new()
        .zip(vec![1, 2, 3, 4, 5].iter().skip(1))
        .map(|(a, b)| a * b)
        .filter(|x| x % 3 == 0)
        .sum()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn add_one_test() {
        assert_eq!(add_one(3), 4);
    }

    #[test]
    fn iterators_test() {
        assert_eq!(iterators(), 18);
    }
}