use crate::*;

fn sum_of(values: Vec<i32>) -> Result<Outcome, FailedTo> {
    if values.is_empty() {
        return Ok(Outcome::Scalar(0));
    }
    let mut ret = Ok(Outcome::Scalar(0));
    for value in values {
        ret = ret.and_then(|outcome: Outcome| match outcome {
            Outcome::List(_) => Err(FailedTo::ProcessInput),
            Outcome::Scalar(acc) => acc
                .checked_add(value)
                .map(|new_acc: i32| Outcome::Scalar(new_acc))
                .ok_or(FailedTo::SumValues),
        })
    }
    ret
}

impl Outcome {
    pub fn sum(self) -> Result<Outcome, FailedTo> {
        match self {
            Outcome::Scalar(value) => Ok(Outcome::Scalar(value)),
            Outcome::List(values) => sum_of(values),
        }
    }
}

#[cfg(test)]
mod unit_tests {
    use super::*;
    #[test]
    fn check_sum() {
        let outcome = Handful::grab(5, 1).roll().sum();
        assert_eq!(outcome, Ok(Outcome::Scalar(5)));
    }
}