use crate::day_solver::DaySolver;
#[cfg(test)]
use crate::util::read_file;

pub struct Day9 {
    histories: Vec<Vec<i32>>
}

impl Day9 {

    pub fn create(input: String) -> Self {
        return Day9 {
            histories: input.lines().map(|h| h.split_whitespace().map(|n| n.parse().unwrap()).collect()).collect()
        }
    }
}

fn find_next_in_history(history: &Vec<i32>) -> i32 {

    if history.iter().all(|n| n == &0) {
        return 0
    }

    let mut history_derivative = Vec::with_capacity(history.len());
    for i in 0..history.len() - 1 {
        history_derivative.push(history[i + 1] - history[i])
    }

    return history.last().unwrap() + find_next_in_history(&history_derivative);

}

impl DaySolver for Day9 {


    fn solve_part1(&mut self) -> String {
        return self.histories.iter()
            .map(|h| {
                let res = find_next_in_history(h);
                // println!("{:?} yields {}", h, res);
                res
            })
            .sum::<i32>().to_string()
    }

    fn solve_part2(&mut self) -> String {
        return self.histories.iter()
            .map(|h| {
                let mut h_reverse = h.clone();
                h_reverse.reverse();
                let res = find_next_in_history(&h_reverse);
                // println!("{:?} yields {}", h, res);
                res
            })
            .sum::<i32>().to_string()
    }
}

#[test]
fn test_part1() {
    let mut day = Day9::create(read_file("input/day09_example.txt"));
    assert_eq!("114", day.solve_part1());
}

#[test]
fn test_part2() {
    let mut day = Day9::create(read_file("input/day09_example.txt"));
    assert_eq!("2", day.solve_part2());
}