use crate::utils::gt_by;

use std::{cmp::Ordering, iter::from_generator};

/// Sorts a slice of data using the shell sort algorithm.
///
/// # Examples
///
/// ```
/// # use sort_steps::{shell_sort};
/// let numbers = [5, 9, 3, 6, 8, 2, 1, 7, 4];
/// println!("Shell Sort Steps:");
/// for (i, v) in shell_sort(&numbers).enumerate() {
///     println!("#{:02}: {:?}", i, v);
/// }
/// ```
pub fn shell_sort<T>(v: &[T]) -> impl Iterator<Item = Vec<T>>
where
    T: PartialOrd + Clone,
{
    shell_sort_by(v, |a, b| a.partial_cmp(b))
}

/// Sorts a slice of data using the shell sort algorithm with a custom comparator.
///
/// # Examples
///
/// ```
/// # use sort_steps::{shell_sort_by};
/// let numbers = [5, 9, 3, 6, 8, 2, 1, 7, 4];
/// println!("Shell Sort Steps:");
/// for (i, v) in shell_sort_by(&numbers, |a, b| a.partial_cmp(b)).enumerate() {
///     println!("#{:02}: {:?}", i, v);
/// }
/// ```
pub fn shell_sort_by<T, F>(v: &[T], compare: F) -> impl Iterator<Item = Vec<T>>
where
    F: Fn(&T, &T) -> Option<Ordering> + Copy,
    T: Clone,
{
    let n = v.len();
    let mut state = v.to_vec();

    let mut gap = n / 2;

    from_generator(move || {
        yield state.to_vec();
        while gap > 0 {
            for i in gap..n {
                let mut j = i;
                let temp = state[i].clone();
                while j >= gap && gt_by(&state[j - gap], &temp, compare) {
                    state[j] = state[j - gap].clone();
                    j -= gap;
                    // yield state.to_vec();
                }
                state[j] = temp;
                yield state.to_vec();
            }
            gap /= 2;
        }
    })
}