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use std::{
    collections::{hash_map::Entry, HashMap},
    hash::Hash,
};

/// Removes all but the last occurrence of elements that
/// resolve to the same key maintaining the order in which they
/// where first found.
///
/// # Examples
///
/// ```
/// use vit_servicing_station_lib::utils::collections::dedup_by_key_keep_last;
///
/// let v = vec![(0, "a"), (0, "b"), (1, "c"), (1, "d"), (2, "e")];
///
/// assert_eq!(dedup_by_key_keep_last(v.into_iter(), |i| i.0), [(0, "b"), (1, "d"), (2, "e")]);
/// ```
pub fn dedup_by_key_keep_last<F, I, K>(iter: I, key_fn: F) -> Vec<I::Item>
where
    I: Iterator,
    F: Fn(&I::Item) -> K,
    K: Eq + Hash,
{
    let mut h = HashMap::new();
    let mut v = Vec::new();

    for i in iter {
        match h.entry(key_fn(&i)) {
            Entry::Occupied(e) => {
                v[*e.get()] = i;
            }
            Entry::Vacant(e) => {
                e.insert(v.len());
                v.push(i);
            }
        }
    }

    v
}