use std::{
    cmp::{Ordering, Reverse},
    ops::Deref,
};

use serde::Serialize;

#[derive(Debug, Clone, Serialize)]
pub struct Item {
    pub novel: String,
    pub post_at: jiff::Zoned,
}

pub struct Closest<'a> {
    queue: &'a mut Queue,
}

impl<'a> Closest<'a> {
    pub fn try_pop(self, now: &jiff::Zoned) -> Option<Item> {
        let last = self.queue.entries.pop().unwrap();

        if now >= &last.post_at {
            Some(last)
        } else {
            self.queue.entries.push(last);
            None
        }
    }
}

impl<'a> Deref for Closest<'a> {
    type Target = Item;

    fn deref(&self) -> &Self::Target {
        let len = self.queue.entries.len() - 1;
        &self.queue.entries[len]
    }
}

fn cmp_items(lhs: &Item, rhs: &Item) -> Ordering {
    Reverse(&lhs.post_at).cmp(&Reverse(&rhs.post_at))
}

#[derive(Debug, Default)]
pub struct Queue {
    entries: Vec<Item>,
}

impl FromIterator<Item> for Queue {
    fn from_iter<T: IntoIterator<Item = Item>>(iter: T) -> Self {
        let mut entries: Vec<Item> = iter.into_iter().collect();
        entries.sort_unstable_by(cmp_items);

        #[cfg(debug_assertions)]
        if entries.len() >= 2 {
            let first = &entries[0].post_at;
            let second = &entries[1].post_at;

            assert!(first >= second);
        }

        Self { entries }
    }
}

impl Queue {
    pub fn len(&self) -> usize {
        self.entries.len()
    }

    pub fn closest(&self) -> Option<&Item> {
        self.entries.last()
    }

    pub fn closest_mut(&mut self) -> Option<Closest<'_>> {
        if self.entries.is_empty() {
            None
        } else {
            Some(Closest { queue: self })
        }
    }

    pub fn add(&mut self, item: Item) {
        // This could be:
        // let Ok(idx) | Err(idx) = ..;
        // But fuck rust, it's not allowed.
        let res = self
            .entries
            .binary_search_by(|probe| cmp_items(probe, &item));

        // The why блядь?
        let idx = match res {
            Ok(i) => i,
            Err(i) => i,
        };

        self.entries.insert(idx, item);
    }

    pub const fn new() -> Self {
        Self {
            entries: Vec::new(),
        }
    }
}