use std::{
    collections::{BTreeMap, HashMap},
    sync::Arc,
};

#[derive(Debug, Clone, PartialEq)]
pub struct RollingSet<T: std::hash::Hash + std::cmp::Eq> {
    value_identifyer: usize,
    capacity: usize,
    time_to_value: BTreeMap<usize, Arc<T>>,
    value_to_time: HashMap<Arc<T>, usize>,
}

impl<T> RollingSet<T>
where
    T: Eq + std::hash::Hash + Clone,
{
    pub fn new(capacity: usize) -> Self {
        Self {
            capacity,
            value_identifyer: 0,
            time_to_value: BTreeMap::new(),
            value_to_time: HashMap::new(),
        }
    }

    pub fn with_capacity(capacity: usize) -> Self {
        Self {
            capacity,
            value_identifyer: 0,
            time_to_value: BTreeMap::new(),

            value_to_time: HashMap::with_capacity(capacity),
        }
    }

    pub fn insert(&mut self, element: T) {
        self.value_identifyer += 1;
        let v = Arc::new(element);
        self.time_to_value.insert(self.value_identifyer, v.clone());
        // Here v is guaranteed to be unique
        self.value_to_time.insert(v, self.value_identifyer);

        if self.len() > self.capacity {
            self.pop();
        }
    }

    pub fn pop(&mut self) -> Option<T> {
        // These clones are always cheap, usize and Arc
        let first = self.time_to_value.first_key_value()?.0.clone();
        let value = self.time_to_value.get(&first)?.clone();
        self.value_to_time.remove(&value);
        self.time_to_value.remove(&first);
        if !self.is_empty() {
            self.value_identifyer = 0;
        }
        Some((*value).clone())
    }

    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    pub fn is_full(&self) -> bool {
        self.len() == self.capacity
    }

    pub fn set_capacity(&mut self, new: usize) -> usize {
        self.capacity = new;
        self.capacity
    }

    pub fn capacity(&self) -> usize {
        self.capacity
    }

    pub fn remove(&mut self, element: &T) -> bool {
        let i = match self.value_to_time.get(element) {
            Some(i) => i,
            None => return false,
        };

        self.time_to_value.remove(i);
        self.value_to_time.remove(element);
        true
    }

    pub fn contains(&self, element: &T) -> bool {
        self.value_to_time.contains_key(element)
    }

    pub fn len(&self) -> usize {
        self.value_to_time.len()
    }

    pub fn clear(&mut self) {
        self.value_identifyer = 0;
        self.time_to_value.clear();
        self.value_to_time.clear();
    }
}

#[cfg(test)]
mod tests {

    use crate::RollingSet;

    #[test]
    fn create() {
        let mut set = RollingSet::new(100);
        set.insert("one");
        set.insert("two");
        set.insert("three");

        assert!(set.contains(&"one"));
        assert!(set.contains(&"two"));
        assert!(set.contains(&"three"));
        assert!(!set.contains(&"four"));
    }

    #[test]
    fn roll() {
        let mut set = RollingSet::new(3);
        set.insert("one");
        set.insert("two");
        set.insert("three");
        // Set rolls here
        set.insert("four");
        assert_eq!(set.len(), 3);
        assert!(!set.contains(&"one"));
        assert!(set.contains(&"two"));
        assert!(set.contains(&"three"));
        assert!(set.contains(&"four"));
    }

    #[test]
    fn remove() {
        let mut set = RollingSet::new(3);
        set.insert("one");
        set.insert("two");
        set.insert("three");
        set.insert("four");

        assert!(set.contains(&"two"));
        assert!(set.contains(&"three"));
        assert!(set.contains(&"four"));

        set.remove(&"two");
        assert_eq!(set.len(), 2);
        assert!(!set.contains(&"two"));
        assert!(set.contains(&"three"));
        assert!(set.contains(&"four"));
    }

    #[test]
    fn len() {
        let mut set = RollingSet::new(3);
        set.insert("one");
        set.insert("two");
        set.insert("three");
        assert_eq!(set.len(), 3);
        set.insert("four");

        // The set should have rolled so the len should still be three
        assert_eq!(set.len(), 3);

        assert!(set.contains(&"two"));
        assert!(set.contains(&"three"));
        assert!(set.contains(&"four"));

        set.remove(&"two");
        assert_eq!(set.len(), 2);
        assert!(!set.contains(&"two"));
        assert!(set.contains(&"three"));
        assert!(set.contains(&"four"));
    }

    #[test]
    fn pop() {
        let mut set = RollingSet::new(3);
        set.insert("one");
        set.insert("two");
        set.insert("three");
        assert_eq!(set.len(), 3);

        let value = set.pop();
        assert_eq!(value, Some("one"));
        assert_eq!(set.len(), 2);

        let value = set.pop();
        assert_eq!(value, Some("two"));
        assert_eq!(set.len(), 1);

        let value = set.pop();
        assert_eq!(value, Some("three"));
        assert_eq!(set.len(), 0);

        set.insert("one");
        set.insert("two");
        set.insert("three");
        set.insert("four");
        assert_eq!(set.len(), 3);

        let value = set.pop();
        assert_eq!(value, Some("two"));
        assert_eq!(set.len(), 2);

        let value = set.pop();
        assert_eq!(value, Some("three"));
        assert_eq!(set.len(), 1);

        let value = set.pop();
        assert_eq!(value, Some("four"));
        assert_eq!(set.len(), 0);
    }

    #[test]
    fn iter() {
        let mut set = RollingSet::new(3);
        set.insert("one");
        set.insert("two");
        set.insert("three");
    }
}