use crate::errors::PoolError;
use smallvec::SmallVec;
use std::collections::VecDeque;

type PResult<T> = Result<T, PoolError>;

pub struct Pool<T>
where
    T: Send + Sync,
{
    items: VecDeque<(i64, T)>,
    current: Option<(i64, usize)>,
    len: usize,
}

impl<T> Pool<T>
where
    T: Send + Sync,
{
    pub fn new(len: usize) -> Self {
        Pool {
            items: VecDeque::new(),
            current: None,
            len,
        }
    }

    pub fn init(&mut self, timestamp: i64, item: T) -> PResult<()> {
        let len = self.items.len();

        if len == 0 {
            self.items.push_back((timestamp, item));
            self.current.replace((timestamp, 0));
            return Ok(());
        } else {
            return Err(PoolError::PoolInitialized("Pool is already initialized"));
        }
    }

    pub fn add(&mut self, item: T, timestamp: i64) -> PResult<()> {
        let len = self.items.len();
        if len == self.len {
            return Err(PoolError::PoolFull);
        }
        if len == 0 {
            return Err(PoolError::PoolInitialized("Pool is not initialized"));
        }
        if len == 1 {
            if self.items[0].0 < timestamp {
                self.items.push_back((timestamp, item));
            } else {
                self.items.push_front((timestamp, item));
                self.current.replace((timestamp, 1));
            }
            return Ok(());
        }

        let back = self
            .items
            .back()
            .map(|(last_timestamp, _)| *last_timestamp < timestamp)
            .unwrap();
        let front = self
            .items
            .front()
            .map(|(first_timestamp, _)| *first_timestamp > timestamp)
            .unwrap();

        if !(back || front) {
            return Err(PoolError::TimestampError);
        }

        if back {
            self.items.push_back((timestamp, item));
        } else {
            self.items.push_front((timestamp, item));
            self.current.as_mut().map(|(_, index)| *index += 1);
        }

        Ok(())
    }

    pub fn prev(&self) -> Option<&T> {
        self.current
            .map(|(_, index)| &self.items[index])
            .map(|(_, item)| item)
    }

    pub fn next(&mut self) -> Option<&T> {
        let len = self.items.len();
        let current = self.current.as_mut().map(|(_, index)| index);

        if let Some(index) = current {
            if *index + 1 < len {
                *index += 1;
                self.current
                    .as_ref()
                    .map(|(_, index)| &self.items[*index])
                    .map(|(_, item)| item)
            } else {
                None
            }
        } else {
            None
        }
    }

    pub fn get(&self, index: isize) -> Option<&T> {
        self.current
            .as_ref()
            .map(|(_, current_index)| *current_index as isize + index)
            .and_then(|index| {
                if index >= 0 && index < self.items.len() as isize {
                    Some(&self.items[index as usize])
                } else {
                    None
                }
            })
            .map(|(_, item)| item)
    }

    pub fn get_mut(&mut self, index: isize) -> Option<&mut T> {
        self.current
            .as_ref()
            .map(|(_, current_index)| *current_index as isize + index)
            .and_then(|index| {
                if index >= 0 && index < self.items.len() as isize {
                    Some(&mut self.items[index as usize])
                } else {
                    None
                }
            })
            .map(|(_, item)| item)
    }

    pub fn iter(&self) -> impl Iterator<Item = &T> {
        self.items.iter().map(|(_, item)| item)
    }

    pub fn iter_mut(&mut self) -> impl Iterator<Item = &mut T> {
        self.items.iter_mut().map(|(_, item)| item)
    }

    pub fn set_current(&mut self, timestamp: i64, item: T) -> PResult<()> {
        if self.items.len() == 0 {
            return Err(PoolError::PoolInitialized("Pool is not initialized"));
        }

        let position = self.items.iter().position(|(time, _)| *time == timestamp);

        if let Some(p) = position {
            let start = (p - self.len / 2).max(0);
            let end = (p + self.len / 2).min(self.items.len() - 1);
            self.items = self.items.drain(start..end).collect();
            self.current.replace((timestamp, self.len / 2));
            return Ok(());
        } else {
            self.items.clear();
            self.init(timestamp, item);
            return Ok(());
        }
    }

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