use crate::{
    database::{
        abstraction::{DatabaseEngine, Tree},
        Config,
    },
    Result,
};
use persy::{ByteVec, OpenOptions, Persy, ValueMode};

use std::{
    cmp::Ordering,
    collections::{btree_map::Entry, BTreeMap, BTreeSet},
    future::Future,
    iter::Peekable,
    pin::Pin,
    sync::{Arc, RwLock},
    time::{Duration, Instant},
};

pub struct PersyEngine {
    persy: Persy,
    write_cache: Arc<RwLock<WriteCache>>,
}

impl DatabaseEngine for PersyEngine {
    fn open(config: &Config) -> Result<Arc<Self>> {
        let mut cfg = persy::Config::new();
        cfg.change_cache_size((config.db_cache_capacity_mb * 1024.0 * 1024.0) as u64);

        let persy = OpenOptions::new()
            .create(true)
            .config(cfg)
            .open(&format!("{}/db.persy", config.database_path))?;
        let write_cache_size = 1000;
        let write_cache_window_millisecs = 1000;
        let write_cache = Arc::new(RwLock::new(WriteCache::new(
            &persy,
            write_cache_size,
            Duration::from_millis(write_cache_window_millisecs),
        )));
        /*
        use timer::Timer;
        let timer = Timer::new();
        let timer_write_cache = write_cache.clone();
        timer.schedule_repeating(
            chrono::Duration::milliseconds((write_cache_window_millisecs / 4) as i64),
            move || timer_write_cache.write().unwrap().flush_timed().unwrap(),
        );
        */
        Ok(Arc::new(PersyEngine { persy, write_cache }))
    }

    fn open_tree(self: &Arc<Self>, name: &'static str) -> Result<Arc<dyn Tree>> {
        // Create if it doesn't exist
        if !self.persy.exists_index(name)? {
            let mut tx = self.persy.begin()?;
            tx.create_index::<ByteVec, ByteVec>(name, ValueMode::REPLACE)?;
            tx.prepare()?.commit()?;
        }

        Ok(Arc::new(PersyTree {
            persy: self.persy.clone(),
            name: name.to_owned(),
            watchers: RwLock::new(BTreeMap::new()),
            write_cache: self.write_cache.clone(),
        }))
    }

    fn flush(self: &Arc<Self>) -> Result<()> {
        self.write_cache.write().unwrap().flush_changes()?;
        Ok(())
    }
}

pub struct PersyTree {
    persy: Persy,
    name: String,
    watchers: RwLock<BTreeMap<Vec<u8>, Vec<tokio::sync::oneshot::Sender<()>>>>,
    write_cache: Arc<RwLock<WriteCache>>,
}

pub struct WriteCache {
    add_cache: BTreeMap<String, BTreeMap<Vec<u8>, Vec<u8>>>,
    remove_cache: BTreeMap<String, BTreeSet<Vec<u8>>>,
    changes_count: u32,
    last_flush: Instant,
    persy: Persy,
    max_size: u32,
    max_time_window: Duration,
}

impl WriteCache {
    fn new(persy: &Persy, max_size: u32, max_time_window: Duration) -> Self {
        Self {
            add_cache: Default::default(),
            remove_cache: Default::default(),
            changes_count: Default::default(),
            last_flush: Instant::now(),
            persy: persy.clone(),
            max_size,
            max_time_window,
        }
    }
}

impl WriteCache {
    pub fn insert(&mut self, index: String, key: &[u8], value: &[u8]) -> Result<()> {
        match self.add_cache.entry(index.clone()) {
            Entry::Vacant(s) => {
                let mut map = BTreeMap::new();
                map.insert(key.to_owned(), value.to_owned());
                s.insert(map);
            }
            Entry::Occupied(mut o) => {
                o.get_mut().insert(key.to_owned(), value.to_owned());
            }
        }
        self.remove_remove(index, key)?;
        self.check_and_flush()?;
        Ok(())
    }

    pub fn remove_remove(&mut self, index: String, key: &[u8]) -> Result<()> {
        match self.remove_cache.entry(index) {
            Entry::Vacant(_) => {}
            Entry::Occupied(mut o) => {
                o.get_mut().remove(key);
            }
        }
        Ok(())
    }

    pub fn remove_insert(&mut self, index: String, key: &[u8]) -> Result<()> {
        match self.add_cache.entry(index) {
            Entry::Vacant(_) => {}
            Entry::Occupied(mut o) => {
                o.get_mut().remove(key);
            }
        }
        Ok(())
    }

    pub fn remove(&mut self, index: String, key: &[u8]) -> Result<()> {
        match self.remove_cache.entry(index.clone()) {
            Entry::Vacant(s) => {
                let mut map = BTreeSet::new();
                map.insert(key.to_owned());
                s.insert(map);
            }
            Entry::Occupied(mut o) => {
                o.get_mut().insert(key.to_owned());
            }
        }
        self.remove_insert(index, key)?;
        self.check_and_flush()?;
        Ok(())
    }
    pub fn check_and_flush(&mut self) -> Result<()> {
        self.changes_count += 1;
        if self.changes_count > self.max_size {
            self.flush_changes()?;
            self.changes_count = 0;
        }
        Ok(())
    }

    pub fn get(&self, index: &str, key: &[u8], value: Option<Vec<u8>>) -> Result<Option<Vec<u8>>> {
        Ok(if let Some(changes) = self.add_cache.get(index) {
            changes.get(key).map(|v| v.to_owned()).or(value)
        } else if let Some(remove) = self.remove_cache.get(index) {
            if remove.contains(key) {
                None
            } else {
                value
            }
        } else {
            value
        })
    }

    fn flush_changes(&mut self) -> Result<()> {
        let mut tx = self.persy.begin()?;

        for (index, changes) in &self.add_cache {
            for (key, value) in changes {
                tx.put::<ByteVec, ByteVec>(
                    &index,
                    ByteVec(key.to_owned()),
                    ByteVec(value.to_owned()),
                )?;
            }
        }
        self.add_cache.clear();
        for (index, changes) in &self.remove_cache {
            for key in changes {
                tx.remove::<ByteVec, ByteVec>(&index, ByteVec(key.to_owned()), None)?;
            }
        }
        self.remove_cache.clear();
        tx.prepare()?.commit()?;
        self.last_flush = Instant::now();
        Ok(())
    }

    pub fn iter<'a>(
        &self,
        index: &str,
        mut iter: Box<dyn Iterator<Item = (Vec<u8>, Vec<u8>)> + Send + Sync + 'a>,
    ) -> Box<dyn Iterator<Item = (Vec<u8>, Vec<u8>)> + Send + Sync + 'a> {
        if let Some(adds) = self.add_cache.get(index) {
            let added = adds.clone().into_iter().map(|(k, v)| (k.into(), v.into()));
            iter = Box::new(UnionIter::new(iter, added, false))
        }

        if let Some(removes) = self.remove_cache.get(index) {
            let to_filter = removes.clone();
            iter = Box::new(iter.filter(move |x| to_filter.contains(&(*x.0).to_owned())))
        }

        iter
    }

    fn iter_from<'a>(
        &self,
        index: &str,
        from: &[u8],
        backwards: bool,
        mut iter: Box<dyn Iterator<Item = (Vec<u8>, Vec<u8>)> + Send + 'a>,
    ) -> Box<dyn Iterator<Item = (Vec<u8>, Vec<u8>)> + Send + 'a> {
        if let Some(adds) = self.add_cache.get(index) {
            let range = if backwards {
                adds.range(..from.to_owned())
            } else {
                adds.range(from.to_owned()..)
            };
            let added = range
                .map(|(k, v)| (k.to_owned().into(), v.to_owned().into()))
                .collect::<Vec<(Vec<u8>, Vec<u8>)>>();
            let add_iter: Box<dyn Iterator<Item = (Vec<u8>, Vec<u8>)> + Send> = if backwards {
                Box::new(added.into_iter().rev())
            } else {
                Box::new(added.into_iter())
            };
            iter = Box::new(UnionIter::new(iter, add_iter, backwards))
        }

        if let Some(removes) = self.remove_cache.get(index) {
            let owned_from = from.to_owned();
            let to_filter = removes.iter();
            let to_filter = if backwards {
                to_filter
                    .filter(|x| (..&owned_from).contains(x))
                    .cloned()
                    .collect::<Vec<Vec<u8>>>()
            } else {
                to_filter
                    .filter(|x| (&owned_from..).contains(x))
                    .cloned()
                    .collect::<Vec<Vec<u8>>>()
            };
            iter = Box::new(iter.filter(move |x| !to_filter.contains(&(*x.0).to_owned())))
        }
        iter
    }

    fn scan_prefix<'a>(
        &self,
        index: &str,
        prefix: Vec<u8>,
        mut iter: Box<dyn Iterator<Item = (Vec<u8>, Vec<u8>)> + Send + 'a>,
    ) -> Box<dyn Iterator<Item = (Vec<u8>, Vec<u8>)> + Send + 'a> {
        if let Some(adds) = self.add_cache.get(index) {
            let owned_prefix = prefix.to_owned();
            let added = adds
                .range(prefix.to_owned()..)
                .take_while(move |(k, _)| k.starts_with(&owned_prefix))
                .map(|(k, v)| (k.to_owned().into(), v.to_owned().into()))
                .collect::<Vec<(Vec<u8>, Vec<u8>)>>();
            iter = Box::new(UnionIter::new(iter, added.into_iter(), false))
        }

        if let Some(removes) = self.remove_cache.get(index) {
            let to_filter = removes
                .iter()
                .filter(move |k| k.starts_with(&prefix))
                .cloned()
                .collect::<Vec<Vec<u8>>>();
            iter = Box::new(iter.filter(move |x| !to_filter.contains(&(*x.0).to_owned())))
        }
        iter
    }

    #[allow(unused)]
    pub fn flush_timed(&mut self) -> Result<()> {
        if self.changes_count > 0 {
            if Instant::now() - self.last_flush > self.max_time_window {
                self.flush_changes()?;
            }
        }
        Ok(())
    }
}

struct UnionIter<T: Iterator<Item = I>, T1: Iterator<Item = I>, I> {
    first: Peekable<T>,
    second: Peekable<T1>,
    backwards: bool,
}

impl<T: Iterator<Item = I>, T1: Iterator<Item = I>, I> UnionIter<T, T1, I> {
    fn new(first: T, second: T1, backwards: bool) -> Self {
        UnionIter {
            first: first.peekable(),
            second: second.peekable(),
            backwards,
        }
    }
}

impl<K: Ord, V, T, T1> Iterator for UnionIter<T, T1, (K, V)>
where
    T: Iterator<Item = (K, V)>,
    T1: Iterator<Item = (K, V)>,
{
    type Item = (K, V);
    fn next(&mut self) -> Option<Self::Item> {
        if let (Some(f), Some(s)) = (self.first.peek(), self.second.peek()) {
            if self.backwards {
                match f.0.cmp(&s.0) {
                    Ordering::Less => self.second.next(),
                    Ordering::Greater => self.first.next(),
                    Ordering::Equal => {
                        self.first.next();
                        self.second.next()
                    }
                }
            } else {
                match f.0.cmp(&s.0) {
                    Ordering::Less => self.first.next(),
                    Ordering::Greater => self.second.next(),
                    Ordering::Equal => {
                        self.first.next();
                        self.second.next()
                    }
                }
            }
        } else {
            self.first.next().or_else(|| self.second.next())
        }
    }
}

impl Tree for PersyTree {
    fn get(&self, key: &[u8]) -> Result<Option<Vec<u8>>> {
        let result = self
            .persy
            .get::<ByteVec, ByteVec>(&self.name, &ByteVec(key.to_vec()))?
            .map(|v| v.into_iter().map(|bv| bv.0).next())
            .flatten();
        let result = self
            .write_cache
            .read()
            .unwrap()
            .get(&self.name, key, result)?;
        Ok(result)
    }

    fn insert(&self, key: &[u8], value: &[u8]) -> Result<()> {
        let watchers = self.watchers.read().unwrap();
        let mut triggered = Vec::new();

        for length in 0..=key.len() {
            if watchers.contains_key(&key[..length]) {
                triggered.push(&key[..length]);
            }
        }

        drop(watchers);

        if !triggered.is_empty() {
            let mut watchers = self.watchers.write().unwrap();
            for prefix in triggered {
                if let Some(txs) = watchers.remove(prefix) {
                    for tx in txs {
                        let _ = tx.send(());
                    }
                }
            }
        }
        self.write_cache
            .write()
            .unwrap()
            .insert(self.name.clone(), key, value)?;
        Ok(())
    }

    fn remove(&self, key: &[u8]) -> Result<()> {
        self.write_cache
            .write()
            .unwrap()
            .remove(self.name.clone(), key)?;
        Ok(())
    }

    fn iter<'a>(&'a self) -> Box<dyn Iterator<Item = (Vec<u8>, Vec<u8>)> + Send + 'a> {
        let iter = self.persy.range::<ByteVec, ByteVec, _>(&self.name, ..);
        match iter {
            Ok(iter) => {
                let result = Box::new(iter.filter_map(|(k, v)| {
                    v.into_iter()
                        .map(|val| (k.0.to_owned().into(), val.0.to_owned().into()))
                        .next()
                }));

                self.write_cache.read().unwrap().iter(&self.name, result)
            }
            Err(e) => {
                log::warn!("error iterating {:?}", e);
                Box::new(std::iter::empty())
            }
        }
    }

    fn iter_from<'a>(
        &'a self,
        from: &[u8],
        backwards: bool,
    ) -> Box<dyn Iterator<Item = (Vec<u8>, Vec<u8>)> + Send + 'a> {
        let range = if backwards {
            self.persy
                .range::<ByteVec, ByteVec, _>(&self.name, ..ByteVec(from.to_owned()))
        } else {
            self.persy
                .range::<ByteVec, ByteVec, _>(&self.name, ByteVec(from.to_owned())..)
        };
        match range {
            Ok(iter) => {
                let map = iter.filter_map(|(k, v)| {
                    v.into_iter()
                        .map(|val| (k.0.to_owned().into(), val.0.to_owned().into()))
                        .next()
                });
                let result: Box<dyn Iterator<Item = (Vec<u8>, Vec<u8>)> + Send + 'a> = if backwards
                {
                    Box::new(map.rev())
                } else {
                    Box::new(map)
                };

                self.write_cache
                    .read()
                    .unwrap()
                    .iter_from(&self.name, from, backwards, result)
            }
            Err(e) => {
                log::warn!("error iterating with prefix {:?}", e);
                Box::new(std::iter::empty())
            }
        }
    }

    fn increment(&self, key: &[u8]) -> Result<Vec<u8>> {
        let old = self.get(key)?;
        let new = crate::utils::increment(old.as_deref()).unwrap();
        self.insert(key, &new)?;
        Ok(new)
    }

    fn scan_prefix<'a>(
        &'a self,
        prefix: Vec<u8>,
    ) -> Box<dyn Iterator<Item = (Vec<u8>, Vec<u8>)> + Send + 'a> {
        let range_prefix = ByteVec(prefix.to_owned());
        let range = self
            .persy
            .range::<ByteVec, ByteVec, _>(&self.name, range_prefix..);

        match range {
            Ok(iter) => {
                let owned_prefix = prefix.clone();
                let result = Box::new(
                    iter.take_while(move |(k, _)| k.0.starts_with(&owned_prefix))
                        .filter_map(|(k, v)| {
                            v.into_iter()
                                .map(|val| (k.0.to_owned().into(), val.0.to_owned().into()))
                                .next()
                        }),
                );

                self.write_cache
                    .read()
                    .unwrap()
                    .scan_prefix(&self.name, prefix, result)
            }
            Err(e) => {
                log::warn!("error scanning prefix {:?}", e);
                Box::new(std::iter::empty())
            }
        }
    }

    fn watch_prefix<'a>(&'a self, prefix: &[u8]) -> Pin<Box<dyn Future<Output = ()> + Send + 'a>> {
        let (tx, rx) = tokio::sync::oneshot::channel();

        self.watchers
            .write()
            .unwrap()
            .entry(prefix.to_vec())
            .or_default()
            .push(tx);

        Box::pin(async move {
            // Tx is never destroyed
            rx.await.unwrap();
        })
    }
}