use super::Config;
use crate::Result;

use std::{future::Future, pin::Pin, sync::Arc};

#[cfg(any(feature = "persy"))]
use std::{collections::BTreeMap, sync::RwLock};

#[cfg(feature = "sled")]
pub mod sled;

#[cfg(feature = "sqlite")]
pub mod sqlite;

#[cfg(feature = "heed")]
pub mod heed;

pub trait DatabaseEngine: Sized {
    fn open(config: &Config) -> Result<Arc<Self>>;
    fn open_tree(self: &Arc<Self>, name: &'static str) -> Result<Arc<dyn Tree>>;
    fn flush(self: &Arc<Self>) -> Result<()>;
}

pub trait Tree: Send + Sync {
    fn get(&self, key: &[u8]) -> Result<Option<Vec<u8>>>;

    fn insert(&self, key: &[u8], value: &[u8]) -> Result<()>;
    fn insert_batch<'a>(&self, iter: &mut dyn Iterator<Item = (Vec<u8>, Vec<u8>)>) -> Result<()>;

    fn remove(&self, key: &[u8]) -> Result<()>;

    fn iter<'a>(&'a self) -> Box<dyn Iterator<Item = (Vec<u8>, Vec<u8>)> + 'a>;

    fn iter_from<'a>(
        &'a self,
        from: &[u8],
        backwards: bool,
    ) -> Box<dyn Iterator<Item = (Vec<u8>, Vec<u8>)> + 'a>;

    fn increment(&self, key: &[u8]) -> Result<Vec<u8>>;
    fn increment_batch<'a>(&self, iter: &mut dyn Iterator<Item = Vec<u8>>) -> Result<()>;

    fn scan_prefix<'a>(
        &'a self,
        prefix: Vec<u8>,
    ) -> Box<dyn Iterator<Item = (Vec<u8>, Vec<u8>)> + 'a>;

    fn watch_prefix<'a>(&'a self, prefix: &[u8]) -> Pin<Box<dyn Future<Output = ()> + Send + 'a>>;

    fn clear(&self) -> Result<()> {
        for (key, _) in self.iter() {
            self.remove(&key)?;
        }

        Ok(())
    }
}

// This is a functional integration at the state of the art of the current
// implementations, it should work and provide the base for stability and performance
// testing, Persy should be pretty resilient to crash and pretty lightweight in memory usage
// the speed in single thread will be pretty low because each transaction commit will wait for data
// to be flushed on disk, multi-thread should guarantee better performances even though I expect
// speed of a few thousand transactions per second.
//
// The current design of the engine right now do not allow to do transactions with multiple keys
// that would allow to reduce the latency quite a lot, anyway support transaction in the engine
// require a massive refactor.

#[cfg(feature = "persy")]
pub struct PersyEngine(persy::Persy);

#[cfg(feature = "persy")]
impl DatabaseEngine for PersyEngine {
    fn open(config: &Config) -> Result<Arc<Self>> {
        let cfg = persy::Config::new();
        // This is for tweak the in memory cache size
        //config.change_cache_size(32 * 1024 * 1024 /*32Mb*/)

        let persy = persy::OpenOptions::new()
            .create(true)
            .config(cfg)
            .open(&config.database_path)?;
        Ok(Arc::new(PersyEngine(persy)))
    }

    fn open_tree(self: &Arc<Self>, name: &'static str) -> Result<Arc<dyn Tree>> {
        // Create if it doesn't exist
        if !self.0.exists_index(name)? {
            let mut tx = self.0.begin()?;
            tx.create_index::<persy::ByteVec, persy::ByteVec>(name, persy::ValueMode::REPLACE)?;
            tx.prepare()?.commit()?;
        }

        Ok(Arc::new(PersyTree {
            db: self.0.clone(),
            name: name.to_owned(),
            watchers: RwLock::new(BTreeMap::new()),
        }))
    }
}

#[cfg(feature = "persy")]
pub struct PersyTree {
    db: persy::Persy,
    name: String,
    watchers: RwLock<BTreeMap<Vec<u8>, Vec<tokio::sync::oneshot::Sender<()>>>>,
}

#[cfg(feature = "persy")]
impl Tree for PersyTree {
    fn get(&self, key: &[u8]) -> Result<Option<Vec<u8>>> {
        Ok(self
            .db
            .get::<persy::ByteVec, persy::ByteVec>(&self.name, &persy::ByteVec(key.to_vec()))?
            .map(|v| v.into_iter().map(|bv| bv.0).next())
            .flatten())
    }

    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(());
                    }
                }
            }
        }

        let mut tx = self.db.begin()?;
        tx.put::<persy::ByteVec, persy::ByteVec>(
            &self.name,
            persy::ByteVec(key.to_owned()),
            persy::ByteVec(value.to_owned()),
        )?;
        tx.prepare()?.commit()?;
        Ok(())
    }

    fn remove(&self, key: &[u8]) -> Result<()> {
        let mut tx = self.db.begin()?;
        tx.remove::<persy::ByteVec, persy::ByteVec>(
            &self.name,
            persy::ByteVec(key.to_owned()),
            None,
        )?;
        tx.prepare()?.commit()?;
        Ok(())
    }

    fn iter<'a>(&'a self) -> Box<dyn Iterator<Item = (Box<[u8]>, Box<[u8]>)> + Send + Sync + 'a> {
        Box::new(
            self.db
                .range::<persy::ByteVec, persy::ByteVec, _>(&self.name, ..)
                .unwrap()
                .filter_map(|(k, v)| {
                    v.into_iter()
                        .map(|val| (k.0.to_owned().into(), val.0.to_owned().into()))
                        .next()
                }),
        )
    }

    fn iter_from<'a>(
        &'a self,
        from: &[u8],
        backwards: bool,
    ) -> Box<dyn Iterator<Item = (Box<[u8]>, Box<[u8]>)> + 'a> {
        Box::new(
            self.db
                .range::<persy::ByteVec, persy::ByteVec, _>(
                    &self.name,
                    persy::ByteVec(from.to_owned())..,
                )
                .unwrap()
                .filter_map(|(k, v)| {
                    v.into_iter()
                        .map(|val| (k.0.to_owned().into(), val.0.to_owned().into()))
                        .next()
                }),
        )
    }

    fn increment(&self, key: &[u8]) -> Result<Vec<u8>> {
        let old = self.get(key)?;
        let new = 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 = (Box<[u8]>, Box<[u8]>)> + Send + 'a> {
        let range_prefix = persy::ByteVec(prefix.to_owned());
        Box::new(
            self.db
                .range::<persy::ByteVec, persy::ByteVec, _>(
                    &self.name,
                    range_prefix.clone()..=range_prefix,
                )
                .unwrap()
                .filter_map(|(k, v)| {
                    v.into_iter()
                        .map(|val| (k.0.to_owned().into(), val.0.to_owned().into()))
                        .next()
                }),
        )
    }

    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();
        })
    }
}