rusty-leveldb 4.0.1

use std::collections::hash_map::HashMap;

use crate::{
    send_response, send_response_result, AsyncDB, Message, Result, Status, StatusCode, WriteBatch,
    DB,
};

pub(crate) const CHANNEL_BUFFER_SIZE: usize = 32;

#[derive(Clone, Copy)]
pub struct SnapshotRef(usize);

/// A request sent to the database thread.
pub(crate) enum Request {
    Close,
    Put { key: Vec<u8>, val: Vec<u8> },
    Delete { key: Vec<u8> },
    Write { batch: WriteBatch, sync: bool },
    Flush,
    GetAt { snapshot: SnapshotRef, key: Vec<u8> },
    Get { key: Vec<u8> },
    GetSnapshot,
    DropSnapshot { snapshot: SnapshotRef },
    CompactRange { from: Vec<u8>, to: Vec<u8> },
}

/// A response received from the database thread.
pub(crate) enum Response {
    OK,
    Error(Status),
    Value(Option<Vec<u8>>),
    Snapshot(SnapshotRef),
}

impl AsyncDB {
    pub async fn close(&self) -> Result<()> {
        let r = self.process_request(Request::Close).await?;
        match r {
            Response::OK => Ok(()),
            Response::Error(s) => Err(s),
            _ => Err(Status {
                code: StatusCode::AsyncError,
                err: "Wrong response type in AsyncDB.".to_string(),
            }),
        }
    }

    pub async fn put(&self, key: Vec<u8>, val: Vec<u8>) -> Result<()> {
        let r = self.process_request(Request::Put { key, val }).await?;
        match r {
            Response::OK => Ok(()),
            Response::Error(s) => Err(s),
            _ => Err(Status {
                code: StatusCode::AsyncError,
                err: "Wrong response type in AsyncDB.".to_string(),
            }),
        }
    }
    pub async fn delete(&self, key: Vec<u8>) -> Result<()> {
        let r = self.process_request(Request::Delete { key }).await?;
        match r {
            Response::OK => Ok(()),
            Response::Error(s) => Err(s),
            _ => Err(Status {
                code: StatusCode::AsyncError,
                err: "Wrong response type in AsyncDB.".to_string(),
            }),
        }
    }
    pub async fn write(&self, batch: WriteBatch, sync: bool) -> Result<()> {
        let r = self.process_request(Request::Write { batch, sync }).await?;
        match r {
            Response::OK => Ok(()),
            Response::Error(s) => Err(s),
            _ => Err(Status {
                code: StatusCode::AsyncError,
                err: "Wrong response type in AsyncDB.".to_string(),
            }),
        }
    }
    pub async fn flush(&self) -> Result<()> {
        let r = self.process_request(Request::Flush).await?;
        match r {
            Response::OK => Ok(()),
            Response::Error(s) => Err(s),
            _ => Err(Status {
                code: StatusCode::AsyncError,
                err: "Wrong response type in AsyncDB.".to_string(),
            }),
        }
    }
    pub async fn get(&self, key: Vec<u8>) -> Result<Option<Vec<u8>>> {
        let r = self.process_request(Request::Get { key }).await?;
        match r {
            Response::Value(v) => Ok(v),
            Response::Error(s) => Err(s),
            _ => Err(Status {
                code: StatusCode::AsyncError,
                err: "Wrong response type in AsyncDB.".to_string(),
            }),
        }
    }
    pub async fn get_at(&self, snapshot: SnapshotRef, key: Vec<u8>) -> Result<Option<Vec<u8>>> {
        let r = self
            .process_request(Request::GetAt { snapshot, key })
            .await?;
        match r {
            Response::Value(v) => Ok(v),
            Response::Error(s) => Err(s),
            _ => Err(Status {
                code: StatusCode::AsyncError,
                err: "Wrong response type in AsyncDB.".to_string(),
            }),
        }
    }
    pub async fn get_snapshot(&self) -> Result<SnapshotRef> {
        let r = self.process_request(Request::GetSnapshot).await?;
        match r {
            Response::Snapshot(sr) => Ok(sr),
            _ => Err(Status {
                code: StatusCode::AsyncError,
                err: "Wrong response type in AsyncDB.".to_string(),
            }),
        }
    }
    /// As snapshots returned by `AsyncDB::get_snapshot()` are sort-of "weak references" to an
    /// actual snapshot, they need to be dropped explicitly.
    pub async fn drop_snapshot(&self, snapshot: SnapshotRef) -> Result<()> {
        let r = self
            .process_request(Request::DropSnapshot { snapshot })
            .await?;
        match r {
            Response::OK => Ok(()),
            _ => Err(Status {
                code: StatusCode::AsyncError,
                err: "Wrong response type in AsyncDB.".to_string(),
            }),
        }
    }
    pub async fn compact_range(&self, from: Vec<u8>, to: Vec<u8>) -> Result<()> {
        let r = self
            .process_request(Request::CompactRange { from, to })
            .await?;
        match r {
            Response::OK => Ok(()),
            Response::Error(s) => Err(s),
            _ => Err(Status {
                code: StatusCode::AsyncError,
                err: "Wrong response type in AsyncDB.".to_string(),
            }),
        }
    }

    pub(crate) fn run_server(mut db: DB, mut recv: impl ReceiverExt<Message>) {
        let mut snapshots = HashMap::new();
        let mut snapshot_counter: usize = 0;

        while let Some(message) = recv.blocking_recv() {
            match message.req {
                Request::Close => {
                    send_response(message.resp_channel, Response::OK);
                    recv.close();
                    return;
                }
                Request::Put { key, val } => {
                    let ok = db.put(&key, &val);
                    send_response_result(message.resp_channel, ok);
                }
                Request::Delete { key } => {
                    let ok = db.delete(&key);
                    send_response_result(message.resp_channel, ok);
                }
                Request::Write { batch, sync } => {
                    let ok = db.write(batch, sync);
                    send_response_result(message.resp_channel, ok);
                }
                Request::Flush => {
                    let ok = db.flush();
                    send_response_result(message.resp_channel, ok);
                }
                Request::GetAt { snapshot, key } => {
                    let snapshot_id = snapshot.0;
                    if let Some(snapshot) = snapshots.get(&snapshot_id) {
                        let ok = db.get_at(snapshot, &key);
                        match ok {
                            Err(e) => {
                                send_response(message.resp_channel, Response::Error(e));
                            }
                            Ok(v) => {
                                let v_vec = v.map(|bytes| bytes.to_vec());
                                send_response(message.resp_channel, Response::Value(v_vec));
                            }
                        };
                    } else {
                        send_response(
                            message.resp_channel,
                            Response::Error(Status {
                                code: StatusCode::AsyncError,
                                err: "Unknown snapshot reference: this is a bug".to_string(),
                            }),
                        );
                    }
                }
                Request::Get { key } => {
                    let r = db.get(&key).map(|bytes| bytes.to_vec());
                    send_response(message.resp_channel, Response::Value(r));
                }
                Request::GetSnapshot => {
                    snapshots.insert(snapshot_counter, db.get_snapshot());
                    let sref = SnapshotRef(snapshot_counter);
                    snapshot_counter += 1;
                    send_response(message.resp_channel, Response::Snapshot(sref));
                }
                Request::DropSnapshot { snapshot } => {
                    snapshots.remove(&snapshot.0);
                    send_response_result(message.resp_channel, Ok(()));
                }
                Request::CompactRange { from, to } => {
                    let ok = db.compact_range(&from, &to);
                    send_response_result(message.resp_channel, ok);
                }
            }
        }
    }
}

pub(crate) trait ReceiverExt<T> {
    fn blocking_recv(&mut self) -> Option<T>;
    fn close(&mut self);
}