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// Copyright 2017 The Exonum Team
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! An implementation of `LevelDB` database.
use profiler;

use leveldb::database::Database as _LevelDB;
use leveldb::iterator::{Iterator as _Iterator, Iterable};
use leveldb::error::Error as _Error;
use leveldb::database::snapshots::Snapshot as _Snapshot;
use leveldb::options::{WriteOptions, ReadOptions};
use leveldb::database::batch::Writebatch;
use leveldb::batch::Batch;
use leveldb::snapshots::Snapshots;

use std::fs;
use std::io;
use std::mem;
use std::path::Path;
use std::error;
use std::sync::Arc;

/// Options to consider when opening a new or pre-existing `LevelDB` database.
pub use leveldb::options::Options as LevelDBOptions;

/// Represents a `LevelDB` cache.
pub use leveldb::database::cache::Cache as LevelDBCache;

use super::{Database, Iterator, Iter, Snapshot, Error, Patch, Change, Result};

const LEVELDB_READ_OPTIONS: ReadOptions<'static> = ReadOptions {
    verify_checksums: false,
    fill_cache: true,
    snapshot: None,
};

const LEVELDB_WRITE_OPTIONS: WriteOptions = WriteOptions { sync: false };

/// Database implementation on the top of `LevelDB` backend.
#[derive(Clone)]
pub struct LevelDB {
    db: Arc<_LevelDB>,
}

/// A snapshot of a `LevelDB`.
struct LevelDBSnapshot {
    _db: Arc<_LevelDB>,
    snapshot: _Snapshot<'static>,
}

/// An iterator over the entries of a `LevelDB`.
struct LevelDBIterator<'a> {
    iter: _Iterator<'a>,
}

impl From<_Error> for Error {
    fn from(err: _Error) -> Self {
        Error::new(error::Error::description(&err))
    }
}

impl From<io::Error> for Error {
    fn from(err: io::Error) -> Self {
        Error::new(error::Error::description(&err))
    }
}

impl LevelDB {
    /// Open a database stored in the specified path with the specified options.
    pub fn open<P: AsRef<Path>>(path: P, options: LevelDBOptions) -> Result<LevelDB> {
        // TODO: configure LRU cache
        if options.create_if_missing {
            fs::create_dir_all(path.as_ref())?;
        }
        let database = _LevelDB::open(path.as_ref(), options)?;
        Ok(LevelDB { db: Arc::new(database) })
    }
}

impl Database for LevelDB {
    fn clone(&self) -> Box<Database> {
        Box::new(Clone::clone(self))
    }

    fn snapshot(&self) -> Box<Snapshot> {
        let _p = profiler::ProfilerSpan::new("LevelDB::snapshot");
        Box::new(LevelDBSnapshot {
            _db: self.db.clone(),
            snapshot: unsafe { mem::transmute(self.db.snapshot()) },
        })
    }

    fn merge(&mut self, patch: Patch) -> Result<()> {
        let _p = profiler::ProfilerSpan::new("LevelDB::merge");
        let mut batch = Writebatch::new();
        for (key, change) in patch {
            match change {
                Change::Put(ref v) => batch.put(key, v),
                Change::Delete => batch.delete(key),
            }
        }
        self.db.write(LEVELDB_WRITE_OPTIONS, &batch).map_err(
            Into::into,
        )
    }
}

impl Snapshot for LevelDBSnapshot {
    fn get(&self, key: &[u8]) -> Option<Vec<u8>> {
        let _p = profiler::ProfilerSpan::new("LevelDBSnapshot::get");
        match self.snapshot.get(LEVELDB_READ_OPTIONS, key) {
            Ok(value) => value,
            Err(err) => panic!(err),
        }
    }

    fn iter<'a>(&'a self, from: &[u8]) -> Iter<'a> {
        let _p = profiler::ProfilerSpan::new("LevelDBSnapshot::iter");
        let mut iter = self.snapshot.iter(LEVELDB_READ_OPTIONS);
        iter.seek(from);
        Box::new(LevelDBIterator { iter: iter })
    }
}

impl<'a> Iterator for LevelDBIterator<'a> {
    fn next(&mut self) -> Option<(&[u8], &[u8])> {
        let _p = profiler::ProfilerSpan::new("LevelDBIterator::next");
        self.iter.next()
    }

    fn peek(&mut self) -> Option<(&[u8], &[u8])> {
        let _p = profiler::ProfilerSpan::new("LevelDBIterator::peek");
        self.iter.peek()
    }
}

impl ::std::fmt::Debug for LevelDB {
    fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
        write!(f, "LevelDB(..)")
    }
}

impl ::std::fmt::Debug for LevelDBSnapshot {
    fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
        write!(f, "LevelDBSnapshot(..)")
    }
}