// Copyright 2014 by Sascha L. Teichmann
// Use of this source code is governed by the MIT license
// that can be found in the LICENSE file.

package main

import (
	"log"

	leveldb "github.com/jmhodges/levigo"
)

type LevelDBBackend struct {
	cache *leveldb.Cache
	db    *leveldb.DB
}

type LevelDBSession struct {
	backend *LevelDBBackend
	tx      *leveldb.WriteBatch
}

func NewLeveDBBackend(path string, cacheSize int) (ldb *LevelDBBackend, err error) {
	cache := leveldb.NewLRUCache(cacheSize * 1024 * 1024)
	opts := leveldb.NewOptions()
	opts.SetCache(cache)
	opts.SetCreateIfMissing(true)
	var db *leveldb.DB
	if db, err = leveldb.Open(path, opts); err != nil {
		cache.Close()
		return
	}
	ldb = &LevelDBBackend{
		cache: cache,
		db:    db}
	return
}

func (ldb *LevelDBBackend) NewSession() (Session, error) {
	return &LevelDBSession{ldb, nil}, nil
}

func (ldbs *LevelDBSession) Close() error {
	if ldbs.tx != nil {
		ldbs.tx.Close()
	}
	return nil
}

func (ldb *LevelDBBackend) Shutdown() error {
	ldb.db.Close()
	ldb.cache.Close()
	return nil
}

func (ldbs *LevelDBSession) Fetch(hash, key []byte) (value []byte, err error) {
	ro := leveldb.NewReadOptions()
	value, err = ldbs.backend.db.Get(ro, key)
	ro.Close()
	return
}

func (ldbs *LevelDBSession) InTransaction() bool {
	return ldbs.tx != nil
}

func (ldbs *LevelDBSession) keyExists(key []byte) (exists bool, err error) {
	ro := leveldb.NewReadOptions()
	defer ro.Close()
	var data []byte
	if data, err = ldbs.backend.db.Get(ro, key); err != nil {
		return
	}
	exists = data != nil
	return
}

func (ldbs *LevelDBSession) Store(hash, key, value []byte) (exists bool, err error) {

	var pos int64
	if pos, err = bytes2pos(key); err != nil {
		return
	}
	// Re-code it to make LevelDB happy.
	key = pos2bytes(pos)

	if exists, err = ldbs.keyExists(key); err != nil {
		return
	}

	if ldbs.tx != nil {
		ldbs.tx.Put(key, value)
		return
	}

	wo := leveldb.NewWriteOptions()
	err = ldbs.backend.db.Put(wo, key, value)
	wo.Close()

	return
}

func (ldbs *LevelDBSession) BeginTransaction() error {
	ldbs.tx = leveldb.NewWriteBatch()
	return nil
}

func (ldbs *LevelDBSession) CommitTransaction() (err error) {
	tx := ldbs.tx
	if tx == nil {
		log.Println("WARN: No transaction running.")
		return
	}
	ldbs.tx = nil
	wo := leveldb.NewWriteOptions()
	err = ldbs.backend.db.Write(wo, tx)
	wo.Close()
	return
}