package database

import (
	"fmt"
	"os"
	"sync"

	log "github.com/corgi-kx/logcustom"
	"github.com/pkg/errors"
	"github.com/syndtr/goleveldb/leveldb"
	"github.com/syndtr/goleveldb/leveldb/iterator"
	"github.com/syndtr/goleveldb/leveldb/opt"
	goleveldbutil "github.com/syndtr/goleveldb/leveldb/util"
)

type dbState int32

const (
	closed dbState = iota
	opened
)

// DB 用于存储区块链账本的levelDB数据库
type DB struct {
	dbPath  string
	db      *leveldb.DB
	dbState dbState
	mutex   sync.RWMutex

	readOpts        *opt.ReadOptions
	writeOptsNoSync *opt.WriteOptions
	writeOptsSync   *opt.WriteOptions
}

// UpdateBatch encloses the details of multiple `updates`
type UpdateBatch struct {
	leveldbBatch *leveldb.Batch
	dbName       string
	size         int
}

type Snapshot struct {
	dbName   string
	snapshot *leveldb.Snapshot
	readOpts *opt.ReadOptions
}

// CreateDB constructs a `DB`
func CreateDB(dp string) *DB {
	readOpts := &opt.ReadOptions{}
	writeOptsNoSync := &opt.WriteOptions{}
	writeOptsSync := &opt.WriteOptions{}
	writeOptsSync.Sync = true

	return &DB{
		dbPath:          dp,
		dbState:         closed,
		readOpts:        readOpts,
		writeOptsNoSync: writeOptsNoSync,
		writeOptsSync:   writeOptsSync,
	}
}

// 打开基础数据库
func (dbInst *DB) Open() {
	dbInst.mutex.Lock()
	defer dbInst.mutex.Unlock()

	if dbInst.dbState == opened {
		return
	}
	dbPath := dbInst.dbPath
	var err error
	if err = os.MkdirAll(dbPath, 0755); err != nil {
		panic(fmt.Sprintf("Error creating dir if missing: %s", err))
	}

	if dbInst.db, err = leveldb.OpenFile(dbPath, nil); err != nil {
		panic(fmt.Sprintf("Error opening leveldb: %s", err))
	}
	dbInst.dbState = opened
}

// IsEmpty returns whether a database is empty
func (dbInst *DB) IsEmpty() (bool, error) {
	dbInst.mutex.RLock()
	defer dbInst.mutex.RUnlock()
	itr := dbInst.db.NewIterator(&goleveldbutil.Range{}, dbInst.readOpts)
	defer itr.Release()
	hasItems := itr.Next()
	return !hasItems,
		errors.Wrapf(itr.Error(), "error while trying to see if the leveldb at path [%s] is empty", dbInst.dbPath)
}

// Close closes the underlying db
func (dbInst *DB) Close() {
	dbInst.mutex.Lock()
	defer dbInst.mutex.Unlock()
	if dbInst.dbState == closed {
		return
	}
	if err := dbInst.db.Close(); err != nil {
		log.Errorf("Error closing leveldb: %s", err)
	}
	dbInst.dbState = closed
}

// Get returns the value for the given key
func (dbInst *DB) Get(key []byte) ([]byte, error) {
	dbInst.mutex.RLock()
	defer dbInst.mutex.RUnlock()
	value, err := dbInst.db.Get(key, dbInst.readOpts)
	if err == leveldb.ErrNotFound {
		value = nil
		err = nil
	}
	if err != nil {
		log.Errorf("Error retrieving leveldb key [%#v]: %s", key, err)
		return nil, errors.Wrapf(err, "error retrieving leveldb key [%#v]", key)
	}
	return value, nil
}

// Put saves the key/value
func (dbInst *DB) Put(key []byte, value []byte, sync bool) error {
	dbInst.mutex.RLock()
	defer dbInst.mutex.RUnlock()
	wo := dbInst.writeOptsNoSync
	if sync {
		wo = dbInst.writeOptsSync
	}
	err := dbInst.db.Put(key, value, wo)
	if err != nil {
		log.Errorf("Error writing leveldb key [%#v]", key)
		return errors.Wrapf(err, "error writing leveldb key [%#v]", key)
	}
	return nil
}

// Delete deletes the given key
func (dbInst *DB) Delete(key []byte, sync bool) error {
	dbInst.mutex.RLock()
	defer dbInst.mutex.RUnlock()
	wo := dbInst.writeOptsNoSync
	if sync {
		wo = dbInst.writeOptsSync
	}
	err := dbInst.db.Delete(key, wo)
	if err != nil {
		log.Errorf("Error deleting leveldb key [%#v]", key)
		return errors.Wrapf(err, "error deleting leveldb key [%#v]", key)
	}
	return nil
}

// GetIterator returns an iterator over key-value store. The iterator should be released after the use.
// The resultSet contains all the keys that are present in the db between the startKey (inclusive) and the endKey (exclusive).
// A nil startKey represents the first available key and a nil endKey represent a logical key after the last available key
func (dbInst *DB) GetIterator(startKey []byte, endKey []byte) iterator.Iterator {
	dbInst.mutex.RLock()
	defer dbInst.mutex.RUnlock()
	return dbInst.db.NewIterator(&goleveldbutil.Range{Start: startKey, Limit: endKey}, dbInst.readOpts)
}

func (dbInst *DB) PrefixQuery(Key []byte) iterator.Iterator {
	dbInst.mutex.RLock()
	defer dbInst.mutex.RUnlock()
	//BytesPrefix返回满足给定前缀的键范围。这仅适用于标准的“字节比较器”
	return dbInst.db.NewIterator(goleveldbutil.BytesPrefix(Key), dbInst.readOpts)
}

// WriteBatch 批量写入
func (dbInst *DB) WriteBatch(batch *leveldb.Batch, sync bool) error {
	dbInst.mutex.RLock()
	defer dbInst.mutex.RUnlock()
	wo := dbInst.writeOptsNoSync
	if sync {
		wo = dbInst.writeOptsSync
	}
	if err := dbInst.db.Write(batch, wo); err != nil {
		return errors.Wrap(err, "error writing batch to leveldb")
	}
	return nil
}

/*type Batch struct {
    data  []byte
    index []batchIndex

    // internalLen is sums of key/value pair length plus 8-bytes internal key.
    internalLen int
}

func (*leveldb.Batch).Delete(key []byte)
func (*leveldb.Batch).Dump() []byte
func (*leveldb.Batch).Len() int
func (*leveldb.Batch).Load(data []byte) error
func (*leveldb.Batch).Put(key []byte, value []byte)
func (*leveldb.Batch).Replay(r leveldb.BatchReplay) error
func (*leveldb.Batch).Reset()
*/