/*
Copyright IBM Corp. 2016 All Rights Reserved.

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.
*/

package stateleveldb

import (
	"bytes"
	"errors"

	"github.com/hyperledger/fabric/common/flogging"
	"github.com/hyperledger/fabric/common/ledger/util/leveldbhelper"
	"github.com/hyperledger/fabric/core/ledger/kvledger/txmgmt/statedb"
	"github.com/hyperledger/fabric/core/ledger/kvledger/txmgmt/version"
	"github.com/hyperledger/fabric/core/ledger/ledgerconfig"
	"github.com/syndtr/goleveldb/leveldb/iterator"
)

var logger = flogging.MustGetLogger("stateleveldb")

var compositeKeySep = []byte{0x00}
var lastKeyIndicator = byte(0x01)
var savePointKey = []byte{0x00}

// VersionedDBProvider implements interface VersionedDBProvider
type VersionedDBProvider struct {
	dbProvider *leveldbhelper.Provider
}

// NewVersionedDBProvider instantiates VersionedDBProvider
func NewVersionedDBProvider() *VersionedDBProvider {
	dbPath := ledgerconfig.GetStateLevelDBPath()
	logger.Debugf("constructing VersionedDBProvider dbPath=%s", dbPath)
	dbProvider := leveldbhelper.NewProvider(&leveldbhelper.Conf{DBPath: dbPath})
	return &VersionedDBProvider{dbProvider}
}

// GetDBHandle gets the handle to a named database
func (provider *VersionedDBProvider) GetDBHandle(dbName string) (statedb.VersionedDB, error) {
	return newVersionedDB(provider.dbProvider.GetDBHandle(dbName), dbName), nil
}

// Close closes the underlying db
func (provider *VersionedDBProvider) Close() {
	provider.dbProvider.Close()
}

// VersionedDB implements VersionedDB interface
type versionedDB struct {
	db     *leveldbhelper.DBHandle
	dbName string
}

// newVersionedDB constructs an instance of VersionedDB
func newVersionedDB(db *leveldbhelper.DBHandle, dbName string) *versionedDB {
	return &versionedDB{db, dbName}
}

// Open implements method in VersionedDB interface
func (vdb *versionedDB) Open() error {
	// do nothing because shared db is used
	return nil
}

// Close implements method in VersionedDB interface
func (vdb *versionedDB) Close() {
	// do nothing because shared db is used
}

// GetState implements method in VersionedDB interface
func (vdb *versionedDB) GetState(namespace string, key string) (*statedb.VersionedValue, error) {
	logger.Debugf("GetState(). ns=%s, key=%s", namespace, key)
	compositeKey := constructCompositeKey(namespace, key)
	dbVal, err := vdb.db.Get(compositeKey)
	if err != nil {
		return nil, err
	}
	if dbVal == nil {
		return nil, nil
	}
	val, ver := statedb.DecodeValue(dbVal)
	return &statedb.VersionedValue{Value: val, Version: ver}, nil
}

// GetStateMultipleKeys implements method in VersionedDB interface
func (vdb *versionedDB) GetStateMultipleKeys(namespace string, keys []string) ([]*statedb.VersionedValue, error) {
	vals := make([]*statedb.VersionedValue, len(keys))
	for i, key := range keys {
		val, err := vdb.GetState(namespace, key)
		if err != nil {
			return nil, err
		}
		vals[i] = val
	}
	return vals, nil
}

// GetStateRangeScanIterator implements method in VersionedDB interface
// startKey is inclusive
// endKey is exclusive
func (vdb *versionedDB) GetStateRangeScanIterator(namespace string, startKey string, endKey string) (statedb.ResultsIterator, error) {
	compositeStartKey := constructCompositeKey(namespace, startKey)
	compositeEndKey := constructCompositeKey(namespace, endKey)
	if endKey == "" {
		compositeEndKey[len(compositeEndKey)-1] = lastKeyIndicator
	}
	dbItr := vdb.db.GetIterator(compositeStartKey, compositeEndKey)
	return newKVScanner(namespace, dbItr), nil
}

// ExecuteQuery implements method in VersionedDB interface
func (vdb *versionedDB) ExecuteQuery(namespace, query string) (statedb.ResultsIterator, error) {
	return nil, errors.New("ExecuteQuery not supported for leveldb")
}

// ApplyUpdates implements method in VersionedDB interface
func (vdb *versionedDB) ApplyUpdates(batch *statedb.UpdateBatch, height *version.Height) error {
	dbBatch := leveldbhelper.NewUpdateBatch()
	namespaces := batch.GetUpdatedNamespaces()
	for _, ns := range namespaces {
		updates := batch.GetUpdates(ns)
		for k, vv := range updates {
			compositeKey := constructCompositeKey(ns, k)
			logger.Debugf("Channel [%s]: Applying key=[%#v]", vdb.dbName, compositeKey)

			if vv.Value == nil {
				dbBatch.Delete(compositeKey)
			} else {
				dbBatch.Put(compositeKey, statedb.EncodeValue(vv.Value, vv.Version))
			}
		}
	}
	dbBatch.Put(savePointKey, height.ToBytes())
	if err := vdb.db.WriteBatch(dbBatch, false); err != nil {
		return err
	}
	return nil
}

// GetLatestSavePoint implements method in VersionedDB interface
func (vdb *versionedDB) GetLatestSavePoint() (*version.Height, error) {
	versionBytes, err := vdb.db.Get(savePointKey)
	if err != nil {
		return nil, err
	}
	if versionBytes == nil {
		return nil, nil
	}
	version, _ := version.NewHeightFromBytes(versionBytes)
	return version, nil
}

func constructCompositeKey(ns string, key string) []byte {
	return append(append([]byte(ns), compositeKeySep...), []byte(key)...)
}

func splitCompositeKey(compositeKey []byte) (string, string) {
	split := bytes.SplitN(compositeKey, compositeKeySep, 2)
	return string(split[0]), string(split[1])
}

type kvScanner struct {
	namespace string
	dbItr     iterator.Iterator
}

func newKVScanner(namespace string, dbItr iterator.Iterator) *kvScanner {
	return &kvScanner{namespace, dbItr}
}

func (scanner *kvScanner) Next() (statedb.QueryResult, error) {
	if !scanner.dbItr.Next() {
		return nil, nil
	}
	dbKey := scanner.dbItr.Key()
	dbVal := scanner.dbItr.Value()
	dbValCopy := make([]byte, len(dbVal))
	copy(dbValCopy, dbVal)
	_, key := splitCompositeKey(dbKey)
	value, version := statedb.DecodeValue(dbValCopy)
	return &statedb.VersionedKV{
		CompositeKey:   statedb.CompositeKey{Namespace: scanner.namespace, Key: key},
		VersionedValue: statedb.VersionedValue{Value: value, Version: version}}, nil
}

func (scanner *kvScanner) Close() {
	scanner.dbItr.Release()
}