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// Copyright 2018 The dexon-consensus-core Authors
// This file is part of the dexon-consensus-core library.
//
// The dexon-consensus-core library is free software: you can redistribute it
// and/or modify it under the terms of the GNU Lesser General Public License as
// published by the Free Software Foundation, either version 3 of the License,
// or (at your option) any later version.
//
// The dexon-consensus-core library is distributed in the hope that it will be
// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
// General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the dexon-consensus-core library. If not, see
// <http://www.gnu.org/licenses/>.

package blockdb

import (
    "encoding/json"
    "sync"

    "github.com/syndtr/goleveldb/leveldb"
    "github.com/syndtr/goleveldb/leveldb/opt"

    "github.com/dexon-foundation/dexon-consensus-core/common"
    "github.com/dexon-foundation/dexon-consensus-core/core/types"
)

// LevelDBBackendBlockDB is a leveldb backend BlockDB implementation.
type LevelDBBackendBlockDB struct {
    db        *leveldb.DB
    index     map[types.ValidatorID]map[uint64]common.Hash
    indexLock sync.RWMutex
}

// NewLevelDBBackendBlockDB initialize a leveldb-backed block database.
func NewLevelDBBackendBlockDB(
    path string) (lvl *LevelDBBackendBlockDB, err error) {

    db, err := leveldb.OpenFile(path, nil)
    if err != nil {
        return
    }
    lvl = &LevelDBBackendBlockDB{db: db}
    err = lvl.syncIndex()
    if err != nil {
        return
    }
    return
}

// Close would release allocated resource.
func (lvl *LevelDBBackendBlockDB) Close() error {
    return lvl.db.Close()
}

// Has implements the Reader.Has method.
func (lvl *LevelDBBackendBlockDB) Has(hash common.Hash) bool {
    exists, err := lvl.db.Has([]byte(hash[:]), nil)
    if err != nil {
        // TODO(missionliao): Modify the interface to return error.
        panic(err)
    }
    return exists
}

// Get implements the Reader.Get method.
func (lvl *LevelDBBackendBlockDB) Get(
    hash common.Hash) (block types.Block, err error) {

    queried, err := lvl.db.Get([]byte(hash[:]), nil)
    if err != nil {
        if err == leveldb.ErrNotFound {
            err = ErrBlockDoesNotExist
        }
        return
    }
    err = json.Unmarshal(queried, &block)
    if err != nil {
        return
    }
    return
}

// GetByValidatorAndHeight implements
// the Reader.GetByValidatorAndHeight method.
func (lvl *LevelDBBackendBlockDB) GetByValidatorAndHeight(
    vID types.ValidatorID, height uint64) (block types.Block, err error) {

    lvl.indexLock.RLock()
    defer lvl.indexLock.RUnlock()

    // Get block's hash from in-memory index.
    vMap, exists := lvl.index[vID]
    if !exists {
        err = ErrBlockDoesNotExist
        return
    }
    hash, exists := vMap[height]
    if !exists {
        err = ErrBlockDoesNotExist
        return
    }

    // Get block from hash.
    queried, err := lvl.db.Get([]byte(hash[:]), nil)
    if err != nil {
        if err == leveldb.ErrNotFound {
            err = ErrBlockDoesNotExist
        }
        return
    }

    err = json.Unmarshal(queried, &block)
    if err != nil {
        return
    }
    return
}

// Update implements the Writer.Update method.
func (lvl *LevelDBBackendBlockDB) Update(block types.Block) (err error) {
    // NOTE: we didn't handle changes of block hash (and it
    //       should not happen).
    marshaled, err := json.Marshal(&block)
    if err != nil {
        return
    }

    if !lvl.Has(block.Hash) {
        err = ErrBlockDoesNotExist
        return
    }
    err = lvl.db.Put(
        []byte(block.Hash[:]),
        marshaled,
        &opt.WriteOptions{
            Sync: true,
        })
    if err != nil {
        return
    }
    return
}

// Put implements the Writer.Put method.
func (lvl *LevelDBBackendBlockDB) Put(block types.Block) (err error) {
    marshaled, err := json.Marshal(&block)
    if err != nil {
        return
    }
    if lvl.Has(block.Hash) {
        err = ErrBlockExists
        return
    }
    syncedOpt := &opt.WriteOptions{
        // We should force to sync for each write, it's safer
        // from crash.
        Sync: true,
    }
    err = lvl.db.Put(
        []byte(block.Hash[:]),
        marshaled,
        syncedOpt)
    if err != nil {
        return
    }

    // Build in-memory index.
    lvl.addIndex(&block)
    return
}

func (lvl *LevelDBBackendBlockDB) syncIndex() (err error) {
    // Reset index.
    lvl.index = make(map[types.ValidatorID]map[uint64]common.Hash)

    // Construct index from DB.
    iter := lvl.db.NewIterator(nil, nil)
    defer func() {
        iter.Release()
        if err == nil {
            // Only return iterator's error when no error
            // is presented so far.
            err = iter.Error()
        }
    }()

    // Build index from blocks in DB, it may take time.
    var block types.Block
    for iter.Next() {
        err = json.Unmarshal(iter.Value(), &block)
        if err != nil {
            return
        }
        lvl.addIndex(&block)
    }
    return
}

func (lvl *LevelDBBackendBlockDB) addIndex(block *types.Block) {
    lvl.indexLock.Lock()
    defer lvl.indexLock.Unlock()

    heightMap, exists := lvl.index[block.ProposerID]
    if !exists {
        heightMap = make(map[uint64]common.Hash)
        lvl.index[block.ProposerID] = heightMap
    }
    heightMap[block.Height] = block.Hash
}