// Copyright 2019 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum 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 go-ethereum 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 go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package snapshot

import (
	"bytes"
	"fmt"
	"math/big"
	"time"

	"github.com/allegro/bigcache"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/core/rawdb"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/rlp"
	"github.com/ethereum/go-ethereum/trie"
)

var (
	// emptyRoot is the known root hash of an empty trie.
	emptyRoot = common.HexToHash("56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421")

	// emptyCode is the known hash of the empty EVM bytecode.
	emptyCode = crypto.Keccak256Hash(nil)
)

// wipeSnapshot iterates over the entire key-value database and deletes all the
// data associated with the snapshot (accounts, storage, metadata). After all is
// done, the snapshot range of the database is compacted to free up unused data
// blocks.
func wipeSnapshot(db ethdb.KeyValueStore) error {
	// Batch deletions together to avoid holding an iterator for too long
	var (
		batch = db.NewBatch()
		items int
	)
	// Iterate over the snapshot key-range and delete all of them
	log.Info("Deleting previous snapshot leftovers")
	start, logged := time.Now(), time.Now()

	it := db.NewIteratorWithStart(rawdb.StateSnapshotPrefix)
	for it.Next() {
		// Skip any keys with the correct prefix but wrong lenth (trie nodes)
		key := it.Key()
		if !bytes.HasPrefix(key, rawdb.StateSnapshotPrefix) {
			break
		}
		if len(key) != len(rawdb.StateSnapshotPrefix)+common.HashLength && len(key) != len(rawdb.StateSnapshotPrefix)+2*common.HashLength {
			continue
		}
		// Delete the key and periodically recreate the batch and iterator
		batch.Delete(key)
		items++

		if items%10000 == 0 {
			// Batch too large (or iterator too long lived, flush and recreate)
			it.Release()
			if err := batch.Write(); err != nil {
				return err
			}
			batch.Reset()
			it = db.NewIteratorWithStart(key)

			if time.Since(logged) > 8*time.Second {
				log.Info("Deleting previous snapshot leftovers", "wiped", items, "elapsed", time.Since(start))
				logged = time.Now()
			}
		}
	}
	it.Release()

	rawdb.DeleteSnapshotBlock(batch)
	if err := batch.Write(); err != nil {
		return err
	}
	log.Info("Deleted previous snapshot leftovers", "wiped", items, "elapsed", time.Since(start))

	// Compact the snapshot section of the database to get rid of unused space
	log.Info("Compacting snapshot area in database")
	start = time.Now()

	end := common.CopyBytes(rawdb.StateSnapshotPrefix)
	end[len(end)-1]++

	if err := db.Compact(rawdb.StateSnapshotPrefix, end); err != nil {
		return err
	}
	log.Info("Compacted snapshot area in database", "elapsed", time.Since(start))

	return nil
}

// generateSnapshot regenerates a brand new snapshot based on an existing state database and head block.
func generateSnapshot(db ethdb.KeyValueStore, journal string, headNumber uint64, headRoot common.Hash) (snapshot, error) {
	// Wipe any previously existing snapshot from the database
	if err := wipeSnapshot(db); err != nil {
		return nil, err
	}
	// Iterate the entire storage trie and re-generate the state snapshot
	var (
		accountCount int
		storageCount int
		storageNodes int
		accountSize  common.StorageSize
		storageSize  common.StorageSize
		logged       time.Time
	)
	batch := db.NewBatch()
	triedb := trie.NewDatabase(db)

	accTrie, err := trie.NewSecure(headRoot, triedb)
	if err != nil {
		return nil, err
	}
	accIt := trie.NewIterator(accTrie.NodeIterator(nil))
	for accIt.Next() {
		var (
			curStorageCount int
			curStorageNodes int
			curAccountSize  common.StorageSize
			curStorageSize  common.StorageSize
		)
		var acc struct {
			Nonce    uint64
			Balance  *big.Int
			Root     common.Hash
			CodeHash []byte
		}
		if err := rlp.DecodeBytes(accIt.Value, &acc); err != nil {
			return nil, err
		}
		data := AccountRLP(acc.Nonce, acc.Balance, acc.Root, acc.CodeHash)
		curAccountSize += common.StorageSize(1 + common.HashLength + len(data))

		rawdb.WriteAccountSnapshot(batch, common.BytesToHash(accIt.Key), data)
		if batch.ValueSize() > ethdb.IdealBatchSize {
			batch.Write()
			batch.Reset()
		}
		if acc.Root != emptyRoot {
			storeTrie, err := trie.NewSecure(acc.Root, triedb)
			if err != nil {
				return nil, err
			}
			storeIt := trie.NewIterator(storeTrie.NodeIterator(nil))
			for storeIt.Next() {
				curStorageSize += common.StorageSize(1 + 2*common.HashLength + len(storeIt.Value))
				curStorageCount++

				rawdb.WriteStorageSnapshot(batch, common.BytesToHash(accIt.Key), common.BytesToHash(storeIt.Key), storeIt.Value)
				if batch.ValueSize() > ethdb.IdealBatchSize {
					batch.Write()
					batch.Reset()
				}
			}
			curStorageNodes = storeIt.Nodes
		}
		accountCount++
		storageCount += curStorageCount
		accountSize += curAccountSize
		storageSize += curStorageSize
		storageNodes += curStorageNodes

		if time.Since(logged) > 8*time.Second {
			fmt.Printf("%#x: %9s + %9s (%6d slots, %6d nodes), total %9s (%d accs, %d nodes) + %9s (%d slots, %d nodes)\n", accIt.Key, curAccountSize.TerminalString(), curStorageSize.TerminalString(), curStorageCount, curStorageNodes, accountSize.TerminalString(), accountCount, accIt.Nodes, storageSize.TerminalString(), storageCount, storageNodes)
			logged = time.Now()
		}
	}
	fmt.Printf("Totals: %9s (%d accs, %d nodes) + %9s (%d slots, %d nodes)\n", accountSize.TerminalString(), accountCount, accIt.Nodes, storageSize.TerminalString(), storageCount, storageNodes)

	// Update the snapshot block marker and write any remainder data
	rawdb.WriteSnapshotBlock(batch, headNumber, headRoot)
	batch.Write()
	batch.Reset()

	// Compact the snapshot section of the database to get rid of unused space
	log.Info("Compacting snapshot in chain database")
	if err := db.Compact([]byte{'s'}, []byte{'s' + 1}); err != nil {
		return nil, err
	}
	// New snapshot generated, construct a brand new base layer
	cache, _ := bigcache.NewBigCache(bigcache.Config{ // TODO(karalabe): dedup
		Shards:             1024,
		LifeWindow:         time.Hour,
		MaxEntriesInWindow: 512 * 1024,
		MaxEntrySize:       512,
		HardMaxCacheSize:   512,
	})
	return &diskLayer{
		journal: journal,
		db:      db,
		cache:   cache,
		number:  headNumber,
		root:    headRoot,
	}, nil
}