// Copyright 2022 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 pathdb

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"time"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/core/rawdb"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/trie/triestate"
	"golang.org/x/exp/slices"
)

// State history records the state changes involved in executing a block. The
// state can be reverted to the previous version by applying the associated
// history object (state reverse diff). State history objects are kept to
// guarantee that the system can perform state rollbacks in case of deep reorg.
//
// Each state transition will generate a state history object. Note that not
// every block has a corresponding state history object. If a block performs
// no state changes whatsoever, no state is created for it. Each state history
// will have a sequentially increasing number acting as its unique identifier.
//
// The state history is written to disk (ancient store) when the corresponding
// diff layer is merged into the disk layer. At the same time, system can prune
// the oldest histories according to config.
//
//                                                        Disk State
//                                                            ^
//                                                            |
//   +------------+     +---------+     +---------+     +---------+
//   | Init State |---->| State 1 |---->|   ...   |---->| State n |
//   +------------+     +---------+     +---------+     +---------+
//
//                     +-----------+      +------+     +-----------+
//                     | History 1 |----> | ...  |---->| History n |
//                     +-----------+      +------+     +-----------+
//
// # Rollback
//
// If the system wants to roll back to a previous state n, it needs to ensure
// all history objects from n+1 up to the current disk layer are existent. The
// history objects are applied to the state in reverse order, starting from the
// current disk layer.

const (
	accountIndexSize = common.AddressLength + 13 // The length of encoded account index
	slotIndexSize    = common.HashLength + 5     // The length of encoded slot index
	historyMetaSize  = 9 + 2*common.HashLength   // The length of encoded history meta

	stateHistoryVersion = uint8(0) // initial version of state history structure.
)

// Each state history entry is consisted of five elements:
//
// # metadata
//  This object contains a few meta fields, such as the associated state root,
//  block number, version tag and so on. This object may contain an extra
//  accountHash list which means the storage changes belong to these accounts
//  are not complete due to large contract destruction. The incomplete history
//  can not be used for rollback and serving archive state request.
//
// # account index
//  This object contains some index information of account. For example, offset
//  and length indicate the location of the data belonging to the account. Besides,
//  storageOffset and storageSlots indicate the storage modification location
//  belonging to the account.
//
//  The size of each account index is *fixed*, and all indexes are sorted
//  lexicographically. Thus binary search can be performed to quickly locate a
//  specific account.
//
// # account data
//  Account data is a concatenated byte stream composed of all account data.
//  The account data can be solved by the offset and length info indicated
//  by corresponding account index.
//
//            fixed size
//         ^             ^
//        /               \
//        +-----------------+-----------------+----------------+-----------------+
//        | Account index 1 | Account index 2 |       ...      | Account index N |
//        +-----------------+-----------------+----------------+-----------------+
//        |
//        |     length
// offset |----------------+
//        v                v
//        +----------------+----------------+----------------+----------------+
//        | Account data 1 | Account data 2 |       ...      | Account data N |
//        +----------------+----------------+----------------+----------------+
//
// # storage index
//  This object is similar with account index. It's also fixed size and contains
//  the location info of storage slot data.
//
// # storage data
//  Storage data is a concatenated byte stream composed of all storage slot data.
//  The storage slot data can be solved by the location info indicated by
//  corresponding account index and storage slot index.
//
//                    fixed size
//                 ^             ^
//                /               \
//                +-----------------+-----------------+----------------+-----------------+
//                | Account index 1 | Account index 2 |       ...      | Account index N |
//                +-----------------+-----------------+----------------+-----------------+
//                |
//                |                    storage slots
// storage offset |-----------------------------------------------------+
//                v                                                     v
//                +-----------------+-----------------+-----------------+
//                | storage index 1 | storage index 2 | storage index 3 |
//                +-----------------+-----------------+-----------------+
//                |     length
//         offset |-------------+
//                v             v
//                +-------------+
//                | slot data 1 |
//                +-------------+

// accountIndex describes the metadata belonging to an account.
type accountIndex struct {
	address       common.Address // The address of account
	length        uint8          // The length of account data, size limited by 255
	offset        uint32         // The offset of item in account data table
	storageOffset uint32         // The offset of storage index in storage index table
	storageSlots  uint32         // The number of mutated storage slots belonging to the account
}

// encode packs account index into byte stream.
func (i *accountIndex) encode() []byte {
	var buf [accountIndexSize]byte
	copy(buf[:], i.address.Bytes())
	buf[common.AddressLength] = i.length
	binary.BigEndian.PutUint32(buf[common.AddressLength+1:], i.offset)
	binary.BigEndian.PutUint32(buf[common.AddressLength+5:], i.storageOffset)
	binary.BigEndian.PutUint32(buf[common.AddressLength+9:], i.storageSlots)
	return buf[:]
}

// decode unpacks account index from byte stream.
func (i *accountIndex) decode(blob []byte) {
	i.address = common.BytesToAddress(blob[:common.AddressLength])
	i.length = blob[common.AddressLength]
	i.offset = binary.BigEndian.Uint32(blob[common.AddressLength+1:])
	i.storageOffset = binary.BigEndian.Uint32(blob[common.AddressLength+5:])
	i.storageSlots = binary.BigEndian.Uint32(blob[common.AddressLength+9:])
}

// slotIndex describes the metadata belonging to a storage slot.
type slotIndex struct {
	hash   common.Hash // The hash of slot key
	length uint8       // The length of storage slot, up to 32 bytes defined in protocol
	offset uint32      // The offset of item in storage slot data table
}

// encode packs slot index into byte stream.
func (i *slotIndex) encode() []byte {
	var buf [slotIndexSize]byte
	copy(buf[:common.HashLength], i.hash.Bytes())
	buf[common.HashLength] = i.length
	binary.BigEndian.PutUint32(buf[common.HashLength+1:], i.offset)
	return buf[:]
}

// decode unpack slot index from the byte stream.
func (i *slotIndex) decode(blob []byte) {
	i.hash = common.BytesToHash(blob[:common.HashLength])
	i.length = blob[common.HashLength]
	i.offset = binary.BigEndian.Uint32(blob[common.HashLength+1:])
}

// meta describes the meta data of state history object.
type meta struct {
	version uint8       // version tag of history object
	parent  common.Hash // prev-state root before the state transition
	root    common.Hash // post-state root after the state transition
	block   uint64      // associated block number
}

// encode packs the meta object into byte stream.
func (m *meta) encode() []byte {
	buf := make([]byte, historyMetaSize)
	buf[0] = m.version
	copy(buf[1:1+common.HashLength], m.parent.Bytes())
	copy(buf[1+common.HashLength:1+2*common.HashLength], m.root.Bytes())
	binary.BigEndian.PutUint64(buf[1+2*common.HashLength:historyMetaSize], m.block)
	return buf[:]
}

// decode unpacks the meta object from byte stream.
func (m *meta) decode(blob []byte) error {
	if len(blob) < 1 {
		return errors.New("no version tag")
	}
	switch blob[0] {
	case stateHistoryVersion:
		if len(blob) != historyMetaSize {
			return fmt.Errorf("invalid state history meta, len: %d", len(blob))
		}
		m.version = blob[0]
		m.parent = common.BytesToHash(blob[1 : 1+common.HashLength])
		m.root = common.BytesToHash(blob[1+common.HashLength : 1+2*common.HashLength])
		m.block = binary.BigEndian.Uint64(blob[1+2*common.HashLength : historyMetaSize])
		return nil
	default:
		return fmt.Errorf("unknown version %d", blob[0])
	}
}

// history represents a set of state changes belong to a block along with
// the metadata including the state roots involved in the state transition.
// State history objects in disk are linked with each other by a unique id
// (8-bytes integer), the oldest state history object can be pruned on demand
// in order to control the storage size.
type history struct {
	meta        *meta                                     // Meta data of history
	accounts    map[common.Address][]byte                 // Account data keyed by its address hash
	accountList []common.Address                          // Sorted account hash list
	storages    map[common.Address]map[common.Hash][]byte // Storage data keyed by its address hash and slot hash
	storageList map[common.Address][]common.Hash          // Sorted slot hash list
}

// newHistory constructs the state history object with provided state change set.
func newHistory(root common.Hash, parent common.Hash, block uint64, states *triestate.Set) *history {
	var (
		accountList []common.Address
		storageList = make(map[common.Address][]common.Hash)
	)
	for addr := range states.Accounts {
		accountList = append(accountList, addr)
	}
	slices.SortFunc(accountList, common.Address.Cmp)

	for addr, slots := range states.Storages {
		slist := make([]common.Hash, 0, len(slots))
		for slotHash := range slots {
			slist = append(slist, slotHash)
		}
		slices.SortFunc(slist, common.Hash.Cmp)
		storageList[addr] = slist
	}
	return &history{
		meta: &meta{
			version: stateHistoryVersion,
			parent:  parent,
			root:    root,
			block:   block,
		},
		accounts:    states.Accounts,
		accountList: accountList,
		storages:    states.Storages,
		storageList: storageList,
	}
}

// encode serializes the state history and returns four byte streams represent
// concatenated account/storage data, account/storage indexes respectively.
func (h *history) encode() ([]byte, []byte, []byte, []byte) {
	var (
		slotNumber     uint32 // the number of processed slots
		accountData    []byte // the buffer for concatenated account data
		storageData    []byte // the buffer for concatenated storage data
		accountIndexes []byte // the buffer for concatenated account index
		storageIndexes []byte // the buffer for concatenated storage index
	)
	for _, addr := range h.accountList {
		accIndex := accountIndex{
			address: addr,
			length:  uint8(len(h.accounts[addr])),
			offset:  uint32(len(accountData)),
		}
		slots, exist := h.storages[addr]
		if exist {
			// Encode storage slots in order
			for _, slotHash := range h.storageList[addr] {
				sIndex := slotIndex{
					hash:   slotHash,
					length: uint8(len(slots[slotHash])),
					offset: uint32(len(storageData)),
				}
				storageData = append(storageData, slots[slotHash]...)
				storageIndexes = append(storageIndexes, sIndex.encode()...)
			}
			// Fill up the storage meta in account index
			accIndex.storageOffset = slotNumber
			accIndex.storageSlots = uint32(len(slots))
			slotNumber += uint32(len(slots))
		}
		accountData = append(accountData, h.accounts[addr]...)
		accountIndexes = append(accountIndexes, accIndex.encode()...)
	}
	return accountData, storageData, accountIndexes, storageIndexes
}

// decoder wraps the byte streams for decoding with extra meta fields.
type decoder struct {
	accountData    []byte // the buffer for concatenated account data
	storageData    []byte // the buffer for concatenated storage data
	accountIndexes []byte // the buffer for concatenated account index
	storageIndexes []byte // the buffer for concatenated storage index

	lastAccount       *common.Address // the address of last resolved account
	lastAccountRead   uint32          // the read-cursor position of account data
	lastSlotIndexRead uint32          // the read-cursor position of storage slot index
	lastSlotDataRead  uint32          // the read-cursor position of storage slot data
}

// verify validates the provided byte streams for decoding state history. A few
// checks will be performed to quickly detect data corruption. The byte stream
// is regarded as corrupted if:
//
// - account indexes buffer is empty(empty state set is invalid)
// - account indexes/storage indexer buffer is not aligned
//
// note, these situations are allowed:
//
// - empty account data: all accounts were not present
// - empty storage set: no slots are modified
func (r *decoder) verify() error {
	if len(r.accountIndexes)%accountIndexSize != 0 || len(r.accountIndexes) == 0 {
		return fmt.Errorf("invalid account index, len: %d", len(r.accountIndexes))
	}
	if len(r.storageIndexes)%slotIndexSize != 0 {
		return fmt.Errorf("invalid storage index, len: %d", len(r.storageIndexes))
	}
	return nil
}

// readAccount parses the account from the byte stream with specified position.
func (r *decoder) readAccount(pos int) (accountIndex, []byte, error) {
	// Decode account index from the index byte stream.
	var index accountIndex
	if (pos+1)*accountIndexSize > len(r.accountIndexes) {
		return accountIndex{}, nil, errors.New("account data buffer is corrupted")
	}
	index.decode(r.accountIndexes[pos*accountIndexSize : (pos+1)*accountIndexSize])

	// Perform validation before parsing account data, ensure
	// - account is sorted in order in byte stream
	// - account data is strictly encoded with no gap inside
	// - account data is not out-of-slice
	if r.lastAccount != nil { // zero address is possible
		if bytes.Compare(r.lastAccount.Bytes(), index.address.Bytes()) >= 0 {
			return accountIndex{}, nil, errors.New("account is not in order")
		}
	}
	if index.offset != r.lastAccountRead {
		return accountIndex{}, nil, errors.New("account data buffer is gaped")
	}
	last := index.offset + uint32(index.length)
	if uint32(len(r.accountData)) < last {
		return accountIndex{}, nil, errors.New("account data buffer is corrupted")
	}
	data := r.accountData[index.offset:last]

	r.lastAccount = &index.address
	r.lastAccountRead = last

	return index, data, nil
}

// readStorage parses the storage slots from the byte stream with specified account.
func (r *decoder) readStorage(accIndex accountIndex) ([]common.Hash, map[common.Hash][]byte, error) {
	var (
		last    common.Hash
		list    []common.Hash
		storage = make(map[common.Hash][]byte)
	)
	for j := 0; j < int(accIndex.storageSlots); j++ {
		var (
			index slotIndex
			start = (accIndex.storageOffset + uint32(j)) * uint32(slotIndexSize)
			end   = (accIndex.storageOffset + uint32(j+1)) * uint32(slotIndexSize)
		)
		// Perform validation before parsing storage slot data, ensure
		// - slot index is not out-of-slice
		// - slot data is not out-of-slice
		// - slot is sorted in order in byte stream
		// - slot indexes is strictly encoded with no gap inside
		// - slot data is strictly encoded with no gap inside
		if start != r.lastSlotIndexRead {
			return nil, nil, errors.New("storage index buffer is gapped")
		}
		if uint32(len(r.storageIndexes)) < end {
			return nil, nil, errors.New("storage index buffer is corrupted")
		}
		index.decode(r.storageIndexes[start:end])

		if bytes.Compare(last.Bytes(), index.hash.Bytes()) >= 0 {
			return nil, nil, errors.New("storage slot is not in order")
		}
		if index.offset != r.lastSlotDataRead {
			return nil, nil, errors.New("storage data buffer is gapped")
		}
		sEnd := index.offset + uint32(index.length)
		if uint32(len(r.storageData)) < sEnd {
			return nil, nil, errors.New("storage data buffer is corrupted")
		}
		storage[index.hash] = r.storageData[r.lastSlotDataRead:sEnd]
		list = append(list, index.hash)

		last = index.hash
		r.lastSlotIndexRead = end
		r.lastSlotDataRead = sEnd
	}
	return list, storage, nil
}

// decode deserializes the account and storage data from the provided byte stream.
func (h *history) decode(accountData, storageData, accountIndexes, storageIndexes []byte) error {
	var (
		accounts    = make(map[common.Address][]byte)
		storages    = make(map[common.Address]map[common.Hash][]byte)
		accountList []common.Address
		storageList = make(map[common.Address][]common.Hash)

		r = &decoder{
			accountData:    accountData,
			storageData:    storageData,
			accountIndexes: accountIndexes,
			storageIndexes: storageIndexes,
		}
	)
	if err := r.verify(); err != nil {
		return err
	}
	for i := 0; i < len(accountIndexes)/accountIndexSize; i++ {
		// Resolve account first
		accIndex, accData, err := r.readAccount(i)
		if err != nil {
			return err
		}
		accounts[accIndex.address] = accData
		accountList = append(accountList, accIndex.address)

		// Resolve storage slots
		slotList, slotData, err := r.readStorage(accIndex)
		if err != nil {
			return err
		}
		if len(slotList) > 0 {
			storageList[accIndex.address] = slotList
			storages[accIndex.address] = slotData
		}
	}
	h.accounts = accounts
	h.accountList = accountList
	h.storages = storages
	h.storageList = storageList
	return nil
}

// readHistory reads and decodes the state history object by the given id.
func readHistory(freezer *rawdb.ResettableFreezer, id uint64) (*history, error) {
	blob := rawdb.ReadStateHistoryMeta(freezer, id)
	if len(blob) == 0 {
		return nil, fmt.Errorf("state history not found %d", id)
	}
	var m meta
	if err := m.decode(blob); err != nil {
		return nil, err
	}
	var (
		dec            = history{meta: &m}
		accountData    = rawdb.ReadStateAccountHistory(freezer, id)
		storageData    = rawdb.ReadStateStorageHistory(freezer, id)
		accountIndexes = rawdb.ReadStateAccountIndex(freezer, id)
		storageIndexes = rawdb.ReadStateStorageIndex(freezer, id)
	)
	if err := dec.decode(accountData, storageData, accountIndexes, storageIndexes); err != nil {
		return nil, err
	}
	return &dec, nil
}

// writeHistory persists the state history with the provided state set.
func writeHistory(freezer *rawdb.ResettableFreezer, dl *diffLayer) error {
	// Short circuit if state set is not available.
	if dl.states == nil {
		return errors.New("state change set is not available")
	}
	var (
		start   = time.Now()
		history = newHistory(dl.rootHash(), dl.parentLayer().rootHash(), dl.block, dl.states)
	)
	accountData, storageData, accountIndex, storageIndex := history.encode()
	dataSize := common.StorageSize(len(accountData) + len(storageData))
	indexSize := common.StorageSize(len(accountIndex) + len(storageIndex))

	// Write history data into five freezer table respectively.
	rawdb.WriteStateHistory(freezer, dl.stateID(), history.meta.encode(), accountIndex, storageIndex, accountData, storageData)

	historyDataBytesMeter.Mark(int64(dataSize))
	historyIndexBytesMeter.Mark(int64(indexSize))
	historyBuildTimeMeter.UpdateSince(start)
	log.Debug("Stored state history", "id", dl.stateID(), "block", dl.block, "data", dataSize, "index", indexSize, "elapsed", common.PrettyDuration(time.Since(start)))

	return nil
}

// checkHistories retrieves a batch of meta objects with the specified range
// and performs the callback on each item.
func checkHistories(freezer *rawdb.ResettableFreezer, start, count uint64, check func(*meta) error) error {
	for count > 0 {
		number := count
		if number > 10000 {
			number = 10000 // split the big read into small chunks
		}
		blobs, err := rawdb.ReadStateHistoryMetaList(freezer, start, number)
		if err != nil {
			return err
		}
		for _, blob := range blobs {
			var dec meta
			if err := dec.decode(blob); err != nil {
				return err
			}
			if err := check(&dec); err != nil {
				return err
			}
		}
		count -= uint64(len(blobs))
		start += uint64(len(blobs))
	}
	return nil
}

// truncateFromHead removes the extra state histories from the head with the given
// parameters. It returns the number of items removed from the head.
func truncateFromHead(db ethdb.Batcher, freezer *rawdb.ResettableFreezer, nhead uint64) (int, error) {
	ohead, err := freezer.Ancients()
	if err != nil {
		return 0, err
	}
	otail, err := freezer.Tail()
	if err != nil {
		return 0, err
	}
	// Ensure that the truncation target falls within the specified range.
	if ohead < nhead || nhead < otail {
		return 0, fmt.Errorf("out of range, tail: %d, head: %d, target: %d", otail, ohead, nhead)
	}
	// Short circuit if nothing to truncate.
	if ohead == nhead {
		return 0, nil
	}
	// Load the meta objects in range [nhead+1, ohead]
	blobs, err := rawdb.ReadStateHistoryMetaList(freezer, nhead+1, ohead-nhead)
	if err != nil {
		return 0, err
	}
	batch := db.NewBatch()
	for _, blob := range blobs {
		var m meta
		if err := m.decode(blob); err != nil {
			return 0, err
		}
		rawdb.DeleteStateID(batch, m.root)
	}
	if err := batch.Write(); err != nil {
		return 0, err
	}
	ohead, err = freezer.TruncateHead(nhead)
	if err != nil {
		return 0, err
	}
	return int(ohead - nhead), nil
}

// truncateFromTail removes the extra state histories from the tail with the given
// parameters. It returns the number of items removed from the tail.
func truncateFromTail(db ethdb.Batcher, freezer *rawdb.ResettableFreezer, ntail uint64) (int, error) {
	ohead, err := freezer.Ancients()
	if err != nil {
		return 0, err
	}
	otail, err := freezer.Tail()
	if err != nil {
		return 0, err
	}
	// Ensure that the truncation target falls within the specified range.
	if otail > ntail || ntail > ohead {
		return 0, fmt.Errorf("out of range, tail: %d, head: %d, target: %d", otail, ohead, ntail)
	}
	// Short circuit if nothing to truncate.
	if otail == ntail {
		return 0, nil
	}
	// Load the meta objects in range [otail+1, ntail]
	blobs, err := rawdb.ReadStateHistoryMetaList(freezer, otail+1, ntail-otail)
	if err != nil {
		return 0, err
	}
	batch := db.NewBatch()
	for _, blob := range blobs {
		var m meta
		if err := m.decode(blob); err != nil {
			return 0, err
		}
		rawdb.DeleteStateID(batch, m.root)
	}
	if err := batch.Write(); err != nil {
		return 0, err
	}
	otail, err = freezer.TruncateTail(ntail)
	if err != nil {
		return 0, err
	}
	return int(ntail - otail), nil
}