// Copyright 2017 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 light

import (
	"encoding/binary"
	"errors"
	"math/big"
	"time"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/bitutil"
	"github.com/ethereum/go-ethereum/core"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/params"
	"github.com/ethereum/go-ethereum/rlp"
	"github.com/ethereum/go-ethereum/trie"
)

const (
	// CHTFrequencyClient is the block frequency for creating CHTs on the client side.
	CHTFrequencyClient = 32768

	// CHTFrequencyServer is the block frequency for creating CHTs on the server side.
	// Eventually this can be merged back with the client version, but that requires a
	// full database upgrade, so that should be left for a suitable moment.
	CHTFrequencyServer = 4096

	HelperTrieConfirmations        = 2048 // number of confirmations before a server is expected to have the given HelperTrie available
	HelperTrieProcessConfirmations = 256  // number of confirmations before a HelperTrie is generated
)

// trustedCheckpoint represents a set of post-processed trie roots (CHT and BloomTrie) associated with
// the appropriate section index and head hash. It is used to start light syncing from this checkpoint
// and avoid downloading the entire header chain while still being able to securely access old headers/logs.
type trustedCheckpoint struct {
	name                                string
	sectionIdx                          uint64
	sectionHead, chtRoot, bloomTrieRoot common.Hash
}

var (
	mainnetCheckpoint = trustedCheckpoint{
		name:          "mainnet",
		sectionIdx:    161,
		sectionHead:   common.HexToHash("75b0c4baa7a62cece48abdcb03b6f31601961c9bece67dcd61df87aad4fc0d8d"),
		chtRoot:       common.HexToHash("bbbfaa67b29716348997ec21a39c03b8d1fb973f6a43740b865595ba26ee812f"),
		bloomTrieRoot: common.HexToHash("d6db6e6248354d7453391ce97830072a28ea4216be0bd95a5db9f53b1a64677b"),
	}

	ropstenCheckpoint = trustedCheckpoint{
		name:          "ropsten",
		sectionIdx:    83,
		sectionHead:   common.HexToHash("3ca623586bc0da35f1fc8d9b6b55950f3b1f69be9c6501846a2df672adb61236"),
		chtRoot:       common.HexToHash("8f08ec7783969768c6ef06e5fe3398223cbf4ae2907b676da7b6fe6c7f55b059"),
		bloomTrieRoot: common.HexToHash("02d86d3c6a87f8f8a92c2a59bbba2132ff6f9f61b0915a5dc28a9d8279219fd0"),
	}
)

// trustedCheckpoints associates each known checkpoint with the genesis hash of the chain it belongs to
var trustedCheckpoints = map[common.Hash]trustedCheckpoint{
	params.MainnetGenesisHash: mainnetCheckpoint,
	params.TestnetGenesisHash: ropstenCheckpoint,
}

var (
	ErrNoTrustedCht       = errors.New("No trusted canonical hash trie")
	ErrNoTrustedBloomTrie = errors.New("No trusted bloom trie")
	ErrNoHeader           = errors.New("Header not found")
	chtPrefix             = []byte("chtRoot-") // chtPrefix + chtNum (uint64 big endian) -> trie root hash
	ChtTablePrefix        = "cht-"
)

// ChtNode structures are stored in the Canonical Hash Trie in an RLP encoded format
type ChtNode struct {
	Hash common.Hash
	Td   *big.Int
}

// GetChtRoot reads the CHT root assoctiated to the given section from the database
// Note that sectionIdx is specified according to LES/1 CHT section size
func GetChtRoot(db ethdb.Database, sectionIdx uint64, sectionHead common.Hash) common.Hash {
	var encNumber [8]byte
	binary.BigEndian.PutUint64(encNumber[:], sectionIdx)
	data, _ := db.Get(append(append(chtPrefix, encNumber[:]...), sectionHead.Bytes()...))
	return common.BytesToHash(data)
}

// GetChtV2Root reads the CHT root assoctiated to the given section from the database
// Note that sectionIdx is specified according to LES/2 CHT section size
func GetChtV2Root(db ethdb.Database, sectionIdx uint64, sectionHead common.Hash) common.Hash {
	return GetChtRoot(db, (sectionIdx+1)*(CHTFrequencyClient/CHTFrequencyServer)-1, sectionHead)
}

// StoreChtRoot writes the CHT root assoctiated to the given section into the database
// Note that sectionIdx is specified according to LES/1 CHT section size
func StoreChtRoot(db ethdb.Database, sectionIdx uint64, sectionHead, root common.Hash) {
	var encNumber [8]byte
	binary.BigEndian.PutUint64(encNumber[:], sectionIdx)
	db.Put(append(append(chtPrefix, encNumber[:]...), sectionHead.Bytes()...), root.Bytes())
}

// ChtIndexerBackend implements core.ChainIndexerBackend
type ChtIndexerBackend struct {
	diskdb               ethdb.Database
	triedb               *trie.Database
	section, sectionSize uint64
	lastHash             common.Hash
	trie                 *trie.Trie
}

// NewBloomTrieIndexer creates a BloomTrie chain indexer
func NewChtIndexer(db ethdb.Database, clientMode bool) *core.ChainIndexer {
	var sectionSize, confirmReq uint64
	if clientMode {
		sectionSize = CHTFrequencyClient
		confirmReq = HelperTrieConfirmations
	} else {
		sectionSize = CHTFrequencyServer
		confirmReq = HelperTrieProcessConfirmations
	}
	idb := ethdb.NewTable(db, "chtIndex-")
	backend := &ChtIndexerBackend{
		diskdb:      db,
		triedb:      trie.NewDatabase(ethdb.NewTable(db, ChtTablePrefix)),
		sectionSize: sectionSize,
	}
	return core.NewChainIndexer(db, idb, backend, sectionSize, confirmReq, time.Millisecond*100, "cht")
}

// Reset implements core.ChainIndexerBackend
func (c *ChtIndexerBackend) Reset(section uint64, lastSectionHead common.Hash) error {
	var root common.Hash
	if section > 0 {
		root = GetChtRoot(c.diskdb, section-1, lastSectionHead)
	}
	var err error
	c.trie, err = trie.New(root, c.triedb)
	c.section = section
	return err
}

// Process implements core.ChainIndexerBackend
func (c *ChtIndexerBackend) Process(header *types.Header) {
	hash, num := header.Hash(), header.Number.Uint64()
	c.lastHash = hash

	td := core.GetTd(c.diskdb, hash, num)
	if td == nil {
		panic(nil)
	}
	var encNumber [8]byte
	binary.BigEndian.PutUint64(encNumber[:], num)
	data, _ := rlp.EncodeToBytes(ChtNode{hash, td})
	c.trie.Update(encNumber[:], data)
}

// Commit implements core.ChainIndexerBackend
func (c *ChtIndexerBackend) Commit() error {
	root, err := c.trie.Commit(nil)
	if err != nil {
		return err
	}
	c.triedb.Commit(root, false)

	if ((c.section+1)*c.sectionSize)%CHTFrequencyClient == 0 {
		log.Info("Storing CHT", "section", c.section*c.sectionSize/CHTFrequencyClient, "head", c.lastHash, "root", root)
	}
	StoreChtRoot(c.diskdb, c.section, c.lastHash, root)
	return nil
}

const (
	BloomTrieFrequency        = 32768
	ethBloomBitsSection       = 4096
	ethBloomBitsConfirmations = 256
)

var (
	bloomTriePrefix      = []byte("bltRoot-") // bloomTriePrefix + bloomTrieNum (uint64 big endian) -> trie root hash
	BloomTrieTablePrefix = "blt-"
)

// GetBloomTrieRoot reads the BloomTrie root assoctiated to the given section from the database
func GetBloomTrieRoot(db ethdb.Database, sectionIdx uint64, sectionHead common.Hash) common.Hash {
	var encNumber [8]byte
	binary.BigEndian.PutUint64(encNumber[:], sectionIdx)
	data, _ := db.Get(append(append(bloomTriePrefix, encNumber[:]...), sectionHead.Bytes()...))
	return common.BytesToHash(data)
}

// StoreBloomTrieRoot writes the BloomTrie root assoctiated to the given section into the database
func StoreBloomTrieRoot(db ethdb.Database, sectionIdx uint64, sectionHead, root common.Hash) {
	var encNumber [8]byte
	binary.BigEndian.PutUint64(encNumber[:], sectionIdx)
	db.Put(append(append(bloomTriePrefix, encNumber[:]...), sectionHead.Bytes()...), root.Bytes())
}

// BloomTrieIndexerBackend implements core.ChainIndexerBackend
type BloomTrieIndexerBackend struct {
	diskdb                                     ethdb.Database
	triedb                                     *trie.Database
	section, parentSectionSize, bloomTrieRatio uint64
	trie                                       *trie.Trie
	sectionHeads                               []common.Hash
}

// NewBloomTrieIndexer creates a BloomTrie chain indexer
func NewBloomTrieIndexer(db ethdb.Database, clientMode bool) *core.ChainIndexer {
	backend := &BloomTrieIndexerBackend{
		diskdb: db,
		triedb: trie.NewDatabase(ethdb.NewTable(db, BloomTrieTablePrefix)),
	}
	idb := ethdb.NewTable(db, "bltIndex-")

	var confirmReq uint64
	if clientMode {
		backend.parentSectionSize = BloomTrieFrequency
		confirmReq = HelperTrieConfirmations
	} else {
		backend.parentSectionSize = ethBloomBitsSection
		confirmReq = HelperTrieProcessConfirmations
	}
	backend.bloomTrieRatio = BloomTrieFrequency / backend.parentSectionSize
	backend.sectionHeads = make([]common.Hash, backend.bloomTrieRatio)
	return core.NewChainIndexer(db, idb, backend, BloomTrieFrequency, confirmReq-ethBloomBitsConfirmations, time.Millisecond*100, "bloomtrie")
}

// Reset implements core.ChainIndexerBackend
func (b *BloomTrieIndexerBackend) Reset(section uint64, lastSectionHead common.Hash) error {
	var root common.Hash
	if section > 0 {
		root = GetBloomTrieRoot(b.diskdb, section-1, lastSectionHead)
	}
	var err error
	b.trie, err = trie.New(root, b.triedb)
	b.section = section
	return err
}

// Process implements core.ChainIndexerBackend
func (b *BloomTrieIndexerBackend) Process(header *types.Header) {
	num := header.Number.Uint64() - b.section*BloomTrieFrequency
	if (num+1)%b.parentSectionSize == 0 {
		b.sectionHeads[num/b.parentSectionSize] = header.Hash()
	}
}

// Commit implements core.ChainIndexerBackend
func (b *BloomTrieIndexerBackend) Commit() error {
	var compSize, decompSize uint64

	for i := uint(0); i < types.BloomBitLength; i++ {
		var encKey [10]byte
		binary.BigEndian.PutUint16(encKey[0:2], uint16(i))
		binary.BigEndian.PutUint64(encKey[2:10], b.section)
		var decomp []byte
		for j := uint64(0); j < b.bloomTrieRatio; j++ {
			data, err := core.GetBloomBits(b.diskdb, i, b.section*b.bloomTrieRatio+j, b.sectionHeads[j])
			if err != nil {
				return err
			}
			decompData, err2 := bitutil.DecompressBytes(data, int(b.parentSectionSize/8))
			if err2 != nil {
				return err2
			}
			decomp = append(decomp, decompData...)
		}
		comp := bitutil.CompressBytes(decomp)

		decompSize += uint64(len(decomp))
		compSize += uint64(len(comp))
		if len(comp) > 0 {
			b.trie.Update(encKey[:], comp)
		} else {
			b.trie.Delete(encKey[:])
		}
	}
	root, err := b.trie.Commit(nil)
	if err != nil {
		return err
	}
	b.triedb.Commit(root, false)

	sectionHead := b.sectionHeads[b.bloomTrieRatio-1]
	log.Info("Storing bloom trie", "section", b.section, "head", sectionHead, "root", root, "compression", float64(compSize)/float64(decompSize))
	StoreBloomTrieRoot(b.diskdb, b.section, sectionHead, root)

	return nil
}