// Copyright 2015 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 core

import (
	crand "crypto/rand"
	"math"
	"math/big"
	mrand "math/rand"
	"sync/atomic"

	"github.com/ledgerwatch/turbo-geth/common"
	"github.com/ledgerwatch/turbo-geth/consensus"
	"github.com/ledgerwatch/turbo-geth/core/rawdb"
	"github.com/ledgerwatch/turbo-geth/core/types"
	"github.com/ledgerwatch/turbo-geth/ethdb"
	"github.com/ledgerwatch/turbo-geth/params"
)

// HeaderChain implements the basic block header chain logic that is shared by
// core.BlockChain and light.LightChain. It is not usable in itself, only as
// a part of either structure.
//
// HeaderChain is responsible for maintaining the header chain including the
// header query and updating.
//
// The components maintained by headerchain includes: (1) total difficult
// (2) header (3) block hash -> number mapping (4) canonical number -> hash mapping
// and (5) head header flag.
//
// It is not thread safe either, the encapsulating chain structures should do
// the necessary mutex locking/unlocking.
type HeaderChain struct {
	config *params.ChainConfig

	chainDb       ethdb.Database
	genesisHeader *types.Header

	currentHeader     atomic.Value // Current head of the header chain (may be above the block chain!)
	currentHeaderHash common.Hash  // Hash of the current head of the header chain (prevent recomputing all the time)

	rand   *mrand.Rand
	engine consensus.Engine
}

// NewHeaderChain creates a new HeaderChain structure.
func NewHeaderChain(chainDb ethdb.Database, config *params.ChainConfig, engine consensus.Engine) (*HeaderChain, error) {

	// Seed a fast but crypto originating random generator
	seed, err := crand.Int(crand.Reader, big.NewInt(math.MaxInt64))
	if err != nil {
		return nil, err
	}

	hc := &HeaderChain{
		config:  config,
		chainDb: chainDb,
		rand:    mrand.New(mrand.NewSource(seed.Int64())),
		engine:  engine,
	}

	hc.genesisHeader = rawdb.ReadHeaderByNumber(chainDb, 0)
	if hc.genesisHeader == nil {
		return nil, ErrNoGenesis
	}

	hc.currentHeader.Store(hc.genesisHeader)
	if head := rawdb.ReadHeadBlockHash(chainDb); head != (common.Hash{}) {
		if chead, _ := rawdb.ReadHeaderByHash(chainDb, head); chead != nil {
			hc.currentHeader.Store(chead)
		}
	}
	hc.currentHeaderHash = rawdb.ReadCurrentHeader(chainDb).Hash()
	//headHeaderGauge.Update(hc.CurrentHeader().Number.Int64())

	return hc, nil
}

// GetBlockNumber retrieves the block number belonging to the given hash
// from the cache or database
func (hc *HeaderChain) GetBlockNumber(dbr ethdb.Database, hash common.Hash) *uint64 {
	number := rawdb.ReadHeaderNumber(dbr, hash)
	return number
}

// GetBlockHashesFromHash retrieves a number of block hashes starting at a given
// hash, fetching towards the genesis block.
func (hc *HeaderChain) GetBlockHashesFromHash(hash common.Hash, max uint64) []common.Hash {
	// Get the origin header from which to fetch
	header := hc.GetHeaderByHash(hash)
	if header == nil {
		return nil
	}
	// Iterate the headers until enough is collected or the genesis reached
	chain := make([]common.Hash, 0, max)
	for i := uint64(0); i < max; i++ {
		next := header.ParentHash
		if header = hc.GetHeader(next, header.Number.Uint64()-1); header == nil {
			break
		}
		chain = append(chain, next)
		if header.Number.Sign() == 0 {
			break
		}
	}
	return chain
}

// GetHeader retrieves a block header from the database by hash and number,
// caching it if found.
func (hc *HeaderChain) GetHeader(hash common.Hash, number uint64) *types.Header {
	header := rawdb.ReadHeader(hc.chainDb, hash, number)
	if header == nil {
		return nil
	}
	return header
}

// GetHeaderByHash retrieves a block header from the database by hash, caching it if
// found.
func (hc *HeaderChain) GetHeaderByHash(hash common.Hash) *types.Header {
	number := hc.GetBlockNumber(hc.chainDb, hash)
	if number == nil {
		return nil
	}
	return hc.GetHeader(hash, *number)
}

// GetHeaderByNumber retrieves a block header from the database by number,
// caching it (associated with its hash) if found.
func (hc *HeaderChain) GetHeaderByNumber(number uint64) *types.Header {
	hash, err := rawdb.ReadCanonicalHash(hc.chainDb, number)
	if err != nil {
		panic(err)
	}

	if hash == (common.Hash{}) {
		return nil
	}
	return hc.GetHeader(hash, number)
}

func (hc *HeaderChain) GetCanonicalHash(number uint64) common.Hash {
	h, err := rawdb.ReadCanonicalHash(hc.chainDb, number)
	if err != nil {
		panic(err)
	}
	return h
}

// CurrentHeader retrieves the current head header of the canonical chain.
func (hc *HeaderChain) CurrentHeader() *types.Header {
	headHash := rawdb.ReadHeadHeaderHash(hc.chainDb)
	headNumber := rawdb.ReadHeaderNumber(hc.chainDb, headHash)
	return rawdb.ReadHeader(hc.chainDb, headHash, *headNumber)
}

// SetCurrentHeader sets the current head header of the canonical chain.
func (hc *HeaderChain) SetCurrentHeader(dbw ethdb.Putter, head *types.Header) {
	rawdb.WriteHeadHeaderHash(dbw, head.Hash())
	hc.currentHeader.Store(head)
	hc.currentHeaderHash = head.Hash()
	//headHeaderGauge.Update(head.Number.Int64())
}

type (
	// UpdateHeadBlocksCallback is a callback function that is called by SetHead
	// before head header is updated. The method will return the actual block it
	// updated the head to (missing state) and a flag if setHead should continue
	// rewinding till that forcefully (exceeded ancient limits)
	UpdateHeadBlocksCallback func(ethdb.Database, *types.Header) (uint64, bool)

	// DeleteBlockContentCallback is a callback function that is called by SetHead
	// before each header is deleted.
	DeleteBlockContentCallback func(ethdb.Database, common.Hash, uint64)
)

// Config retrieves the header chain's chain configuration.
func (hc *HeaderChain) Config() *params.ChainConfig { return hc.config }

// Engine retrieves the header chain's consensus engine.
func (hc *HeaderChain) Engine() consensus.Engine { return hc.engine }

func (hc *HeaderChain) SetEngine(engine consensus.Engine) {
	hc.engine = engine
}

// GetBlock implements consensus.ChainReader, and returns nil for every input as
// a header chain does not have blocks available for retrieval.
func (hc *HeaderChain) GetBlock(hash common.Hash, number uint64) *types.Block {
	return nil
}