// 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 light implements on-demand retrieval capable state and chain objects
// for the Ethereum Light Client.
package light

import (
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/rlp"
	"golang.org/x/net/context"
)

// OdrBackend is an interface to a backend service that handles odr retrievals
type OdrBackend interface {
	Database() ethdb.Database
	Retrieve(ctx context.Context, req OdrRequest) error
}

// OdrRequest is an interface for retrieval requests
type OdrRequest interface {
	StoreResult(db ethdb.Database)
}

// TrieRequest is the ODR request type for state/storage trie entries
type TrieRequest struct {
	OdrRequest
	root  common.Hash
	key   []byte
	proof []rlp.RawValue
}

// StoreResult stores the retrieved data in local database
func (req *TrieRequest) StoreResult(db ethdb.Database) {
	storeProof(db, req.proof)
}

// storeProof stores the new trie nodes obtained from a merkle proof in the database
func storeProof(db ethdb.Database, proof []rlp.RawValue) {
	for _, buf := range proof {
		hash := crypto.Keccak256(buf)
		val, _ := db.Get(hash)
		if val == nil {
			db.Put(hash, buf)
		}
	}
}

// NodeDataRequest is the ODR request type for node data (used for retrieving contract code)
type NodeDataRequest struct {
	OdrRequest
	hash common.Hash
	data []byte
}

// GetData returns the retrieved node data after a successful request
func (req *NodeDataRequest) GetData() []byte {
	return req.data
}

// StoreResult stores the retrieved data in local database
func (req *NodeDataRequest) StoreResult(db ethdb.Database) {
	db.Put(req.hash[:], req.GetData())
}

var sha3_nil = crypto.Keccak256Hash(nil)

// retrieveNodeData tries to retrieve node data with the given hash from the network
func retrieveNodeData(ctx context.Context, odr OdrBackend, hash common.Hash) ([]byte, error) {
	if hash == sha3_nil {
		return nil, nil
	}
	res, _ := odr.Database().Get(hash[:])
	if res != nil {
		return res, nil
	}
	r := &NodeDataRequest{hash: hash}
	if err := odr.Retrieve(ctx, r); err != nil {
		return nil, err
	} else {
		return r.GetData(), nil
	}
}