// 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 state

import (
	"fmt"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/trie"
	lru "github.com/hashicorp/golang-lru"
)

// MaxTrieCacheGen limit after which to evict trie nodes from memory.
var MaxTrieCacheGen = uint16(120)

const (
	// Number of past tries to keep. This value is chosen such that
	// reasonable chain reorg depths will hit an existing trie.
	maxPastTries = 12

	// Number of codehash->size associations to keep.
	codeSizeCacheSize = 100000
)

// Database wraps access to tries and contract code.
type Database interface {
	// OpenTrie opens the main account trie.
	OpenTrie(root common.Hash) (Trie, error)

	// OpenStorageTrie opens the storage trie of an account.
	OpenStorageTrie(addrHash, root common.Hash) (Trie, error)

	// CopyTrie returns an independent copy of the given trie.
	CopyTrie(Trie) Trie

	// ContractCode retrieves a particular contract's code.
	ContractCode(addrHash, codeHash common.Hash) ([]byte, error)

	// ContractCodeSize retrieves a particular contracts code's size.
	ContractCodeSize(addrHash, codeHash common.Hash) (int, error)

	// TrieDB retrieves the low level trie database used for data storage.
	TrieDB() *trie.Database
}

// Trie is a Ethereum Merkle Patricia trie.
type Trie interface {
	// GetKey returns the sha3 preimage of a hashed key that was previously used
	// to store a value.
	//
	// TODO(fjl): remove this when SecureTrie is removed
	GetKey([]byte) []byte

	// TryGet returns the value for key stored in the trie. The value bytes must
	// not be modified by the caller. If a node was not found in the database, a
	// trie.MissingNodeError is returned.
	TryGet(key []byte) ([]byte, error)

	// TryUpdate associates key with value in the trie. If value has length zero, any
	// existing value is deleted from the trie. The value bytes must not be modified
	// by the caller while they are stored in the trie. If a node was not found in the
	// database, a trie.MissingNodeError is returned.
	TryUpdate(key, value []byte) error

	// TryDelete removes any existing value for key from the trie. If a node was not
	// found in the database, a trie.MissingNodeError is returned.
	TryDelete(key []byte) error

	// Hash returns the root hash of the trie. It does not write to the database and
	// can be used even if the trie doesn't have one.
	Hash() common.Hash

	// Commit writes all nodes to the trie's memory database, tracking the internal
	// and external (for account tries) references.
	Commit(onleaf trie.LeafCallback) (common.Hash, error)

	// NodeIterator returns an iterator that returns nodes of the trie. Iteration
	// starts at the key after the given start key.
	NodeIterator(startKey []byte) trie.NodeIterator

	// Prove constructs a Merkle proof for key. The result contains all encoded nodes
	// on the path to the value at key. The value itself is also included in the last
	// node and can be retrieved by verifying the proof.
	//
	// If the trie does not contain a value for key, the returned proof contains all
	// nodes of the longest existing prefix of the key (at least the root), ending
	// with the node that proves the absence of the key.
	Prove(key []byte, fromLevel uint, proofDb ethdb.KeyValueWriter) error
}

// NewDatabase creates a backing store for state. The returned database is safe for
// concurrent use, but does not retain any recent trie nodes in memory. To keep some
// historical state in memory, use the NewDatabaseWithCache constructor.
func NewDatabase(db ethdb.Database) Database {
	return NewDatabaseWithCache(db, 0)
}

// NewDatabaseWithCache creates a backing store for state. The returned database
// is safe for concurrent use and retains a lot of collapsed RLP trie nodes in a
// large memory cache.
func NewDatabaseWithCache(db ethdb.Database, cache int) Database {
	csc, _ := lru.New(codeSizeCacheSize)
	return &cachingDB{
		db:            trie.NewDatabaseWithCache(db, cache),
		codeSizeCache: csc,
	}
}

type cachingDB struct {
	db            *trie.Database
	codeSizeCache *lru.Cache
}

// OpenTrie opens the main account trie at a specific root hash.
func (db *cachingDB) OpenTrie(root common.Hash) (Trie, error) {
	return trie.NewSecure(root, db.db)
}

// OpenStorageTrie opens the storage trie of an account.
func (db *cachingDB) OpenStorageTrie(addrHash, root common.Hash) (Trie, error) {
	return trie.NewSecure(root, db.db)
}

// CopyTrie returns an independent copy of the given trie.
func (db *cachingDB) CopyTrie(t Trie) Trie {
	switch t := t.(type) {
	case *trie.SecureTrie:
		return t.Copy()
	default:
		panic(fmt.Errorf("unknown trie type %T", t))
	}
}

// ContractCode retrieves a particular contract's code.
func (db *cachingDB) ContractCode(addrHash, codeHash common.Hash) ([]byte, error) {
	code, err := db.db.Node(codeHash)
	if err == nil {
		db.codeSizeCache.Add(codeHash, len(code))
	}
	return code, err
}

// ContractCodeSize retrieves a particular contracts code's size.
func (db *cachingDB) ContractCodeSize(addrHash, codeHash common.Hash) (int, error) {
	if cached, ok := db.codeSizeCache.Get(codeHash); ok {
		return cached.(int), nil
	}
	code, err := db.ContractCode(addrHash, codeHash)
	return len(code), err
}

// TrieDB retrieves any intermediate trie-node caching layer.
func (db *cachingDB) TrieDB() *trie.Database {
	return db.db
}