// Copyright 2024 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 (
	"errors"
	"fmt"
	"time"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/hexutil"
	"github.com/ethereum/go-ethereum/core/rawdb"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/rlp"
	"github.com/ethereum/go-ethereum/triedb/database"
)

// The types of locations where the node is found.
const (
	locDirtyCache = "dirty" // dirty cache
	locCleanCache = "clean" // clean cache
	locDiskLayer  = "disk"  // persistent state
	locDiffLayer  = "diff"  // diff layers
)

// nodeLoc is a helpful structure that contains the location where the node
// is found, as it's useful for debugging purposes.
type nodeLoc struct {
	loc   string
	depth int
}

// string returns the string representation of node location.
func (loc *nodeLoc) string() string {
	return fmt.Sprintf("loc: %s, depth: %d", loc.loc, loc.depth)
}

// reader implements the database.NodeReader interface, providing the functionalities to
// retrieve trie nodes by wrapping the internal state layer.
type reader struct {
	db          *Database
	state       common.Hash
	noHashCheck bool
	layer       layer
}

// Node implements database.NodeReader interface, retrieving the node with specified
// node info. Don't modify the returned byte slice since it's not deep-copied
// and still be referenced by database.
func (r *reader) Node(owner common.Hash, path []byte, hash common.Hash) ([]byte, error) {
	blob, got, loc, err := r.layer.node(owner, path, 0)
	if err != nil {
		return nil, err
	}
	// Error out if the local one is inconsistent with the target.
	if !r.noHashCheck && got != hash {
		// Location is always available even if the node
		// is not found.
		switch loc.loc {
		case locCleanCache:
			nodeCleanFalseMeter.Mark(1)
		case locDirtyCache:
			nodeDirtyFalseMeter.Mark(1)
		case locDiffLayer:
			nodeDiffFalseMeter.Mark(1)
		case locDiskLayer:
			nodeDiskFalseMeter.Mark(1)
		}
		blobHex := "nil"
		if len(blob) > 0 {
			blobHex = hexutil.Encode(blob)
		}
		log.Error("Unexpected trie node", "location", loc.loc, "owner", owner.Hex(), "path", path, "expect", hash.Hex(), "got", got.Hex(), "blob", blobHex)
		return nil, fmt.Errorf("unexpected node: (%x %v), %x!=%x, %s, blob: %s", owner, path, hash, got, loc.string(), blobHex)
	}
	return blob, nil
}

// AccountRLP directly retrieves the account associated with a particular hash.
// An error will be returned if the read operation exits abnormally. Specifically,
// if the layer is already stale.
//
// Note:
// - the returned account data is not a copy, please don't modify it
// - no error will be returned if the requested account is not found in database
func (r *reader) AccountRLP(hash common.Hash) ([]byte, error) {
	l, err := r.db.tree.lookupAccount(hash, r.state)
	if err != nil {
		return nil, err
	}
	// If the located layer is stale, fall back to the slow path to retrieve
	// the account data. This is an edge case where the located layer is the
	// disk layer (e.g., the requested account was not changed in all the diff
	// layers), and it becomes stale within a very short time window.
	//
	// This fallback mechanism is essential, because the traversal starts from
	// the entry point layer and goes down, the staleness of the disk layer does
	// not affect the result unless the entry point layer is also stale.
	blob, err := l.account(hash, 0)
	if errors.Is(err, errSnapshotStale) {
		return r.layer.account(hash, 0)
	}
	return blob, err
}

// Account directly retrieves the account associated with a particular hash in
// the slim data format. An error will be returned if the read operation exits
// abnormally. Specifically, if the layer is already stale.
//
// Note:
// - the returned account object is safe to modify
// - no error will be returned if the requested account is not found in database
func (r *reader) Account(hash common.Hash) (*types.SlimAccount, error) {
	blob, err := r.AccountRLP(hash)
	if err != nil {
		return nil, err
	}
	if len(blob) == 0 {
		return nil, nil
	}
	account := new(types.SlimAccount)
	if err := rlp.DecodeBytes(blob, account); err != nil {
		panic(err)
	}
	return account, nil
}

// Storage directly retrieves the storage data associated with a particular hash,
// within a particular account. An error will be returned if the read operation
// exits abnormally. Specifically, if the layer is already stale.
//
// Note:
// - the returned storage data is not a copy, please don't modify it
// - no error will be returned if the requested slot is not found in database
func (r *reader) Storage(accountHash, storageHash common.Hash) ([]byte, error) {
	l, err := r.db.tree.lookupStorage(accountHash, storageHash, r.state)
	if err != nil {
		return nil, err
	}
	// If the located layer is stale, fall back to the slow path to retrieve
	// the storage data. This is an edge case where the located layer is the
	// disk layer (e.g., the requested account was not changed in all the diff
	// layers), and it becomes stale within a very short time window.
	//
	// This fallback mechanism is essential, because the traversal starts from
	// the entry point layer and goes down, the staleness of the disk layer does
	// not affect the result unless the entry point layer is also stale.
	blob, err := l.storage(accountHash, storageHash, 0)
	if errors.Is(err, errSnapshotStale) {
		return r.layer.storage(accountHash, storageHash, 0)
	}
	return blob, err
}

// NodeReader retrieves a layer belonging to the given state root.
func (db *Database) NodeReader(root common.Hash) (database.NodeReader, error) {
	layer := db.tree.get(root)
	if layer == nil {
		return nil, fmt.Errorf("state %#x is not available", root)
	}
	return &reader{
		db:          db,
		state:       root,
		noHashCheck: db.isVerkle,
		layer:       layer,
	}, nil
}

// StateReader returns a reader that allows access to the state data associated
// with the specified state.
func (db *Database) StateReader(root common.Hash) (database.StateReader, error) {
	layer := db.tree.get(root)
	if layer == nil {
		return nil, fmt.Errorf("state %#x is not available", root)
	}
	return &reader{
		db:    db,
		state: root,
		layer: layer,
	}, nil
}

// HistoricalStateReader is a wrapper over history reader, providing access to
// historical state.
type HistoricalStateReader struct {
	db     *Database
	reader *historyReader
	id     uint64
}

// HistoricReader constructs a reader for accessing the requested historic state.
func (db *Database) HistoricReader(root common.Hash) (*HistoricalStateReader, error) {
	// Bail out if the state history hasn't been fully indexed
	if db.indexer == nil || !db.indexer.inited() {
		return nil, errors.New("state histories haven't been fully indexed yet")
	}
	if db.freezer == nil {
		return nil, errors.New("state histories are not available")
	}
	// States at the current disk layer or above are directly accessible via
	// db.StateReader.
	//
	// States older than the current disk layer (including the disk layer
	// itself) are available through historic state access.
	//
	// Note: the requested state may refer to a stale historic state that has
	// already been pruned. This function does not validate availability, as
	// underlying states may be pruned dynamically. Validity is checked during
	// each actual state retrieval.
	id := rawdb.ReadStateID(db.diskdb, root)
	if id == nil {
		return nil, fmt.Errorf("state %#x is not available", root)
	}
	return &HistoricalStateReader{
		id:     *id,
		db:     db,
		reader: newHistoryReader(db.diskdb, db.freezer),
	}, nil
}

// AccountRLP directly retrieves the account RLP associated with a particular
// address in the slim data format. An error will be returned if the read
// operation exits abnormally. Specifically, if the layer is already stale.
//
// Note:
// - the returned account is not a copy, please don't modify it.
// - no error will be returned if the requested account is not found in database.
func (r *HistoricalStateReader) AccountRLP(address common.Address) ([]byte, error) {
	defer func(start time.Time) {
		historicalAccountReadTimer.UpdateSince(start)
	}(time.Now())

	// TODO(rjl493456442): Theoretically, the obtained disk layer could become stale
	// within a very short time window.
	//
	// While reading the account data while holding `db.tree.lock` can resolve
	// this issue, but it will introduce a heavy contention over the lock.
	//
	// Let's optimistically assume the situation is very unlikely to happen,
	// and try to define a low granularity lock if the current approach doesn't
	// work later.
	dl := r.db.tree.bottom()
	hash := crypto.Keccak256Hash(address.Bytes())
	latest, err := dl.account(hash, 0)
	if err != nil {
		return nil, err
	}
	return r.reader.read(newAccountIdentQuery(address, hash), r.id, dl.stateID(), latest)
}

// Account directly retrieves the account associated with a particular address in
// the slim data format. An error will be returned if the read operation exits
// abnormally. Specifically, if the layer is already stale.
//
// No error will be returned if the requested account is not found in database
func (r *HistoricalStateReader) Account(address common.Address) (*types.SlimAccount, error) {
	blob, err := r.AccountRLP(address)
	if err != nil {
		return nil, err
	}
	if len(blob) == 0 {
		return nil, nil
	}
	account := new(types.SlimAccount)
	if err := rlp.DecodeBytes(blob, account); err != nil {
		panic(err)
	}
	return account, nil
}

// Storage directly retrieves the storage data associated with a particular key,
// within a particular account. An error will be returned if the read operation
// exits abnormally. Specifically, if the layer is already stale.
//
// Note:
// - the returned storage data is not a copy, please don't modify it.
// - no error will be returned if the requested slot is not found in database.
func (r *HistoricalStateReader) Storage(address common.Address, key common.Hash) ([]byte, error) {
	defer func(start time.Time) {
		historicalStorageReadTimer.UpdateSince(start)
	}(time.Now())

	// TODO(rjl493456442): Theoretically, the obtained disk layer could become stale
	// within a very short time window.
	//
	// While reading the account data while holding `db.tree.lock` can resolve
	// this issue, but it will introduce a heavy contention over the lock.
	//
	// Let's optimistically assume the situation is very unlikely to happen,
	// and try to define a low granularity lock if the current approach doesn't
	// work later.
	dl := r.db.tree.bottom()
	addrHash := crypto.Keccak256Hash(address.Bytes())
	keyHash := crypto.Keccak256Hash(key.Bytes())
	latest, err := dl.storage(addrHash, keyHash, 0)
	if err != nil {
		return nil, err
	}
	return r.reader.read(newStorageIdentQuery(address, addrHash, key, keyHash), r.id, dl.stateID(), latest)
}
