// Copyright 2025 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 overlay

import (
	"fmt"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/params"
	"github.com/ethereum/go-ethereum/triedb/database"
)

// TransitionState is a structure that holds the progress markers of the
// translation process.
// TODO gballet:
// * see if I can get rid of the pointer now that this piece
// has been rewritten.
// * the conversion pointers should no longer be necessary,
// remove them when it's been confirmed.
// * we can't keep the preimage offset in the file, since
// some clients might decide to record their preimages and
// skip the use of the file altogether. Therefore, they can't
// know what the offset it, unless they keep track of how many
// bytes have been read since the start, which is a possibility.
type TransitionState struct {
	CurrentAccountAddress *common.Address // addresss of the last translated account
	CurrentSlotHash       common.Hash     // hash of the last translated storage slot
	CurrentPreimageOffset int64           // next byte to read from the preimage file
	Started, Ended        bool

	// Mark whether the storage for an account has been processed. This is useful if the
	// maximum number of leaves of the conversion is reached before the whole storage is
	// processed.
	StorageProcessed bool

	BaseRoot common.Hash // hash of the last read-only MPT base tree
}

// InTransition returns true if the translation process is in progress.
func (ts *TransitionState) InTransition() bool {
	return ts != nil && ts.Started && !ts.Ended
}

// Transitioned returns true if the translation process has been completed.
func (ts *TransitionState) Transitioned() bool {
	return ts != nil && ts.Ended
}

// Copy returns a deep copy of the TransitionState object.
func (ts *TransitionState) Copy() *TransitionState {
	ret := &TransitionState{
		Started:               ts.Started,
		Ended:                 ts.Ended,
		CurrentSlotHash:       ts.CurrentSlotHash,
		CurrentPreimageOffset: ts.CurrentPreimageOffset,
		StorageProcessed:      ts.StorageProcessed,
		BaseRoot:              ts.BaseRoot,
	}
	if ts.CurrentAccountAddress != nil {
		addr := *ts.CurrentAccountAddress
		ret.CurrentAccountAddress = &addr
	}
	return ret
}

var (
	conversionProgressAddressKey       = common.Hash{1}
	conversionProgressSlotKey          = common.Hash{2}
	conversionProgressStorageProcessed = common.Hash{3}
)

// LoadTransitionState retrieves the Verkle transition state associated with
// the given state root hash from the database.
func LoadTransitionState(reader database.StateReader, root common.Hash) *TransitionState {
	addrHash := crypto.Keccak256Hash(params.BinaryTransitionRegistryAddress[:])
	currentAccountBytes, err := reader.Storage(addrHash, conversionProgressAddressKey)
	if err != nil {
		panic(fmt.Errorf("error reading conversion account pointer: %w", err))
	}
	currentAccount := common.BytesToAddress(currentAccountBytes[12:])

	currentSlotBytes, err := reader.Storage(addrHash, conversionProgressSlotKey)
	if err != nil {
		panic(fmt.Errorf("error reading conversion slot pointer: %w", err))
	}
	currentSlotHash := common.BytesToHash(currentSlotBytes)

	storageProcessedBytes, err := reader.Storage(addrHash, conversionProgressStorageProcessed)
	if err != nil {
		panic(fmt.Errorf("error reading conversion storage processing completion status: %w", err))
	}
	storageProcessed := storageProcessedBytes[0] == 1

	return &TransitionState{
		CurrentAccountAddress: &currentAccount,
		CurrentSlotHash:       currentSlotHash,
		StorageProcessed:      storageProcessed,
	}
}