// Copyright 2023 The XDC Network Authors
// This file is part of the XDC Network library.
//
// The XDC Network 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.

// Package les implements the Light Ethereum Subprotocol.
package les

import (
	"context"
	"math/big"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/core/state"
	"github.com/ethereum/go-ethereum/core/types"
)

// XDCApiBackend implements XDPoS-specific API methods for light clients
type XDCApiBackend struct {
	// Embed the base LesApiBackend
	// LesApiBackend
}

// GetMasternodesXDC returns the masternode list for an epoch (light client version)
func (b *XDCApiBackend) GetMasternodesXDC(ctx context.Context, epoch uint64) ([]common.Address, error) {
	// Light clients would fetch this from full nodes
	// This is a placeholder implementation
	return nil, nil
}

// GetCandidatesXDC returns the candidate list for an epoch (light client version)
func (b *XDCApiBackend) GetCandidatesXDC(ctx context.Context, epoch uint64) ([]common.Address, error) {
	// Light clients would fetch this from full nodes
	return nil, nil
}

// GetEpochXDC returns the epoch number for a block
func (b *XDCApiBackend) GetEpochXDC(ctx context.Context, blockNumber uint64) (uint64, error) {
	// Would be calculated from block number and epoch size
	return 0, nil
}

// GetBlockSignerXDC returns the signer of a block
func (b *XDCApiBackend) GetBlockSignerXDC(ctx context.Context, blockHash common.Hash) (common.Address, error) {
	// Light clients would need to verify this from header
	return common.Address{}, nil
}

// GetPenalizedValidatorsXDC returns the penalized validators for an epoch
func (b *XDCApiBackend) GetPenalizedValidatorsXDC(ctx context.Context, epoch uint64) ([]common.Address, error) {
	return nil, nil
}

// LightChainReaderXDC interface for light chain XDPoS access
type LightChainReaderXDC interface {
	// GetHeaderByNumber retrieves a header by number
	GetHeaderByNumber(ctx context.Context, number uint64) (*types.Header, error)
	
	// GetHeaderByHash retrieves a header by hash
	GetHeaderByHash(ctx context.Context, hash common.Hash) (*types.Header, error)
	
	// GetTd retrieves total difficulty
	GetTd(ctx context.Context, hash common.Hash) (*big.Int, error)
	
	// CurrentHeader returns the current header
	CurrentHeader() *types.Header
}

// XDCLightSyncConfig contains light client sync configuration for XDPoS
type XDCLightSyncConfig struct {
	// Whether to sync masternode data
	SyncMasternodes bool
	
	// Whether to sync validator data
	SyncValidators bool
	
	// Checkpoint block hash for initial sync
	CheckpointHash common.Hash
	
	// Checkpoint block number
	CheckpointNumber uint64
}

// XDCLightVerifier verifies XDPoS data for light clients
type XDCLightVerifier struct {
	chain LightChainReaderXDC
}

// NewXDCLightVerifier creates a new light verifier
func NewXDCLightVerifier(chain LightChainReaderXDC) *XDCLightVerifier {
	return &XDCLightVerifier{chain: chain}
}

// VerifyHeader verifies a header for light client
func (v *XDCLightVerifier) VerifyHeader(ctx context.Context, header *types.Header) error {
	// Verify header based on XDPoS rules
	// Light clients need to verify:
	// 1. Block is signed by a valid masternode
	// 2. Block number is correct
	// 3. Parent hash matches
	return nil
}

// VerifySignature verifies a block signature
func (v *XDCLightVerifier) VerifySignature(ctx context.Context, header *types.Header) (common.Address, error) {
	// Extract signer from header
	// Verify signature is valid
	return common.Address{}, nil
}

// VerifyMasternode verifies a signer is a valid masternode
func (v *XDCLightVerifier) VerifyMasternode(ctx context.Context, signer common.Address, blockNumber uint64) (bool, error) {
	// Check if signer was a masternode at the given block
	return false, nil
}

// XDCODRBackend interface for On-Demand Retrieval of XDPoS data
type XDCODRBackend interface {
	// RetrieveMasternodes retrieves masternode list from network
	RetrieveMasternodes(ctx context.Context, epoch uint64) ([]common.Address, error)
	
	// RetrieveValidatorState retrieves validator state
	RetrieveValidatorState(ctx context.Context, address common.Address, blockHash common.Hash) (*state.StateDB, error)
}

// XDCLightCheckpoint represents a checkpoint for light client sync
type XDCLightCheckpoint struct {
	BlockNumber  uint64           `json:"blockNumber"`
	BlockHash    common.Hash      `json:"blockHash"`
	Epoch        uint64           `json:"epoch"`
	Masternodes  []common.Address `json:"masternodes"`
	StateRoot    common.Hash      `json:"stateRoot"`
	TotalStake   *big.Int         `json:"totalStake"`
}

// ValidateCheckpoint validates a checkpoint
func ValidateCheckpoint(checkpoint *XDCLightCheckpoint, header *types.Header) error {
	// Verify checkpoint matches header
	if checkpoint.BlockHash != header.Hash() {
		return ErrCheckpointMismatch
	}
	if checkpoint.StateRoot != header.Root {
		return ErrCheckpointMismatch
	}
	return nil
}

// Errors
var (
	ErrCheckpointMismatch = &CheckpointError{"checkpoint hash mismatch"}
	ErrInvalidSignature   = &CheckpointError{"invalid block signature"}
	ErrNotMasternode      = &CheckpointError{"signer is not a masternode"}
)

type CheckpointError struct {
	message string
}

func (e *CheckpointError) Error() string {
	return e.message
}