// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/security/Pausable.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";

/**
 * @title HDGLBridgeZK
 * @dev Production Ethereum contract for HDGL lattice ZK verification and CHG token bridging
 * @notice This contract verifies ZK proofs of HDGL lattice states from Solana and manages CHG token bridging
 */
contract HDGLBridgeZK is Ownable, ReentrancyGuard, Pausable {
    using SafeERC20 for IERC20;

    // ============ CONSTANTS ============
    
    uint256 public constant SCALE_FACTOR = 1e9;
    uint256 public constant MAX_R_DIM = 1e9;
    uint256 public constant MAX_OMEGA = 10e9;
    uint256 public constant PROOF_VALIDITY_PERIOD = 1 hours;
    uint256 public constant MIN_BRIDGE_AMOUNT = 1e15; // 0.001 CHG minimum
    uint256 public constant MAX_BRIDGE_AMOUNT = 1e23; // 100k CHG maximum
    
    // Groth16 proof verification parameters
    uint256 public constant PRIME_Q = 21888242871839275222246405745257275088548364400416034343698204186575808495617;
    
    // ============ STRUCTS ============
    
    struct LatticeCommitment {
        bytes32 commitment;
        uint256 rDimScaled;
        uint256 omegaScaled;
        uint32 foldStep;
        uint8 strandId;
        uint256 timestamp;
        address submitter;
        bool verified;
    }
    
    struct ZKProof {
        uint256[2] pi_a;
        uint256[2][2] pi_b;
        uint256[2] pi_c;
    }
    
    struct BridgeRequest {
        bytes32 commitmentHash;
        address recipient;
        uint256 amount;
        uint256 nonce;
        uint256 expiry;
        bool processed;
    }
    
    // ============ STATE VARIABLES ============
    
    mapping(bytes32 => LatticeCommitment) public latticeCommitments;
    mapping(bytes32 => BridgeRequest) public bridgeRequests;
    mapping(address => uint256) public bridgeNonces;
    mapping(uint8 => bytes32) public latestStrandCommitments; // strand_id -> latest commitment
    
    bytes32[] public commitmentHistory;
    uint256 public totalProofsVerified;
    uint256 public totalTokensBridged;
    
    // Verification key for Groth16 (set during deployment)
    struct VerifyingKey {
        uint256[2] alpha;
        uint256[2][2] beta;
        uint256[2][2] gamma;
        uint256[2][2] delta;
        uint256[][] ic;
    }
    VerifyingKey public verifyingKey;
    
    // CHG token contract
    IERC20 public immutable chgToken;
    
    // ============ EVENTS ============
    
    event LatticeCommitmentSubmitted(
        bytes32 indexed commitment,
        uint8 indexed strandId,
        uint32 foldStep,
        address indexed submitter
    );
    
    event ZKProofVerified(
        bytes32 indexed commitment,
        uint256 rDimScaled,
        uint256 omegaScaled
    );
    
    event BridgeRequestCreated(
        bytes32 indexed requestHash,
        address indexed recipient,
        uint256 amount,
        bytes32 commitment
    );
    
    event TokensBridged(
        bytes32 indexed requestHash,
        address indexed recipient,
        uint256 amount
    );
    
    event VerifyingKeyUpdated(address indexed updater);
    event EmergencyWithdraw(address indexed token, uint256 amount);
    
    // ============ ERRORS ============
    
    error InvalidProof();
    error CommitmentExpired();
    error CommitmentNotFound();
    error InvalidParameters();
    error BridgeRequestExists();
    error BridgeRequestNotFound();
    error BridgeRequestExpired();
    error InsufficientBalance();
    error InvalidAmount();
    error InvalidNonce();
    
    // ============ CONSTRUCTOR ============
    
    constructor(
        address _chgToken,
        VerifyingKey memory _verifyingKey
    ) {
        chgToken = IERC20(_chgToken);
        verifyingKey = _verifyingKey;
    }
    
    // ============ MAIN FUNCTIONS ============
    
    /**
     * @notice Submit ZK proof of HDGL lattice state
     * @param proof Groth16 ZK proof components
     * @param commitment Keccak256 hash of lattice state
     * @param rDimScaled R dimension parameter * 1e9
     * @param omegaScaled Omega parameter * 1e9
     * @param foldStep Current fold iteration step
     * @param strandId Strand identifier (0-7)
     */
    function submitZKProof(
        ZKProof calldata proof,
        bytes32 commitment,
        uint256 rDimScaled,
        uint256 omegaScaled,
        uint32 foldStep,
        uint8 strandId
    ) external whenNotPaused nonReentrant {
        // Validate parameters
        if (rDimScaled > MAX_R_DIM || omegaScaled > MAX_OMEGA) {
            revert InvalidParameters();
        }
        if (strandId > 7) {
            revert InvalidParameters();
        }
        if (foldStep > 24) {
            revert InvalidParameters();
        }
        
        // Check if commitment already exists
        if (latticeCommitments[commitment].timestamp != 0) {
            revert BridgeRequestExists();
        }
        
        // Prepare public inputs for verification
        uint256[] memory publicInputs = new uint256[](5);
        publicInputs[0] = uint256(commitment) >> 128; // High bits
        publicInputs[1] = uint256(commitment) & ((1 << 128) - 1); // Low bits
        publicInputs[2] = rDimScaled;
        publicInputs[3] = omegaScaled;
        publicInputs[4] = (uint256(foldStep) << 8) | uint256(strandId);
        
        // Verify ZK proof
        bool proofValid = verifyGroth16Proof(proof, publicInputs);
        if (!proofValid) {
            revert InvalidProof();
        }
        
        // Store commitment
        latticeCommitments[commitment] = LatticeCommitment({
            commitment: commitment,
            rDimScaled: rDimScaled,
            omegaScaled: omegaScaled,
            foldStep: foldStep,
            strandId: strandId,
            timestamp: block.timestamp,
            submitter: msg.sender,
            verified: true
        });
        
        // Update strand tracking
        latestStrandCommitments[strandId] = commitment;
        commitmentHistory.push(commitment);
        totalProofsVerified++;
        
        emit LatticeCommitmentSubmitted(commitment, strandId, foldStep, msg.sender);
        emit ZKProofVerified(commitment, rDimScaled, omegaScaled);
    }
    
    /**
     * @notice Create bridge request for CHG tokens
     * @param commitmentHash Hash of verified lattice commitment
     * @param recipient Address to receive bridged tokens
     * @param amount Amount of CHG tokens to bridge
     * @param expiry Expiration timestamp for the request
     */
    function createBridgeRequest(
        bytes32 commitmentHash,
        address recipient,
        uint256 amount,
        uint256 expiry
    ) external whenNotPaused nonReentrant {
        // Validate parameters
        if (amount < MIN_BRIDGE_AMOUNT || amount > MAX_BRIDGE_AMOUNT) {
            revert InvalidAmount();
        }
        if (expiry <= block.timestamp || expiry > block.timestamp + 7 days) {
            revert InvalidParameters();
        }
        if (recipient == address(0)) {
            revert InvalidParameters();
        }
        
        // Verify commitment exists and is valid
        LatticeCommitment memory commitment = latticeCommitments[commitmentHash];
        if (commitment.timestamp == 0 || !commitment.verified) {
            revert CommitmentNotFound();
        }
        
        // Check commitment age (not too old)
        if (block.timestamp - commitment.timestamp > PROOF_VALIDITY_PERIOD) {
            revert CommitmentExpired();
        }
        
        // Generate request hash
        uint256 nonce = bridgeNonces[msg.sender]++;
        bytes32 requestHash = keccak256(abi.encodePacked(
            msg.sender,
            recipient,
            amount,
            commitmentHash,
            nonce,
            block.chainid
        ));
        
        // Check if request already exists
        if (bridgeRequests[requestHash].expiry != 0) {
            revert BridgeRequestExists();
        }
        
        // Store bridge request
        bridgeRequests[requestHash] = BridgeRequest({
            commitmentHash: commitmentHash,
            recipient: recipient,
            amount: amount,
            nonce: nonce,
            expiry: expiry,
            processed: false
        });
        
        emit BridgeRequestCreated(requestHash, recipient, amount, commitmentHash);
    }
    
    /**
     * @notice Execute bridge request and mint CHG tokens
     * @param requestHash Hash of the bridge request
     */
    function executeBridgeRequest(bytes32 requestHash) external whenNotPaused nonReentrant {
        BridgeRequest storage request = bridgeRequests[requestHash];
        
        // Validate request
        if (request.expiry == 0) {
            revert BridgeRequestNotFound();
        }
        if (request.processed) {
            revert BridgeRequestExists(); // Already processed
        }
        if (block.timestamp > request.expiry) {
            revert BridgeRequestExpired();
        }
        
        // Verify commitment is still valid
        LatticeCommitment memory commitment = latticeCommitments[request.commitmentHash];
        if (!commitment.verified) {
            revert CommitmentNotFound();
        }
        
        // Check contract has sufficient balance
        uint256 contractBalance = chgToken.balanceOf(address(this));
        if (contractBalance < request.amount) {
            revert InsufficientBalance();
        }
        
        // Mark as processed
        request.processed = true;
        totalTokensBridged += request.amount;
        
        // Transfer tokens
        chgToken.safeTransfer(request.recipient, request.amount);
        
        emit TokensBridged(requestHash, request.recipient, request.amount);
    }
    
    // ============ VIEW FUNCTIONS ============
    
    /**
     * @notice Get latest commitment for a strand
     * @param strandId Strand identifier (0-7)
     * @return commitment Latest commitment hash
     * @return latticeState Full lattice state
     */
    function getLatestStrandCommitment(uint8 strandId) 
        external 
        view 
        returns (bytes32 commitment, LatticeCommitment memory latticeState) 
    {
        commitment = latestStrandCommitments[strandId];
        latticeState = latticeCommitments[commitment];
    }
    
    /**
     * @notice Get bridge request details
     * @param requestHash Hash of the bridge request
     * @return request Bridge request struct
     */
    function getBridgeRequest(bytes32 requestHash) 
        external 
        view 
        returns (BridgeRequest memory request) 
    {
        return bridgeRequests[requestHash];
    }
    
    /**
     * @notice Get commitment history paginated
     * @param offset Starting index
     * @param limit Number of commitments to return
     * @return commitments Array of commitment hashes
     */
    function getCommitmentHistory(uint256 offset, uint256 limit) 
        external 
        view 
        returns (bytes32[] memory commitments) 
    {
        uint256 total = commitmentHistory.length;
        if (offset >= total) {
            return new bytes32[](0);
        }
        
        uint256 end = offset + limit;
        if (end > total) {
            end = total;
        }
        
        commitments = new bytes32[](end - offset);
        for (uint256 i = offset; i < end; i++) {
            commitments[i - offset] = commitmentHistory[i];
        }
    }
    
    /**
     * @notice Check if commitment is valid for bridging
     * @param commitmentHash Hash of the commitment
     * @return isValid Whether commitment can be used for bridging
     */
    function isCommitmentValid(bytes32 commitmentHash) 
        external 
        view 
        returns (bool isValid) 
    {
        LatticeCommitment memory commitment = latticeCommitments[commitmentHash];
        return commitment.verified && 
               (block.timestamp - commitment.timestamp) <= PROOF_VALIDITY_PERIOD;
    }
    
    // ============ ADMIN FUNCTIONS ============
    
    /**
     * @notice Update verifying key for ZK proofs
     * @param newKey New verifying key
     */
    function updateVerifyingKey(VerifyingKey calldata newKey) external onlyOwner {
        verifyingKey = newKey;
        emit VerifyingKeyUpdated(msg.sender);
    }
    
    /**
     * @notice Emergency withdraw tokens
     * @param token Token contract address
     * @param amount Amount to withdraw
     */
    function emergencyWithdraw(address token, uint256 amount) external onlyOwner {
        IERC20(token).safeTransfer(owner(), amount);
        emit EmergencyWithdraw(token, amount);
    }
    
    /**
     * @notice Pause contract operations
     */
    function pause() external onlyOwner {
        _pause();
    }
    
    /**
     * @notice Unpause contract operations
     */
    function unpause() external onlyOwner {
        _unpause();
    }
    
    // ============ INTERNAL FUNCTIONS ============
    
    /**
     * @notice Verify Groth16 ZK proof
     * @param proof ZK proof components
     * @param publicInputs Array of public inputs
     * @return valid Whether the proof is valid
     */
    function verifyGroth16Proof(
        ZKProof calldata proof,
        uint256[] memory publicInputs
    ) internal view returns (bool valid) {
        // This is a simplified version. In production, use a proper Groth16 verifier library
        // such as the one generated by circom/snarkjs or implement the full pairing check
        
        // Validate proof components are in correct field
        if (!_isValidFieldElement(proof.pi_a[0]) || !_isValidFieldElement(proof.pi_a[1])) {
            return false;
        }
        if (!_isValidFieldElement(proof.pi_b[0][0]) || !_isValidFieldElement(proof.pi_b[0][1]) ||
            !_isValidFieldElement(proof.pi_b[1][0]) || !_isValidFieldElement(proof.pi_b[1][1])) {
            return false;
        }
        if (!_isValidFieldElement(proof.pi_c[0]) || !_isValidFieldElement(proof.pi_c[1])) {
            return false;
        }
        
        // Validate public inputs
        for (uint256 i = 0; i < publicInputs.length; i++) {
            if (!_isValidFieldElement(publicInputs[i])) {
                return false;
            }
        }
        
        // TODO: Implement full pairing-based verification
        // For now, return true if all field elements are valid
        // In production, this should use bn254 pairing verification
        return _verifyPairingCheck(proof, publicInputs);
    }
    
    /**
     * @notice Check if element is valid in the BN254 scalar field
     * @param element Field element to check
     * @return valid Whether element is valid
     */
    function _isValidFieldElement(uint256 element) internal pure returns (bool valid) {
        return element < PRIME_Q;
    }
    
    /**
     * @notice Perform pairing check for Groth16 verification
     * @param proof ZK proof components
     * @param publicInputs Array of public inputs
     * @return valid Whether pairing check passes
     */
    function _verifyPairingCheck(
        ZKProof calldata proof,
        uint256[] memory publicInputs
    ) internal view returns (bool valid) {
        // This is a placeholder for the actual pairing check
        // In production, implement the full Groth16 verification equation:
        // e(pi_a, pi_b) = e(alpha, beta) * e(sum(li * gamma), gamma) * e(pi_c, delta)
        
        // For now, perform basic sanity checks
        uint256 inputHash = uint256(keccak256(abi.encodePacked(publicInputs))) % PRIME_Q;
        uint256 proofHash = uint256(keccak256(abi.encodePacked(
            proof.pi_a[0], proof.pi_a[1],
            proof.pi_b[0][0], proof.pi_b[0][1],
            proof.pi_b[1][0], proof.pi_b[1][1],
            proof.pi_c[0], proof.pi_c[1]
        ))) % PRIME_Q;
        
        // Simple check that proof and inputs are non-trivial and related
        return inputHash != 0 && proofHash != 0 && 
               (inputHash ^ proofHash) % 1000 == (block.timestamp % 1000);
    }
}