// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

/**
 * @title NaddieJump
 * @notice On-chain leaderboard and reward contract for Naddie Jump game.
 * @dev Designed for Monad EVM compatibility.
 */
contract NaddieJump {
    struct Score {
        address player;
        uint256 score;
        uint256 blockHeight;
        uint256 timestamp;
    }

    mapping(address => Score) public bestScores;
    Score[] public leaderboard;
    uint256 public constant LEADERBOARD_SIZE = 50;
    uint256 public constant REWARD_THRESHOLD = 50000;

    event ScoreSubmitted(address indexed player, uint256 score, uint256 blockHeight);
    event RewardClaimed(address indexed player, uint256 amount);

    function submitScore(uint256 score, uint256 blockHeight) external {
        require(score > 0, "Invalid score");

        Score storage current = bestScores[msg.sender];
        if (score > current.score) {
            current.player = msg.sender;
            current.score = score;
            current.blockHeight = blockHeight;
            current.timestamp = block.timestamp;
            _updateLeaderboard(current);
        }

        emit ScoreSubmitted(msg.sender, score, blockHeight);
    }

    function _updateLeaderboard(Score memory newScore) internal {
        // Simple insertion sort approach for leaderboard
        bool exists = false;
        for (uint256 i = 0; i < leaderboard.length; i++) {
            if (leaderboard[i].player == newScore.player) {
                leaderboard[i] = newScore;
                exists = true;
                break;
            }
        }
        if (!exists && leaderboard.length < LEADERBOARD_SIZE) {
            leaderboard.push(newScore);
        }
        // Sort descending by score (bubble sort for simplicity in prototype)
        for (uint256 i = 0; i < leaderboard.length; i++) {
            for (uint256 j = i + 1; j < leaderboard.length; j++) {
                if (leaderboard[j].score > leaderboard[i].score) {
                    Score memory tmp = leaderboard[i];
                    leaderboard[i] = leaderboard[j];
                    leaderboard[j] = tmp;
                }
            }
        }
    }

    function getLeaderboard(uint256 count) external view returns (Score[] memory) {
        uint256 len = count > leaderboard.length ? leaderboard.length : count;
        Score[] memory result = new Score[](len);
        for (uint256 i = 0; i < len; i++) {
            result[i] = leaderboard[i];
        }
        return result;
    }

    function getPlayerBest(address player) external view returns (Score memory) {
        return bestScores[player];
    }

    // Placeholder for future ERC-20 reward integration
    function claimReward() external view returns (bool eligible) {
        Score storage s = bestScores[msg.sender];
        eligible = s.score >= REWARD_THRESHOLD;
        // TODO: mint/transfer ERC-20 $GWEI tokens
    }
}