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

/**
 * StarPostSeal — Tamper-proof timestamping for Star Post letters.
 *
 * Each postcard sealed by Star Post emits a permanent on-chain record containing:
 *   - The order ID (e.g. "SP-XXXXXX")
 *   - A SHA-256 hash of the encrypted postcard content
 *   - The scheduled delivery date (Unix timestamp)
 *   - The seal timestamp (block.timestamp)
 *
 * Anyone can verify a postcard's integrity by:
 *   1. Looking up the order ID on Polygonscan
 *   2. Checking the dataHash matches the encrypted file they hold
 *   3. Confirming the delivery date was set at sealing time
 *
 * This creates a 50-year-proof public record that no one —
 * including Star Post — can alter after sealing.
 */
contract StarPostSeal {

    event PostcardSealed(
        string  indexed orderId,
        bytes32         dataHash,
        uint256         deliveryDate,
        uint256         sealedAt
    );

    address public immutable owner;

    constructor() {
        owner = msg.sender;
    }

    modifier onlyOwner() {
        require(msg.sender == owner, "StarPostSeal: not owner");
        _;
    }

    /**
     * Seal a postcard on-chain.
     *
     * @param orderId       Star Post order ID, e.g. "SP-AB12CD"
     * @param dataHash      SHA-256 hash of (orderId + encryptedImageHex + deliveryDateISO)
     * @param deliveryDate  Scheduled delivery as Unix timestamp
     */
    function seal(
        string  calldata orderId,
        bytes32          dataHash,
        uint256          deliveryDate
    ) external onlyOwner {
        emit PostcardSealed(orderId, dataHash, deliveryDate, block.timestamp);
    }
}