// SPDX-License-Identifier: MIT
pragma solidity 0.8.30;

/// @notice A public fixed schedule of wallet reservations, not proof of a real service booking.
contract SlotryxSchedule {
    struct Reservation { address holder; uint64 version; }
    uint64 public immutable startTime;
    uint32 public immutable slotDuration;
    uint16 public immutable slotCount;
    mapping(uint16 => Reservation) public reservations;
    event Reserved(uint16 indexed slot, address indexed holder, uint64 version);
    event Released(uint16 indexed slot, address indexed holder, uint64 version);
    error InvalidSchedule(); error InvalidSlot(); error SlotStarted();
    error VersionChanged(); error Occupied(); error NotHolder();

    constructor(uint64 startTime_, uint32 slotDuration_, uint16 slotCount_) {
        if (startTime_ <= block.timestamp || slotDuration_ < 60 || slotDuration_ > 86400 || slotCount_ == 0 || slotCount_ > 128 || uint256(startTime_) + uint256(slotDuration_) * slotCount_ > type(uint64).max) revert InvalidSchedule();
        startTime = startTime_;
        slotDuration = slotDuration_;
        slotCount = slotCount_;
    }

    function slotStart(uint16 slot) public view returns (uint64) {
        if (slot >= slotCount) revert InvalidSlot();
        return startTime + uint64(slot) * slotDuration;
    }

    function reserve(uint16 slot, uint64 expectedVersion) external {
        if (block.timestamp >= slotStart(slot)) revert SlotStarted();
        Reservation storage r = reservations[slot];
        if (r.version != expectedVersion) revert VersionChanged();
        if (r.holder != address(0)) revert Occupied();
        r.holder = msg.sender;
        ++r.version;
        emit Reserved(slot, msg.sender, r.version);
    }

    function release(uint16 slot, uint64 expectedVersion) external {
        if (block.timestamp >= slotStart(slot)) revert SlotStarted();
        Reservation storage r = reservations[slot];
        if (r.version != expectedVersion) revert VersionChanged();
        if (r.holder != msg.sender) revert NotHolder();
        r.holder = address(0);
        ++r.version;
        emit Released(slot, msg.sender, r.version);
    }
}