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

/// One bounded, public wallet roster; not a ticket, verified identity or admission guarantee.
contract EventryxSession {
    uint16 public immutable capacity;
    uint16 public participants;
    mapping(address => bool) public joined;
    event Joined(address indexed participant, uint16 occupied);
    event Left(address indexed participant, uint16 occupied);
    error InvalidCapacity(); error AlreadyJoined(); error SessionFull(); error NotJoined();
    constructor(uint16 capacity_) {
        if (capacity_ == 0 || capacity_ > 500) revert InvalidCapacity();
        capacity = capacity_;
    }
    function join() external {
        if (joined[msg.sender]) revert AlreadyJoined();
        if (participants >= capacity) revert SessionFull();
        joined[msg.sender] = true; ++participants;
        emit Joined(msg.sender, participants);
    }
    function leave() external {
        if (!joined[msg.sender]) revert NotJoined();
        joined[msg.sender] = false; --participants;
        emit Left(msg.sender, participants);
    }
}