// SPDX-License-Identifier: BUSL-1.1
pragma solidity 0.8.24;

import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import {SafeERC20} from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import {ReentrancyGuard} from "@openzeppelin/contracts/utils/ReentrancyGuard.sol";
import {IUSDR} from "./interfaces/IUSDR.sol";

/// @title EmergencySettlement — global shutdown, last resort (White Paper v3.2 §7 step 5)
/// @notice One-way switch (timelock-gated). After trigger, USDR holders claim a
///         pro-rata share of every registered collateral pool at $1 valuation.
///         "Loss is bounded, tiered, and transparent — never an all-erasing spiral."
contract EmergencySettlement is ReentrancyGuard {
    using SafeERC20 for IERC20;

    error NotTimelock();
    error NotTriggered();
    error AlreadyTriggered();
    error NothingToClaim();

    IUSDR public immutable usdr;
    address public immutable timelock;

    bool public triggered;
    uint256 public supplySnapshot;
    address[] public assets; // all collateral + stables registered at trigger time
    mapping(address => uint256) public assetSnapshot; // balances captured at trigger

    event Triggered(uint256 supplySnapshot);
    event Claimed(address indexed holder, uint256 usdrBurned);

    constructor(address _usdr, address _timelock) {
        usdr = IUSDR(_usdr);
        timelock = _timelock;
    }

    /// @notice Trigger shutdown. Asset holders (vault, reserve, escrow) must have
    ///         approved/transferred pools here as part of the governance action.
    function trigger(address[] calldata _assets) external {
        if (msg.sender != timelock) revert NotTimelock();
        if (triggered) revert AlreadyTriggered();
        triggered = true;
        supplySnapshot = usdr.totalSupply();
        for (uint256 i = 0; i < _assets.length; i++) {
            assets.push(_assets[i]);
            assetSnapshot[_assets[i]] = IERC20(_assets[i]).balanceOf(address(this));
        }
        emit Triggered(supplySnapshot);
    }

    /// @notice Burn USDR, receive pro-rata share of every asset in the pool.
    function claim(uint256 usdrAmount) external nonReentrant {
        if (!triggered) revert NotTriggered();
        if (usdrAmount == 0) revert NothingToClaim();
        usdr.burn(msg.sender, usdrAmount);
        for (uint256 i = 0; i < assets.length; i++) {
            uint256 share = assetSnapshot[assets[i]] * usdrAmount / supplySnapshot;
            if (share > 0) IERC20(assets[i]).safeTransfer(msg.sender, share);
        }
        emit Claimed(msg.sender, usdrAmount);
    }
}