// SPDX-License-Identifier: MIT
pragma solidity 0.8.23;

import "@openzeppelin/contracts/security/ReentrancyGuard.sol";

/**
 * @title AereSlashingInsurance — delegator slashing-loss coverage vault (native AERE)
 * @notice A discretion fund that reimburses a portion of the loss a DELEGATOR
 *         suffers when a validator they delegated to is slashed. It custodies
 *         NATIVE AERE only. It is NOT a token: it mints nothing, has no balances
 *         of its own units, and issues no transferable claim on itself. It simply
 *         holds native AERE and can pay some of it out, under strict rules, to a
 *         slashed delegator.
 *
 *         MECHANICS
 *           1. Anyone can fund it (permissionless `donate`, or a plain transfer
 *              caught by `receive`). Funds are sticky.
 *           2. Coverage is a 2-step, timelocked process so a single key cannot
 *              instantly move money:
 *                a. Foundation calls `proposeCoverage(delegator, slashedAmount,
 *                   evidenceHash)`. Payout is computed at proposal time as
 *                   min(slashedAmount * COVERAGE_BPS / 10000, PER_EVENT_CAP) and
 *                   frozen into the claim. A claim becomes executable only after
 *                   CLAIM_DELAY.
 *                b. During the delay, ANYONE may `cancelCoverage` a claim they
 *                   believe is fraudulent (e.g. a compromised Foundation key
 *                   proposing a payout to itself). Cancellation is permissionless.
 *                c. After the delay, `executeCoverage` pays the FROZEN payout to
 *                   the FROZEN delegator address. The recipient cannot be
 *                   redirected after proposal.
 *           3. Per-event cap (PER_EVENT_CAP) bounds any single payout; a global
 *              COOLDOWN_SECONDS between executed coverages bounds the drain RATE.
 *           4. NO admin withdrawal. There is no function that lets the Foundation
 *              (or anyone) pull principal to an arbitrary address. The ONLY outflow
 *              is `executeCoverage` paying the delegator named in a claim that
 *              survived the public delay window.
 *
 *         TRUST MODEL (same shape as AereInsuranceFund)
 *           - Foundation key compromise alone  = NO loss (community cancels the
 *             pending claim during CLAIM_DELAY).
 *           - Foundation key compromise + an undetected full CLAIM_DELAY window
 *             = at most PER_EVENT_CAP per COOLDOWN_SECONDS can be drained.
 *           This is materially weaker than "cannot rug" but materially stronger
 *           than "can rug at will".
 */
contract AereSlashingInsurance is ReentrancyGuard {

    /* ------------------------------- immutable ------------------------------ */

    address public immutable FOUNDATION;
    uint16  public immutable COVERAGE_BPS;      // fraction of a slash covered, <= 10000
    uint256 public immutable PER_EVENT_CAP;     // max native AERE paid per coverage
    uint64  public immutable COOLDOWN_SECONDS;  // min seconds between executed coverages
    uint64  public immutable CLAIM_DELAY;       // timelock between propose and execute
    uint16  public constant BPS_DENOM = 10000;

    /* --------------------------------- state -------------------------------- */

    struct Claim {
        bool    exists;
        address delegator;      // frozen recipient
        uint256 slashedAmount;  // reported loss (informational)
        uint256 payout;         // frozen native AERE payout
        uint64  readyAt;        // executable at/after this timestamp
        bytes32 evidenceHash;   // off-chain evidence pointer (slashing tx / report)
    }

    mapping(uint256 => Claim) public claims;
    uint256 public nextClaimId;

    uint256 public totalDonated;
    uint256 public totalCovered;
    uint64  public lastCoverageAt;

    /* --------------------------------- events ------------------------------- */

    event Donated(address indexed donor, uint256 amount, uint256 newBalance);
    event CoverageProposed(
        uint256 indexed claimId, address indexed delegator, uint256 slashedAmount,
        uint256 payout, uint64 readyAt, bytes32 evidenceHash
    );
    event CoverageCancelled(uint256 indexed claimId, address indexed canceller, string reason);
    event CoveragePaid(uint256 indexed claimId, address indexed delegator, uint256 payout);

    /* --------------------------------- errors ------------------------------- */

    error NotFoundation();
    error ZeroAddress();
    error ZeroAmount();
    error BadBps();
    error NoClaim();
    error TimelockNotElapsed(uint64 readyAt);
    error CooldownActive(uint256 readyAt);
    error InsufficientBalance(uint256 have, uint256 want);
    error PayFailed();

    /* ------------------------------- modifiers ------------------------------ */

    modifier onlyFoundation() {
        if (msg.sender != FOUNDATION) revert NotFoundation();
        _;
    }

    /* ------------------------------ constructor ----------------------------- */

    constructor(
        address foundation,
        uint16  coverageBps,
        uint256 perEventCap,
        uint64  cooldownSeconds,
        uint64  claimDelay
    ) {
        if (foundation == address(0)) revert ZeroAddress();
        if (coverageBps == 0 || coverageBps > BPS_DENOM) revert BadBps();
        if (perEventCap == 0) revert ZeroAmount();
        FOUNDATION = foundation;
        COVERAGE_BPS = coverageBps;
        PER_EVENT_CAP = perEventCap;
        COOLDOWN_SECONDS = cooldownSeconds;
        CLAIM_DELAY = claimDelay;
    }

    /* -------------------------------- funding ------------------------------- */

    receive() external payable {
        totalDonated += msg.value;
        emit Donated(msg.sender, msg.value, address(this).balance);
    }

    function donate() external payable {
        if (msg.value == 0) revert ZeroAmount();
        totalDonated += msg.value;
        emit Donated(msg.sender, msg.value, address(this).balance);
    }

    /* ------------------------------- coverage ------------------------------- */

    /// @notice Foundation proposes coverage for a slashed delegator. Payout is
    ///         frozen now and only becomes executable after CLAIM_DELAY, during
    ///         which anyone may cancel a suspicious claim.
    function proposeCoverage(address delegator, uint256 slashedAmount, bytes32 evidenceHash)
        external onlyFoundation returns (uint256 claimId)
    {
        if (delegator == address(0)) revert ZeroAddress();
        if (slashedAmount == 0) revert ZeroAmount();
        uint256 payout = (slashedAmount * COVERAGE_BPS) / BPS_DENOM;
        if (payout > PER_EVENT_CAP) payout = PER_EVENT_CAP;
        if (payout == 0) revert ZeroAmount();
        uint64 readyAt = uint64(block.timestamp) + CLAIM_DELAY;
        claimId = nextClaimId++;
        claims[claimId] = Claim({
            exists: true,
            delegator: delegator,
            slashedAmount: slashedAmount,
            payout: payout,
            readyAt: readyAt,
            evidenceHash: evidenceHash
        });
        emit CoverageProposed(claimId, delegator, slashedAmount, payout, readyAt, evidenceHash);
    }

    /// @notice Permissionless: cancel a pending claim during its delay window.
    ///         Lets community observers block a fraudulent proposal before it can
    ///         be executed. Foundation can re-propose a legitimate claim.
    function cancelCoverage(uint256 claimId, string calldata reason) external {
        if (!claims[claimId].exists) revert NoClaim();
        delete claims[claimId];
        emit CoverageCancelled(claimId, msg.sender, reason);
    }

    /// @notice Execute a matured claim: pay the frozen payout to the frozen
    ///         delegator. Callable by anyone once the timelock has elapsed (the
    ///         recipient and amount are fixed, so a third-party trigger cannot
    ///         redirect funds). Enforces the global cooldown between payouts.
    function executeCoverage(uint256 claimId) external nonReentrant {
        Claim memory c = claims[claimId];
        if (!c.exists) revert NoClaim();
        if (block.timestamp < uint256(c.readyAt)) revert TimelockNotElapsed(c.readyAt);
        if (lastCoverageAt != 0 && block.timestamp < uint256(lastCoverageAt) + COOLDOWN_SECONDS) {
            revert CooldownActive(uint256(lastCoverageAt) + COOLDOWN_SECONDS);
        }
        uint256 bal = address(this).balance;
        if (bal < c.payout) revert InsufficientBalance(bal, c.payout);

        // effects before interaction
        delete claims[claimId];
        totalCovered += c.payout;
        lastCoverageAt = uint64(block.timestamp);

        (bool ok, ) = payable(c.delegator).call{value: c.payout}("");
        if (!ok) revert PayFailed();
        emit CoveragePaid(claimId, c.delegator, c.payout);
    }

    /* ---------------------------------- views ------------------------------- */

    /// @notice Preview the frozen payout for a given reported slash amount.
    function coverageFor(uint256 slashedAmount) external view returns (uint256 payout) {
        payout = (slashedAmount * COVERAGE_BPS) / BPS_DENOM;
        if (payout > PER_EVENT_CAP) payout = PER_EVENT_CAP;
    }

    /// @notice Native AERE currently available to pay coverage.
    function available() external view returns (uint256) {
        return address(this).balance;
    }

    /// @notice True if the global cooldown permits an execution right now.
    function cooldownReady() external view returns (bool) {
        if (lastCoverageAt == 0) return true;
        return block.timestamp >= uint256(lastCoverageAt) + COOLDOWN_SECONDS;
    }
}