// Copyright 2023, Offchain Labs, Inc.
// For license information, see https://github.com/offchainlabs/bold/blob/main/LICENSE
// SPDX-License-Identifier: BUSL-1.1
//
pragma solidity ^0.8.17;

import "../challengeV2/IEdgeChallengeManager.sol";
import "../state/Deserialize.sol";

contract SimpleOneStepProofEntry is IOneStepProofEntry {
    using GlobalStateLib for GlobalState;

    // End the batch after 2000 steps. This results in 11 blocks for an honest validator.
    // This constant must be synchronized with the one in execution/engine.go
    uint64 public constant STEPS_PER_BATCH = 2000;

    function getStartMachineHash(
        bytes32 globalStateHash,
        bytes32 wasmModuleRoot
    ) external pure returns (bytes32) {
        return keccak256(abi.encodePacked("Machine:", globalStateHash, wasmModuleRoot));
    }

    function proveOneStep(
        ExecutionContext calldata execCtx,
        uint256 step,
        bytes32 beforeHash,
        bytes calldata proof
    ) external view returns (bytes32 afterHash) {
        if (proof.length == 0) {
            revert("EMPTY_PROOF");
        }
        GlobalState memory globalState;
        uint256 offset;
        (globalState.u64Vals[0], offset) = Deserialize.u64(proof, offset);
        (globalState.u64Vals[1], offset) = Deserialize.u64(proof, offset);
        if (step > 0 && (beforeHash[0] == 0 || globalState.getPositionInMessage() == 0)) {
            // We end the block when the first byte of the hash hits 0 or we advance a batch
            return beforeHash;
        }
        if (globalState.getInboxPosition() >= execCtx.maxInboxMessagesRead) {
            // We can't continue further because we've hit the max inbox messages read
            return beforeHash;
        }
        require(globalState.hash() == beforeHash, "BAD_PROOF");
        globalState.u64Vals[1]++;
        if (globalState.u64Vals[1] % STEPS_PER_BATCH == 0) {
            globalState.u64Vals[0]++;
            globalState.u64Vals[1] = 0;
        }
        return globalState.hash();
    }

    function getMachineHash(
        ExecutionState calldata execState
    ) external pure override returns (bytes32) {
        require(execState.machineStatus == MachineStatus.FINISHED, "BAD_MACHINE_STATUS");
        return execState.globalState.hash();
    }
}