// SPDX-License-Identifier: MIT
pragma solidity >0.5.0 <0.9.0;

/* Library Imports */
import { Lib_OVMCodec } from "../../libraries/codec/Lib_OVMCodec.sol";

/* Interface Imports */
import { IChainStorageContainer } from "./IChainStorageContainer.sol";

/**
 * @title ICanonicalTransactionChain
 */
interface ICanonicalTransactionChain {
    /**********
     * Events *
     **********/

    event L2GasParamsUpdated(
        uint256 l2GasDiscountDivisor,
        uint256 enqueueGasCost,
        uint256 enqueueL2GasPrepaid
    );

    event TransactionEnqueued(
        address indexed _l1TxOrigin,
        address indexed _target,
        uint256 _gasLimit,
        bytes _data,
        uint256 indexed _queueIndex,
        uint256 _timestamp
    );

    event QueueBatchAppended(
        uint256 _startingQueueIndex,
        uint256 _numQueueElements,
        uint256 _totalElements
    );

    event SequencerBatchAppended(
        uint256 _startingQueueIndex,
        uint256 _numQueueElements,
        uint256 _totalElements
    );

    event TransactionBatchAppended(
        uint256 indexed _batchIndex,
        bytes32 _batchRoot,
        uint256 _batchSize,
        uint256 _prevTotalElements,
        bytes _extraData
    );

    /***********
     * Structs *
     ***********/

    struct BatchContext {
        uint256 numSequencedTransactions;
        uint256 numSubsequentQueueTransactions;
        uint256 timestamp;
        uint256 blockNumber;
    }

    /*******************************
     * Authorized Setter Functions *
     *******************************/

    /**
     * Allows the Burn Admin to update the parameters which determine the amount of gas to burn.
     * The value of enqueueL2GasPrepaid is immediately updated as well.
     */
    function setGasParams(uint256 _l2GasDiscountDivisor, uint256 _enqueueGasCost) external;

    /********************
     * Public Functions *
     ********************/

    /**
     * Accesses the batch storage container.
     * @return Reference to the batch storage container.
     */
    function batches() external view returns (IChainStorageContainer);

    /**
     * Retrieves the total number of elements submitted.
     * @return _totalElements Total submitted elements.
     */
    function getTotalElements() external view returns (uint256 _totalElements);

    /**
     * Retrieves the total number of batches submitted.
     * @return _totalBatches Total submitted batches.
     */
    function getTotalBatches() external view returns (uint256 _totalBatches);

    /**
     * Returns the index of the next element to be enqueued.
     * @return Index for the next queue element.
     */
    function getNextQueueIndex() external view returns (uint40);

    /**
     * Gets the queue element at a particular index.
     * @param _index Index of the queue element to access.
     * @return _element Queue element at the given index.
     */
    function getQueueElement(uint256 _index)
        external
        view
        returns (Lib_OVMCodec.QueueElement memory _element);

    /**
     * Returns the timestamp of the last transaction.
     * @return Timestamp for the last transaction.
     */
    function getLastTimestamp() external view returns (uint40);

    /**
     * Returns the blocknumber of the last transaction.
     * @return Blocknumber for the last transaction.
     */
    function getLastBlockNumber() external view returns (uint40);

    /**
     * Get the number of queue elements which have not yet been included.
     * @return Number of pending queue elements.
     */
    function getNumPendingQueueElements() external view returns (uint40);

    /**
     * Retrieves the length of the queue, including
     * both pending and canonical transactions.
     * @return Length of the queue.
     */
    function getQueueLength() external view returns (uint40);

    /**
     * Adds a transaction to the queue.
     * @param _target Target contract to send the transaction to.
     * @param _gasLimit Gas limit for the given transaction.
     * @param _data Transaction data.
     */
    function enqueue(
        address _target,
        uint256 _gasLimit,
        bytes memory _data
    ) external;

    /**
     * Allows the sequencer to append a batch of transactions.
     * @dev This function uses a custom encoding scheme for efficiency reasons.
     * .param _shouldStartAtElement Specific batch we expect to start appending to.
     * .param _totalElementsToAppend Total number of batch elements we expect to append.
     * .param _contexts Array of batch contexts.
     * .param _transactionDataFields Array of raw transaction data.
     */
    function appendSequencerBatch(
        // uint40 _shouldStartAtElement,
        // uint24 _totalElementsToAppend,
        // BatchContext[] _contexts,
        // bytes[] _transactionDataFields
    ) external;
}