# Multi-bridge Message Sender

### Features

* Supports sending messages via multiple bridge sender adapters
* Only a predefined dApp contract can use this multi-bridge sender for cross-chain remote calls
* Allows adding and removing bridge sender adapters
* The caller is responsible for determining the fees to be paid to each of the bridges to be used.
* The caller can choose to omit a set of bridges for a given message
* Emits events for sent messages, sender adapter updates, and error when sending messages

### Functions

#### remoteCall

```solidity
    function remoteCall(
        uint256 _dstChainId,
        address _target,
        bytes calldata _callData,
        uint256 _nativeValue,
        uint256 _expiration,
        address _refundAddress,
        uint256[] calldata _fees,
        uint256 _successThreshold,
        address[] calldata _excludedAdapters
    ) external payable onlyCaller validateExpiration(_expiration)
```

This function allows a remote function to be called on a destination chain. It does this by sending multiple copies of a cross-chain message through available bridges. Only the predefined `caller` contract can call this function. The call is successful if a minimum number of bridge adapters, defined by the `_successThreshold` parameter, successfully dispatch the cross-chain message.

It takes the following parameters:

* `_dstChainId`: The destination chainId
* `_target` is the target execution point on the destination chain
* `_callData` is the data to be sent to \_target by low-level call(eg. address(\_target).call(\_callData))
* `_nativeValue` is the value to be sent to \_target by low-level call (eg. address(\_target).call{value: \_nativeValue}(\_callData))
* `_expiration` refers to the number of seconds that a message remains valid before it is considered stale and can no longer be executed.
* `_refundAddress` refers to the refund address for any extra native tokens paid
* `_fees` refers to the fees to pay to each sender adapter that is not in the exclusion list specified by \_excludedAdapters. The fees are in the same order as the sender adapters in the senderAdapters list, after the exclusion list is applied.
* `_successThreshold` specifies the minimum number of bridges that must successfully dispatch the message for this call to succeed.
* `excludedAdapters` are the sender adapters to be excluded from relaying the message, in ascending order by address

#### addSenderAdapters

```solidity
function addSenderAdapters(address[] calldata _senderAdapters) external onlyOwner
```

Adds an array of bridge sender adapter addresses, that must be provided in ascending order. This function is only callable by the `owner`.

#### removeSenderAdapters

```solidity
function removeSenderAdapters(address[] calldata _senderAdapters) external onlyOwner
```

Removes an array of bridge sender adapter addresses, that must be provided in ascending order. This function is only callable by the predefined `owner` contract.

### Events

* `MultiBridgeMessageSent`: is emitted after a call to `remoteCall()` completes, sending a given message through one or more bridges. The details of this event should be inspected to see if any bridges have failed. 
* `MessageSendFailed` : is emitted if sending a message through a specific AMB fails.
* `SenderAdapterUpdated`: is emitted when a sender adapter is added or removed

### Dependencies

The contract depends on the following files:

* `IMessageSenderAdapter.sol`: Interface for bridge sender adapters
* `IMultiBridgeMessageReceiver.sol`: Interface for MultiBridgeMessageReceiver contracts on the destination chain
* `MessageSenderGAC`: Global Access Control contract.
* It also uses a `Message.sol` file for the message structure.


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