/*

  Copyright 2019 ZeroEx Intl.

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.

*/

pragma solidity ^0.5.9;

import "../archive/MixinAssetProxyDispatcher.sol";
import "../archive/MixinAuthorizable.sol";


contract MultiAssetProxy is
    MixinAssetProxyDispatcher,
    MixinAuthorizable
{
    // Id of this proxy.
    bytes4 constant internal PROXY_ID = bytes4(keccak256("MultiAsset(uint256[],bytes[])"));

    // solhint-disable-next-line payable-fallback
    function ()
        external
    {
        // NOTE: The below assembly assumes that clients do some input validation and that the input is properly encoded according to the AbiV2 specification.
        // It is technically possible for inputs with very large lengths and offsets to cause overflows. However, this would make the calldata prohibitively
        // expensive and we therefore do not check for overflows in these scenarios.
        assembly {
            // The first 4 bytes of calldata holds the function selector
            let selector := and(calldataload(0), 0xffffffff00000000000000000000000000000000000000000000000000000000)

            // `transferFrom` will be called with the following parameters:
            // assetData Encoded byte array.
            // from Address to transfer asset from.
            // to Address to transfer asset to.
            // amount Amount of asset to transfer.
            // bytes4(keccak256("transferFrom(bytes,address,address,uint256)")) = 0xa85e59e4
            if eq(selector, 0xa85e59e400000000000000000000000000000000000000000000000000000000) {

                // To lookup a value in a mapping, we load from the storage location keccak256(k, p),
                // where k is the key left padded to 32 bytes and p is the storage slot
                mstore(0, caller)
                mstore(32, authorized_slot)

                // Revert if authorized[msg.sender] == false
                if iszero(sload(keccak256(0, 64))) {
                    // Revert with `Error("SENDER_NOT_AUTHORIZED")`
                    mstore(0, 0x08c379a000000000000000000000000000000000000000000000000000000000)
                    mstore(32, 0x0000002000000000000000000000000000000000000000000000000000000000)
                    mstore(64, 0x0000001553454e4445525f4e4f545f415554484f52495a454400000000000000)
                    mstore(96, 0)
                    revert(0, 100)
                }

                // `transferFrom`.
                // The function is marked `external`, so no abi decoding is done for
                // us. Instead, we expect the `calldata` memory to contain the
                // following:
                //
                // | Area     | Offset | Length  | Contents                            |
                // |----------|--------|---------|-------------------------------------|
                // | Header   | 0      | 4       | function selector                   |
                // | Params   |        | 4 * 32  | function parameters:                |
                // |          | 4      |         |   1. offset to assetData (*)        |
                // |          | 36     |         |   2. from                           |
                // |          | 68     |         |   3. to                             |
                // |          | 100    |         |   4. amount                         |
                // | Data     |        |         | assetData:                          |
                // |          | 132    | 32      | assetData Length                    |
                // |          | 164    | **      | assetData Contents                  |
                //
                // (*): offset is computed from start of function parameters, so offset
                //      by an additional 4 bytes in the calldata.
                //
                // (**): see table below to compute length of assetData Contents
                //
                // WARNING: The ABIv2 specification allows additional padding between
                //          the Params and Data section. This will result in a larger
                //          offset to assetData.

                // Load offset to `assetData`
                let assetDataOffset := add(calldataload(4), 4)

                // Load length in bytes of `assetData`
                let assetDataLength := calldataload(assetDataOffset)

                // Asset data itself is encoded as follows:
                //
                // | Area     | Offset      | Length  | Contents                            |
                // |----------|-------------|---------|-------------------------------------|
                // | Header   | 0           | 4       | assetProxyId                        |
                // | Params   |             | 2 * 32  | function parameters:                |
                // |          | 4           |         |   1. offset to amounts (*)          |
                // |          | 36          |         |   2. offset to nestedAssetData (*)  |
                // | Data     |             |         | amounts:                            |
                // |          | 68          | 32      | amounts Length                      |
                // |          | 100         | a       | amounts Contents                    |
                // |          |             |         | nestedAssetData:                    |
                // |          | 100 + a     | 32      | nestedAssetData Length              |
                // |          | 132 + a     | b       | nestedAssetData Contents (offsets)  |
                // |          | 132 + a + b |         | nestedAssetData[0, ..., len]        |

                // Assert that the length of asset data:
                // 1. Must be at least 68 bytes (see table above)
                // 2. Must be a multiple of 32 (excluding the 4-byte selector)
                if or(lt(assetDataLength, 68), mod(sub(assetDataLength, 4), 32)) {
                    // Revert with `Error("INVALID_ASSET_DATA_LENGTH")`
                    mstore(0, 0x08c379a000000000000000000000000000000000000000000000000000000000)
                    mstore(32, 0x0000002000000000000000000000000000000000000000000000000000000000)
                    mstore(64, 0x00000019494e56414c49445f41535345545f444154415f4c454e475448000000)
                    mstore(96, 0)
                    revert(0, 100)
                }

                // End of asset data in calldata
                // assetDataOffset
                // + 32 (assetData len)
                let assetDataEnd := add(assetDataOffset, add(assetDataLength, 32))
                if gt(assetDataEnd, calldatasize()) {
                    // Revert with `Error("INVALID_ASSET_DATA_END")`
                    mstore(0, 0x08c379a000000000000000000000000000000000000000000000000000000000)
                    mstore(32, 0x0000002000000000000000000000000000000000000000000000000000000000)
                    mstore(64, 0x00000016494e56414c49445f41535345545f444154415f454e44000000000000)
                    mstore(96, 0)
                    revert(0, 100)
                }

                // In order to find the offset to `amounts`, we must add:
                // assetDataOffset
                // + 32 (assetData len)
                // + 4 (assetProxyId)
                let amountsOffset := calldataload(add(assetDataOffset, 36))

                // In order to find the offset to `nestedAssetData`, we must add:
                // assetDataOffset
                // + 32 (assetData len)
                // + 4 (assetProxyId)
                // + 32 (amounts offset)
                let nestedAssetDataOffset := calldataload(add(assetDataOffset, 68))

                // In order to find the start of the `amounts` contents, we must add:
                // assetDataOffset
                // + 32 (assetData len)
                // + 4 (assetProxyId)
                // + amountsOffset
                // + 32 (amounts len)
                let amountsContentsStart := add(assetDataOffset, add(amountsOffset, 68))

                // Load number of elements in `amounts`
                let amountsLen := calldataload(sub(amountsContentsStart, 32))

                // In order to find the start of the `nestedAssetData` contents, we must add:
                // assetDataOffset
                // + 32 (assetData len)
                // + 4 (assetProxyId)
                // + nestedAssetDataOffset
                // + 32 (nestedAssetData len)
                let nestedAssetDataContentsStart := add(assetDataOffset, add(nestedAssetDataOffset, 68))

                // Load number of elements in `nestedAssetData`
                let nestedAssetDataLen := calldataload(sub(nestedAssetDataContentsStart, 32))

                // Revert if number of elements in `amounts` differs from number of elements in `nestedAssetData`
                if sub(amountsLen, nestedAssetDataLen) {
                    // Revert with `Error("LENGTH_MISMATCH")`
                    mstore(0, 0x08c379a000000000000000000000000000000000000000000000000000000000)
                    mstore(32, 0x0000002000000000000000000000000000000000000000000000000000000000)
                    mstore(64, 0x0000000f4c454e4754485f4d49534d4154434800000000000000000000000000)
                    mstore(96, 0)
                    revert(0, 100)
                }

                // Copy `transferFrom` selector, offset to `assetData`, `from`, and `to` from calldata to memory
                calldatacopy(
                    0,   // memory can safely be overwritten from beginning
                    0,   // start of calldata
                    100  // length of selector (4) and 3 params (32 * 3)
                )

                // Overwrite existing offset to `assetData` with our own
                mstore(4, 128)

                // Load `amount`
                let amount := calldataload(100)

                // Calculate number of bytes in `amounts` contents
                let amountsByteLen := mul(amountsLen, 32)

                // Initialize `assetProxyId` and `assetProxy` to 0
                let assetProxyId := 0
                let assetProxy := 0

                // Loop through `amounts` and `nestedAssetData`, calling `transferFrom` for each respective element
                for {let i := 0} lt(i, amountsByteLen) {i := add(i, 32)} {

                    // Calculate the total amount
                    let amountsElement := calldataload(add(amountsContentsStart, i))
                    let totalAmount := mul(amountsElement, amount)

                    // Revert if `amount` != 0 and multiplication resulted in an overflow
                    if iszero(or(
                        iszero(amount),
                        eq(div(totalAmount, amount), amountsElement)
                    )) {
                        // Revert with `Error("UINT256_OVERFLOW")`
                        mstore(0, 0x08c379a000000000000000000000000000000000000000000000000000000000)
                        mstore(32, 0x0000002000000000000000000000000000000000000000000000000000000000)
                        mstore(64, 0x0000001055494e543235365f4f564552464c4f57000000000000000000000000)
                        mstore(96, 0)
                        revert(0, 100)
                    }

                    // Write `totalAmount` to memory
                    mstore(100, totalAmount)

                    // Load offset to `nestedAssetData[i]`
                    let nestedAssetDataElementOffset := calldataload(add(nestedAssetDataContentsStart, i))

                    // In order to find the start of the `nestedAssetData[i]` contents, we must add:
                    // assetDataOffset
                    // + 32 (assetData len)
                    // + 4 (assetProxyId)
                    // + nestedAssetDataOffset
                    // + 32 (nestedAssetData len)
                    // + nestedAssetDataElementOffset
                    // + 32 (nestedAssetDataElement len)
                    let nestedAssetDataElementContentsStart := add(
                        assetDataOffset,
                        add(
                            nestedAssetDataOffset,
                            add(nestedAssetDataElementOffset, 100)
                        )
                    )

                    // Load length of `nestedAssetData[i]`
                    let nestedAssetDataElementLenStart := sub(nestedAssetDataElementContentsStart, 32)
                    let nestedAssetDataElementLen := calldataload(nestedAssetDataElementLenStart)

                    // Revert if the `nestedAssetData` does not contain a 4 byte `assetProxyId`
                    if lt(nestedAssetDataElementLen, 4) {
                        // Revert with `Error("LENGTH_GREATER_THAN_3_REQUIRED")`
                        mstore(0, 0x08c379a000000000000000000000000000000000000000000000000000000000)
                        mstore(32, 0x0000002000000000000000000000000000000000000000000000000000000000)
                        mstore(64, 0x0000001e4c454e4754485f475245415445525f5448414e5f335f524551554952)
                        mstore(96, 0x4544000000000000000000000000000000000000000000000000000000000000)
                        revert(0, 100)
                    }

                    // Load AssetProxy id
                    let currentAssetProxyId := and(
                        calldataload(nestedAssetDataElementContentsStart),
                        0xffffffff00000000000000000000000000000000000000000000000000000000
                    )

                    // Only load `assetProxy` if `currentAssetProxyId` does not equal `assetProxyId`
                    // We do not need to check if `currentAssetProxyId` is 0 since `assetProxy` is also initialized to 0
                    if sub(currentAssetProxyId, assetProxyId) {
                        // Update `assetProxyId`
                        assetProxyId := currentAssetProxyId
                        // To lookup a value in a mapping, we load from the storage location keccak256(k, p),
                        // where k is the key left padded to 32 bytes and p is the storage slot
                        mstore(132, assetProxyId)
                        mstore(164, assetProxies_slot)
                        assetProxy := sload(keccak256(132, 64))
                    }

                    // Revert if AssetProxy with given id does not exist
                    if iszero(assetProxy) {
                        // Revert with `Error("ASSET_PROXY_DOES_NOT_EXIST")`
                        mstore(0, 0x08c379a000000000000000000000000000000000000000000000000000000000)
                        mstore(32, 0x0000002000000000000000000000000000000000000000000000000000000000)
                        mstore(64, 0x0000001a41535345545f50524f58595f444f45535f4e4f545f45584953540000)
                        mstore(96, 0)
                        revert(0, 100)
                    }

                    // Copy `nestedAssetData[i]` from calldata to memory
                    calldatacopy(
                        132,                                // memory slot after `amounts[i]`
                        nestedAssetDataElementLenStart,     // location of `nestedAssetData[i]` in calldata
                        add(nestedAssetDataElementLen, 32)  // `nestedAssetData[i].length` plus 32 byte length
                    )

                    // call `assetProxy.transferFrom`
                    let success := call(
                        gas,                                    // forward all gas
                        assetProxy,                             // call address of asset proxy
                        0,                                      // don't send any ETH
                        0,                                      // pointer to start of input
                        add(164, nestedAssetDataElementLen),    // length of input
                        0,                                      // write output over memory that won't be reused
                        0                                       // don't copy output to memory
                    )

                    // Revert with reason given by AssetProxy if `transferFrom` call failed
                    if iszero(success) {
                        returndatacopy(
                            0,                // copy to memory at 0
                            0,                // copy from return data at 0
                            returndatasize()  // copy all return data
                        )
                        revert(0, returndatasize())
                    }
                }

                // Return if no `transferFrom` calls reverted
                return(0, 0)
            }

            // Revert if undefined function is called
            revert(0, 0)
        }
    }

    /// @dev Gets the proxy id associated with the proxy address.
    /// @return Proxy id.
    function getProxyId()
        external
        pure
        returns (bytes4)
    {
        return PROXY_ID;
    }
}
