.. index:: ! examples

.. _examples:

########
Example
########

The following example shows how to create a swap with web3js and calling `make`, followed by trading the swap by calling `take`.

The DEX contract utlitizes ABIEncoderV2 to pass arrays of structs as function arguments, and to our knowledge,
web3js can only pass such arguments through a raw transaction, which requires the private key of the sender.


Initialize contract
=======================

::

    // config variables
    let dexAddress       = "<dex-contract-address>";
    let dexABIFilePath   = "<dex-abi-file-path>";
    let makerAddress     = "<maker-address>";
    let makerPrivateKey  = "<maker-private-key>";
    let takerAddress     = "<taker-address>";

    // create contract
    let abi = JSON.parse(fs.readFileSync(dexABIFilePath));
    let contract = new web3.eth.Contract(abi, dexAddress);


Send `make` transaction helper
==============================

::

    sendMakeTransaction = async function(make, take, whitelist) {
        // encoded make function signature
        let encoded = contract.methods.makeSwap(make, take, false, 0, whitelist).encodeABI();

        // build transaction
        let transaction = {
            from: senderAddress,
            to: dexAddress,
            data: encoded,
            value: 0,
            nonce: await web3.eth.getTransactionCount(from),
            gasPrice: await web3.eth.getGasPrice(),
            gasLimit: 1000000,
            chainId: web3.eth.net.getId(),
        };

        // send raw transaction
        let signed = await web3.eth.accounts.signTransaction(transaction, makerPrivateKey);
        let receipt = await web3.eth.sendSignedTransaction(signed.rawTransaction);

        // extract swap id from SwapMade event
        let event = await dex_contract.getPastEvents('SwapMade', {from_block: 0, toBlock: 'latest'});
        let swapId = event[0].returnValues.id;

        return swapId;
    }


Open a swap with `make`
=======================

::

    makeExampleSwap = async function() {

        // components for the make-side of the swap
        let make = [
            // ERC1155 component (asset type 0)
            {
                tokenAddress: t.art,
                tokenIds: [],
                amounts: [],
                assetType: 0
            },
            // ERC20 component (asset type 2)
            {
                tokenAddress: t.art,
                tokenIds: [],
                amounts: [],
                assetType: 2
            },
            // ETHER component (asset type 3)
            {
                tokenAddress: '',
                tokenIds: [],
                amounts: [],
                assetType: 3
            },
        ];

        // components for the take-side of the swap
        let take = [
            // ERC721 component (asset type 1)
            {
                tokenAddress: t.art,
                tokenIds: tokenIds,
                amounts: [],
                assetType: 1
            }
        ];

        let swapId = await sendMakeTransaction(make, take, []);

        console.log(swapId);
    }


Trade a swap with `take`
========================

::

    takeExampleSwap = async function(swapId) {
        // Calculate fee through the contract.
        // If taker has enough NFT.org tokens, the fee is reduced or even waived.
        let fee = await this.dex_contract.methods.fees().call({
            from: takerAddress
        });

        // Check that the fee is within the expected range
        assert(web3.utils.toBN(fee).lte(web3.utils.toBN('1000000000000000')),
            'fee is higher than expected');

        // Take the swap
        let receipt = await dex_contract.methods.take(swapId).send({
            from: takerAddress,
            gas: 1000000,
            value: fee
        });

        console.log(receipt);
    }


Inspect the traded swap
=======================

::

    inspectExampleSwap = async function(swapId) {
        let swap = await dex_contract.methods.swap(swapId).call({
            from: makerAddress
        });

        console.log(swap);
    }