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Check for required solidity file.

2017 was a revolutionary year in terms of mainstream adoption of blockchain technologies. Bitcoin, Ethereum and many other altcoins observed a meteoric rise in price and ICOs - initial coin offerings - raised more capital than traditional VC (venture capital).

For many it's a paradigm shift, for me it's one of the many steps on the path of global awakening. People waking up, becoming more resilient, independent, anti-fragile... Now we don't need to rely on centralized government, we can have independent food, water, energy production. Private schools, private hospitals, private roads, private trains and most importantly - decentralized money, transparency, consensus protocol.

It's no longer Central Banks (or Federal Reserve) printing money and financing war or sugar subsidies - this time around it is code, math and cryptography that govern the rules. You can participate in this change in a number of ways - running your own blockchain project or becoming a developer are surely one of the most exciting options.


It's difficult for a single article to be "everything for everyone" but I'll do my best to be approachable, digestible, easy to follow.

You should have some knowledge about Ethereum and programming.

Core components of Ethereum

This is a great article about Ethereum by Preethi Kasireddy and according to Medium it's 33 minutes read. Don't read it now, save it for later (long haul flight) and while you are doing so check another article written by her: Fundamental challenges with public blockchains, this time around it's "only" 29 minutes.

Time well spent, depending on the priorities. If you need to level up your Ethereum knowledge, there are plenty of resources out there I don't want to distract you with links, instead let's carry on with the essential content of this tutorial.

More great learning resources

This tutorial assumes some existing Solidity knowledge. If you want to learn basics I highly recommend two great video course explaining everything from scratch.

If you are a beginner to Ethereum, you should probably start with much more approachable resources here:

Proper credit to these guys, it takes a lot of effort to create a proper tutorial! This time around reserve at least a few hours - these are detailed, step by step video tutorials with very decent production quality.

It's not "Hello World"...'s the ICO crowdsale. It means there is serious money on the line. Proceed with caution. Ask for review. Publish your contract upfront (GitHub and Etherscan) - verify on Etherscan so that anyone can see. Hire professional auditors. Not kidding. The additional upside of such approach - potential investors will see that you are taking trust and security matters seriously.

You should always test your smart contract thoroughly and when working in development mode - deploy to your local instance testrpc or testnet (Ropsten is one of the most popular options here).

This tutorial will present an approachable way to integrate WINGS forecasting features into your existing ICO contract.

There is an even easier way - to use pre-populated, default, built-in Wings ICO contract - during the project creation wizard you'll be presented with an option:

(this tutorial focuses on using custom ICO contract, you can always use default WINGS)

Comment about comments

Code is the best documentation. I hate to see comments onlyOwner // only owner - is it meaningful in any way? I thought so :) Everything should be self-explanatory. That's the skill of writing code - it's run by computers, but read and modified by other programmers. The process of typing on the keyboard the characters that end up in the production code is maybe 1% of the total development time. All the rest is endless refactoring, testing and making sure that everything works well together.

Debbugging and error messages

Ethereum ecosystem is changing rapidly. It may happen that a certain command will give you an error message, or I've missed some obvious detail and thing does not work. Please let me know so I can update the tutorial.

You can always do a micro your-favourite-search-engine-not-namedropping query and resolve the matter yourself. Or just stick to the common sense and general programming knowledge - you can do it!

Core Components of WINGS on Ethereum

WINGS is DAO (decentralised autonomous organisation) that curates and evaluates projects, and based on their performance receive service reward payments in the form of ERC20 tokens and Ether.




The main advantages of using WINGS DAO are transparency, crowd AI and decentralized curation.

In order to operate in a fully decentralised way, the ICO contract needs to implement certain methods - in this tutorial we show you step by step what has to be done.

ICO WINGS Integration, "technical deep dive"

We will base our code on WINGS Integration repository

It is also available as npm package

Or you can just copy-page individual files from GitHub repository. Personally I don't like installing too many dependencies, personally I prefer to keep my code minimal - less code to maintain, less surface for error.

Other tools we will use

The best thing is - you don't have to install pretty much anything - most of the things run online. The only exception - Metamask - Chrome extension but chances are you have it already set up.

  • Solidity - programming language used to create smart contracts
  • OpenZeppelin - collection of great smart contracts
  • Remix IDE - powerful tool for creating Solidity code
  • Metamask - Chrome extension allowing interfacing with smart contracts
  • Etherscan - for veryfying source code of our smart contract


Many programming languages support inheritance. It's a way of saying that Tesla is derived from Car and we don't have to explain explicitly that is has Wheels (because they are derived from the base Car class).

(note that I didn't say SteeringWheel because chances are they replace with self-driving component of some futuristic joystick)

The two pieces of inheritance:

  • ICrowdsaleProcessor.sol - it's the interface, it contains name and signature of the methods that you need to implement, you can find this file
  • BasicCrowdsale.sol - it's the basic implementation containing some, but not every method required by the ICrowdsaleProcessor interface

ERC20 token

In our example we will use a custom token based on OpenZeppelin implementation. You have probably seen so many implementations of ERC20 standard, here (for simplicity) all the fluff is removed. You can use your own token, as long as it is ERC20 compatible and you properly implement all methods required by ICrowdsaleProcessor interface - it is the essence of WINGS integration.

contract ERC20 {

  using SafeMath for uint256;

  mapping(address => uint256) balances;
  mapping (address => mapping (address => uint256)) internal allowed;
  event Transfer(address indexed from, address indexed to, uint256 value);
  event Approval(address indexed owner, address indexed spender, uint256 value);

  uint256 totalSupply_;

  function totalSupply() public view returns (uint256) {
    return totalSupply_;

  function transfer(address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));
    require(_value <= balances[msg.sender]);

    balances[msg.sender] = balances[msg.sender].sub(_value);
    balances[_to] = balances[_to].add(_value);
    Transfer(msg.sender, _to, _value);
    return true;

  function balanceOf(address _owner) public view returns (uint256 balance) {
    return balances[_owner];

  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));
    require(_value <= balances[_from]);
    require(_value <= allowed[_from][msg.sender]);

    balances[_from] = balances[_from].sub(_value);
    balances[_to] = balances[_to].add(_value);
    allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
    Transfer(_from, _to, _value);
    return true;

  function approve(address _spender, uint256 _value) public returns (bool) {
    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);
    return true;

  function allowance(address _owner, address _spender) public view returns (uint256) {
    return allowed[_owner][_spender];

(simple, minimalistic, implementation of ERC20 token standard directly from OpenZeppelin repository)

Access modifiers

Ownable and HasManager are similar to each other. Just like in real life - you could be either a owner of a restaurant or work in a restaurant as a manager.

contract Ownable {
  address public owner;

  function Ownable() public {
    owner = msg.sender;

  modifier onlyOwner() {
    require(msg.sender == owner);

  function transferOwnership(address newOwner) public onlyOwner {
    require(newOwner != address(0));
    owner = newOwner;
contract HasManager {
  address public manager;

  modifier onlyManager {
    require(msg.sender == manager);

  function transferManager(address _newManager) public onlyManager() {
    require(_newManager != address(0));
    manager = _newManager;

You probably noticed that HasManager does not have a constructor. It means that we need to set it up in the of the base class, see for example: BasicCrowdsale.sol

function BasicCrowdsale(address _owner, address _manager) public {
  owner = _owner;
  manager = _manager;

(you don't have to worry, it is happening automatically in the BasicCrowdsale)

ERC20 "MyToken"

Based on the ERC20 we create MyToken that will be used for the crowdsale. Note that every time we mint it, we increase the total supply. MyToken is Ownable - because mint function has onlyOwner() modifier it means that only owner can mint.

pragma solidity ^0.4.18;

contract MyToken is ERC20, Ownable {

  string public name;
  string public symbol;
  uint8 public decimals;
  uint256 public totalSupply;
  bool public releasedForTransfer;

  function MyToken() public {
    name = "MyTokenExample";
    symbol = "MTE";
    decimals = 18;

  // override
  function transfer(address _to, uint256 _value) public returns (bool) {
    return super.transfer(_to, _value);

  // override 
  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
    return super.transferFrom(_from, _to, _value);

  function release() public onlyOwner() {
    releasedForTransfer = true;
  function mint(address _recepient, uint256 _amount) public onlyOwner() {
    require (!releasedForTransfer);
    balances[_recepient] += _amount;
    totalSupply += _amount;

File structure

We can structure files the following way:

(because Ethereum ecosystem is evolving very rapidly, chances are the view of Remix IDE will change)

Another option is to keep everything in the single file - up to you. It's just like a discussion about tabs and spaces. My humble 2 satoshis in this discussion - do whatever works best for you. Solidity compiler will compile everything to EVM (Ethereum Virtual Machine) code anyway.


First we need to deploy MyToken. For deployment we will use the Remix IDE, Metamask (Chrome extension) and Ropsten testnet. The biggest advantage of using these tools is that we don't have to operate the full node (sometimes it takes forever to synchronise) on our machine and deployment is literally one-click process.

If you don't have a Metamask account, you can create one with easy and "buy" test Ether - there is a faucet allowing you to get some test Ether for free. It's very handy and practical when testing your code, you should always deploy to the testnet first (no excuses here).

Why not Truffle framework?

Many tutorials are using Truffle framework. However, it's not immediately obvious which Solidity compiler is being used, see this question on StackOverflow and from my own experience it's easier to use a combination of Remix and Metamask.

Deploying the token

We cannot deploy everything all at once, we need to deploy MyToken contract first. Then, when deploying MyCrowdsalewe will pass the MyToken contract address to the constructor.

Choose MyToken

Confirm in Metamask: 

After few moments (block confirmation) you should see:

Deploying the crowdsale

MyCrowdsale inherits from BasicCrowdsale.sol (that implements some methods) and ICrowdsaleProcessor.sol... Now we need to implement the remainder:

pragma solidity ^0.4.18;

contract MyCrowdsale is BasicCrowdsale {
  mapping(address => uint256) participants;

  uint256 tokensPerEthPrice;
  MyToken crowdsaleToken;

  // Ctor. In this example, minimalGoal, hardCap, and price are not changeable.
  // In more complex cases, those parameters may be changed until start() is called.
  // simplest case where manager==owner. See onlyOwner() and onlyManager() modifiers
  // before functions to figure out the cases in which those addresses should differ
  function MyCrowdsale(uint256 _minimalGoal, uint256 _hardCap, uint256 _tokensPerEthPrice, address _token) public BasicCrowdsale(msg.sender, msg.sender) {
    minimalGoal = _minimalGoal;
    hardCap = _hardCap;
    tokensPerEthPrice = _tokensPerEthPrice;
    crowdsaleToken = MyToken(_token);

  function getToken() public returns(address) {
    return address(crowdsaleToken);

  // called by CrowdsaleController to transfer reward part of
  // tokens sold by successful crowdsale to Forecasting contract.
  // This call is made upon closing successful crowdfunding process.
  function mintTokenRewards(address _contract, uint256 _amount) public onlyManager()  {, _amount); // crowdsale token is mintable in this example, tokens are created here

  // transfers crowdsale token from mintable to transferrable state
  function releaseTokens() public onlyManager() hasntStopped() whenCrowdsaleSuccessful() {

  // DEFAULT FUNCTION - allows for ETH transfers to the contract
  function () payable public {
    require(msg.value > 0);
    sellTokens(msg.sender, msg.value);

  function sellTokens(address _recepient, uint256 _value) internal hasBeenStarted() hasntStopped() whenCrowdsaleAlive() {
    uint256 newTotalCollected = totalCollected + _value;

    if (hardCap < newTotalCollected) {
      // don't sell anything above the hard cap

      uint256 refund = newTotalCollected - hardCap;
      uint256 diff = _value - refund;

      // send the ETH part which exceeds the hard cap back to the buyer
      _value = diff;

    // token amount as per price (fixed in this example)
    uint256 tokensSold = _value * tokensPerEthPrice;

    // create new tokens for this buyer, tokensSold);

    // remember the buyer so he/she/it may refund its ETH if crowdsale failed
    participants[_recepient] += _value;

    // update total ETH collected
    totalCollected += _value;

    // update totel tokens sold
    totalSold += tokensSold;

  // project's owner withdraws ETH funds to the funding address upon successful crowdsale
  function withdraw(uint256 _amount) public onlyOwner() hasntStopped() whenCrowdsaleSuccessful() {
    require(_amount <= this.balance);

  // backers refund their ETH if the crowdsale was cancelled or has failed
  function refund() public {
    require(stopped || isFailed()); // either cancelled or failed
    uint256 amount = participants[msg.sender];
    require(amount > 0); // prevent from doing it twice
    participants[msg.sender] = 0;

I genuinely believe that code is the best documentation and everything should be quite clear. At the same time - it's 0.1version of this tutorial and we are receiptive to feedback - the end goal is to make it as easy as possible to integrate it!

Constructor parameters

The constructor accepts the following parameters:

  • uint256 _minimalGoal
  • uint256 _hardCap
  • uint256 _tokensPerEthPrice
  • address _token

Now you should see the importance of creating MyToken contract first - we will pass MyToken contract address to the constructor.

Big numbers in Solidity and JavaScript

One thing to keep in mind - Solidity has built-in human-readable names such as ether or secondsminuteshours. You can see more in the docs:

However, when passing uint256 we will have to use a converter for example: 1 ether = 1000000000000000000 wei

Because the number is too big for JavaScript (we are using Remix IDE in the browser) we need to put quotes around the number, see this StackOverflow question.

In my instance the complete constructor parameters look like that: "10000000000000000000", "100000000000000000000", 1000, "0xcebaf9eee389fd5589194a04801698be41e4bd78"

(it will be different in your case because of the MyToken contract address)

Once we have a proper construction parameters in place, we can deploy MyCrowdsale. Metamask will ask for confirmation and after the block is mined we can see the transaction on Ethercan.

Verification on Etherscan

Once we have token deployed, we can verify source code on Etherscan - that is always the best practice - so that anyone can see the source and verify that we do is right. Note, that very few people have skill or ability to review the code and sometimes $150m bugs are left intact for 100+ days. If you don't believe just use your preferred search engine and ask for "parity hack".

Because we separated our code into a few individual files, for Etherscan verification we will simply copy and paste into a single file.

You can find the whole file here.

Starting the forecast

After the contract is deployed we should call the start function:

function start(uint256 _startTimestamp, uint256 _endTimestamp, address _fundingAddress )
    onlyManager()   // manager is CrowdsaleController instance
    hasntStarted()  // not yet started
    hasntStopped()  // crowdsale wasn't cancelled

There is a number of ways how to call a smart contract function, probably the easiest one is using MyCrypto / MyEtherWallet.

Note that you'll need to provide contract address and ABI. Also note onlyManager() modifier - in our example we used msg.sender which means the account who initially deployed the smart contract.

WINGS project creation

We deployed our ICO contract that implements ICrowdsaleProcessor.sol and therefore making it compatible with WINGS DAO.

Now, we can proceed to WINGS and complete all the required data.





Smart contract

It is 5000 WINGS tokens to start a project

To create the project you require 5000 WINGS. Make sure you have enough before submitting the project.


Allocate rewards

As a project creator you can also allocate a portion of raised ETH and token to the forecasting community. Screenshots below will guide you through the process.

Step 1

Step 2

Step 3

Step 4

Upon successful creating your WINGS campaign forecasters from all around the world will be able to make their predictions about the success of your ICO.

After forecasting and crowdsale is finished

Forecasting happens before the crowdsale.

After the forecasting finishes, you have up to 45 days to start the crowdsale.

Paying rewards to forecasters

Best practice is to release tokens within a reasonable time after finished crowdsale. The first estimate that came to my mind is "within two weeks" but don't quote me on that.

Note that WINGS have no power over the owners of the ICO. At the same time we are aware that someone withdrawing their commitment would commit reputational suicide and it is unlikely to happen.

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