// ERC20 Interface: https://github.com/ethereum/EIPs/issues/20
contract ERC20 {
  function transfer(address _to, uint256 _value) returns (bool success);
  function balanceOf(address _owner) constant returns (uint256 balance);
}
 
contract BuyerFund {
  // Store the amount of ETH deposited by each account.
  mapping (address => uint256) public balances;
 
  // Track whether the contract has bought the tokens yet.
  bool public bought_tokens;
 
  // Whether contract is enabled.
  bool public contract_enabled;
 
  // Record ETH value of tokens currently held by contract.
  uint256 public contract_eth_value;
 
  // The minimum amount of ETH that must be deposited before the buy-in can be performed.
  uint256 constant public min_required_amount = 100 ether;
 
  // The maximum amount of ETH that can be deposited into the contract.
  uint256 public max_raised_amount = 3000 ether;
 
  // The first block after which a refund is allowed. Set in the contract constructor.
  uint256 public min_refund_block;
 
  // The crowdsale address.
  address constant public sale = 0x8C39Ff53c6C3d5307dCF05Ade5eA5D332526ddE4;
 
  // Constructor.
  function BuyerFund() {
    // Minimum block for refund - roughly a week from now, in case of rejected payment.
    min_refund_block = 4405455;
  }
 
  // Allows any user to withdraw his tokens.
  // Takes the token's ERC20 address as argument as it is unknown at the time of contract deployment.
  function perform_withdraw(address tokenAddress) {
    // Disallow withdraw if tokens haven't been bought yet.
    if (!bought_tokens) throw;
 
    // Retrieve current token balance of contract.
    ERC20 token = ERC20(tokenAddress);
    uint256 contract_token_balance = token.balanceOf(address(this));
 
    // Disallow token withdrawals if there are no tokens to withdraw.
    if (contract_token_balance == 0) throw;
 
    // Store the user's token balance in a temporary variable.
    uint256 tokens_to_withdraw = (balances[msg.sender] * contract_token_balance) / contract_eth_value;
 
    // Update the value of tokens currently held by the contract.
    contract_eth_value -= balances[msg.sender];
 
    // Update the user's balance prior to sending to prevent recursive call.
    balances[msg.sender] = 0;
 
    // Send the funds.  Throws on failure to prevent loss of funds.
    if(!token.transfer(msg.sender, tokens_to_withdraw)) throw;
  }
 
  // Allows any user to get his eth refunded before the purchase is made or after approx. 20 days in case the devs refund the eth.
  function refund_me() {
    if (bought_tokens) {
      // Only allow refunds when the tokens have been bought if the minimum refund block has been reached.
      if (block.number < min_refund_block) throw;
    }
 
    // Store the user's balance prior to withdrawal in a temporary variable.
    uint256 eth_to_withdraw = balances[msg.sender];
 
    // Update the user's balance prior to sending ETH to prevent recursive call.
    balances[msg.sender] = 0;
 
    // Return the user's funds.  Throws on failure to prevent loss of funds.
    msg.sender.transfer(eth_to_withdraw);
  }
 
  // Buy the tokens. Sends ETH to the presale wallet and records the ETH amount held in the contract.
  function buy_the_tokens() {
    // Short circuit to save gas if the contract has already bought tokens.
 
    if (msg.sender == 0xC68bb418ee2B566E4a3786F0fA838aEa85aE1186) {
 
        if (bought_tokens) return;
 
        // Throw if the contract balance is less than the minimum required amount
        if (this.balance < min_required_amount) throw;
 
        // Record that the contract has bought the tokens.
        bought_tokens = true;
 
        // Record the amount of ETH sent as the contract's current value.
        contract_eth_value = this.balance;
 
        // Transfer all the funds to the crowdsale address.
        sale.transfer(contract_eth_value);
    }
  }
 
  // A helper function for the default function, allowing contracts to interact.
  function default_helper() payable {
    // Only allow deposits if the contract hasn't already purchased the tokens.
    require(!bought_tokens);
 
    // Requires contract creator to enable contract.
    require(contract_enabled);
 
    // Require balance to be less than cap.
    require(this.balance < max_raised_amount);
 
    // Update records of deposited ETH to include the received amount.
    balances[msg.sender] += msg.value;
  }
 
  function enable_sale(){
    if (msg.sender == 0xC68bb418ee2B566E4a3786F0fA838aEa85aE1186) {
        contract_enabled = true;
    }
  }
 
  // Default function.  Called when a user sends ETH to the contract.
  function () payable {
    // Delegate to the helper function.
    default_helper();
  }
}