First example of a Scripted Crowdsale on the Master Protocol

scriptedCrowdsale.java

/**
 This method is called by Master Protocol parser when parsing an incoming transaction into a crowdsale address. It is called once per incoming tx. 
*/
handlePayment();

The method handlePayment() can call on auxilery methods to access some parameters:

/**
  0 for BTC, 1 for MSC, etc... as per [the spec](https://github.com/mastercoin-MSC/spec#transaction-field-definitions)
*/
getIncomingCurrencyId();

/**
  Returns the number of tokens that are incoming in the current payment (in base units e.g. satoshis or willets).
*/
getIncomingAmount();

/**
  in milliseconds since the start of the crowdsale
*/
getTimeOfPayment();

/**
  Only enabled for crowdsale that are time-limited, and is automatically calculated from getTimeOfPayment();
*/
getTimeUntilCrowdsaleEnds();

/**
 the ordered ordinal of the token. The first ever payment into the crowdsale address gets this value as 0, the second value gets 1, etc...
*/
getPaymentOrdinal();

/**
  Send @amount tokens to the source address of the current payment. 
  
  @currencyID - this allows for future support in crowdsales that simultaniously create more than one type of token.
*/
sendTokens(currencyID, amount);

Following are sample implementations of handlePayment for the above models:

/** Implements the original Mastercoin crowdsale model */
handlePaymentTimeBased() {
  if (getIncomingCurrencyId() != CURRENCY_ID_BTC) {
    // Only accept BTC
	refundPayment(); // OPTIONAL - this refunds payments that are above some minimal anti-spam level ... assuming the tokens can be refunded for free. The tokens themselves can be used to buy the required BTC/MSC needed to send the refund transaction.
    return;
  }
  
  if (getTimeUntilCrowdsaleEnds() <= 0) {
    // The crowdsale has already expired
	refundPayment();
	return;
  }
  
  // Valid incoming tx ... let's send some MSC!
  def amount = getIncomingAmount() * 100 * (1 + getTimeUntilCrowdsaleEnds / (MILLIS_IN_WEEK * 10))
  sendPayment(getCreatedCurrencyId(), amount);
}