announcement.cash

pragma cashscript ^0.12.0;

/* This is a contract showcasing covenants outside of regular transactional use.
 * It enforces the contract to make an "announcement" on Memo.cash, and send the
 * remainder of contract funds back to the contract.
 */
contract Announcement() {
    function announce() {
        // Create the memo.cash announcement output
        bytes announcement = new LockingBytecodeNullData([
            0x6d02,
            bytes('A contract may not injure a human being or, through inaction, allow a human being to come to harm.')
        ]);

        // Check that the first tx output matches the announcement
        require(tx.outputs[0].value == 0);
        require(tx.outputs[0].lockingBytecode == announcement);

        // Calculate leftover money after fee (1000 sats)
        // Check that the second tx output sends the change back if there's enough leftover for another announcement
        int minerFee = 1000;
        int changeAmount = tx.inputs[this.activeInputIndex].value - minerFee;
        if (changeAmount >= minerFee) {
            require(tx.outputs[1].lockingBytecode == tx.inputs[this.activeInputIndex].lockingBytecode);
            require(tx.outputs[1].value == changeAmount);
        }
    }
}