This is a base contract (or the base functions) to use a contract as an index for a chat forum or “chan”.
Aside from being the index for all chat messages, it would also allow the original author to edit their message or remove offensive message for a cost.
This contract uses the sats on a utxo as a variable to convert old messages into “coupons” for locking FBCH.
pragma cashscript ~0.10.0;
// FutureChan - A message board contract.
//
// Message board for data written in mutable or immutable NFT commitments.
//
// - Messages can be removed after a week.
// - Messages can be censored early by paying a 9 times multiplier penalty.
// - Messages must contain a value greater than 1/100th of a block time 2.5 months.
// - Messages with insufficient value may be cleared by anyone at any time.
//
// - Messages can be edited (or deleted) using an NFT with minting capability.
//
// - Clearing (or censoring) messages must create 0.1 FBCH (or 1 FBCH) coupons.
//
// - Many different channels can be used by using a different channel identifier.
// - Note: `cashc` compiler must be patched to not error from channel identifier usage.
//
//
contract FutureChan(bytes channel) {
// OP_OVER OP_0 OP_NUMEQUAL OP_IF
function clearMessage() {
// Chan messages will create a 0.1 FBCH coupon targeting a FBCH vault
// where vault time is specified using the number of sats on the message.
// Example #1: 9873 sats => ( 9873 % 10 ) * 1000 => FBCH-0987000; 0.1 BCH coupon
// #2: 543 sats => ( 543 % 10 ) * 1000 => MEV BURN
// #3: 9873 sats => 98,730 => FBCH-0987000; 1 BCH coupon
// OP_INPUTINDEX OP_UTXOVALUE OP_10 OP_DIV e803 OP_MUL
int vaultTime = int(tx.inputs[this.activeInputIndex].value / 10)*1000;
// Default to a 0.1 BCH series coupon
// 80969800
int amount = 10000000;
// If the message is being censored, the burner must provide 9 X the initial value to a 1 BCH coupon
// OP_INPUTINDEX OP_OUTPUTVALUE OP_INPUTINDEX OP_UTXOVALUE OP_10 OP_MUL OP_NUMEQUAL
bool isPrematureBurn = tx.outputs[this.activeInputIndex].value == tx.inputs[this.activeInputIndex].value*10;
// If this is an early burn (moderation), create a 1 BCH coupon
// OP_DUP OP_IF
if(isPrematureBurn){
// 00e1f505 OP_ROT OP_DROP OP_SWAP
amount = 100000000;
} // OP_ENDIF
// If the message has matured, the full value is used for a coupon
// OP_INPUTINDEX OP_OUTPUTVALUE OP_INPUTINDEX OP_UTXOVALUE OP_NUMEQUAL
bool hasMatured = tx.outputs[this.activeInputIndex].value == tx.inputs[this.activeInputIndex].value;
// If not early, require the message is a week old
// OP_DUP OP_IF
if(hasMatured){
// Require the message be at least a week old
// e803 OP_CHECKSEQUENCEVERIFY
require(tx.age >= 1000);
} // OP_DROP OP_ENDIF
// If sats specifed a bad locktime (allow an early burn, no coupon, pure MEV)
// OP_NOT OP_SWAP OP_NOT OP_BOOLAND OP_IF
if(!hasMatured && !isPrematureBurn){
// If the vault time indicated is less than ~2.5 months into the future.
// Let the message be cleared and the value be taken by anyone.
// OP_OVER 1027 OP_SUB OP_CHECKLOCKTIMEVERIFY OP_DROP
require(tx.time >= ( vaultTime - 10000 ));
}
// Otherwise, the sats must pay an FBCH coupon
// OP_ELSE
else{
// Calculate the future vault corresponding to the locktime
// OP_OVER OP_SIZE
// OP_NIP OP_2 OP_PICK
// OP_CAT c0d3c0d0a06376b17568c0cec0d188c0cdc0c788c0d0c0c693c0d3c0cc939c77 OP_CAT
bytes theVault = bytes(bytes(vaultTime).length) +
bytes(vaultTime) +
0xc0d3c0d0a06376b17568c0cec0d188c0cdc0c788c0d0c0c693c0d3c0cc939c77;
// Construct P2SH32 locking bytecode from redeem bytecode
// aa20 OP_OVER OP_HASH256 OP_CAT 87
bytes vaultLockingBytecode = 0xaa20 + hash256(theVault) + 0x87;
// Calculate the coupon vault corresponding to the locktime
// OP_CAT OP_2 OP_PICK OP_SIZE OP_NIP
// OP_3 OP_PICK OP_CAT OP_OVER OP_SIZE OP_NIP
// OP_CAT OP_OVER OP_CAT 00cc00c694a16900c788c08bc39c OP_CAT
bytes theCoupon = bytes(bytes(amount).length) + bytes(amount) +
bytes(vaultLockingBytecode.length) + vaultLockingBytecode +
0x00cc00c694a16900c788c08bc39c;
// Construct P2SH32 locking bytecode from redeem bytecode
// aa20 OP_OVER OP_HASH256 OP_CAT 87 OP_CAT
bytes couponLockingBytecode = 0xaa20 + hash256(theCoupon) + 0x87;
// Send the message value to the coupon vault.
// OP_INPUTINDEX OP_OUTPUTBYTECODE OP_OVER OP_EQUALVERIFY
require(tx.outputs[this.activeInputIndex].lockingBytecode == couponLockingBytecode);
} // OP_2DROP OP_2DROP OP_ENDIF
// Without CashTokens
// OP_INPUTINDEX OP_OUTPUTTOKENCATEGORY OP_0 OP_EQUALVERIFY
require(tx.outputs[this.activeInputIndex].tokenCategory == 0x);
} // OP_2DROP OP_2DROP
// Messages on mutable NFTs may be edited (or deleted) using a minting NFT of the same token category.
// Messages on immutable NFTs may only be deleted.
//
// oldMessage[0] -> editedMessage[0]
// oldMessage[1] -> editedMessage[1]
// oldMessage[n] -> editedMessage[n]
// mintingBaton[in.len-1] -> extendedMessage[n+1]
// -> extendedMessage[n+2]
// -> mintingBaton[out.len-1]
//
// OP_1 OP_ELSE OP_SWAP OP_1 OP_NUMEQUALVERIFY
function editMessage(){
// Sats must be carried forward.
// OP_INPUTINDEX OP_OUTPUTVALUE OP_INPUTINDEX OP_UTXOVALUE OP_NUMEQUALVERIFY
require(tx.outputs[this.activeInputIndex].value == tx.inputs[this.activeInputIndex].value);
// ... to an output on this same contract
// OP_INPUTINDEX OP_OUTPUTBYTECODE OP_INPUTINDEX OP_UTXOBYTECODE OP_EQUALVERIFY
require(tx.outputs[this.activeInputIndex].lockingBytecode == tx.inputs[this.activeInputIndex].lockingBytecode);
// But neither the commitment, NFT nor token data are required as outputs. They may be omitted.
// As long as last input carried a matching minting NFT
// OP_TXINPUTCOUNT OP_1SUB OP_UTXOTOKENCATEGORY OP_INPUTINDEX OP_UTXOTOKENCATEGORY 20 OP_SPLIT OP_DROP OP_2 OP_CAT OP_EQUAL
require(tx.inputs[tx.inputs.length - 1].tokenCategory == tx.inputs[this.activeInputIndex].tokenCategory.split(32)[0] + 0x02);
} // OP_NIP
} // OP_ENDIF