pragma cashscript ^0.13.0;

////////////////////////////////////////////////////////////////////////////////
// ShareContract — one instance per node (M=3, K=2)
//
// Holds one node's monthly share UTXO until K-of-M operators approve claim.
//
// Operation: claim
// inputs:
//   0   ShareContract              [BCH]  (this share UTXO)
//   1?  feePayer                   [BCH]  (optional P2PKH fee input)
// outputs:
//   0   nodePayout                 [BCH]  (P2PKH to this node's nodePkh)
////////////////////////////////////////////////////////////////////////////////

contract ShareContract(
    pubkey node0,
    pubkey node1,
    pubkey node2,
    bytes20 nodePkh
) {
    function claim(sig s0, sig s1, sig s2) {
        // CRITICAL: limit outputs first
        require(tx.outputs.length == 1, "claim: expected exactly 1 output");

        // K-of-M (K=2): empty sig (0x) returns false; never pass invalid non-empty sigs (NULLFAIL)
        int validCount = 0;
        if (checkSig(s0, node0)) {
            validCount = validCount + 1;
        }
        if (checkSig(s1, node1)) {
            validCount = validCount + 1;
        }
        if (checkSig(s2, node2)) {
            validCount = validCount + 1;
        }
        require(validCount >= 2, "claim: need at least 2-of-3 signatures");

        // Terminating spend to this node's payout address (no self-replication)
        require(
            tx.outputs[0].lockingBytecode == new LockingBytecodeP2PKH(nodePkh),
            "claim: output must pay nodePkh"
        );
        require(tx.outputs[0].tokenCategory == 0x, "claim: output must be pure BCH");

        // Value conservation (fee = inputs - output)
        int inSum = 0;
        for (int i = 0; i < tx.inputs.length; i = i + 1) {
            inSum = inSum + tx.inputs[i].value;
        }
        require(tx.outputs[0].value <= inSum, "claim: value not conserved");
        require(tx.outputs[0].value > 0, "claim: zero payout");
    }
}