helper.fc

forall X -> tuple change_tuple(tuple t, int pos, X value) asm(t value pos) "SETINDEXVAR";
tuple get_c7() asm "c7 PUSHCTR";

slice vm::invoke_get_addr(slice owner_address, tuple c7, cell master_data, cell master_code) asm
  "CTOS            // owner_addr c7 md mc"
  "2 PUSHINT       // owner_addr c7 md mc args"
  "103289 PUSHINT  // owner_addr c7 md mc args get_jwa_method_id"
  "5 0 REVERSE DUMPSTK    // owner_addr get_jwa_method_id args mc md c7"
  "53 RUNVM DUMPSTK       // address exit_code c4' c5'"
  "3 BLKDROP       // address";

slice get_addr(slice owner_address, cell code, cell data, slice master_addr) inline_ref {
    tuple c7 = get_c7();
    c7 = c7.change_tuple(0,
        c7.at(0).change_tuple(8, master_addr)
                .change_tuple(10, code)
    );
    return vm::invoke_get_addr(owner_address, c7, data, code);
}

slice calc_my_jetton_wallet(slice master_addr, cell code, cell data) inline {
    return get_addr(my_address(), code, data, master_addr);
}

main.tact

import "./helper.fc";

@name(calc_my_jetton_wallet)
native calcMyJettonWallet(master_address: Address, master_code: Cell, master_data: Cell): Address;


message(0x0f8a7ea5) JettonTransfer {
    query_id: Int as uint64;
    amount: Int as coins;
    destination: Address;
    response_destination: Address;
    custom_payload: Cell?;
    forward_ton_amount: Int as coins;
    forward_payload: Slice as remaining;
}


@interface("ton.experimental.pcrafter.jettonseller")
contract JettonSeller {
    const forward_ton_amount: Int = ton("0.000001");
    
    jetton_master: Address;
    jetton_wallet: Address;  // what we are selling
    nanoton_per_jetton: Int as coins;
    
    init(jetton_master: Address, master_code: Cell, master_data: Cell, nanoton_per_jetton: Int) {
        self.jetton_wallet = calcMyJettonWallet(jetton_master, master_code, master_data);
        self.nanoton_per_jetton = nanoton_per_jetton;
    }

    fun transferJettonTo(jetton_wallet: Address, destination: Address, amount: Int, query_id: Int, message: String) {
        if (amount > 0) {
            send(SendParameters{
                to: jetton_wallet,
                value: ton("0.1"),
                mode: 0,
                body: JettonTransfer{query_id: query_id, amount: amount, destination: destination, response_destination: destination, custom_payload: null, forward_ton_amount: self.forward_ton_amount, forward_payload: message.asComment()}.toCell()
            });
        }
    }

    receive() {
        let nanoton = context().value - ton("0.1");
        transferJettonTo(self.jetton_wallet, sender(), nanoton / self.nanoton_per_jetton, 0, "swap completed");
    }
    
    get fun getJetton(): Address {
        return self.jetton_master;
    }
    
    get fun getJettonPrice(): Int {
        return self.nanoton_per_jetton;
    }
}