As Smart Contract, I should an accompanying WASM proxy to collect user payments

[melpadden]

Since purchasing a ticket requires transferring CSPR from the account main purse to the contract, we would need to use a WASM-proxy implementing the reusable purse approach.

#[no_mangle]
pub extern "C" fn call() {
    let amount: U512 = runtime::get_named_arg(ARG_AMOUNT);
    let lottery_contract_hash: ContractHash =
        runtime::get_named_arg(ARG_LOTTERY_CONTRACT_HASH);
    let lottery_contract_entry_point: String =
        runtime::get_named_arg(ARG_LOTTERY_CONTRACT_HASH);

    let contract_treasure_purse: URef = runtime::call_contract(
        lottery_contract_hash,
        LOTTERY_CONTRACT_GET_TREASURY_PURSE_ENTRY_POINT_NAME,
        runtime_args! {},
    );

    system::transfer_from_purse_to_purse(
        account::get_main_purse(),
        contract_treasure_purse,
        amount,
        None,
    )
    .unwrap_or_revert();

    runtime::call_contract(
        lottery_contract_hash,
        lottery_contract_entry_point,
        runtime_args! {}
    )
}

For this implementation, the contract has to implement the get_treasure_purse entry point that returns the purse with the ADD access only:

treasury_purse.into_add()