Native token interface.

[zie1ony]

Handle native token:

• standard transfers,
• passing tokens with contract calls when calling contract from the outside,
• passing tokens with contract to contract call.
• proper gas metering in tests that allows testing token transfers. The best would be zero-cost gas table.
• #[odra(payable)] to mark entrypoint that accept tokens. (also in #[odra::external_contract]?).
• TestEnv check of token.
• Handle potential different types of integers for native tokens in backends (Casper has u512, Ethereum u256).

In test script.

let one = TestEnv::one_token();
TestEnv::with_tokens(1000 * one);
TestEnv::set_caller(user1);
contract.deposit();

assert_eq!(
    TestEnv::token_balance(user1),
    TestEnv::token_balance(contract.address())
)

In contract.

#[odra(init)]
#[odra(payable)]
pub fn start() {
    let caller = ContracEnv::caller();
    let contract_balance = ContracEnv::self_balance();
    let transfered_amount = ContracEnv::attached_value();
    let threshold = ContractEnv::one_token() * 100;
    if contract_balance > threshold {
        ContractEnv::transfer_tokens(caller, transfered_amount);
    } else {
        ContracEnv::with_tokens(contract_balance);
        AnotherContract::at(caller).do_something();
    }
}