use near_sdk::json_types::U128;
use near_sdk::{ext_contract, AccountId, PromiseOrValue};
#[ext_contract(ext_ft_receiver)]
pub trait FungibleTokenReceiver {
/// Called by fungible token contract after `ft_transfer_call` was initiated by
/// `sender_id` of the given `amount` with the transfer message given in `msg` field.
/// The `amount` of tokens were already transferred to this contract account and ready to be used.
///
/// The method must return the amount of tokens that are *not* used/accepted by this contract from the transferred
/// amount. Examples:
/// - The transferred amount was `500`, the contract completely takes it and must return `0`.
/// - The transferred amount was `500`, but this transfer call only needs `450` for the action passed in the `msg`
/// field, then the method must return `50`.
/// - The transferred amount was `500`, but the action in `msg` field has expired and the transfer must be
/// cancelled. The method must return `500` or panic.
///
/// Arguments:
/// - `sender_id` - the account ID that initiated the transfer.
/// - `amount` - the amount of tokens that were transferred to this account in a decimal string representation.
/// - `msg` - a string message that was passed with this transfer call.
///
/// Returns the amount of unused tokens that should be returned to sender, in a decimal string representation.
fn ft_on_transfer(
&mut self,
sender_id: AccountId,
amount: U128,
msg: String,
) -> PromiseOrValue<U128>;
}