pub trait PurchaseFunctions {
// Required methods
fn get_unique_id(&self) -> u64;
fn has_unique_id(&self, other: u64) -> bool;
fn get_user_id(&self) -> &u32;
fn has_user_id(&self) -> bool;
fn get_item_id(&self) -> &u32;
fn has_item_id(&self) -> bool;
fn get_timestamp(&self) -> &i64;
fn get_special_set_price(&self) -> Option<u32>;
fn is_special(&self) -> bool;
}