Flash Loans

#![no_std]
use soroban_sdk::{contract, contracterror, contractimpl, contracttype, token, Address, Env, log};
 
#[contracterror]
#[derive(Copy, Clone, PartialEq, Eq)]
#[repr(u32)]
pub enum ReceiverError {
    InitFailed = 1,
    NotInitialized = 2,
}
 
pub trait FlashLoanReceiver {
    fn exec_op(env: Env) -> Result<(), ReceiverError>;
}
 
#[contracttype]
pub enum DataKey {
    Token,
    Amount,
    PoolAddress,
}
 
#[contract]
pub struct FlashLoanReceiverContract;
 
fn compute_fee(amount: &i128) -> i128 {
    amount / 1250 // 0.05%, still TBD
}
 
#[contractimpl]
impl FlashLoanReceiver for FlashLoanReceiverContract {
    fn exec_op(e: Env) -> Result<(), ReceiverError> {
        let token_client = if let Some(token) = &e
            .storage()
            .instance()
            .get::<DataKey, Address>(&DataKey::Token)
        {
            token::Client::new(&e, &token)
        } else {
            return Err(ReceiverError::NotInitialized);
        };
 
        let borrowed = e
            .storage()
            .instance()
            .get::<DataKey, i128>(&DataKey::Amount)
            .unwrap();
 
        let total_amount = borrowed + compute_fee(&borrowed);
 
        /// @dev should remove logs before deploying smart contracts
        log!(&e, "Total amount - {}", total_amount);
 
        let flash_loan = e
            .storage()
            .instance()
            .get::<DataKey, Address>(&DataKey::PoolAddress)
            .unwrap();
 
        token_client.approve(
            &e.current_contract_address(),
            &flash_loan,
            &total_amount,
            &(e.ledger().sequence() + 1),
        );
 
        Ok(())
    }
}
 
#[contractimpl]
impl FlashLoanReceiverContract {
    pub fn init(
        e: Env,
        token_id: Address,
        fl_address: Address,
        amount: i128,
    ) -> Result<(), ReceiverError> {
        e.storage().instance().set(&DataKey::Token, &token_id);
        e.storage()
            .instance()
            .set(&DataKey::PoolAddress, &fl_address);
        e.storage().instance().set(&DataKey::Amount, &amount);
 
        Ok(())
    }
}
 
#[cfg(test)]
mod test;