pub fn create_loan(
    env: Env,
    borrower: Address,
    vendor: Address,
    amount: i128,
    installments: u32,
    loan_type: LoanType,
) -> Loan

pub fn approve_loan(env: Env, loan_id: u64) -> Loan

pub fn repay_installment(
    env: Env,
    loan_id: u64,
    installment_index: u32,
) -> Loan

pub fn get_loan(env: Env, loan_id: u64) -> Option<Loan>

pub struct Loan {
    pub id: u64,
    pub borrower: Address,
    pub vendor: Address,
    pub amount: i128,
    pub installments: u32,
    pub paid_installments: u32,
    pub status: LoanStatus,
    pub loan_type: LoanType,
    pub created_at: u64,
    pub repayments: Vec<RepaymentInstallment>,
}

pub enum LoanStatus {
    Pending,
    Active,
    Repaid,
    Defaulted,
}