Contractless/src/verifications/async_funcs/verify_borrower.rs

use crate::blocks::loan_payment::ContractPaymentTransaction;
use crate::blocks::loans::LoanContractTransaction;
use crate::common::types::BORROWER_FEE;
use crate::records::wallet_registry::{
    require_canonical_registered_short_address, resolve_pubkey_from_short_address,
};
use crate::rpc::commands::transaction_by_txid::request_transaction_by_txid;
use crate::rpc::responses::RpcResponse;
use crate::sled::Db;
use crate::verifications::async_funcs::checks::balance_check::balance_checkup;
use crate::verifications::async_funcs::checks::mempool_check::memcheck;
use crate::verifications::async_funcs::checks::verify_db::db_hex_verification;
use crate::verifications::async_funcs::total_payments::get_total_payments;
use crate::wallets::structures::Wallet;
use crate::{decode, encode};

impl ContractPaymentTransaction {
    pub async fn verify(&self, db: &Db) -> Result<String, String> {
        let hash = self.unsigned_contract_payment.hash().await;
        let signature = &self.signature;

        // Transactions already present in the mempool can short-circuit
        // the deeper verification path and reuse their stored signature.
        if memcheck(signature, &hash).await {
            return Ok(signature.to_string());
        }

        // Loan payments must come from a valid wallet address and carry a
        // valid signature from the payer.
        let address = &self.unsigned_contract_payment.address;
        if !Wallet::short_address_validation(address) {
            return Err("Lender Wallet Address is Invalid.").map_err(|s| s.to_string())?;
        }
        require_canonical_registered_short_address(db, address, "Lender Wallet Address")?;
        let payer_pubkey = resolve_pubkey_from_short_address(db, address)
            .map_err(|_| "Lender Wallet Address is not registered.".to_string())?
            .ok_or_else(|| "Lender Wallet Address is not registered.".to_string())?;
        let payer_pubkey_hex = encode(&payer_pubkey);
        if !Wallet::verify_transaction_with_public_key(&hash, signature, &payer_pubkey_hex).await {
            return Err("Invalid signature the ContractPaymentTransaction.")
                .map_err(|s| s.to_string())?;
        }

        // Resolve the referenced loan contract from the saved chain so the
        // payment can be validated against its repayment terms.
        let contract_hash = &self.unsigned_contract_payment.contract_hash;
        let contract_key =
            decode(contract_hash).map_err(|e| format!("Invalid contract hash: {e}"))?;
        let contract_bytes = request_transaction_by_txid(db, contract_key.clone()).await;
        let RpcResponse::Binary(bytes) = contract_bytes;

        if bytes.is_empty() {
            return Err("Invalid loan contract: empty transaction bytes".to_string());
        }

        let txtype = bytes[0];
        if txtype != 7 {
            return Err(
                "Invalid loan contract: referenced transaction is not a loan contract".to_string(),
            );
        }

        let body = &bytes[1..];

        let contract = LoanContractTransaction::from_bytes(txtype, body)
            .await
            .map_err(|e| format!("Invalid loan contract: {e}"))?;

        // Payments can only be made against an active contract whose
        // collateral has not already been claimed or closed out.
        let loantree = db.open_tree("loan").unwrap();
        match loantree.get(contract_key) {
            Ok(Some(loan_value)) => {
                if loan_value == "false" {
                    return Err(
                        "The collateral has already been claimed on this contract".to_string()
                    );
                }
            }
            Ok(None) => {
                return Err("This contract is not valid".to_string());
            }
            Err(_) => {
                return Err("This contract is not valid".to_string());
            }
        }

        // Use the saved payment history to prevent overpayment and to
        // determine how much of the contract remains outstanding.
        let total_paidback_amount = get_total_payments(db, contract_hash).await;
        let total_to_be_paidback = contract
            .unsigned_loan_contract
            .payment_amount
            .checked_mul(contract.unsigned_loan_contract.payment_number as u64)
            .ok_or_else(|| "Loan repayment total overflowed.".to_string())?;
        if total_paidback_amount >= total_to_be_paidback {
            return Err("All payments have been made".to_string());
        }

        // Reject payments that would overshoot the remaining balance.
        let payback_amount = self.unsigned_contract_payment.payback_amount;
        let remaining_balance = total_to_be_paidback.saturating_sub(total_paidback_amount);
        if payback_amount > remaining_balance {
            return Err("Payment exceeds the remaining contract balance".to_string());
        }

        // Borrower payments must cover the fixed base-coin fee and an
        // asset-denominated tip of at least 1% of the payment amount.
        let txfee = self.unsigned_contract_payment.txfee;
        if txfee < BORROWER_FEE {
            return Err(format!(
                "Loan payment transaction fee is below the minimum required fee of {BORROWER_FEE}."
            ));
        }
        let tip = self.unsigned_contract_payment.tip;
        let loaned_coin = contract.unsigned_loan_contract.loan_coin;
        let payback_amount = self.unsigned_contract_payment.payback_amount;
        let minimum_tip = payback_amount.div_ceil(100);
        if tip < minimum_tip {
            return Err("Loan payment tip must be at least 1% of the payment amount".to_string());
        }

        // Balance checks combine confirmed wallet state with pending
        // mempool usage so in-flight loan payments cannot overspend.
        let value = tip
            .checked_add(payback_amount)
            .ok_or_else(|| "Loan payment total overflowed.".to_string())?;
        if !balance_checkup(db, value, txfee, loaned_coin, address).await {
            return Err("Insuficient funds for this Transfer Transaction!".to_string());
        }

        // Saved-chain duplicates are rejected by txid even if the mempool
        // did not already contain the transaction.
        let tree = "txid";
        if !db_hex_verification(db, tree, &hash).await {
            return Err("This transaction already exists.".to_string());
        }

        // Verification returns no auxiliary cleanup marker for this transaction type.
        let sign = "";
        Ok(sign.to_string())
    }
}