Webflux-Payments/src/main/java/com/test/payment/service/PaymentLimitStore.java

package com.test.payment.service;

import com.test.payment.dto.PaymentRequest;
import com.test.payment.dto.ProviderLimitDto;
import com.test.payment.exceptions.PaymentLimitExceededException;
import com.test.payment.models.LimitPeriod;
import com.test.payment.models.LimitScope;
import com.test.payment.models.PaymentProviderType;
import com.test.payment.models.ProviderLimit;
import com.test.payment.repository.PaymentInitiationRepository;
import com.test.payment.repository.ProviderLimitRepository;
import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.http.HttpStatus;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.web.server.ResponseStatusException;

import java.math.BigDecimal;
import java.time.LocalDateTime;
import java.util.Arrays;
import java.util.List;

/**
 * The blocking, transactional half of {@link PaymentLimitService} — see
 * {@link PaymentLifecycleStore} for why the split exists.
 */
@Service
@RequiredArgsConstructor
@Slf4j
public class PaymentLimitStore {

    private final ProviderLimitRepository limitRepository;
    private final PaymentInitiationRepository initiationRepository;
    private final StatusCatalog statuses;

    /**
     * Returns normally when the request is within every active limit; throws
     * PaymentLimitExceededException on the first breach.
     */
    @Transactional(readOnly = true)
    public void enforce(PaymentProviderType provider, PaymentRequest request) {
        BigDecimal amount = BigDecimal.valueOf(request.getAmount());
        LocalDateTime now = LocalDateTime.now();

        for (ProviderLimit limit : limitRepository.findByProviderAndActiveTrue(provider)) {
            check(limit, provider, request.getPhoneNumber(), amount, now);
        }
    }

    @Transactional(readOnly = true)
    public List<ProviderLimit> list(PaymentProviderType provider) {
        return provider == null
                ? limitRepository.findAllByOrderByProviderAscPeriodAsc()
                : limitRepository.findByProviderOrderByPeriod(provider);
    }

    /**
     * Creates or updates the ceiling for one provider/period/scope triple.
     * Scope defaults to PER_PAYER when the caller omits it.
     */
    @Transactional
    public ProviderLimit upsert(ProviderLimitDto dto) {
        PaymentProviderType provider = parseProvider(dto.getProvider());
        String period = dto.getPeriod().toUpperCase();
        String scope = dto.getScope() == null ? LimitScope.PER_PAYER.name() : dto.getScope().toUpperCase();
        validateNames(period, scope);

        LocalDateTime now = LocalDateTime.now();
        ProviderLimit limit = limitRepository.findByProviderAndPeriodAndScope(provider, period, scope)
                .orElseGet(() -> ProviderLimit.builder()
                        .Provider(provider)
                        .Period(period)
                        .Scope(scope)
                        .CreatedAt(now)
                        .build());

        limit.setMaxAmount(dto.getMaxAmount());
        limit.setCurrency(dto.getCurrency() != null ? dto.getCurrency() : limit.getCurrency());
        limit.setActive(dto.getActive() == null ? Boolean.TRUE : dto.getActive());
        limit.setUpdatedAt(now);

        ProviderLimit saved = limitRepository.save(limit);
        log.info("Provider limit set: {} {} = {}", saved.getProvider(), saved.getPeriod(), saved.getMaxAmount());
        return saved;
    }

    private void check(ProviderLimit limit, PaymentProviderType provider, String phoneNumber,
                       BigDecimal amount, LocalDateTime now) {
        LimitPeriod period = parsePeriod(limit);
        if (period == null) {
            return;
        }

        if (!period.isCumulative()) {
            if (amount.compareTo(limit.getMaxAmount()) > 0) {
                throw breach(limit, provider, amount, BigDecimal.ZERO);
            }
            return;
        }

        LocalDateTime since = period.windowStart(now);
        BigDecimal alreadySpent = scopeOf(limit) == LimitScope.MERCHANT
                ? initiationRepository.sumAmountInWindowForProvider(provider, since, statuses.failedName())
                : initiationRepository.sumAmountInWindow(provider, phoneNumber, since, statuses.failedName());
        if (alreadySpent == null) {
            alreadySpent = BigDecimal.ZERO;
        }

        if (alreadySpent.add(amount).compareTo(limit.getMaxAmount()) > 0) {
            throw breach(limit, provider, amount, alreadySpent);
        }
    }

    private PaymentLimitExceededException breach(ProviderLimit limit, PaymentProviderType provider,
                                                 BigDecimal amount, BigDecimal alreadySpent) {
        String currency = limit.getCurrency() == null ? "" : limit.getCurrency() + " ";
        String window = LimitPeriod.valueOf(limit.getPeriod()).isCumulative()
                ? limit.getPeriod() + " " + scopeOf(limit)
                : limit.getPeriod();
        String detail = alreadySpent.signum() > 0
                ? " (%s%s already used in this period)".formatted(currency, alreadySpent.toPlainString())
                : "";
        String message = "%s %s limit exceeded: requested %s%s against a maximum of %s%s%s".formatted(
                provider,
                window,
                currency, amount.toPlainString(),
                currency, limit.getMaxAmount().toPlainString(),
                detail);
        log.info("Rejecting payment — {}", message);
        return new PaymentLimitExceededException(message);
    }

    /** Parses the market-qualified provider from a request body, e.g. "airtel_ke". */
    private PaymentProviderType parseProvider(String value) {
        try {
            return PaymentProviderType.valueOf(value.trim().toUpperCase());
        } catch (IllegalArgumentException | NullPointerException ex) {
            throw new ResponseStatusException(HttpStatus.BAD_REQUEST,
                    "provider must be one of " + Arrays.toString(PaymentProviderType.values()));
        }
    }

    private void validateNames(String period, String scope) {
        try {
            LimitPeriod.valueOf(period);
            LimitScope.valueOf(scope);
        } catch (IllegalArgumentException ex) {
            throw new ResponseStatusException(HttpStatus.BAD_REQUEST,
                    "provider must be one of %s, period one of %s and scope one of %s".formatted(
                            Arrays.toString(PaymentProviderType.values()),
                            Arrays.toString(LimitPeriod.values()),
                            Arrays.toString(LimitScope.values())));
        }
    }

    /**
     * An unset or unrecognised scope falls back to PER_PAYER — the tighter of the two,
     * so a bad row can never silently widen a ceiling.
     */
    private LimitScope scopeOf(ProviderLimit limit) {
        try {
            return LimitScope.valueOf(limit.getScope());
        } catch (IllegalArgumentException | NullPointerException ex) {
            return LimitScope.PER_PAYER;
        }
    }

    /**
     * A row whose period no longer maps to a LimitPeriod constant is skipped rather
     * than failing every payment for that provider.
     */
    private LimitPeriod parsePeriod(ProviderLimit limit) {
        try {
            return LimitPeriod.valueOf(limit.getPeriod());
        } catch (IllegalArgumentException | NullPointerException ex) {
            log.warn("Ignoring provider limit {} with unknown period '{}'", limit.getId(), limit.getPeriod());
            return null;
        }
    }
}