package com.sb.web.account.service;

import com.sb.web.account.domain.AccountEntry;
import com.sb.web.account.domain.Recurring;
import com.sb.web.account.dto.RecurringRequest;
import com.sb.web.account.dto.RecurringResponse;
import com.sb.web.account.mapper.AccountEntryMapper;
import com.sb.web.account.mapper.RecurringMapper;
import com.sb.web.common.exception.ApiException;
import lombok.RequiredArgsConstructor;
import org.springframework.http.HttpStatus;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import java.time.LocalDate;
import java.time.YearMonth;
import java.util.List;

/**
 * 정기/반복 거래 서비스. CRUD + 밀린 회차 자동 생성(중복 없이).
 */
@Service
@RequiredArgsConstructor
public class RecurringService {

    private final RecurringMapper recurringMapper;
    private final AccountEntryMapper entryMapper;

    public List<RecurringResponse> list(Long memberId) {
        return recurringMapper.findByMember(memberId).stream().map(this::toResponse).toList();
    }

    @Transactional
    public RecurringResponse create(RecurringRequest req, Long memberId) {
        Recurring r = toEntity(req);
        r.setMemberId(memberId);
        recurringMapper.insert(r);
        return toResponse(recurringMapper.findByIdAndMember(r.getId(), memberId));
    }

    @Transactional
    public RecurringResponse update(Long id, RecurringRequest req, Long memberId) {
        mustFind(id, memberId);
        Recurring r = toEntity(req);
        r.setId(id);
        r.setMemberId(memberId);
        recurringMapper.update(r);
        return toResponse(recurringMapper.findByIdAndMember(id, memberId));
    }

    @Transactional
    public void delete(Long id, Long memberId) {
        mustFind(id, memberId);
        recurringMapper.delete(id, memberId);
    }

    /** 활성 규칙의 밀린 회차를 오늘까지 생성 (중복 없음). 생성 건수 반환 */
    @Transactional
    public int run(Long memberId) {
        LocalDate today = LocalDate.now();
        int count = 0;
        for (Recurring r : recurringMapper.findActiveByMember(memberId)) {
            LocalDate cursor = r.getLastRunDate() != null ? r.getLastRunDate() : r.getStartDate().minusDays(1);
            LocalDate next = nextOccurrence(r, cursor);
            LocalDate generatedUpTo = null;
            int guard = 0;
            while (next != null && !next.isAfter(today)
                    && (r.getEndDate() == null || !next.isAfter(r.getEndDate()))
                    && guard++ < 1000) {
                entryMapper.insert(buildEntry(r, next, memberId));
                generatedUpTo = next;
                count++;
                next = nextOccurrence(r, next);
            }
            if (generatedUpTo != null) {
                recurringMapper.updateLastRun(r.getId(), generatedUpTo);
            }
        }
        return count;
    }

    /* ===================== 내부 ===================== */

    private AccountEntry buildEntry(Recurring r, LocalDate date, Long memberId) {
        boolean transfer = "TRANSFER".equals(r.getType());
        // 메모가 없으면 제목으로 채워 '확인 필요' 목록에서 알아보기 쉽게 한다.
        String memo = (r.getMemo() != null && !r.getMemo().isBlank()) ? r.getMemo() : r.getTitle();
        return AccountEntry.builder()
                .memberId(memberId)
                .entryDate(date)
                .type(r.getType())
                .category(transfer ? null : r.getCategory())
                .amount(r.getAmount())
                .memo(memo)
                .walletId(r.getWalletId())
                .toWalletId(transfer ? r.getToWalletId() : null)
                // 실제 결제/이체가 일어났는지 사용자가 확인하도록 '확인 필요'로 생성
                .pending(true)
                .build();
    }

    /** from 이후 첫 발생일 (없으면 null) */
    private LocalDate nextOccurrence(Recurring r, LocalDate from) {
        return switch (r.getFrequency()) {
            case "DAILY" -> from.plusDays(1);
            case "WEEKLY" -> {
                int dow = r.getDayOfWeek() != null ? r.getDayOfWeek() : 1;
                LocalDate d = from.plusDays(1);
                while (d.getDayOfWeek().getValue() != dow) d = d.plusDays(1);
                yield d;
            }
            case "MONTHLY" -> {
                int dom = r.getDayOfMonth() != null ? r.getDayOfMonth() : 1;
                YearMonth ym = YearMonth.from(from);
                LocalDate c = clamp(ym, dom);
                if (!c.isAfter(from)) c = clamp(ym.plusMonths(1), dom);
                yield c;
            }
            case "YEARLY" -> {
                int moy = r.getMonthOfYear() != null ? r.getMonthOfYear() : 1;
                int dom = r.getDayOfMonth() != null ? r.getDayOfMonth() : 1;
                LocalDate c = clamp(YearMonth.of(from.getYear(), moy), dom);
                if (!c.isAfter(from)) c = clamp(YearMonth.of(from.getYear() + 1, moy), dom);
                yield c;
            }
            default -> null;
        };
    }

    private LocalDate clamp(YearMonth ym, int dom) {
        return ym.atDay(Math.min(dom, ym.lengthOfMonth()));
    }

    private Recurring toEntity(RecurringRequest req) {
        return Recurring.builder()
                .title(req.getTitle().trim())
                .type(req.getType())
                .amount(req.getAmount())
                .category("TRANSFER".equals(req.getType()) ? null : blankToNull(req.getCategory()))
                .memo(blankToNull(req.getMemo()))
                .walletId(req.getWalletId())
                .toWalletId("TRANSFER".equals(req.getType()) ? req.getToWalletId() : null)
                .frequency(req.getFrequency())
                .dayOfMonth(req.getDayOfMonth())
                .dayOfWeek(req.getDayOfWeek())
                .monthOfYear(req.getMonthOfYear())
                .startDate(req.getStartDate())
                .endDate(req.getEndDate())
                .active(req.isActive())
                .build();
    }

    private RecurringResponse toResponse(Recurring r) {
        LocalDate cursor = r.getLastRunDate() != null ? r.getLastRunDate() : r.getStartDate().minusDays(1);
        LocalDate next = nextOccurrence(r, cursor);
        if (next != null && r.getEndDate() != null && next.isAfter(r.getEndDate())) {
            next = null;
        }
        return RecurringResponse.builder()
                .id(r.getId()).title(r.getTitle()).type(r.getType()).amount(r.getAmount())
                .category(r.getCategory()).memo(r.getMemo())
                .walletId(r.getWalletId()).walletName(r.getWalletName())
                .toWalletId(r.getToWalletId()).toWalletName(r.getToWalletName())
                .frequency(r.getFrequency()).dayOfMonth(r.getDayOfMonth())
                .dayOfWeek(r.getDayOfWeek()).monthOfYear(r.getMonthOfYear())
                .startDate(r.getStartDate()).endDate(r.getEndDate()).lastRunDate(r.getLastRunDate())
                .nextDate(next).active(Boolean.TRUE.equals(r.getActive()))
                .build();
    }

    private Recurring mustFind(Long id, Long memberId) {
        Recurring r = recurringMapper.findByIdAndMember(id, memberId);
        if (r == null) {
            throw new ApiException(HttpStatus.NOT_FOUND, "정기 거래를 찾을 수 없습니다.");
        }
        return r;
    }

    private String blankToNull(String s) {
        return (s == null || s.isBlank()) ? null : s.trim();
    }
}