feat: recurring transactions

internal/service/recurring_event.go

@@ -0,0 +1,427 @@
+package service
+
+import (
+	"fmt"
+	"log/slog"
+	"strings"
+	"time"
+
+	"git.juancwu.dev/juancwu/budgit/internal/model"
+	"git.juancwu.dev/juancwu/budgit/internal/repository"
+	"github.com/google/uuid"
+	"github.com/shopspring/decimal"
+)
+
+// RecurringEventService manages recurring bills, funds, and transfers and
+// materializes due events into actual transactions via TransactionService.
+type RecurringEventService struct {
+	repo           repository.RecurringEventRepository
+	txService      *TransactionService
+	accountService *AccountService
+}
+
+func NewRecurringEventService(
+	repo repository.RecurringEventRepository,
+	txService *TransactionService,
+	accountService *AccountService,
+) *RecurringEventService {
+	return &RecurringEventService{
+		repo:           repo,
+		txService:      txService,
+		accountService: accountService,
+	}
+}
+
+type CreateRecurringEventInput struct {
+	SpaceID         string
+	Kind            model.RecurringEventKind
+	SourceAccountID string
+	Title           string
+	Amount          decimal.Decimal
+	Description     string
+
+	Frequency     model.RecurringFrequency
+	IntervalCount int
+	DayOfWeek     *int
+	DayOfMonth    *int
+	MonthOfYear   *int
+	FireHour      int
+	FireMinute    int
+	Timezone      string
+
+	// StartDate is the local calendar date (Y-M-D) of the first intended firing
+	// in the event's timezone. The first NextRunAt is computed from StartDate,
+	// FireHour, FireMinute, and Timezone — clamped to the recurrence anchors.
+	StartDate time.Time
+}
+
+func (s *RecurringEventService) Create(input CreateRecurringEventInput) (*model.RecurringEvent, error) {
+	if err := validateRule(input.Kind, input.SourceAccountID, input.Frequency, input.IntervalCount, input.DayOfWeek, input.DayOfMonth, input.MonthOfYear, input.FireHour, input.FireMinute, input.Timezone); err != nil {
+		return nil, err
+	}
+	title := strings.TrimSpace(input.Title)
+	if title == "" {
+		return nil, fmt.Errorf("title is required")
+	}
+	if !input.Amount.IsPositive() {
+		return nil, fmt.Errorf("amount must be greater than zero")
+	}
+	if input.SpaceID == "" {
+		return nil, fmt.Errorf("space id is required")
+	}
+
+	loc, err := time.LoadLocation(input.Timezone)
+	if err != nil {
+		return nil, fmt.Errorf("invalid timezone: %w", err)
+	}
+	if input.StartDate.IsZero() {
+		return nil, fmt.Errorf("start date is required")
+	}
+
+	firstFire, err := firstFireOnOrAfter(input.Frequency, input.IntervalCount, input.DayOfWeek, input.DayOfMonth, input.MonthOfYear, input.FireHour, input.FireMinute, loc, input.StartDate)
+	if err != nil {
+		return nil, err
+	}
+
+	var description *string
+	if d := strings.TrimSpace(input.Description); d != "" {
+		description = &d
+	}
+
+	now := time.Now().UTC()
+	ev := &model.RecurringEvent{
+		ID:              uuid.NewString(),
+		SpaceID:         input.SpaceID,
+		Kind:            input.Kind,
+		SourceAccountID: input.SourceAccountID,
+		Title:           title,
+		Amount:          input.Amount,
+		Description:     description,
+		Frequency:       input.Frequency,
+		IntervalCount:   input.IntervalCount,
+		DayOfWeek:       input.DayOfWeek,
+		DayOfMonth:      input.DayOfMonth,
+		MonthOfYear:     input.MonthOfYear,
+		FireHour:        input.FireHour,
+		FireMinute:      input.FireMinute,
+		Timezone:        input.Timezone,
+		NextRunAt:       firstFire.UTC(),
+		Paused:          false,
+		CreatedAt:       now,
+		UpdatedAt:       now,
+	}
+
+	if err := s.repo.Create(ev); err != nil {
+		return nil, fmt.Errorf("failed to create recurring event: %w", err)
+	}
+	return ev, nil
+}
+
+type UpdateRecurringEventInput struct {
+	ID              string
+	Kind            model.RecurringEventKind
+	SourceAccountID string
+	Title           string
+	Amount          decimal.Decimal
+	Description     string
+
+	Frequency     model.RecurringFrequency
+	IntervalCount int
+	DayOfWeek     *int
+	DayOfMonth    *int
+	MonthOfYear   *int
+	FireHour      int
+	FireMinute    int
+	Timezone      string
+
+	// StartDate, if non-zero, recomputes the next firing. If zero, the current
+	// cursor is kept (useful for purely cosmetic edits like renaming).
+	StartDate time.Time
+}
+
+func (s *RecurringEventService) Update(input UpdateRecurringEventInput) (*model.RecurringEvent, error) {
+	if err := validateRule(input.Kind, input.SourceAccountID, input.Frequency, input.IntervalCount, input.DayOfWeek, input.DayOfMonth, input.MonthOfYear, input.FireHour, input.FireMinute, input.Timezone); err != nil {
+		return nil, err
+	}
+	title := strings.TrimSpace(input.Title)
+	if title == "" {
+		return nil, fmt.Errorf("title is required")
+	}
+	if !input.Amount.IsPositive() {
+		return nil, fmt.Errorf("amount must be greater than zero")
+	}
+
+	existing, err := s.repo.ByID(input.ID)
+	if err != nil {
+		return nil, err
+	}
+
+	loc, err := time.LoadLocation(input.Timezone)
+	if err != nil {
+		return nil, fmt.Errorf("invalid timezone: %w", err)
+	}
+
+	nextRun := existing.NextRunAt
+	if !input.StartDate.IsZero() {
+		firstFire, err := firstFireOnOrAfter(input.Frequency, input.IntervalCount, input.DayOfWeek, input.DayOfMonth, input.MonthOfYear, input.FireHour, input.FireMinute, loc, input.StartDate)
+		if err != nil {
+			return nil, err
+		}
+		nextRun = firstFire.UTC()
+	}
+
+	var description *string
+	if d := strings.TrimSpace(input.Description); d != "" {
+		description = &d
+	}
+
+	existing.Kind = input.Kind
+	existing.SourceAccountID = input.SourceAccountID
+	existing.Title = title
+	existing.Amount = input.Amount
+	existing.Description = description
+	existing.Frequency = input.Frequency
+	existing.IntervalCount = input.IntervalCount
+	existing.DayOfWeek = input.DayOfWeek
+	existing.DayOfMonth = input.DayOfMonth
+	existing.MonthOfYear = input.MonthOfYear
+	existing.FireHour = input.FireHour
+	existing.FireMinute = input.FireMinute
+	existing.Timezone = input.Timezone
+	existing.NextRunAt = nextRun
+
+	if err := s.repo.Update(existing); err != nil {
+		return nil, err
+	}
+	return existing, nil
+}
+
+func (s *RecurringEventService) Delete(id string) error {
+	return s.repo.Delete(id)
+}
+
+func (s *RecurringEventService) SetPaused(id string, paused bool) error {
+	return s.repo.SetPaused(id, paused)
+}
+
+func (s *RecurringEventService) Get(id string) (*model.RecurringEvent, error) {
+	return s.repo.ByID(id)
+}
+
+func (s *RecurringEventService) ListBySpace(spaceID string) ([]*model.RecurringEvent, error) {
+	return s.repo.BySpaceID(spaceID)
+}
+
+func (s *RecurringEventService) ListByAccount(accountID string) ([]*model.RecurringEvent, error) {
+	return s.repo.ByAccountID(accountID)
+}
+
+// ProcessDue materializes every recurring event whose next_run_at is at or
+// before `now`, advancing each cursor and backfilling missed occurrences. One
+// event's failure is logged but does not stop processing of others.
+func (s *RecurringEventService) ProcessDue(now time.Time) error {
+	events, err := s.repo.DueBefore(now)
+	if err != nil {
+		return fmt.Errorf("failed to list due events: %w", err)
+	}
+	for _, ev := range events {
+		if err := s.fireUntilCaughtUp(ev, now); err != nil {
+			slog.Error("recurring event materialization failed",
+				"error", err, "event_id", ev.ID, "kind", ev.Kind)
+		}
+	}
+	return nil
+}
+
+func (s *RecurringEventService) fireUntilCaughtUp(ev *model.RecurringEvent, now time.Time) error {
+	loc, err := time.LoadLocation(ev.Timezone)
+	if err != nil {
+		return fmt.Errorf("invalid timezone %q: %w", ev.Timezone, err)
+	}
+	for !ev.NextRunAt.After(now) {
+		if err := s.materialize(ev); err != nil {
+			return fmt.Errorf("materialize: %w", err)
+		}
+		next, err := nextFireAfter(ev, ev.NextRunAt, loc)
+		if err != nil {
+			return fmt.Errorf("compute next: %w", err)
+		}
+		last := ev.NextRunAt
+		if err := s.repo.UpdateCursor(ev.ID, next, last); err != nil {
+			return fmt.Errorf("persist cursor: %w", err)
+		}
+		ev.LastRunAt = &last
+		ev.NextRunAt = next
+	}
+	return nil
+}
+
+func (s *RecurringEventService) materialize(ev *model.RecurringEvent) error {
+	desc := ""
+	if ev.Description != nil {
+		desc = *ev.Description
+	}
+	switch ev.Kind {
+	case model.RecurringEventKindBill:
+		_, err := s.txService.PayBill(PayBillInput{
+			AccountID:   ev.SourceAccountID,
+			Title:       ev.Title,
+			Amount:      ev.Amount,
+			OccurredAt:  ev.NextRunAt,
+			Description: desc,
+		})
+		return err
+	case model.RecurringEventKindFund:
+		_, err := s.txService.Deposit(DepositInput{
+			AccountID:   ev.SourceAccountID,
+			Title:       ev.Title,
+			Amount:      ev.Amount,
+			OccurredAt:  ev.NextRunAt,
+			Description: desc,
+		})
+		return err
+	}
+	return fmt.Errorf("unknown recurring event kind: %s", ev.Kind)
+}
+
+// ----- Recurrence math -----
+
+func validateRule(kind model.RecurringEventKind, src string, freq model.RecurringFrequency, interval int, dow, dom, moy *int, hour, minute int, tz string) error {
+	switch kind {
+	case model.RecurringEventKindBill, model.RecurringEventKindFund:
+		// ok
+	default:
+		return fmt.Errorf("invalid kind: %s", kind)
+	}
+	if src == "" {
+		return fmt.Errorf("source account is required")
+	}
+	if interval < 1 {
+		return fmt.Errorf("interval must be at least 1")
+	}
+	if hour < 0 || hour > 23 || minute < 0 || minute > 59 {
+		return fmt.Errorf("invalid time of day")
+	}
+	if tz == "" {
+		return fmt.Errorf("timezone is required")
+	}
+	if _, err := time.LoadLocation(tz); err != nil {
+		return fmt.Errorf("invalid timezone: %w", err)
+	}
+	switch freq {
+	case model.RecurringFrequencyDaily:
+		// no anchors required
+	case model.RecurringFrequencyWeekly:
+		if dow == nil || *dow < 0 || *dow > 6 {
+			return fmt.Errorf("weekly events require day of week")
+		}
+	case model.RecurringFrequencyMonthly:
+		if dom == nil || *dom < 1 || *dom > 31 {
+			return fmt.Errorf("monthly events require day of month")
+		}
+	case model.RecurringFrequencyYearly:
+		if dom == nil || *dom < 1 || *dom > 31 {
+			return fmt.Errorf("yearly events require day of month")
+		}
+		if moy == nil || *moy < 1 || *moy > 12 {
+			return fmt.Errorf("yearly events require month of year")
+		}
+	default:
+		return fmt.Errorf("invalid frequency: %s", freq)
+	}
+	return nil
+}
+
+// firstFireOnOrAfter computes the first firing in `loc` at or after the local
+// midnight of startDate, snapped to the recurrence anchors and time-of-day.
+func firstFireOnOrAfter(freq model.RecurringFrequency, interval int, dow, dom, moy *int, hour, minute int, loc *time.Location, startDate time.Time) (time.Time, error) {
+	startLocal := time.Date(startDate.Year(), startDate.Month(), startDate.Day(), 0, 0, 0, 0, loc)
+	threshold := startLocal.Add(-time.Nanosecond) // nextFireAfter computes strictly-after; -1ns lets the first candidate land on startDate
+	ev := &model.RecurringEvent{
+		Frequency:     freq,
+		IntervalCount: interval,
+		DayOfWeek:     dow,
+		DayOfMonth:    dom,
+		MonthOfYear:   moy,
+		FireHour:      hour,
+		FireMinute:    minute,
+	}
+	return nextFireAfter(ev, threshold, loc)
+}
+
+// nextFireAfter computes the next firing strictly after `after`, in UTC.
+func nextFireAfter(ev *model.RecurringEvent, after time.Time, loc *time.Location) (time.Time, error) {
+	afterLocal := after.In(loc)
+	switch ev.Frequency {
+	case model.RecurringFrequencyDaily:
+		c := time.Date(afterLocal.Year(), afterLocal.Month(), afterLocal.Day(), ev.FireHour, ev.FireMinute, 0, 0, loc)
+		for !c.After(after) {
+			c = c.AddDate(0, 0, ev.IntervalCount)
+		}
+		return c.UTC(), nil
+
+	case model.RecurringFrequencyWeekly:
+		if ev.DayOfWeek == nil {
+			return time.Time{}, fmt.Errorf("weekly event missing day of week")
+		}
+		c := time.Date(afterLocal.Year(), afterLocal.Month(), afterLocal.Day(), ev.FireHour, ev.FireMinute, 0, 0, loc)
+		shift := (int(time.Weekday(*ev.DayOfWeek)) - int(c.Weekday()) + 7) % 7
+		c = c.AddDate(0, 0, shift)
+		for !c.After(after) {
+			c = c.AddDate(0, 0, 7*ev.IntervalCount)
+		}
+		return c.UTC(), nil
+
+	case model.RecurringFrequencyMonthly:
+		if ev.DayOfMonth == nil {
+			return time.Time{}, fmt.Errorf("monthly event missing day of month")
+		}
+		y, m := afterLocal.Year(), afterLocal.Month()
+		c := monthlyCandidate(y, m, *ev.DayOfMonth, ev.FireHour, ev.FireMinute, loc)
+		for !c.After(after) {
+			y, m = addMonths(y, m, ev.IntervalCount)
+			c = monthlyCandidate(y, m, *ev.DayOfMonth, ev.FireHour, ev.FireMinute, loc)
+		}
+		return c.UTC(), nil
+
+	case model.RecurringFrequencyYearly:
+		if ev.DayOfMonth == nil || ev.MonthOfYear == nil {
+			return time.Time{}, fmt.Errorf("yearly event missing anchors")
+		}
+		moy := time.Month(*ev.MonthOfYear)
+		y := afterLocal.Year()
+		c := monthlyCandidate(y, moy, *ev.DayOfMonth, ev.FireHour, ev.FireMinute, loc)
+		for !c.After(after) {
+			y += ev.IntervalCount
+			c = monthlyCandidate(y, moy, *ev.DayOfMonth, ev.FireHour, ev.FireMinute, loc)
+		}
+		return c.UTC(), nil
+	}
+	return time.Time{}, fmt.Errorf("unknown frequency: %s", ev.Frequency)
+}
+
+// monthlyCandidate constructs a fire time at year/month, clamping the day to
+// that month's actual length (e.g. day=31 in February becomes the 28th/29th).
+func monthlyCandidate(year int, month time.Month, dom, hour, minute int, loc *time.Location) time.Time {
+	last := lastDayOfMonth(year, month, loc)
+	if dom > last {
+		dom = last
+	}
+	return time.Date(year, month, dom, hour, minute, 0, 0, loc)
+}
+
+func lastDayOfMonth(year int, month time.Month, loc *time.Location) int {
+	firstOfNext := time.Date(year, month+1, 1, 0, 0, 0, 0, loc)
+	return firstOfNext.AddDate(0, 0, -1).Day()
+}
+
+func addMonths(y int, m time.Month, n int) (int, time.Month) {
+	total := (int(m) - 1) + n
+	years := total / 12
+	rem := total % 12
+	if rem < 0 {
+		rem += 12
+		years--
+	}
+	return y + years, time.Month(rem + 1)
+}