Push plan to Google Calendar (Feature 16) (#127)

Co-authored-by: orchestrator-agent <20+orchestrator-agent@code.cubecraftcreations.com>

internal/gcal/calendars.go

@@ -71,7 +71,8 @@ func (s *Service) Calendars(ctx context.Context) ([]Calendar, error) {
 // and name. id must be among Calendars at the time of the call; anything
 // else, including a calendar chosen earlier that has since been deleted or
 // is no longer writable, is ErrUnknownCalendar and leaves the stored
-// choice as it was.
+// choice as it was. Choosing another calendar than the one chosen returns
+// every plan pushed to that one to not synced; see saveSelection.
 func (s *Service) SelectCalendar(ctx context.Context, id string) (Selection, error) {
 	s.account.Lock()
 	defer s.account.Unlock()
@@ -84,28 +85,73 @@ func (s *Service) SelectCalendar(ctx context.Context, id string) (Selection, err
 			continue
 		}
 		sel := Selection{CalendarID: c.ID, CalendarName: c.Summary}
-		n, err := db.New(s.st.Writer).SetIntegrationsGoogleCalendar(ctx, db.SetIntegrationsGoogleCalendarParams{
-			CalendarID:   sql.NullString{String: sel.CalendarID, Valid: true},
-			CalendarName: sql.NullString{String: sel.CalendarName, Valid: true},
-			UpdatedAt:    store.Timestamp{Time: s.now().UTC().Truncate(time.Millisecond)}.String(),
-		})
-		if err != nil {
-			return Selection{}, fmt.Errorf("gcal: save calendar: %w", err)
-		}
-		if n != 1 {
-			// The lock is held since the connection was read, so only a
-			// change outside this service gets here.
-			return Selection{}, ErrNotConnected
+		if err := s.saveSelection(ctx, sel); err != nil {
+			return Selection{}, err
 		}
 		return sel, nil
 	}
 	return Selection{}, ErrUnknownCalendar
 }
 
+// saveSelection stores sel as the chosen calendar. Choosing another calendar
+// than the one stored also forgets every plan day's calendar event id, in
+// the same transaction, since those events are on the calendar no longer
+// chosen (forgetEvents): each plan with one is edited, so a synced plan
+// becomes changed and its next push writes every day to sel. The caller
+// holds s.account, which a push also holds from its event writes through
+// recording them, so a push never records events written to another
+// calendar than the chosen one.
+func (s *Service) saveSelection(ctx context.Context, sel Selection) error {
+	return s.st.WithTx(ctx, func(tx *sql.Tx) error {
+		q := db.New(tx)
+		row, err := q.GetIntegrationsGoogle(ctx)
+		if errors.Is(err, sql.ErrNoRows) {
+			// The lock is held since the connection was read, so only a
+			// change outside this service gets here.
+			return ErrNotConnected
+		}
+		if err != nil {
+			return fmt.Errorf("gcal: read Google integration: %w", err)
+		}
+		now := store.Timestamp{Time: s.now().UTC().Truncate(time.Millisecond)}.String()
+		if _, err := q.SetIntegrationsGoogleCalendar(ctx, db.SetIntegrationsGoogleCalendarParams{
+			CalendarID:   sql.NullString{String: sel.CalendarID, Valid: true},
+			CalendarName: sql.NullString{String: sel.CalendarName, Valid: true},
+			UpdatedAt:    now,
+		}); err != nil {
+			return fmt.Errorf("gcal: save calendar: %w", err)
+		}
+		if row.CalendarID.Valid && row.CalendarID.String == sel.CalendarID {
+			return nil
+		}
+		return forgetEvents(ctx, q, now)
+	})
+}
+
+// forgetEvents records, in the caller's transaction q, that no calendar
+// event id stored is on the chosen calendar any more: every plan with one is
+// edited (a synced plan becomes changed, and a push that read it before is
+// refused), then every id is cleared. Every change that ends the chosen
+// calendar — choosing another (saveSelection) or disconnecting
+// (Disconnect) — runs it in the transaction that makes the change.
+func forgetEvents(ctx context.Context, q *db.Queries, now string) error {
+	if err := q.MarkCalendarPlansEdited(ctx, now); err != nil {
+		return fmt.Errorf("gcal: mark plans pushed to the earlier calendar edited: %w", err)
+	}
+	if err := q.ClearCalendarEvents(ctx, now); err != nil {
+		return fmt.Errorf("gcal: forget events on the earlier calendar: %w", err)
+	}
+	return nil
+}
+
 // calendars lists the writable calendars, each once, with the stored refresh
 // token. The caller holds s.account.
 func (s *Service) calendars(ctx context.Context) ([]Calendar, error) {
-	access, err := s.accessToken(ctx)
+	row, err := s.connection(ctx)
+	if err != nil {
+		return nil, err
+	}
+	access, err := s.accessToken(ctx, row)
 	if err != nil {
 		return nil, err
 	}
@@ -136,16 +182,21 @@ func (s *Service) calendars(ctx context.Context) ([]Calendar, error) {
 	return nil, &CalendarError{msg: fmt.Sprintf("gcal: Google listed more than %d pages of calendars", maxCalendarPages)}
 }
 
-// accessToken trades the stored refresh token for an access token. A grant
-// Google reports as invalid_grant is ErrReconnect.
-func (s *Service) accessToken(ctx context.Context) (string, error) {
+// connection reads the connected account, or ErrNotConnected.
+func (s *Service) connection(ctx context.Context) (db.IntegrationsGoogle, error) {
 	row, err := db.New(s.st.Reader).GetIntegrationsGoogle(ctx)
 	if errors.Is(err, sql.ErrNoRows) {
-		return "", ErrNotConnected
+		return db.IntegrationsGoogle{}, ErrNotConnected
 	}
 	if err != nil {
-		return "", fmt.Errorf("gcal: read Google integration: %w", err)
+		return db.IntegrationsGoogle{}, fmt.Errorf("gcal: read Google integration: %w", err)
 	}
+	return row, nil
+}
+
+// accessToken trades row's refresh token for an access token. A grant
+// Google reports as invalid_grant is ErrReconnect.
+func (s *Service) accessToken(ctx context.Context, row db.IntegrationsGoogle) (string, error) {
 	refresh, err := s.box.Decrypt(row.RefreshTokenCt)
 	if err != nil {
 		return "", fmt.Errorf("gcal: open refresh token: %w", err)