Add public/private calendars, full iCal support, and iCal URL import

- Public/private: toggle is_public via PUT /calendars/{id}; generate/clear
  public_token and return ical_url when public
- Public feed: GET /cal/{token}/feed.ics (no auth) for subscription in
  Google/Apple/Outlook calendars
- Full iCal export: use golang-ical; VALARM, ATTENDEE, all-day (VALUE=DATE),
  RRULE, DTSTAMP, CREATED, LAST-MODIFIED
- Full iCal import: parse TZID, VALUE=DATE, VALARM, ATTENDEE, RRULE
- Import from URL: POST /calendars/import-url with calendar_id + url
- Migration: unique index on public_token, calendar_subscriptions table
- Config: BASE_URL for ical_url; Calendar model + API: ical_url field
- Docs: OpenAPI, llms.txt, README, SKILL.md, about/overview

Made-with: Cursor

internal/service/calendar.go

@@ -2,6 +2,9 @@ package service
 
 import (
 	"context"
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
 
 	"github.com/calendarapi/internal/models"
 	"github.com/calendarapi/internal/repository"
@@ -16,10 +19,26 @@ type CalendarService struct {
 	pool    *pgxpool.Pool
 	queries *repository.Queries
 	audit   *AuditService
+	baseURL string
 }
 
-func NewCalendarService(pool *pgxpool.Pool, queries *repository.Queries, audit *AuditService) *CalendarService {
-	return &CalendarService{pool: pool, queries: queries, audit: audit}
+func NewCalendarService(pool *pgxpool.Pool, queries *repository.Queries, audit *AuditService, baseURL string) *CalendarService {
+	return &CalendarService{pool: pool, queries: queries, audit: audit, baseURL: baseURL}
+}
+
+func generatePublicToken() (string, error) {
+	b := make([]byte, 32)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
+	}
+	return base64.RawURLEncoding.EncodeToString(b), nil
+}
+
+func (s *CalendarService) icalURL(token string) string {
+	if token == "" {
+		return ""
+	}
+	return fmt.Sprintf("%s/cal/%s/feed.ics", s.baseURL, token)
 }
 
 func (s *CalendarService) Create(ctx context.Context, userID uuid.UUID, name, color string) (*models.Calendar, error) {
@@ -72,6 +91,7 @@ func (s *CalendarService) Create(ctx context.Context, userID uuid.UUID, name, co
 		Name:      cal.Name,
 		Color:     cal.Color,
 		IsPublic:  cal.IsPublic,
+		ICalURL:   s.icalURL(utils.FromPgTextValue(cal.PublicToken)),
 		Role:      "owner",
 		CreatedAt: utils.FromPgTimestamptz(cal.CreatedAt),
 		UpdatedAt: utils.FromPgTimestamptz(cal.UpdatedAt),
@@ -96,6 +116,17 @@ func (s *CalendarService) List(ctx context.Context, userID uuid.UUID) ([]models.
 			UpdatedAt: utils.FromPgTimestamptz(r.UpdatedAt),
 		}
 	}
+
+	// Populate ICalURL for public calendars (requires a separate lookup since ListCalendarsByUser doesn't select public_token)
+	for i := range calendars {
+		if calendars[i].IsPublic {
+			cal, err := s.queries.GetCalendarByID(ctx, utils.ToPgUUID(calendars[i].ID))
+			if err == nil && cal.PublicToken.Valid {
+				calendars[i].ICalURL = s.icalURL(cal.PublicToken.String)
+			}
+		}
+	}
+
 	return calendars, nil
 }
 
@@ -118,6 +149,7 @@ func (s *CalendarService) Get(ctx context.Context, userID uuid.UUID, calID uuid.
 		Name:      cal.Name,
 		Color:     cal.Color,
 		IsPublic:  cal.IsPublic,
+		ICalURL:   s.icalURL(utils.FromPgTextValue(cal.PublicToken)),
 		Role:      role,
 		CreatedAt: utils.FromPgTimestamptz(cal.CreatedAt),
 		UpdatedAt: utils.FromPgTimestamptz(cal.UpdatedAt),
@@ -166,6 +198,26 @@ func (s *CalendarService) Update(ctx context.Context, userID uuid.UUID, calID uu
 		return nil, models.ErrInternal
 	}
 
+	if isPublic != nil {
+		if *isPublic && !cal.PublicToken.Valid {
+			token, err := generatePublicToken()
+			if err != nil {
+				return nil, models.ErrInternal
+			}
+			_ = s.queries.SetCalendarPublicToken(ctx, repository.SetCalendarPublicTokenParams{
+				ID:          utils.ToPgUUID(calID),
+				PublicToken: pgtype.Text{String: token, Valid: true},
+			})
+			cal.PublicToken = pgtype.Text{String: token, Valid: true}
+		} else if !*isPublic && cal.PublicToken.Valid {
+			_ = s.queries.SetCalendarPublicToken(ctx, repository.SetCalendarPublicTokenParams{
+				ID:          utils.ToPgUUID(calID),
+				PublicToken: pgtype.Text{Valid: false},
+			})
+			cal.PublicToken = pgtype.Text{Valid: false}
+		}
+	}
+
 	s.audit.Log(ctx, "calendar", calID, "UPDATE_CALENDAR", userID)
 
 	return &models.Calendar{
@@ -173,6 +225,7 @@ func (s *CalendarService) Update(ctx context.Context, userID uuid.UUID, calID uu
 		Name:      cal.Name,
 		Color:     cal.Color,
 		IsPublic:  cal.IsPublic,
+		ICalURL:   s.icalURL(utils.FromPgTextValue(cal.PublicToken)),
 		Role:      role,
 		CreatedAt: utils.FromPgTimestamptz(cal.CreatedAt),
 		UpdatedAt: utils.FromPgTimestamptz(cal.UpdatedAt),