From 6fdd09bfe030ce91ee188f18c198fd6a57c7b42f Mon Sep 17 00:00:00 2001
From: Peter Stone <thepeterstone@gmail.com>
Date: Sun, 12 Jul 2026 11:12:55 +0000
Subject: feat(widget): add recurrence lookup endpoint (GET
 /api/widget/recurrence)

---
 internal/api/google_calendar.go | 99 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)

(limited to 'internal/api/google_calendar.go')

diff --git a/internal/api/google_calendar.go b/internal/api/google_calendar.go
index 7381527..bb17812 100644
--- a/internal/api/google_calendar.go
+++ b/internal/api/google_calendar.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"log"
 	"sort"
+	"strconv"
 	"strings"
 	"time"
 
@@ -83,6 +84,86 @@ func deduplicateEvents(events []models.CalendarEvent) []models.CalendarEvent {
 	return unique
 }
 
+var recurrenceFreqNames = map[string]string{
+	"DAILY":   "daily",
+	"WEEKLY":  "weekly",
+	"MONTHLY": "monthly",
+	"YEARLY":  "yearly",
+}
+
+var recurrenceFreqUnits = map[string]string{
+	"DAILY":   "day",
+	"WEEKLY":  "week",
+	"MONTHLY": "month",
+	"YEARLY":  "year",
+}
+
+var recurrenceWeekdayNames = map[string]string{
+	"SU": "Sunday",
+	"MO": "Monday",
+	"TU": "Tuesday",
+	"WE": "Wednesday",
+	"TH": "Thursday",
+	"FR": "Friday",
+	"SA": "Saturday",
+}
+
+// formatRecurrence turns Google Calendar RRULE strings into short English.
+// This intentionally covers only the common cases (FREQ, INTERVAL, BYDAY) --
+// not a full RFC 5545 parser. Anything it can't confidently describe falls
+// back to "Recurring event" rather than showing nothing or an error.
+func formatRecurrence(rrules []string) string {
+	for _, rule := range rrules {
+		rule = strings.TrimPrefix(rule, "RRULE:")
+		parts := make(map[string]string)
+		for _, kv := range strings.Split(rule, ";") {
+			pieces := strings.SplitN(kv, "=", 2)
+			if len(pieces) == 2 {
+				parts[pieces[0]] = pieces[1]
+			}
+		}
+
+		freqKey := parts["FREQ"]
+		unit, ok := recurrenceFreqUnits[freqKey]
+		if !ok {
+			continue
+		}
+
+		interval := 1
+		if iv := parts["INTERVAL"]; iv != "" {
+			if n, err := strconv.Atoi(iv); err == nil && n > 0 {
+				interval = n
+			}
+		}
+
+		var phrase string
+		if interval == 1 {
+			phrase = "Repeats " + recurrenceFreqNames[freqKey]
+		} else {
+			phrase = fmt.Sprintf("Repeats every %d %ss", interval, unit)
+		}
+
+		if byday := parts["BYDAY"]; byday != "" {
+			var days []string
+			for _, code := range strings.Split(byday, ",") {
+				code = strings.TrimSpace(code)
+				if len(code) >= 2 {
+					code = code[len(code)-2:]
+				}
+				if name, ok := recurrenceWeekdayNames[code]; ok {
+					days = append(days, name)
+				}
+			}
+			if len(days) > 0 {
+				phrase += " on " + strings.Join(days, ", ")
+			}
+		}
+
+		return phrase
+	}
+	return "Recurring event"
+}
+
 // NewGoogleCalendarClient creates a client that fetches from multiple calendars.
 // calendarIDs can be comma-separated (e.g., "cal1@group.calendar.google.com,cal2@group.calendar.google.com")
 // timezone is the IANA timezone name for display (e.g., "Pacific/Honolulu")
@@ -203,3 +284,21 @@ func (c *GoogleCalendarClient) GetCalendarList(ctx context.Context) ([]models.Ca
 	}
 	return calendars, nil
 }
+
+// GetRecurrenceRule looks up a recurring event's master record and returns
+// its formatted recurrence schedule. Google's API only puts the RRULE on
+// the master event, not on expanded instances (see parseEventTime's
+// SingleEvents(true) callers), so this does a live lookup by the instance's
+// RecurringEventId. There's no per-event calendar attribution stored today
+// (events from all configured calendars are merged without recording which
+// one they came from), so this tries each configured calendar in turn.
+func (c *GoogleCalendarClient) GetRecurrenceRule(ctx context.Context, recurringEventID string) (string, error) {
+	for _, calendarID := range c.calendarIDs {
+		event, err := c.srv.Events.Get(calendarID, recurringEventID).Do()
+		if err != nil {
+			continue
+		}
+		return formatRecurrence(event.Recurrence), nil
+	}
+	return "", fmt.Errorf("recurring event %s not found on any configured calendar", recurringEventID)
+}
-- 
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