feat: add WannPassts booking app with Go backend and Vue frontend

Initial project setup for a privacy-focused, self-hosted scheduling app:

- Go backend with JWT auth, SQLite storage, and chi router
- Calendar integrations via Google OAuth (FreeBusy), CalDAV, and ICS links
- Public booking pages with configurable slots and booking requests
- AES-256-GCM encryption for stored provider tokens
- Vue 3 + TypeScript frontend with Vite, Pinia, and Vue Router
- Docs, .gitignore, and .env.example for local development

backend/internal/calendar/google.go

@@ -0,0 +1,151 @@
+package calendar
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+
+	"golang.org/x/oauth2"
+	"golang.org/x/oauth2/google"
+)
+
+// GoogleConnConfig ist der verschlüsselt gespeicherte Zustand einer
+// Google-Kalenderverbindung.
+type GoogleConnConfig struct {
+	Token      *oauth2.Token `json:"token"`
+	CalendarID string        `json:"calendar_id"`
+}
+
+// GoogleOAuthConfig baut die OAuth2-Konfiguration. Die FreeBusy-API von Google
+// liefert ausschließlich busy-Zeiträume – gar keine Termindetails.
+func GoogleOAuthConfig(clientID, clientSecret, redirectURL string) *oauth2.Config {
+	return &oauth2.Config{
+		ClientID:     clientID,
+		ClientSecret: clientSecret,
+		RedirectURL:  redirectURL,
+		Scopes:       []string{"https://www.googleapis.com/auth/calendar.readonly"},
+		Endpoint:     google.Endpoint,
+	}
+}
+
+type GoogleProvider struct {
+	conf         *oauth2.Config
+	cfg          GoogleConnConfig
+	onTokenSaved func(*oauth2.Token) // wird aufgerufen, wenn das Token erneuert wurde
+}
+
+func NewGoogleProvider(conf *oauth2.Config, cfg GoogleConnConfig, onTokenSaved func(*oauth2.Token)) *GoogleProvider {
+	return &GoogleProvider{conf: conf, cfg: cfg, onTokenSaved: onTokenSaved}
+}
+
+type googleFreeBusyRequest struct {
+	TimeMin string                          `json:"timeMin"`
+	TimeMax string                          `json:"timeMax"`
+	Items   []googleFreeBusyRequestItem     `json:"items"`
+}
+
+type googleFreeBusyRequestItem struct {
+	ID string `json:"id"`
+}
+
+type googleFreeBusyResponse struct {
+	Calendars map[string]struct {
+		Busy []struct {
+			Start time.Time `json:"start"`
+			End   time.Time `json:"end"`
+		} `json:"busy"`
+		Errors []struct {
+			Reason string `json:"reason"`
+		} `json:"errors"`
+	} `json:"calendars"`
+}
+
+func (p *GoogleProvider) FetchBusy(ctx context.Context, from, to time.Time) ([]Interval, error) {
+	ts := p.conf.TokenSource(ctx, p.cfg.Token)
+	tok, err := ts.Token()
+	if err != nil {
+		return nil, fmt.Errorf("Google-Zugriff ungültig (neu verbinden): %w", err)
+	}
+	if tok.AccessToken != p.cfg.Token.AccessToken {
+		saved := *tok
+		p.cfg.Token = &saved
+		if p.onTokenSaved != nil {
+			p.onTokenSaved(&saved)
+		}
+	}
+
+	body, err := json.Marshal(googleFreeBusyRequest{
+		TimeMin: from.UTC().Format(time.RFC3339),
+		TimeMax: to.UTC().Format(time.RFC3339),
+		Items:   []googleFreeBusyRequestItem{{ID: p.cfg.CalendarID}},
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	client := oauth2.NewClient(ctx, ts)
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
+		"https://www.googleapis.com/calendar/v3/freeBusy", bytes.NewReader(body))
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("Google FreeBusy-Anfrage fehlgeschlagen: %w", err)
+	}
+	defer resp.Body.Close()
+	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("Google FreeBusy-Fehler (HTTP %d): %.200s", resp.StatusCode, string(raw))
+	}
+
+	var out googleFreeBusyResponse
+	if err := json.Unmarshal(raw, &out); err != nil {
+		return nil, fmt.Errorf("Google FreeBusy-Antwort unlesbar: %w", err)
+	}
+
+	cal, ok := out.Calendars[p.cfg.CalendarID]
+	if !ok {
+		return nil, fmt.Errorf("Google: Kalender %s nicht in Antwort", p.cfg.CalendarID)
+	}
+	if len(cal.Errors) > 0 {
+		return nil, fmt.Errorf("Google: %s", cal.Errors[0].Reason)
+	}
+	intervals := make([]Interval, 0, len(cal.Busy))
+	for _, b := range cal.Busy {
+		intervals = append(intervals, Interval{Start: b.Start, End: b.End})
+	}
+	return intervals, nil
+}
+
+// GooglePrimaryCalendar liefert ID und Namen des Primärkalenders – genutzt
+// direkt nach dem OAuth-Flow.
+func GooglePrimaryCalendar(ctx context.Context, client *http.Client) (id, summary string, err error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet,
+		"https://www.googleapis.com/calendar/v3/calendars/primary", nil)
+	if err != nil {
+		return "", "", err
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return "", "", err
+	}
+	defer resp.Body.Close()
+	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	if resp.StatusCode != http.StatusOK {
+		return "", "", fmt.Errorf("Google: Primärkalender nicht lesbar (HTTP %d): %.200s", resp.StatusCode, string(raw))
+	}
+	var cal struct {
+		ID      string `json:"id"`
+		Summary string `json:"summary"`
+	}
+	if err := json.Unmarshal(raw, &cal); err != nil {
+		return "", "", err
+	}
+	return cal.ID, cal.Summary, nil
+}