Read the persisted summary interval from a cookie

This cookie will be read only if the `interval` or `from` query params
are not set. If the cookie is also unset, it will still default to
the "today" interval.

TODO: The cookie still needs to be set on the client
with a `Set-Cookie` response header.

models/shared.go

@@ -12,9 +12,10 @@ import (
 )
 
 const (
-	UserKey       = "user"
-	ImprintKey    = "imprint"
-	AuthCookieKey = "wakapi_auth"
+	UserKey               = "user"
+	ImprintKey            = "imprint"
+	AuthCookieKey         = "wakapi_auth"
+	PersistentIntervalKey = "wakapi_summary_interval"
 )
 
 type MigrationFunc func(db *gorm.DB) error

routes/summary.go

@@ -43,8 +43,14 @@ func (h *SummaryHandler) GetIndex(w http.ResponseWriter, r *http.Request) {
 	rawQuery := r.URL.RawQuery
 	q := r.URL.Query()
 	if q.Get("interval") == "" && q.Get("from") == "" {
-		q.Set("interval", "today")
+		if intervalCookie, _ := r.Cookie(models.PersistentIntervalKey); intervalCookie != nil {
+			q.Set("interval", intervalCookie.Value)
+		} else {
+			q.Set("interval", "today")
+		}
 		r.URL.RawQuery = q.Encode()
+	} else {
+		// TODO: Add a `Set-Cookie: interval` header to persit it on the front-end
 	}
 
 	summaryParams, _ := utils.ParseSummaryParams(r)