Fix mapping task priorities from Vikunja to calDAV

Resolves #866

pkg/caldav/priority.go

@@ -0,0 +1,66 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-2021 Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public Licensee as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public Licensee for more details.
+//
+// You should have received a copy of the GNU Affero General Public Licensee
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package caldav
+
+// In caldav, priority values are an int from 0 to 9 where 1 is the highest priority and 9 the lowest. 0 is "unset".
+// Vikunja only has priorites from 0 to 5 where 0 is unset and 5 is the highest
+// See https://icalendar.org/iCalendar-RFC-5545/3-8-1-9-priority.html
+func mapPriorityToCaldav(priority int64) (caldavPriority int) {
+	switch priority {
+	case 0:
+		return 0
+	case 1: // Low
+		return 9
+	case 2: // Medium
+		return 5
+	case 3: // High
+		return 3
+	case 4: // Urgent
+		return 2
+	case 5: // DO NOW
+		return 1
+	}
+	return 0
+}
+
+// See mapPriorityToCaldav
+func parseVTODOPriority(priority int64) (vikunjaPriority int64) {
+	switch priority {
+	case 0:
+		return 0
+	case 1:
+		return 5
+	case 2:
+		return 4
+	case 3:
+		return 3
+	case 4:
+		return 3
+	case 5:
+		return 2
+	case 6:
+		return 1
+	case 7:
+		return 1
+	case 8:
+		return 1
+	case 9:
+		return 1
+	}
+
+	return 0
+}