feat: serve a subscribable ICS calendar feed
This commit is contained in:
Jakub Zych
235
classes/calendar.go
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235
classes/calendar.go
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package classes
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import (
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"strconv"
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"strings"
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"time"
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"git.golem15.com/jakub/sm-bm-plugin/models"
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)
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// CalendarUIDDomain is the right-hand side of every UID in the feed. It
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// stays fixed, whatever host serves the feed, so a calendar that has
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// subscribed keeps matching its events.
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const CalendarUIDDomain = "bm.jakubzych.com"
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// CalendarName is the X-WR-CALNAME of the feed.
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const CalendarName = "BM UWr – plan zajęć"
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// CalendarOptions selects what a feed lists.
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type CalendarOptions struct {
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// ExcludedCourseIDs are left out, with their sessions and deadlines.
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ExcludedCourseIDs []uint
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// IncludeMeetings adds the meetings as all-day events.
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IncludeMeetings bool
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// IncludeDeadlines adds the deadlines.
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IncludeDeadlines bool
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// SiteURL is the student app's base URL (no trailing slash), used for the
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// course links in the descriptions. Empty leaves the links out.
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SiteURL string
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}
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// CalendarData is what a feed is built from. Sessions need their Course and
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// Meeting loaded, deadlines their Course.
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type CalendarData struct {
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Sessions []models.ClassSession
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Meetings []models.Meeting
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Deadlines []models.Deadline
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}
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// formLabels are the Polish names of the course forms in a summary. "inne"
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// has none: the course name says enough.
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var formLabels = map[string]string{
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models.FormWyklad: "wykład",
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models.FormCwiczenia: "ćwiczenia",
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models.FormKonwersatorium: "konwersatorium",
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models.FormSeminarium: "seminarium",
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}
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// deadlineLead is how long before its due time a deadline event starts:
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// most calendars show a zero-length event badly.
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const deadlineLead = 30 * time.Minute
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// BuildCalendar writes the feed: a VCALENDAR with the class sessions of the
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// courses not excluded, then the meetings and the deadlines when included.
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// Times are written in UTC, so no VTIMEZONE is needed.
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func BuildCalendar(data CalendarData, opt CalendarOptions) []byte {
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excluded := make(map[uint]bool, len(opt.ExcludedCourseIDs))
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for _, id := range opt.ExcludedCourseIDs {
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excluded[id] = true
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}
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var w ICS
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w.Begin("VCALENDAR")
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w.Prop("PRODID", "-//jakubzych//BM UWr//PL")
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w.Prop("VERSION", "2.0")
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w.Prop("CALSCALE", "GREGORIAN")
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w.Prop("METHOD", "PUBLISH")
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w.Text("X-WR-CALNAME", CalendarName)
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w.Prop("X-WR-TIMEZONE", "Europe/Warsaw")
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w.Prop("REFRESH-INTERVAL;VALUE=DURATION", "PT6H")
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w.Prop("X-PUBLISHED-TTL", "PT6H")
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for _, s := range data.Sessions {
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if excluded[s.CourseID] {
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continue
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}
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writeSession(&w, s, opt.SiteURL)
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}
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if opt.IncludeMeetings {
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for _, m := range data.Meetings {
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writeMeeting(&w, m)
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}
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}
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if opt.IncludeDeadlines {
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for _, d := range data.Deadlines {
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if d.CourseID != nil && excluded[*d.CourseID] {
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continue
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}
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writeDeadline(&w, d)
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}
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}
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w.End("VCALENDAR")
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return w.Bytes()
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}
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func uid(kind string, id uint) string {
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return kind + "-" + strconv.FormatUint(uint64(id), 10) + "@" + CalendarUIDDomain
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}
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// stamp writes DTSTAMP and LAST-MODIFIED from the row's update time, so an
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// unchanged row gives the same bytes on every fetch.
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func stamp(w *ICS, updated time.Time) {
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if updated.IsZero() {
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updated = time.Unix(0, 0)
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}
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w.UTC("DTSTAMP", updated)
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w.UTC("LAST-MODIFIED", updated)
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}
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// SessionSummary is the title of a class session: the course name, the form
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// in Polish (none for "inne") and " (online)" for an online session.
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func SessionSummary(s models.ClassSession) string {
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var b strings.Builder
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if s.Course != nil {
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b.WriteString(s.Course.Name)
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if label := formLabels[s.Course.Form]; label != "" {
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b.WriteString(" – ")
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b.WriteString(label)
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}
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} else {
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b.WriteString("Zajęcia")
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}
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if s.IsOnline {
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b.WriteString(" (online)")
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}
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return b.String()
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}
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func writeSession(w *ICS, s models.ClassSession, siteURL string) {
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w.Begin("VEVENT")
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w.Prop("UID", uid("session", s.ID))
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stamp(w, s.UpdatedAt)
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w.Prop("SEQUENCE", "0")
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w.UTC("DTSTART", s.StartsAt.MustTime())
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w.UTC("DTEND", s.EndsAt.MustTime())
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w.Text("SUMMARY", SessionSummary(s))
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switch {
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case s.IsOnline:
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w.Text("LOCATION", "online")
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case s.Room != nil && strings.TrimSpace(*s.Room) != "":
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w.Text("LOCATION", "Koszarowa 3, s. "+strings.TrimSpace(*s.Room)+" (bud. 21 ISMiB)")
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}
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var lines []string
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if s.Course != nil && s.Course.Lecturer != nil && *s.Course.Lecturer != "" {
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lines = append(lines, "Prowadzący: "+*s.Course.Lecturer)
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}
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if s.Meeting != nil {
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lines = append(lines, "Zjazd "+strconv.Itoa(s.Meeting.Number))
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}
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if s.Notes != nil && strings.TrimSpace(*s.Notes) != "" {
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lines = append(lines, strings.TrimSpace(*s.Notes))
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}
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if s.Course != nil && s.Course.ElectiveGroup != nil {
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lines = append(lines, "Przedmiot do wyboru")
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}
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if siteURL != "" {
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link := siteURL + "/przedmioty/" + strconv.FormatUint(uint64(s.CourseID), 10)
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lines = append(lines, link)
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w.Prop("URL", link)
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}
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if len(lines) > 0 {
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w.Text("DESCRIPTION", strings.Join(lines, "\n"))
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}
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w.Prop("STATUS", "CONFIRMED")
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w.End("VEVENT")
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}
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// MeetingSummary is the title of a meeting: "3. zjazd (stacjonarny)", with
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// the mode read from the start of the notes.
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func MeetingSummary(m models.Meeting) string {
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out := strconv.Itoa(m.Number) + ". zjazd"
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if m.Notes != nil {
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notes := strings.ToLower(strings.TrimSpace(*m.Notes))
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switch {
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case strings.HasPrefix(notes, "online"):
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out += " (online)"
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case strings.HasPrefix(notes, "stacjonarn"):
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out += " (stacjonarny)"
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}
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}
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return out
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}
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func writeMeeting(w *ICS, m models.Meeting) {
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start, err := m.StartsOn.Time()
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if err != nil {
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return
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}
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end, err := m.EndsOn.Time()
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if err != nil || end.Before(start) {
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end = start
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}
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w.Begin("VEVENT")
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w.Prop("UID", uid("meeting", m.ID))
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stamp(w, m.UpdatedAt)
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w.Prop("SEQUENCE", "0")
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w.Date("DTSTART", start)
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// DTEND of an all-day event is exclusive: the day after the last day.
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w.Date("DTEND", end.AddDate(0, 0, 1))
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w.Text("SUMMARY", MeetingSummary(m))
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if m.Notes != nil && strings.TrimSpace(*m.Notes) != "" {
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w.Text("DESCRIPTION", strings.TrimSpace(*m.Notes))
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}
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w.Prop("TRANSP", "TRANSPARENT")
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w.End("VEVENT")
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}
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func writeDeadline(w *ICS, d models.Deadline) {
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due, err := d.DueAt.Time()
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if err != nil {
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return
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}
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summary := "Termin: " + d.Title
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w.Begin("VEVENT")
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w.Prop("UID", uid("deadline", d.ID))
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stamp(w, d.UpdatedAt)
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w.Prop("SEQUENCE", "0")
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w.UTC("DTSTART", due.Add(-deadlineLead))
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w.UTC("DTEND", due)
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w.Text("SUMMARY", summary)
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var lines []string
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if d.Course != nil {
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lines = append(lines, "Przedmiot: "+d.Course.Name)
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}
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if d.Description != nil && strings.TrimSpace(*d.Description) != "" {
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lines = append(lines, strings.TrimSpace(*d.Description))
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}
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if len(lines) > 0 {
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w.Text("DESCRIPTION", strings.Join(lines, "\n"))
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}
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w.Begin("VALARM")
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w.Prop("ACTION", "DISPLAY")
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w.Text("DESCRIPTION", summary)
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w.Prop("TRIGGER", "-P1D")
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w.End("VALARM")
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w.End("VEVENT")
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}
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105
classes/ics.go
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105
classes/ics.go
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@@ -0,0 +1,105 @@
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package classes
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import (
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"bytes"
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"strings"
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"time"
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"unicode/utf8"
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)
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// ICS writes an iCalendar (RFC 5545) stream: CRLF line endings, content
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// lines folded at 75 octets without splitting a UTF-8 sequence, and TEXT
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// values escaped. The zero value is ready to use.
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type ICS struct {
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buf bytes.Buffer
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}
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// icsLineOctets is the longest content line RFC 5545 allows, not counting
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// the CRLF.
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const icsLineOctets = 75
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// Begin writes BEGIN:<component>.
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func (w *ICS) Begin(component string) { w.Line("BEGIN:" + component) }
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// End writes END:<component>.
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func (w *ICS) End(component string) { w.Line("END:" + component) }
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// Prop writes name:value with the value as it is (a value of a type that
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// needs no escaping, such as a date, a duration or a URI).
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func (w *ICS) Prop(name, value string) { w.Line(name + ":" + value) }
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// Text writes name:value with the value escaped as TEXT.
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func (w *ICS) Text(name, value string) { w.Line(name + ":" + EscapeText(value)) }
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// UTC writes name:<t in UTC>, such as DTSTART:20261003T060000Z.
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func (w *ICS) UTC(name string, t time.Time) { w.Prop(name, FormatUTC(t)) }
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// Date writes name;VALUE=DATE:<YYYYMMDD> for an all-day value.
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func (w *ICS) Date(name string, t time.Time) { w.Prop(name+";VALUE=DATE", t.Format("20060102")) }
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// Line writes one content line, folded.
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func (w *ICS) Line(line string) {
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line = strings.NewReplacer("\r", "", "\n", "").Replace(line)
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w.buf.WriteString(FoldLine(line))
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w.buf.WriteString("\r\n")
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}
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// Bytes returns the stream written so far.
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func (w *ICS) Bytes() []byte { return w.buf.Bytes() }
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// FormatUTC formats t as an RFC 5545 UTC date-time (20261003T060000Z).
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func FormatUTC(t time.Time) string { return t.UTC().Format("20060102T150405Z") }
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// EscapeText escapes a TEXT value: backslash, semicolon, comma and line
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// breaks (as \n). A lone CR is dropped.
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func EscapeText(s string) string {
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var b strings.Builder
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b.Grow(len(s))
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s = strings.ReplaceAll(s, "\r\n", "\n")
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for _, r := range s {
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switch r {
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case '\\':
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b.WriteString(`\\`)
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case ';':
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b.WriteString(`\;`)
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case ',':
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b.WriteString(`\,`)
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case '\n':
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b.WriteString(`\n`)
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case '\r':
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default:
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b.WriteRune(r)
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}
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}
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return b.String()
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}
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// FoldLine folds a content line (without its CRLF) so that no physical line
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// is longer than 75 octets. Continuation lines start with one space, which
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// counts towards their 75 octets; a multi-octet UTF-8 character is never
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// split.
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func FoldLine(line string) string {
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if len(line) <= icsLineOctets {
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return line
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}
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var b strings.Builder
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n := 0
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for i := 0; i < len(line); {
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size := runeBytes(line[i:])
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if n+size > icsLineOctets {
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b.WriteString("\r\n ")
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n = 1
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}
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b.WriteString(line[i : i+size])
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n += size
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i += size
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}
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return b.String()
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}
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// runeBytes is the length in bytes of the first character of s, also for an
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// invalid sequence (one byte).
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func runeBytes(s string) int {
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_, size := utf8.DecodeRuneInString(s)
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return size
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}
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