first commit

internal/ical/ical.go

@@ -0,0 +1,150 @@
+// Package ical implements a minimal RFC 5545 iCalendar parser/builder — just
+// VEVENT with the fields CalDAV needs: UID, SUMMARY, DTSTART, DTEND,
+// DESCRIPTION, LOCATION. Not full RFC 5545 (no VTODO/VJOURNAL/VALARM, no
+// RRULE recurrence) — enough for real calendar clients to create, fetch, and
+// list single events, with recurrence and other component types as natural
+// next additions once client compatibility testing calls for them.
+package ical
+
+import (
+	"fmt"
+	"strings"
+	"time"
+)
+
+const icalTimeLayout = "20060102T150405Z"
+
+type Event struct {
+	UID         string
+	Summary     string
+	Description string
+	Location    string
+	DTStart     time.Time
+	DTEnd       time.Time
+}
+
+// Parse reads a VCALENDAR containing one VEVENT.
+func Parse(data string) (*Event, error) {
+	lines := unfold(data)
+	e := &Event{}
+	inEvent := false
+
+	for _, line := range lines {
+		line = strings.TrimSpace(line)
+		if line == "" {
+			continue
+		}
+		upper := strings.ToUpper(line)
+		switch {
+		case upper == "BEGIN:VEVENT":
+			inEvent = true
+			continue
+		case upper == "END:VEVENT":
+			inEvent = false
+			continue
+		}
+		if !inEvent {
+			continue
+		}
+
+		name, value, found := splitProperty(line)
+		if !found {
+			continue
+		}
+		switch strings.ToUpper(name) {
+		case "UID":
+			e.UID = value
+		case "SUMMARY":
+			e.Summary = unescape(value)
+		case "DESCRIPTION":
+			e.Description = unescape(value)
+		case "LOCATION":
+			e.Location = unescape(value)
+		case "DTSTART":
+			if t, err := time.Parse(icalTimeLayout, value); err == nil {
+				e.DTStart = t
+			}
+		case "DTEND":
+			if t, err := time.Parse(icalTimeLayout, value); err == nil {
+				e.DTEnd = t
+			}
+		}
+	}
+
+	if e.UID == "" {
+		return nil, fmt.Errorf("ical missing required UID property")
+	}
+	return e, nil
+}
+
+// Build renders an Event back into a full VCALENDAR/VEVENT block, CRLF line
+// endings per spec.
+func (e *Event) Build() string {
+	var b strings.Builder
+	b.WriteString("BEGIN:VCALENDAR\r\n")
+	b.WriteString("VERSION:2.0\r\n")
+	b.WriteString("PRODID:-//GoMail//CalDAV//EN\r\n")
+	b.WriteString("BEGIN:VEVENT\r\n")
+	b.WriteString("UID:" + e.UID + "\r\n")
+	if !e.DTStart.IsZero() {
+		b.WriteString("DTSTART:" + e.DTStart.UTC().Format(icalTimeLayout) + "\r\n")
+	}
+	if !e.DTEnd.IsZero() {
+		b.WriteString("DTEND:" + e.DTEnd.UTC().Format(icalTimeLayout) + "\r\n")
+	}
+	if e.Summary != "" {
+		b.WriteString("SUMMARY:" + escape(e.Summary) + "\r\n")
+	}
+	if e.Description != "" {
+		b.WriteString("DESCRIPTION:" + escape(e.Description) + "\r\n")
+	}
+	if e.Location != "" {
+		b.WriteString("LOCATION:" + escape(e.Location) + "\r\n")
+	}
+	b.WriteString("END:VEVENT\r\n")
+	b.WriteString("END:VCALENDAR\r\n")
+	return b.String()
+}
+
+func splitProperty(line string) (name, value string, found bool) {
+	colonIdx := strings.Index(line, ":")
+	if colonIdx == -1 {
+		return "", "", false
+	}
+	namePart := line[:colonIdx]
+	value = line[colonIdx+1:]
+	if semiIdx := strings.Index(namePart, ";"); semiIdx != -1 {
+		namePart = namePart[:semiIdx]
+	}
+	return namePart, value, true
+}
+
+// unfold reverses RFC 5545 §3.1 line folding, same rule as vCard's.
+func unfold(data string) []string {
+	raw := strings.Split(strings.ReplaceAll(data, "\r\n", "\n"), "\n")
+	var out []string
+	for _, line := range raw {
+		if len(line) > 0 && (line[0] == ' ' || line[0] == '\t') && len(out) > 0 {
+			out[len(out)-1] += line[1:]
+		} else {
+			out = append(out, line)
+		}
+	}
+	return out
+}
+
+func escape(s string) string {
+	s = strings.ReplaceAll(s, "\\", "\\\\")
+	s = strings.ReplaceAll(s, ",", "\\,")
+	s = strings.ReplaceAll(s, ";", "\\;")
+	s = strings.ReplaceAll(s, "\n", "\\n")
+	return s
+}
+
+func unescape(s string) string {
+	s = strings.ReplaceAll(s, "\\n", "\n")
+	s = strings.ReplaceAll(s, "\\,", ",")
+	s = strings.ReplaceAll(s, "\\;", ";")
+	s = strings.ReplaceAll(s, "\\\\", "\\")
+	return s
+}