projax/caldav/parse.go

package caldav

import (
	"strconv"
	"strings"
	"time"
)

// parseVTodos extracts every VTODO block from a calendar-data string. Hand-
// rolled because importing a full iCalendar parser for the half-dozen fields
// projax cares about is overkill. Tolerates folded lines per RFC 5545 §3.1.
func parseVTodos(ics string) []Todo {
	ics = unfold(ics)
	lines := strings.Split(ics, "\n")
	var out []Todo
	var inTodo bool
	var cur Todo
	for _, ln := range lines {
		ln = strings.TrimRight(ln, "\r")
		if ln == "BEGIN:VTODO" {
			inTodo = true
			cur = Todo{Status: "NEEDS-ACTION"}
			continue
		}
		if ln == "END:VTODO" {
			if cur.UID != "" {
				out = append(out, cur)
			}
			inTodo = false
			continue
		}
		if !inTodo {
			continue
		}
		key, val := splitLine(ln)
		switch key {
		case "UID":
			cur.UID = val
		case "SUMMARY":
			cur.Summary = unescapeText(val)
		case "STATUS":
			cur.Status = strings.ToUpper(val)
		case "PRIORITY":
			if n, err := strconv.Atoi(val); err == nil {
				cur.Priority = n
			}
		case "DUE":
			if t, ok := parseICalTime(val); ok {
				cur.Due = &t
			}
		case "LAST-MODIFIED":
			if t, ok := parseICalTime(val); ok {
				cur.LastModified = &t
			}
		}
	}
	return out
}

// unfold collapses RFC 5545 line continuations (a CRLF followed by a single
// SP or HT continues the previous line).
func unfold(s string) string {
	s = strings.ReplaceAll(s, "\r\n", "\n")
	var b strings.Builder
	lines := strings.Split(s, "\n")
	for i, ln := range lines {
		if i > 0 && len(ln) > 0 && (ln[0] == ' ' || ln[0] == '\t') {
			b.WriteString(ln[1:])
			continue
		}
		if i > 0 {
			b.WriteByte('\n')
		}
		b.WriteString(ln)
	}
	return b.String()
}

// splitLine separates "KEY;PARAMS:VALUE" into ("KEY", "VALUE"). Params dropped
// — we don't need TZID etc. for v1.
func splitLine(ln string) (string, string) {
	colon := strings.Index(ln, ":")
	if colon < 0 {
		return "", ""
	}
	head := ln[:colon]
	val := ln[colon+1:]
	if semi := strings.Index(head, ";"); semi >= 0 {
		head = head[:semi]
	}
	return head, val
}

// parseICalTime recognises both `YYYYMMDDTHHMMSSZ` (UTC) and bare `YYYYMMDD`.
// Floating local-time forms are coerced to UTC for ranking — single user, no
// tz acrobatics needed at v1.
func parseICalTime(v string) (time.Time, bool) {
	v = strings.TrimSpace(v)
	if len(v) == 8 {
		if t, err := time.Parse("20060102", v); err == nil {
			return t, true
		}
	}
	if len(v) >= 15 {
		layouts := []string{"20060102T150405Z", "20060102T150405"}
		for _, l := range layouts {
			if t, err := time.Parse(l, v); err == nil {
				return t, true
			}
		}
	}
	return time.Time{}, false
}

// unescapeText reverses RFC 5545 §3.3.11 text encoding.
func unescapeText(s string) string {
	s = strings.ReplaceAll(s, `\n`, "\n")
	s = strings.ReplaceAll(s, `\N`, "\n")
	s = strings.ReplaceAll(s, `\,`, ",")
	s = strings.ReplaceAll(s, `\;`, ";")
	s = strings.ReplaceAll(s, `\\`, `\`)
	return s
}