package calendar

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

// ReminderUIDPrefix namespaces every event maven publishes. Two reasons it is a
// fixed prefix and not a random UUID: the render is idempotent (the same
// reminder always lands on the same UID, so re-rendering overwrites instead of
// duplicating), and everything maven owns in the target collection is
// identifiable at a glance — she never touches a file she did not create.
const ReminderUIDPrefix = "maven-reminder-"

// DefaultReminderDuration — how long a rendered reminder occupies. A reminder
// is an instant, a calendar entry is a span, so one has to be invented; 30
// minutes reads as a block in a calendar app without swallowing the afternoon.
const DefaultReminderDuration = 30 * time.Minute

// ReminderEvent maps a reminder to the event that represents it. id and fire
// come from the store; payload is the RU text as the owner said it, rendered
// verbatim as the summary — the calendar is a view of sqlite, not a place to
// rephrase.
func ReminderEvent(id int64, fire time.Time, payload string, dur time.Duration) Event {
	if dur <= 0 {
		dur = DefaultReminderDuration
	}
	summary := strings.TrimSpace(payload)
	if summary == "" {
		summary = "напоминание"
	}
	return Event{
		UID:     fmt.Sprintf("%s%d", ReminderUIDPrefix, id),
		Summary: summary,
		Start:   fire,
		End:     fire.Add(dur),
	}
}

// ReminderPath is the collection-relative filename for a rendered reminder.
// One event per resource, per the CalDAV convention.
func ReminderPath(id int64) string {
	return fmt.Sprintf("%s%d.ics", ReminderUIDPrefix, id)
}

// ReminderIDFromPath reads back what ReminderPath wrote, given an href out of a
// PROPFIND. It reports false for anything that is not a resource maven
// published, which is what keeps a reconciliation pass from touching a file it
// did not create.
func ReminderIDFromPath(href string) (int64, bool) {
	name := href
	if i := strings.LastIndex(name, "/"); i >= 0 {
		name = name[i+1:]
	}
	if !strings.HasPrefix(name, ReminderUIDPrefix) || !strings.HasSuffix(name, ".ics") {
		return 0, false
	}
	digits := name[len(ReminderUIDPrefix) : len(name)-len(".ics")]
	if digits == "" {
		return 0, false
	}
	id, err := strconv.ParseInt(digits, 10, 64)
	if err != nil || id <= 0 {
		return 0, false
	}
	return id, true
}