package calendar

import (
	"strings"
	"time"

	ics "github.com/arran4/golang-ical"
)

// CalendarClass is a class that represents what "class" the specified event is
//
// Currently, I have only observed this value as being `PUBLIC`, but other
// values are handled as panics
type CalendarClass byte

const (
	ClassPublic CalendarClass = iota
)

func ParseClass(raw string) CalendarClass {
	switch raw {
	case "PUBLIC":
		return ClassPublic
	}
	panic("Unknown class: " + raw)
}

func (cc CalendarClass) String() string {
	switch cc {
	case ClassPublic:
		return "PUBLIC"
	default:
		panic("Unknown class")
	}
}

// CalendarEvent represents a single event in a calendar that is tied to a certain date
type CalendarEvent struct {
	UID string
	// A summary of the event, including the name of the event
	// This value is set every time as far as I can tell
	Summary string
	// A fescription of the event, including more specific information. Not always
	// set, so don't rely on it
	Description string
	// Access class? of the event
	Class        CalendarClass
	LastModified time.Time
	DateStamp    time.Time
	StartTime    time.Time
	EndTime      time.Time
	// Every event comes with a category. This usually contains the name of the
	// class, along with some other information (Semester code, CRN, sections)
	Category struct {
		ClassName string
		OtherData string
	}
}

const calendarTimeFormat = "20060102T150405Z"

// FromVEvent parses an ICS VEvent's format and outputs a specific calendar event, or an error
func FromVEvent(external *ics.VEvent) (event CalendarEvent, err error) {
	if len(external.Components) > 0 {
		panic("Event has unhandled components")
	}

	for _, prop := range external.Properties {
		if len(prop.ICalParameters) > 0 {
			panic("Property has unhandled ICalParameters")
		}

		switch prop.IANAToken {
		case "UID":
			event.UID = prop.Value
		case "SUMMARY":
			event.Summary = prop.Value
		case "DESCRIPTION":
			event.Description = prop.Value
		case "CLASS":
			event.Class = ParseClass(prop.Value)
		case "LAST-MODIFIED":
			event.LastModified, err = time.Parse(calendarTimeFormat, prop.Value)
			if err != nil {
				return event, err
			}
		case "DTSTAMP":
			event.DateStamp, err = time.Parse(calendarTimeFormat, prop.Value)
			if err != nil {
				return event, err
			}
		case "DTSTART":
			event.StartTime, err = time.Parse(calendarTimeFormat, prop.Value)
			if err != nil {
				return event, err
			}
		case "DTEND":
			event.EndTime, err = time.Parse(calendarTimeFormat, prop.Value)
			if err != nil {
				return event, err
			}
		case "CATEGORIES":
			dashIndex := strings.Index(prop.Value, "-")

			// If there was no dash found, treat the property as its entire name
			if dashIndex == -1 {
				event.Category.ClassName = prop.Value
			} else {
				event.Category.ClassName = prop.Value[:dashIndex]
				event.Category.OtherData = prop.Value[dashIndex:]
			}
		default:
			panic("Unknown token when parsing event: " + prop.IANAToken)
		}
	}
	return event, nil
}