package calendar

import (
	"fmt"
	"time"

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

// EventTime is a timestamp for calendar events. It either represents a real
// point-in time or a calender day, if it's a whole-day event.
type EventTime struct {
	// Time is a timestamp in the timezone originally defined for this event if
	// WholeDay is true. Otherwise, it's a UTC time from which a year, month
	// and day can be extracted and treated as the indication of a 'calendar
	// day' in an unknown timezone.
	Time time.Time
	// WholeDay is true if this EventTime represents an entire calendar day.
	WholeDay bool
}

func (e *EventTime) String() string {
	if e.WholeDay {
		return fmt.Sprintf("%s (whole day)", e.Time.Format("2006/01/02"))
	} else {
		return e.Time.String()
	}
}

// parseICSTime attempts to parse a given ICS DT{START,END} object into an
// EventTime, trying to figure out if the given object represents a timestamp
// or a whole-day event.
func parseICSTime(p *ics.IANAProperty) (*EventTime, error) {
	// If this is has a VALUE of DATE, then this is a whole-day time.
	// Otherwise, it's an actual timestamp.
	valueList, ok := p.ICalParameters[string(ics.ParameterValue)]
	if ok {
		if len(valueList) != 1 || valueList[0] != "DATE" {
			return nil, fmt.Errorf("unsupported time type: %v", valueList)
		}
		ts, err := time.Parse("20060102", p.Value)
		if err != nil {
			return nil, fmt.Errorf("could not parse date %q: %w", p.Value, err)
		}
		return &EventTime{
			Time:     ts,
			WholeDay: true,
		}, nil
	}
	// You would expect that nextcloud would emit VALUE == DATE-TIME for
	// timestamps, but that just doesn't seem to be the case. Maye I should
	// read the ICS standard...

	tzidList, ok := p.ICalParameters[string(ics.ParameterTzid)]
	if !ok || len(tzidList) != 1 {
		return nil, fmt.Errorf("TZID missing")
	}
	tzid := tzidList[0]
	location, err := time.LoadLocation(tzid)
	if err != nil {
		return nil, fmt.Errorf("could not parse TZID %q: %w", tzid, err)
	}

	ts, err := time.ParseInLocation("20060102T150405", p.Value, location)
	if err != nil {
		return nil, fmt.Errorf("could not parse time %q: %w", p.Value, err)
	}

	return &EventTime{
		Time:     ts,
		WholeDay: false,
	}, nil
}