package timeutil

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

type Period struct {
	Start time.Time `json:"start"`
	End   time.Time `json:"end"`
}

func (p Period) IsValid() bool {
	return p.End.After(p.Start)
}

func (p Period) Overlaps(other Period) bool {
	return p.Start.Before(other.End) && other.Start.Before(p.End)
}

func (p Period) Contains(t time.Time) bool {
	return !t.Before(p.Start) && t.Before(p.End)
}

func (p Period) Intersection(other Period) (Period, bool) {
	if !p.Overlaps(other) {
		return Period{}, false
	}
	start := p.Start
	if other.Start.After(start) {
		start = other.Start
	}
	end := p.End
	if other.End.Before(end) {
		end = other.End
	}
	return Period{Start: start, End: end}, true
}

func ParseClock(value string) (time.Duration, error) {
	parts := strings.Split(value, ":")
	if len(parts) != 2 {
		return 0, fmt.Errorf("expected HH:MM")
	}
	hour, err := strconv.Atoi(parts[0])
	if err != nil {
		return 0, fmt.Errorf("invalid hour")
	}
	minute, err := strconv.Atoi(parts[1])
	if err != nil {
		return 0, fmt.Errorf("invalid minute")
	}
	if hour < 0 || hour > 24 {
		return 0, fmt.Errorf("hour must be between 00 and 24")
	}
	if minute < 0 || minute > 59 {
		return 0, fmt.Errorf("minute must be between 00 and 59")
	}
	if hour == 24 && minute != 0 {
		return 0, fmt.Errorf("24 is only valid as 24:00")
	}
	return time.Duration(hour)*time.Hour + time.Duration(minute)*time.Minute, nil
}

func CivilDay(date time.Time, location *time.Location) Period {
	local := date.In(location)
	start := time.Date(local.Year(), local.Month(), local.Day(), 0, 0, 0, 0, location)
	return Period{Start: start, End: start.AddDate(0, 0, 1)}
}

func ClockWindow(date time.Time, location *time.Location, startClock time.Duration, endClock time.Duration) Period {
	day := CivilDay(date, location)
	start := day.Start.Add(startClock)
	end := day.Start.Add(endClock)
	if !end.After(start) {
		end = end.AddDate(0, 0, 1)
	}
	return Period{Start: start, End: end}
}