package objects

import "fmt"
import "time"
import "git.tebibyte.media/tomo/tomo"
import "git.tebibyte.media/tomo/tomo/event"
import "git.tebibyte.media/tomo/objects/layouts"

var _ tomo.Object = new(Calendar)

// Calendar is an object that can display a date and allow the user to change
// it. It can display one month at a time.
// 
// Sub-components:
//   - CalendarGrid organizes the days into a grid.
//   - CalendarWeekdayHeader appears at the top of each grid column, and shows
//     the day of the week that column represents.
//   - CalendarDay appears within the grid for each day of the current month.
//
// CalendarDay tags:
//   - [weekend] The day is a weekend.
//   - [weekday] The day is a weekday.
type Calendar struct {
	box tomo.ContainerBox
	
	grid tomo.ContainerBox
	time time.Time
	monthLabel *Label
	
	on struct {
		valueChange event.FuncBroadcaster
	}
}

// NewCalendar creates a new calendar with the specified date.
func NewCalendar (tm time.Time) *Calendar {
	calendar := &Calendar {
		box:  tomo.NewContainerBox(),
		time: tm,
	}
	calendar.box.SetRole(tomo.R("objects", "Calendar"))
	calendar.box.SetAttr(tomo.ALayout(layouts.ContractVertical))
	
	prevButton := NewButton("")
	prevButton.SetIcon(tomo.IconGoPrevious)
	prevButton.OnClick(func () {
		calendar.prevMonth()
		calendar.on.valueChange.Broadcast()
	})
	nextButton := NewButton("")
	nextButton.SetIcon(tomo.IconGoNext)
	nextButton.OnClick(func () {
		calendar.nextMonth()
		calendar.on.valueChange.Broadcast()
	})
	calendar.monthLabel = NewLabel("")
	calendar.monthLabel.SetAlign(tomo.AlignMiddle, tomo.AlignMiddle)
	
	calendar.grid = tomo.NewContainerBox()
	calendar.grid.SetRole(tomo.R("objects", "CalendarGrid"))
	calendar.grid.SetAttr(tomo.ALayout(layouts.NewGrid (
		true, true, true, true, true, true, true)()))
	calendar.box.Add(NewContainer (
		layouts.Row { false, true, false },
		prevButton, calendar.monthLabel, nextButton))
	calendar.box.Add(calendar.grid)
	
	calendar.box.OnScroll(calendar.handleScroll)
	
	calendar.refresh()
	return calendar
}

// GetBox returns the underlying box.
func (this *Calendar) GetBox () tomo.Box {
	return this.box
}

// Value returns the time this calendar is displaying.
func (this *Calendar) Value () time.Time {
	return this.time
}

// SetValue sets the date the calendar will display.
func (this *Calendar) SetValue (tm time.Time) {
	if this.time == tm { return }
	this.time = tm
	this.refresh()
}

// OnValueChange sets a function to be called when the user changes the date on
// the calendar.
func (this *Calendar) OnValueChange (callback func ()) {
	this.on.valueChange.Connect(callback)
}

func (this *Calendar) prevMonth () {
	this.time = firstOfMonth(this.time.Add(24 * time.Hour * -20))
	this.refresh()
}

func (this *Calendar) nextMonth () {
	this.time = firstOfMonth(this.time.Add(24 * time.Hour * 40))
	this.refresh()
}

var weekdayAbbreviations = []string {
	"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat",
}

func (this *Calendar) refresh () {
	this.monthLabel.SetText(this.time.Format("2006 January"))

	this.grid.Clear()
	for _, day := range weekdayAbbreviations {
		dayLabel := tomo.NewTextBox()
		dayLabel.SetRole(tomo.R("objects", "CalendarWeekdayHeader"))
		dayLabel.SetText(day)
		dayLabel.SetAttr(tomo.AAlign(tomo.AlignMiddle, tomo.AlignMiddle))
		this.grid.Add(dayLabel)
	}
	
	dayIter := 0 - int(firstOfMonth(this.time).Weekday())
	if dayIter <= -6 {
		dayIter = 1
	}
	weekday := 0
	totalDays := daysInMonth(this.time)
	for ; dayIter <= totalDays; dayIter ++ {
		weekday = (weekday + 1) % 7
		if dayIter > 0 {
			day := tomo.NewTextBox()
			day.SetText(fmt.Sprint(dayIter))
			if weekday == 1 || weekday == 0 {
				day.SetRole(tomo.R("objects", "CalendarDay"))
				day.SetTag("weekend", true)
			} else {
				day.SetRole(tomo.R("objects", "CalendarDay"))
				day.SetTag("weekday", true)
			}
			this.grid.Add(day)
		} else {
			this.grid.Add(tomo.NewBox())
		}
	}
}

func (this *Calendar) handleScroll (x, y float64) bool {
	if y < 0 {
		this.prevMonth()
	} else {
		this.nextMonth()
	}
	return true
}

func firstOfMonth (tm time.Time) time.Time {
	return time.Date(tm.Year(), tm.Month(), 0, 0, 0, 0, 0, time.Local)
}

func daysInMonth (tm time.Time) (days int) {
	year  := tm.Year()
	month := tm.Month()
	switch month {
	case 1:  days = 31
	case 2:
		// betcha didn't know this about leap years
		if year % 4 == 0 && (year % 100 != 0 || year % 400 == 0) {
			days = 29
		} else {
			days = 28
		}
	case 3:  days = 31
	case 4:  days = 30
	case 5:  days = 31
	case 6:  days = 30
	case 7:  days = 31
	case 8:  days = 31
	case 9:  days = 30
	case 10: days = 31
	case 11: days = 30
	case 12: days = 31
	}

	return
}

func canonMonth (tm time.Time) int {
	return int(tm.Month() - 1) + tm.Year() * 12
}