package drw

import (
	"strconv"
	"time"

	"github.com/gdamore/tcell/v2"

	"gitlab.com/tvrdosrz/ck/util"
)

const (
	dayWidth       = 2
	smallGap       = 1
	largeGap       = 3
	maxMonthWidth  = 7*dayWidth + 6*smallGap
	maxMonthHeight = (31+6+(7-1))/7 + 2
	/* maxMonthHeight is the height of a 31-day month starting on Sunday (month
	name and weekdays included) */

	titleHeight = smallGap + 1
)

var (
	Wall tcell.Screen

	monthsWide  int
	monthsHigh  int
	monthsDrawn int
)

func offset(m time.Month) int {
	return (int(util.Date(util.SelTime.Year(), m, 1).Weekday()) + 6) % 7

}

func lastDay(m time.Month) time.Time {
	return util.Date(util.SelTime.Year(), m+1, 0)
}

func monthHeight(m time.Month) int {
	return (offset(m) + lastDay(m).Day() - 1) / 7
}

func bottomOfMonth(m time.Month, w time.Weekday) (time time.Time) {
	last := lastDay(m)

	day := last.Day()
	if w > last.Weekday() {
		day -= 7
	}

	day += int(w - last.Weekday())

	time = util.Date(util.SelTime.Year(), m, day)
	return
}

func topOfMonth(m time.Month, w time.Weekday) (time time.Time) {
	first := util.Date(util.SelTime.Year(), m, 1)
	day := 1

	if w < first.Weekday() {
		day += 7
	}

	day += int(w - first.Weekday())

	time = util.Date(util.SelTime.Year(), m, day)
	return
}

func rowInMonth(m time.Month, day int) int {
	return (day + offset(m) - 1) / 7
}

func leftmostInRow(m time.Month, row int) time.Time {
	if row == 0 {
		return util.Date(util.SelTime.Year(), m, 1)
	}
	if row > monthHeight(m) {
		row = monthHeight(m)
	}

	day := row*7 + 1 - offset(m)

	return util.Date(util.SelTime.Year(), m, day)
}

func rightmostInRow(m time.Month, row int) time.Time {
	if row >= monthHeight(m) {
		return lastDay(m)
	}

	day := row*7 + 7 - offset(m)

	return util.Date(util.SelTime.Year(), m, day)
}

func MoveUp() {
	weekday := util.SelTime.Weekday()
	newTime := util.SelTime.AddDate(0, 0, -7)
	if newTime.Month() == util.SelTime.Month() {
		util.SelTime = newTime
	} else if int(util.SelTime.Month())-monthsWide >= 1 {
		newMonth := util.SelTime.Month() - time.Month(monthsWide)
		util.SelTime = bottomOfMonth(newMonth, weekday)
	}
}

func MoveDown() {
	weekday := util.SelTime.Weekday()
	newTime := util.SelTime.AddDate(0, 0, +7)
	if newTime.Month() == util.SelTime.Month() {
		util.SelTime = newTime
	} else if int(util.SelTime.Month())+monthsWide <= 12 {
		newMonth := util.SelTime.Month() + time.Month(monthsWide)
		util.SelTime = topOfMonth(newMonth, weekday)
	}
}

func MoveRight() {
	if util.SelTime.Weekday() != time.Sunday && util.SelTime.Day() != lastDay(util.SelTime.Month()).Day() {
		util.SelTime = util.SelTime.AddDate(0, 0, 1)
	} else if int(util.SelTime.Month())%monthsWide != 0 && util.SelTime.Month() != time.December {
		util.SelTime = leftmostInRow(util.SelTime.Month()+1, rowInMonth(util.SelTime.Month(), util.SelTime.Day()))
	}
}

func MoveLeft() {
	if util.SelTime.Weekday() != time.Monday && util.SelTime.Day() != 1 {
		util.SelTime = util.SelTime.AddDate(0, 0, -1)
	} else if int(util.SelTime.Month())%monthsWide != 1 && monthsWide != 1 { // special case, if monthsWide
		// is 1, (x%monthsWide) is 0
		util.SelTime = rightmostInRow(util.SelTime.Month()-1, rowInMonth(util.SelTime.Month(), util.SelTime.Day()))
	}
}

func drawMonth(m time.Month, x, y int) {
	centeredText(months[m], x, y, maxMonthWidth, Wall, DefStyle)

	for i := 1; i <= 7; i++ {
		centeredText(weekdays[i%7], x+(i-1)*(dayWidth+smallGap), y+1, dayWidth, Wall, DefStyle)
	}

	dayNum := util.Date(util.SelTime.Year(), m+1, 0).Day()
	for i := 1; i <= dayNum; i++ {
		weekday := int(util.Date(util.SelTime.Year(), m, i).Weekday())
		style := DefStyle
		if util.Today.Day() == i && util.Today.Month() == m {
			style = TodayStyle
		} else if util.SelTime.Day() == i && util.SelTime.Month() == m {
			style = SelStyle
		}
		centeredText(
			strconv.Itoa(i),
			x+((weekday-1+7)%7)*(dayWidth+smallGap),
			y+2,
			2,
			Wall,
			style)
		if weekday == 0 {
			y++
		}
	}
}

func DrawWall() {
	Wall.Clear()
	w, h := Wall.Size()
	if w < maxMonthWidth+2*smallGap || h < maxMonthHeight+2*smallGap+titleHeight {
		wrappedText("Екран је премали за календар.", Wall, DefStyle) // The screen is too small for the calender
		return
	}
	monthsWide = (w - 2*smallGap + largeGap) / (maxMonthWidth + largeGap)
	monthsHigh = (h - smallGap - titleHeight) / (maxMonthHeight + smallGap)
	monthsDrawn = util.Min(monthsHigh*monthsWide, 12)

	startingMonth := time.Month((int(util.SelTime.Month())-1)/monthsDrawn*monthsDrawn + 1)
	endingMonth := time.Month(util.Min(12, int(startingMonth)+monthsDrawn-1))

	centerVert := (w - monthsWide*maxMonthWidth - (monthsWide-1)*largeGap) / 2
	for i, m := 0, startingMonth; i < monthsHigh; i++ {
		for j := 0; j < monthsWide; j++ {
			drawMonth(m, centerVert+j*(maxMonthWidth+largeGap), titleHeight+smallGap+i*(maxMonthHeight+smallGap))
			if m >= endingMonth {
				return
			}
			m++
		}
	}
}