// datepick shows a month, and prints the day you click.
//
//	datepick                 one date, as yyyy-mm-dd
//	datepick -r              two, a range, one per line
//	datepick -d 2026-08-01   open on that month
//	datepick -t              a time too: yyyy-mm-dd hh:mm
//	datepick -o file         write it there as well
//	datepick -s              put it on /dev/snarf as well
//
// The last two exist because a window started from wctl has nowhere
// useful to print: nothing is reading its standard output.
//
// It is a program rather than a widget so that anything can use it:
//
//	pim/agenda -d `{datepick}
//	pim/invite 'review' `{datepick}' 15:00'
//
// which is the same reason plumb and 9fs are programs. A widget would
// only ever be usable by whatever linked it.
package main

import (
	"flag"
	"fmt"
	"os"
	"strings"
	"time"

	"9front/gui/draw"
	"9front/gui/ui"
)

const (
	fontpath = "/lib/font/bit/lucidasans/unicode.8.font"
	pad      = 6
)

type picker struct {
	ui.UI
	at   time.Time   // the month on show
	got  []time.Time // what has been clicked
	want int         // how many we need
	mc   *draw.Mousectl
	done bool

	// With -t each answer is picked in stages: the day, then the hour,
	// then the minute. Splitting it keeps every target big enough to
	// hit, where a grid of 96 five-minute slots would not be.
	withTime bool
	stage    int // 0 day, 1 hour, 2 minute
	day      time.Time
	hour     int
}

func main() {
	rng := flag.Bool("r", false, "pick a range: two dates, earliest first")
	from := flag.String("d", "", "open on this month (yyyy-mm-dd)")
	tim := flag.Bool("t", false, "pick a time as well, giving yyyy-mm-dd hh:mm")
	out := flag.String("o", "", "write the answer here as well as to standard output")
	snarf := flag.Bool("s", false, "put the answer on /dev/snarf too")
	flag.Usage = func() {
		fmt.Fprintf(os.Stderr, "usage: datepick [-r] [-t] [-s] [-o file] [-d yyyy-mm-dd]\n")
		os.Exit(2)
	}
	flag.Parse()

	p := &picker{at: time.Now(), want: 1}
	p.withTime = *tim
	if *rng {
		p.want = 2
	}
	if *from != "" {
		t, err := time.Parse("2006-01-02", *from)
		if err != nil {
			fmt.Fprintf(os.Stderr, "datepick: %v\n", err)
			os.Exit(1)
		}
		p.at = t
	}
	if err := p.run(); err != nil {
		fmt.Fprintf(os.Stderr, "datepick: %v\n", err)
		os.Exit(1)
	}
	// nothing chosen is not an error, it is a change of mind, but it
	// should not look like a date to whatever runs us
	if len(p.got) < p.want {
		os.Exit(1)
	}
	var b strings.Builder
	for _, t := range p.got {
		fmt.Fprintln(&b, t.Format(p.layout()))
	}
	fmt.Print(b.String())
	// A window started from wctl has nowhere useful to print, so it can
	// hand the answer over by file or by snarf instead.
	if *out != "" {
		os.WriteFile(*out, []byte(b.String()), 0600)
	}
	if *snarf {
		draw.Snarf("/dev", b.String())
	}
}

func (p *picker) run() error {
	var err error
	if p.D, err = draw.Init("/dev"); err != nil {
		return err
	}
	defer p.D.Close()
	if p.F, err = p.D.OpenFont(fontpath); err != nil {
		return err
	}
	p.Col = map[string]*draw.Image{}
	for k, v := range map[string]uint32{
		"bg":     0xFFFFEAFF,
		"tag":    0xEAFFFFFF,
		"rule":   0x99994CFF,
		"ink":    0x000000FF,
		"today":  0xFFFFAAFF,
		"pick":   0xEEF2FFFF,
		"chosen": 0x99AAEEFF,
		"border": 0x8888CCFF,
	} {
		if p.Col[k], err = p.D.Color(v); err != nil {
			return err
		}
	}
	if p.Win, err = p.D.Window("/dev"); err != nil {
		return err
	}
	kb, err := draw.OpenKeyboard("/dev")
	if err == nil {
		defer kb.Close()
	}
	var keys <-chan rune
	if kb != nil {
		keys = kb.C
	}
	if p.mc, err = draw.OpenMouse("/dev"); err != nil {
		return err
	}
	defer p.mc.Close()

	p.redraw()
	var wasDown bool
	for !p.done {
		select {
		case m, ok := <-p.mc.C:
			if !ok {
				return nil
			}
			if m.Buttons&4 != 0 {
				p.Menu([]ui.Item{
					{Label: "Today", Do: func() { p.at = time.Now(); p.redraw() }},
					{Label: "Restart", Do: func() { p.restart() }},
					{Label: "Cancel", Do: func() { p.done = true }},
				}, m.Point, p.mc, p.redraw)
				wasDown = false
				continue
			}
			switch {
			case m.Buttons&8 != 0:
				p.step(-1)
			case m.Buttons&16 != 0:
				p.step(1)
			}
			down := m.Buttons&1 != 0
			if down && !wasDown {
				p.Click(m.Point)
			}
			wasDown = down
		case r, ok := <-keys:
			if !ok {
				keys = nil
				continue
			}
			switch r {
			case 'q', 0x1B:
				return nil
			case 'h':
				p.step(-1)
			case 'l':
				p.step(1)
			case 't':
				p.at = time.Now()
				p.redraw()
			case 'r':
				p.restart()
			}
		case <-p.mc.Resize:
			if p.Win, err = p.D.Reattach("/dev", p.Win); err != nil {
				return err
			}
			p.redraw()
		}
	}
	return nil
}

// restart forgets what has been picked and goes back to the first
// question. Getting the second date wrong should not mean killing the
// window and starting the command again.
func (p *picker) restart() {
	p.got = p.got[:0]
	p.stage = 0
	p.hour = 0
	p.day = time.Time{}
	p.redraw()
}

func (p *picker) step(n int) {
	p.at = p.at.AddDate(0, n, 0)
	p.redraw()
}

// chooseDay takes the day, and then the clock if we were asked for one.
func (p *picker) chooseDay(d time.Time) {
	if p.withTime {
		p.day = d
		p.stage = 1
		p.redraw()
		return
	}
	p.choose(d)
}

func (p *picker) choose(d time.Time) {
	p.got = append(p.got, d)
	p.stage = 0
	if len(p.got) >= p.want {
		// a range is a range whichever end you clicked first
		if len(p.got) == 2 && p.got[1].Before(p.got[0]) {
			p.got[0], p.got[1] = p.got[1], p.got[0]
		}
		p.done = true
		return
	}
	p.redraw()
}

// layout is how an answer is written: with the time, if we asked for one.
func (p *picker) layout() string {
	if p.withTime {
		return "2006-01-02 15:04"
	}
	return "2006-01-02"
}

func (p *picker) redraw() {
	p.Reset()
	r := p.Body()
	p.Fill(r, "bg")
	if p.stage != 0 {
		p.drawClock(r)
		return
	}

	lh := int32(p.F.Height) + 4
	hdr := draw.Rect(r.Min.X, r.Min.Y, r.Max.X, r.Min.Y+lh+4)
	p.Fill(hdr, "tag")

	x := r.Max.X - pad
	mk := func(label string, do func()) {
		w := p.F.Width(label) + 16
		br := draw.Rect(x-w, hdr.Min.Y+2, x, hdr.Max.Y-2)
		p.Button(br, label, false, do)
		x = br.Min.X - 4
	}
	mk(">", func() { p.step(1) })
	mk("<", func() { p.step(-1) })

	title := p.at.Format("January 2006")
	if p.want == 2 {
		if len(p.got) == 0 {
			title += "   pick from"
		} else {
			// having chosen one end, show it: otherwise the second
			// question is asked with no sign of the first answer
			title += "   from " + p.got[0].Format(p.layout()) + " -- pick to"
		}
	}
	p.Text(draw.Point{X: r.Min.X + pad, Y: hdr.Min.Y + 3}, "ink", title)

	// the grid: whole weeks, Monday first
	first := time.Date(p.at.Year(), p.at.Month(), 1, 0, 0, 0, 0, time.Local)
	off := (int(first.Weekday()) + 6) % 7
	start := first.AddDate(0, 0, -off)

	body := draw.Rect(r.Min.X, hdr.Max.Y+2, r.Max.X, r.Max.Y)
	cw := body.Dx() / 7
	ch := (body.Dy() - lh) / 6

	for i, d := range []string{"Mo", "Tu", "We", "Th", "Fr", "Sa", "Su"} {
		p.Text(draw.Point{X: body.Min.X + int32(i)*cw + 4, Y: body.Min.Y}, "rule", d)
	}

	today := time.Now().Format("2006-01-02")
	for i := 0; i < 42; i++ {
		d := start.AddDate(0, 0, i)
		key := d.Format("2006-01-02")
		cx := body.Min.X + int32(i%7)*cw
		cy := body.Min.Y + lh + int32(i/7)*ch
		cell := draw.Rect(cx, cy, cx+cw-2, cy+ch-2)

		switch {
		case len(p.got) > 0 && key == p.got[0].Format("2006-01-02"):
			p.Fill(cell, "chosen") // the end already picked
		case len(p.got) > 0 && d.After(p.got[0]) && p.want == 2:
			p.Fill(cell, "pick") // still selectable as the other end
		case key == today:
			p.Fill(cell, "today")
		}
		c := "ink"
		if d.Month() != p.at.Month() {
			c = "rule"
		}
		p.Text(draw.Point{X: cell.Min.X + 4, Y: cell.Min.Y + 2}, c, d.Format("2"))
		dd := d
		p.On(cell, func() { p.chooseDay(dd) })
	}
	p.D.Flush()
}

// drawClock is the hour, then the minute. Two grids of a couple of dozen
// cells each, rather than one of ninety-six: the point of picking with a
// mouse is that the target is easy to hit.
func (p *picker) drawClock(r draw.Rectangle) {
	lh := int32(p.F.Height) + 4
	hdr := draw.Rect(r.Min.X, r.Min.Y, r.Max.X, r.Min.Y+lh+4)
	p.Fill(hdr, "tag")

	title := p.day.Format("Monday 2 January")
	if p.stage == 1 {
		title += "   hour"
	} else {
		title += fmt.Sprintf("   %02d:__", p.hour)
	}
	if p.want == 2 && len(p.got) == 1 {
		title = "from " + p.got[0].Format(p.layout()) + " -- " + title
	}
	p.Text(draw.Point{X: r.Min.X + pad, Y: hdr.Min.Y + 3}, "ink", title)

	x := r.Max.X - pad
	w := p.F.Width("back") + 16
	p.Button(draw.Rect(x-w, hdr.Min.Y+2, x, hdr.Max.Y-2), "back", false, func() {
		p.stage--
		p.redraw()
	})

	body := draw.Rect(r.Min.X, hdr.Max.Y+2, r.Max.X, r.Max.Y)

	var labels []string
	var vals []int
	if p.stage == 1 {
		for h := 0; h < 24; h++ {
			labels = append(labels, fmt.Sprintf("%02d", h))
			vals = append(vals, h)
		}
	} else {
		for m := 0; m < 60; m += 5 {
			labels = append(labels, fmt.Sprintf(":%02d", m))
			vals = append(vals, m)
		}
	}

	cols := int32(6)
	rows := (int32(len(labels)) + cols - 1) / cols
	cw := body.Dx() / cols
	ch := body.Dy() / rows
	if ch > lh*3 {
		ch = lh * 3
	}

	for i, lab := range labels {
		cx := body.Min.X + int32(i)%cols*cw
		cy := body.Min.Y + int32(i)/cols*ch
		cell := draw.Rect(cx+1, cy+1, cx+cw-2, cy+ch-2)
		p.Fill(cell, "tag")
		p.Border(cell, "border")
		tw := p.F.Width(lab)
		p.Text(draw.Point{X: cell.Min.X + (cell.Dx()-tw)/2, Y: cell.Min.Y + 2}, "ink", lab)
		v := vals[i]
		p.On(cell, func() {
			if p.stage == 1 {
				p.hour = v
				p.stage = 2
				p.redraw()
				return
			}
			p.choose(time.Date(p.day.Year(), p.day.Month(), p.day.Day(),
				p.hour, v, 0, 0, time.Local))
		})
	}
	p.D.Flush()
}