package main

import (
	"fmt"
	"math"
	"time"
)

var (
	uiBg     = rgb{0x12, 0x14, 0x18}
	uiOKFill = rgb{0x18, 0x42, 0x26}
	uiOKEdge = rgb{0x3c, 0xe0, 0x70}
	uiErrFil = rgb{0x54, 0x18, 0x1c}
	uiErrEdg = rgb{0xff, 0x46, 0x46}
	uiButton = rgb{0x25, 0x2b, 0x33}
	uiFg     = rgb{0xe6, 0xe8, 0xea}
	uiDim    = rgb{0x9a, 0xa2, 0xac}
	uiCyan   = rgb{0x5c, 0xc8, 0xe0}
	uiGreen  = rgb{0x6c, 0xdc, 0x86}
	uiRed    = rgb{0xf0, 0x6b, 0x6b}
	uiYellow = rgb{0xe0, 0xb0, 0x40}
)

const (
	uiMargin = 16
	uiPad    = 14
	uiBorder = 12
	rowGap   = 5
	blockGap = 16

	btnW         = 240
	btnH         = 64
	holdDuration = time.Second
)

type rect struct {
	x, y, w, h int
}

func (r rect) contains(x, y int) bool {
	return x >= r.x && x < r.x+r.w && y >= r.y && y < r.y+r.h
}

type display struct {
	fb    *framebuffer
	huge  *textFace
	grid  *textFace
	gridB *textFace

	nowPanel   rect
	sincePanel rect
	nowH       int
	sinceH     int
	resetBtn   rect
	holdStart  time.Time
	holdFrac   float64
	fired      bool
}

func newDisplay() (*display, error) {
	fb, err := openFramebuffer()
	if err != nil {
		return nil, err
	}
	d := &display{fb: fb}
	for _, spec := range []struct {
		dst  **textFace
		bold bool
		size float64
	}{
		{&d.huge, true, 60},
		{&d.grid, false, 22},
		{&d.gridB, true, 22},
	} {
		face, err := loadFace(spec.bold, spec.size)
		if err != nil {
			fb.close()
			return nil, err
		}
		*spec.dst = face
	}
	if d.grid.cellW != d.gridB.cellW {
		fb.close()
		return nil, fmt.Errorf("grid faces disagree on cell width: %d vs %d",
			d.grid.cellW, d.gridB.cellW)
	}
	// Guessed heights collide on a screen this small, so the split follows what
	// the loaded faces actually measure.
	gridLine := d.grid.cellH + rowGap
	errH := len(errRows) * gridLine
	d.nowH = d.huge.cellH + rowGap + gridLine + blockGap + errH
	d.sinceH = 4*gridLine + blockGap + errH + blockGap + btnH

	inner := fb.w - 2*uiMargin
	chrome := 2 * (uiBorder + uiPad)
	avail := fb.h - 2*uiMargin - blockGap
	h1 := (avail-2*chrome)*d.nowH/(d.nowH+d.sinceH) + chrome
	d.nowPanel = rect{uiMargin, uiMargin, inner, h1}
	d.sincePanel = rect{uiMargin, uiMargin + h1 + blockGap, inner, avail - h1}
	d.resetBtn = rect{
		x: d.sincePanel.x + (inner-btnW)/2,
		y: d.sincePanel.y + d.sincePanel.h - uiBorder - uiPad - btnH,
		w: btnW,
		h: btnH,
	}
	return d, nil
}

// Tracks a press and hold on the reset button, returning true once it has been
// held long enough. Lifting or sliding off cancels, and the press has to be
// released before it can arm again.
func (d *display) holdReset(x, y int, down bool, now time.Time) bool {
	if !down {
		d.holdStart, d.holdFrac, d.fired = time.Time{}, 0, false
		return false
	}
	if d.fired || !d.resetBtn.contains(x, y) {
		d.holdStart, d.holdFrac = time.Time{}, 0
		return false
	}
	if d.holdStart.IsZero() {
		d.holdStart = now
	}
	d.holdFrac = now.Sub(d.holdStart).Seconds() / holdDuration.Seconds()
	if d.holdFrac < 1 {
		return false
	}
	d.holdFrac, d.fired, d.holdStart = 0, true, time.Time{}
	return true
}

func (d *display) drawResetButton() {
	r := d.resetBtn
	d.fb.rect(r.x, r.y, r.w, r.h, uiButton)

	if d.holdFrac > 0 {
		w := int(float64(r.w) * math.Min(d.holdFrac, 1))
		d.fb.rect(r.x, r.y, w, r.h, uiCyan)
	}
	for _, e := range []rect{
		{r.x, r.y, r.w, 2},
		{r.x, r.y + r.h - 2, r.w, 2},
		{r.x, r.y, 2, r.h},
		{r.x + r.w - 2, r.y, 2, r.h},
	} {
		d.fb.rect(e.x, e.y, e.w, e.h, uiCyan)
	}

	label := "RESET"
	lx := r.x + (r.w-len(label)*d.gridB.cellW)/2
	ly := r.y + (r.h-d.gridB.cellH)/2
	// The label straddles the fill, so each glyph takes the colour that reads
	// against whatever is behind it.
	split := r.x + int(float64(r.w)*math.Min(d.holdFrac, 1))
	for i, c := range label {
		gx := lx + i*d.gridB.cellW
		col := uiFg
		if gx+d.gridB.cellW/2 < split {
			col = uiBg
		}
		d.gridB.draw(d.fb, gx, ly, string(c), col)
	}
}

func (d *display) close() {
	d.fb.close()
}

func (d *display) right(f *textFace, xEnd, y int, s string, col rgb) {
	f.draw(d.fb, xEnd-len([]rune(s))*f.cellW, y, s, col)
}

func (d *display) row(f *textFace, x, w, y int, label, value string, col rgb) int {
	f.draw(d.fb, x, y, label, uiDim)
	d.right(f, x+w, y, value, col)
	return y + f.cellH + rowGap
}

func (d *display) rateRow(x, w, y int, label string, gb, target float64) int {
	d.gridB.draw(d.fb, x, y+(d.huge.cellH-d.gridB.cellH)/2, label, uiDim)
	d.right(d.huge, x+w, y, fmt.Sprintf("%.2f Gb/s", gb), rateColor(gb, target))
	return y + d.huge.cellH + rowGap
}

var errRows = []struct {
	label string
	get   func(errs) uint64
}{
	{"lost", func(e errs) uint64 { return e.lost }},
	{"late", func(e errs) uint64 { return e.late }},
	{"crc", func(e errs) uint64 { return e.crc }},
	{"bad magic", func(e errs) uint64 { return e.badMagic }},
	{"bad length", func(e errs) uint64 { return e.badLen }},
	{"kernel drops", func(e errs) uint64 { return e.kdrop }},
	{"link", func(e errs) uint64 { return e.link }},
}

func (d *display) errBlock(x, w, y int, e errs) int {
	for _, r := range errRows {
		n := r.get(e)
		y = d.row(d.grid, x, w, y, r.label, commas(n), errColor(n))
	}
	return y
}

func (d *display) panel(p rect, e errs, contentH int) (int, int, int) {
	fill, edge := uiOKFill, uiOKEdge
	if e.total() > 0 {
		fill, edge = uiErrFil, uiErrEdg
	}
	d.fb.rect(p.x, p.y, p.w, p.h, edge)
	d.fb.rect(p.x+uiBorder, p.y+uiBorder,
		p.w-2*uiBorder, p.h-2*uiBorder, fill)

	inset := uiBorder + uiPad
	x, w := p.x+inset, p.w-2*inset
	y := p.y + inset
	if slack := (p.y + p.h - inset) - y - contentH; slack > 0 {
		y += slack / 2
	}
	return x, w, y
}

// Rendered rates are quantised so the text only changes when the value moves
// meaningfully. Without this the low digits churn every frame no matter how
// long the averaging window is.
func roundPPS(v float64) uint64 {
	const unit = 1000
	if v < 0 {
		return 0
	}
	return uint64((v+unit/2)/unit) * unit
}

func errColor(n uint64) rgb {
	if n == 0 {
		return uiGreen
	}
	return uiRed
}

func rateColor(gb, target float64) rgb {
	switch {
	case gb >= target*rateGreenFrac:
		return uiGreen
	case gb >= target*rateYellowFrac:
		return uiYellow
	default:
		return uiRed
	}
}

func (d *display) render(v view, elapsed time.Duration, target float64, cable string) error {
	fb := d.fb
	fb.fill(uiBg)

	x, w, y := d.panel(d.nowPanel, v.window, d.nowH)
	y = d.rateRow(x, w, y, "RX", v.rxGbps, target)
	y = d.row(d.grid, x, w, y, "packets/s", commas(roundPPS(v.rxPPS)), uiFg)
	d.errBlock(x, w, y+blockGap, v.window)

	x, w, y = d.panel(d.sincePanel, v.since, d.sinceH)
	y = d.row(d.grid, x, w, y, "uptime", uptime(elapsed), uiFg)
	y = d.row(d.grid, x, w, y, "frames", commas(v.rxFrames), uiFg)
	y = d.row(d.grid, x, w, y, "data", humanBytes(v.rxGot), uiFg)
	y = d.row(d.grid, x, w, y, "cable", cable, uiCyan)
	d.errBlock(x, w, y+blockGap, v.since)

	d.drawResetButton()
	return fb.flush()
}