// Package icon draws the KeepOrg padlock at any size.
//
// The glyph is geometry rather than a shipped image, so one definition serves
// the tray (a small PNG, or an ICO on Windows, made at run time) and the
// packages (the Linux icon theme and the macOS .icns, written at build time
// by tools/genicon).
package icon

import (
	"bytes"
	"encoding/binary"
	"image"
	"image/color"
	"image/png"
	"math"
)

// design is the edge length of the coordinate system the shapes are drawn in.
const design = 32.0

// subsamples is the per-axis supersampling rate that antialiases the curves.
const subsamples = 4

var (
	// Brand is the padlock's colour where it stands on its own, in a tray
	// that may be light or dark.
	Brand = color.NRGBA{R: 0x2f, G: 0x6f, B: 0xd6, A: 0xff}
	// Template is the macOS menu-bar form: black, which the system recolours
	// for light and dark menu bars from the alpha channel alone.
	Template = color.NRGBA{A: 0xff}
)

// lock reports whether a design-space point is inside the padlock.
func lock(x, y float64) bool {
	if keyhole(x, y) {
		return false
	}
	// Body: a rounded rectangle.
	if roundedRect(x, y, 5, 14.5, 27, 29, 3) {
		return true
	}
	// Shackle: the top half of a ring, with straight legs into the body.
	d := math.Hypot(x-16, y-12)
	if y <= 12 && d >= 5 && d <= 8.5 {
		return true
	}
	return y > 12 && y < 15 && ((x >= 7.5 && x <= 11) || (x >= 21 && x <= 24.5))
}

func keyhole(x, y float64) bool {
	return math.Hypot(x-16, y-20.5) <= 2.6 || (x >= 15 && x <= 17 && y >= 20.5 && y <= 25.5)
}

// badge is the app icon's background: a rounded square filling the canvas.
func badge(x, y float64) bool { return roundedRect(x, y, 0.5, 0.5, 31.5, 31.5, 7) }

func roundedRect(x, y, x0, y0, x1, y1, r float64) bool {
	if x < x0 || x > x1 || y < y0 || y > y1 {
		return false
	}
	cx := math.Max(x0+r, math.Min(x, x1-r))
	cy := math.Max(y0+r, math.Min(y, y1-r))
	return math.Hypot(x-cx, y-cy) <= r
}

// coverage estimates how much of an output pixel a shape covers.
func coverage(in func(x, y float64) bool, px, py int, scale float64) float64 {
	step := scale / subsamples
	hits := 0
	for sy := 0; sy < subsamples; sy++ {
		for sx := 0; sx < subsamples; sx++ {
			if in(float64(px)*scale+(float64(sx)+0.5)*step, float64(py)*scale+(float64(sy)+0.5)*step) {
				hits++
			}
		}
	}
	return float64(hits) / (subsamples * subsamples)
}

// Tray draws the bare padlock in c on a transparent background, for the
// system tray or the macOS menu bar.
func Tray(size int, c color.NRGBA) *image.NRGBA {
	img := image.NewNRGBA(image.Rect(0, 0, max(size, 0), max(size, 0)))
	scale := design / float64(max(size, 1))
	for py := 0; py < size; py++ {
		for px := 0; px < size; px++ {
			if a := coverage(lock, px, py, scale); a > 0 {
				img.SetNRGBA(px, py, color.NRGBA{c.R, c.G, c.B, uint8(float64(c.A)*a + 0.5)})
			}
		}
	}
	return img
}

// App draws the application icon: a white padlock on a brand-coloured
// rounded square, for launchers, the Dock and file managers.
func App(size int) *image.NRGBA {
	img := image.NewNRGBA(image.Rect(0, 0, max(size, 0), max(size, 0)))
	scale := design / float64(max(size, 1))
	// The padlock is drawn smaller inside the badge, around its centre.
	inner := func(x, y float64) bool { return lock((x-16)/0.72+16, (y-16.5)/0.72+16) }
	for py := 0; py < size; py++ {
		for px := 0; px < size; px++ {
			bg := coverage(badge, px, py, scale)
			if bg == 0 {
				continue
			}
			fg := coverage(inner, px, py, scale)
			mix := func(b, w uint8) uint8 { return uint8(float64(b)*(1-fg) + float64(w)*fg + 0.5) }
			img.SetNRGBA(px, py, color.NRGBA{mix(Brand.R, 0xff), mix(Brand.G, 0xff),
				mix(Brand.B, 0xff), uint8(255*bg + 0.5)})
		}
	}
	return img
}

// PNG encodes an image. Encoding an in-memory NRGBA cannot fail.
func PNG(img image.Image) []byte {
	var b bytes.Buffer
	_ = png.Encode(&b, img)
	return b.Bytes()
}

// ICO wraps PNG-encoded images in an ICO container, which is what the
// Windows tray takes. PNG entries are valid in ICO since Windows Vista.
func ICO(images ...*image.NRGBA) []byte {
	var hdr, data bytes.Buffer
	le := binary.LittleEndian
	_ = binary.Write(&hdr, le, [3]uint16{0, 1, uint16(len(images))})
	offset := 6 + 16*len(images)
	for _, img := range images {
		p := PNG(img)
		w, h := img.Bounds().Dx(), img.Bounds().Dy()
		dim := func(n int) uint8 { // 0 means 256 in an ICO directory entry
			if n >= 256 {
				return 0
			}
			return uint8(n)
		}
		_ = binary.Write(&hdr, le, struct {
			W, H, Colors, Reserved uint8
			Planes, Bits           uint16
			Size, Offset           uint32
		}{dim(w), dim(h), 0, 0, 1, 32, uint32(len(p)), uint32(offset)})
		data.Write(p)
		offset += len(p)
	}
	return append(hdr.Bytes(), data.Bytes()...)
}