package icons

import (
	"bytes"
	"encoding/binary"
	"image/png"
	"math"
	"runtime"

	"github.com/fogleman/gg"
)

const iconSize = 64

// Render generates a tray icon for the given state.
// Returns ICO bytes on Windows, PNG bytes on other platforms.
func Render(state State) ([]byte, error) {
	dc := gg.NewContext(iconSize, iconSize)
	drawSyncIcon(dc, state)

	var buf bytes.Buffer
	if err := png.Encode(&buf, dc.Image()); err != nil {
		return nil, err
	}

	pngData := buf.Bytes()
	if runtime.GOOS == "windows" {
		return wrapPNGInICO(pngData, iconSize, iconSize), nil
	}
	return pngData, nil
}

// drawSyncIcon draws a circular sync arrows icon in the state's color.
func drawSyncIcon(dc *gg.Context, state State) {
	c := colorForState(state)
	cx := float64(iconSize) / 2
	cy := float64(iconSize) / 2
	radius := float64(iconSize)*0.35
	arrowWidth := 5.0

	dc.SetColor(c)
	dc.SetLineWidth(arrowWidth)
	dc.SetLineCap(gg.LineCapRound)

	// Draw two circular arcs (sync arrows)
	// Top arc: from 220° to 320°
	drawArcWithArrow(dc, cx, cy, radius, degToRad(220), degToRad(320), arrowWidth)
	// Bottom arc: from 40° to 140°
	drawArcWithArrow(dc, cx, cy, radius, degToRad(40), degToRad(140), arrowWidth)
}

func drawArcWithArrow(dc *gg.Context, cx, cy, radius, startAngle, endAngle, lineWidth float64) {
	// Draw the arc
	dc.DrawArc(cx, cy, radius, startAngle, endAngle)
	dc.Stroke()

	// Draw arrowhead at the end of the arc
	endX := cx + radius*math.Cos(endAngle)
	endY := cy + radius*math.Sin(endAngle)

	// Arrow direction is tangent to the circle at the endpoint
	tangentAngle := endAngle + math.Pi/2
	arrowLen := lineWidth * 2.5

	// Two points of the arrowhead
	a1x := endX + arrowLen*math.Cos(tangentAngle+0.5)
	a1y := endY + arrowLen*math.Sin(tangentAngle+0.5)
	a2x := endX + arrowLen*math.Cos(tangentAngle-0.5)
	a2y := endY + arrowLen*math.Sin(tangentAngle-0.5)

	dc.MoveTo(a1x, a1y)
	dc.LineTo(endX, endY)
	dc.LineTo(a2x, a2y)
	dc.Stroke()
}

func degToRad(deg float64) float64 {
	return deg * math.Pi / 180
}

// wrapPNGInICO wraps raw PNG bytes in a minimal ICO container.
func wrapPNGInICO(pngData []byte, width, height int) []byte {
	const headerSize = 6
	const entrySize = 16
	imageOffset := headerSize + entrySize

	buf := new(bytes.Buffer)

	// ICONDIR header
	binary.Write(buf, binary.LittleEndian, uint16(0)) // Reserved
	binary.Write(buf, binary.LittleEndian, uint16(1)) // Type: 1 = icon
	binary.Write(buf, binary.LittleEndian, uint16(1)) // Count: 1 image

	// ICONDIRENTRY
	w := byte(width)
	if width >= 256 {
		w = 0
	}
	h := byte(height)
	if height >= 256 {
		h = 0
	}
	buf.WriteByte(w)
	buf.WriteByte(h)
	buf.WriteByte(0)                                             // ColorCount
	buf.WriteByte(0)                                             // Reserved
	binary.Write(buf, binary.LittleEndian, uint16(1))            // Planes
	binary.Write(buf, binary.LittleEndian, uint16(32))           // BitCount
	binary.Write(buf, binary.LittleEndian, uint32(len(pngData))) // BytesInRes
	binary.Write(buf, binary.LittleEndian, uint32(imageOffset))  // ImageOffset

	buf.Write(pngData)
	return buf.Bytes()
}