package radarfetch

import (
	"image"
	"image/color"
	"image/png"
	"os"
)

var colors15 = []string{
	"#0000F6", "#01A0F6", "#00ECEC", "#01FF00", "#00C800",
	"#019000", "#FFFF00", "#E7C000", "#FF9000", "#FF0000",
	"#D60000", "#C00000", "#FF00F0", "#780084", "#AD90F0",
}

func hexToRGBA(s string, a uint8) color.RGBA {
	if len(s) >= 7 && s[0] == '#' {
		r := xtoi(s[1:3])
		g := xtoi(s[3:5])
		b := xtoi(s[5:7])
		return color.RGBA{uint8(r), uint8(g), uint8(b), a}
	}
	return color.RGBA{0, 0, 0, 0}
}

func xtoi(h string) int {
	v := 0
	for i := 0; i < len(h); i++ {
		c := h[i]
		v <<= 4
		switch {
		case c >= '0' && c <= '9':
			v |= int(c - '0')
		case c >= 'a' && c <= 'f':
			v |= int(c-'a') + 10
		case c >= 'A' && c <= 'F':
			v |= int(c-'A') + 10
		}
	}
	return v
}

func colorForDBZ(dbz float64) color.RGBA {
	if dbz < 0 {
		return color.RGBA{0, 0, 0, 0}
	}
	idx := int(dbz / 5.0)
	if idx < 0 {
		idx = 0
	}
	if idx >= len(colors15) {
		idx = len(colors15) - 1
	}
	return hexToRGBA(colors15[idx], 255)
}

// RenderBinToPNG renders 256x256 BE int16 .bin into a PNG using CMA-style colors.
func RenderBinToPNG(srcPath, dstPath string, flipY bool) error {
	b, err := os.ReadFile(srcPath)
	if err != nil {
		return err
	}
	const w, h = 256, 256
	if len(b) != w*h*2 {
		return ErrSize
	}
	img := image.NewRGBA(image.Rect(0, 0, w, h))
	for row := 0; row < h; row++ {
		outRow := row
		if flipY {
			outRow = h - 1 - row
		}
		for col := 0; col < w; col++ {
			off := (row*w + col) * 2
			u := uint16(b[off])<<8 | uint16(b[off+1])
			v := int16(u)
			if v == 32767 || v < 0 {
				img.SetRGBA(col, outRow, color.RGBA{0, 0, 0, 0})
				continue
			}
			dbz := float64(v) / 10.0
			img.SetRGBA(col, outRow, colorForDBZ(dbz))
		}
	}
	f, err := os.Create(dstPath)
	if err != nil {
		return err
	}
	defer f.Close()
	return png.Encode(f, img)
}

var ErrSize = errSize{}

type errSize struct{}

func (errSize) Error() string { return "unexpected .bin size (expected 131072 bytes)" }