package probe

import (
	"image"
	"math"
	"os"

	_ "image/gif"
	_ "image/jpeg"
	_ "image/png"

	_ "golang.org/x/image/bmp"
	_ "golang.org/x/image/tiff"
	_ "golang.org/x/image/webp"
)

// AnalyzeBrightness 打开并解码图片，分析明暗程度。
// darkScore: 暗色像素（亮度 < 80）占比；lightScore: 亮色像素（亮度 > 175）占比。
func AnalyzeBrightness(filePath string) (darkScore float64, lightScore float64, err error) {
	f, err := os.Open(filePath)
	if err != nil {
		return 0, 0, err
	}
	defer f.Close()
	img, _, err := image.Decode(f)
	if err != nil {
		return 0, 0, err
	}
	dark, light := analyzeBrightness(img)
	return dark, light, nil
}

// analyzeBrightness 统计暗色/亮色像素占比（ITU-R BT.601 亮度公式），大图自动采样加速
func analyzeBrightness(img image.Image) (darkScore float64, lightScore float64) {
	bounds := img.Bounds()
	totalPixels := bounds.Dx() * bounds.Dy()
	if totalPixels == 0 {
		return 0, 0
	}

	darkCount, lightCount, sampleCount := 0, 0, 0
	sampleStep := 1
	if totalPixels > 1_000_000 {
		sampleStep = int(math.Sqrt(float64(totalPixels) / 100_000))
	}

	for y := bounds.Min.Y; y < bounds.Max.Y; y += sampleStep {
		for x := bounds.Min.X; x < bounds.Max.X; x += sampleStep {
			r, g, b, _ := img.At(x, y).RGBA()
			r8 := uint8(r >> 8)
			g8 := uint8(g >> 8)
			b8 := uint8(b >> 8)
			brightness := 0.299*float64(r8) + 0.587*float64(g8) + 0.114*float64(b8)
			if brightness < 80 {
				darkCount++
			} else if brightness > 175 {
				lightCount++
			}
			sampleCount++
		}
	}

	if sampleCount == 0 {
		return 0, 0
	}
	return float64(darkCount) / float64(sampleCount), float64(lightCount) / float64(sampleCount)
}