package vision

import (
	"image"
	"math/bits"

	"github.com/disintegration/imaging"
)

// PHash 计算图像的感知哈希值 (Perceptual Hash)
// 返回 64 位整数。Hamming 距离越小，图片越相似。
func PHash(img image.Image) uint64 {
	// 1. 缩小尺寸到 8x8
	resized := imaging.Resize(img, 8, 8, imaging.Lanczos)
	// 2. 转为灰度
	gray := imaging.Grayscale(resized)
	
	// 3. 计算像素平均值
	var sum uint64
	pixels := make([]uint8, 64)
	for y := 0; y < 8; y++ {
		for x := 0; x < 8; x++ {
			r, _, _, _ := gray.At(x, y).RGBA()
			v := uint8(r >> 8)
			pixels[y*8+x] = v
			sum += uint64(v)
		}
	}
	avg := uint8(sum / 64)

	// 4. 根据平均值生成哈希
	var hash uint64
	for i, v := range pixels {
		if v >= avg {
			hash |= (1 << uint(i))
		}
	}
	return hash
}

// Distance 计算两个哈希值之间的 Hamming 距离
func Distance(h1, h2 uint64) int {
	return bits.OnesCount64(h1 ^ h2)
}