using System;
using System.IO;

namespace AutoFocusTool
{
    /// <summary>
    /// 自检用轻量图像诊断（不依赖 WPF）。
    /// 统计像素亮度，判断是全黑/全白/有图；裸写 24bpp BMP 存盘供肉眼确认。
    /// </summary>
    internal static class Diag
    {
        /// <summary>返回 (最小, 最大, 平均) 灰度。</summary>
        public static (int min, int max, double mean) Stats(byte[] bgr24)
        {
            int min = 255, max = 0;
            long sum = 0;
            // 每3字节取灰度，步进采样(每隔9像素)加速
            int n = 0;
            for (int i = 0; i + 2 < bgr24.Length; i += 27)
            {
                int g = (bgr24[i] * 29 + bgr24[i + 1] * 150 + bgr24[i + 2] * 77) >> 8;
                if (g < min) min = g;
                if (g > max) max = g;
                sum += g; n++;
            }
            return (min, max, n > 0 ? (double)sum / n : 0);
        }

        /// <summary>裸写 24bpp BMP（含 FlipY 翻正）。</summary>
        public static void SaveBmp(byte[] bgr24, int w, int h, string path)
        {
            int rowSize = ((w * 3 + 3) / 4) * 4; // 4字节对齐
            int imgSize = rowSize * h;
            int fileSize = 54 + imgSize;
            using var fs = new FileStream(path, FileMode.Create);
            using var bw = new BinaryWriter(fs);
            // BMP 文件头 14
            bw.Write((byte)'B'); bw.Write((byte)'M');
            bw.Write(fileSize); bw.Write(0); bw.Write(54);
            // DIB 头 40
            bw.Write(40); bw.Write(w); bw.Write(h); // h>0 → 自底向上，正好翻正相机的倒像
            bw.Write((short)1); bw.Write((short)24);
            bw.Write(0); bw.Write(imgSize);
            bw.Write(2835); bw.Write(2835); bw.Write(0); bw.Write(0);
            // 像素：BMP 自底向上存，相机数据是倒的，直接顺序写即翻正
            byte[] pad = new byte[rowSize - w * 3];
            for (int y = 0; y < h; y++)
            {
                int row = y * w * 3;
                bw.Write(bgr24, row, w * 3);
                if (pad.Length > 0) bw.Write(pad);
            }
        }
    }
}