// ============================================================
//  PdfiumNative:pdfium.dll 原生库 P/Invoke 封装
//  dll 来源:pypdfium2 win32 wheel(pypdfium2_raw/pdfium.dll,x86)
//  调用约定:cdecl(pypdfium2 ctypes.CDLL 已验证)
// ============================================================
using System;
using System.Runtime.InteropServices;

namespace pdfbt
{
    /// <summary>pdfium C API 最小封装(仅本项目用到的函数)。</summary>
    internal static class PdfiumNative
    {
        public const string DllName = "pdfium.dll";

        // 渲染标志:渲染注释/批注
        public const int FPDF_ANNOT = 0x01;

        // FPDF_ERR_* 错误码(GetLastError 返回)
        public const int FPDF_ERR_SUCCESS = 0;   // 无错误
        public const int FPDF_ERR_UNKNOWN = 1;   // 未知错误
        public const int FPDF_ERR_FILE = 2;      // 文件无法打开或读取
        public const int FPDF_ERR_FORMAT = 3;    // 文件不是 PDF 或已损坏
        public const int FPDF_ERR_PASSWORD = 4;  // 需要密码或密码错误
        public const int FPDF_ERR_SECURITY = 5;  // 不支持的安全方案
        public const int FPDF_ERR_PAGE = 6;      // 页面无法加载

        private static bool _inited;
        private static readonly object _initLock = new object();

        /// <summary>初始化 pdfium(进程内只需一次,线程安全)。</summary>
        public static void InitLibrary()
        {
            lock (_initLock)
            {
                if (_inited) return;
                FPDF_InitLibrary();
                _inited = true;
            }
        }

        [DllImport(DllName)]
        private static extern void FPDF_InitLibrary();

        [DllImport(DllName)]
        private static extern void FPDF_DestroyLibrary();

        [DllImport(DllName, CharSet = CharSet.Ansi)]
        private static extern IntPtr FPDF_LoadDocument(string file_path, string password);

        [DllImport(DllName)]
        private static extern void FPDF_CloseDocument(IntPtr document);

        [DllImport(DllName)]
        private static extern uint FPDF_GetLastError();

        [DllImport(DllName)]
        private static extern int FPDF_GetPageCount(IntPtr document);

        [DllImport(DllName)]
        private static extern IntPtr FPDF_LoadPage(IntPtr document, int page_index);

        [DllImport(DllName)]
        private static extern void FPDF_ClosePage(IntPtr page);

        // ★ 新版 GetPageSizeByIndexF 是 FS_SIZEF* 参数(易错);用稳定的旧版 double API
        [DllImport(DllName)]
        private static extern int FPDF_GetPageSizeByIndex(IntPtr document, int page_index,
            out double width, out double height);

        [DllImport(DllName)]
        private static extern IntPtr FPDFBitmap_Create(int width, int height, int alpha);

        [DllImport(DllName)]
        private static extern void FPDFBitmap_FillRect(IntPtr bitmap, int left, int top,
            int width, int height, uint color);

        [DllImport(DllName)]
        private static extern void FPDFBitmap_Destroy(IntPtr bitmap);

        [DllImport(DllName)]
        private static extern IntPtr FPDFBitmap_GetBuffer(IntPtr bitmap);

        [DllImport(DllName)]
        private static extern int FPDFBitmap_GetStride(IntPtr bitmap);

        [DllImport(DllName)]
        private static extern void FPDF_RenderPageBitmap(IntPtr bitmap, IntPtr page,
            int start_x, int start_y, int size_x, int size_y,
            int rotate, int flags);


        [DllImport(DllName)]
        private static extern IntPtr FPDF_LoadMemDocument(byte[] data, int size, string password);

        public static IntPtr LoadDocumentFromBytes(byte[] data, string password)
        {
            InitLibrary();
            if (data == null || data.Length == 0) return IntPtr.Zero;
            return FPDF_LoadMemDocument(data, data.Length, string.IsNullOrEmpty(password) ? null : password);
        }

        // ------------------------------------------------------------
        //  上层直接使用的安全包装
        // ------------------------------------------------------------

        /// <summary>打开 PDF 文件。失败返回 IntPtr.Zero,可用 LastErrorText 查原因。</summary>
        public static IntPtr LoadDocument(string path, string password)
        {
            InitLibrary();
            if (string.IsNullOrEmpty(path)) return IntPtr.Zero;
            return FPDF_LoadDocument(path, string.IsNullOrEmpty(password) ? null : password);
        }

        public static void CloseDocument(IntPtr doc)
        {
            if (doc != IntPtr.Zero) FPDF_CloseDocument(doc);
        }

        public static int GetPageCount(IntPtr doc)
        {
            if (doc == IntPtr.Zero) return 0;
            return FPDF_GetPageCount(doc);
        }

        /// <summary>取指定页尺寸(PDF 点,1/72 英寸)。失败返回 false。</summary>
        public static bool GetPageSize(IntPtr doc, int pageIndex, out float widthPt, out float heightPt)
        {
            widthPt = 0; heightPt = 0;
            if (doc == IntPtr.Zero) return false;
            double w, h;
            bool ok = FPDF_GetPageSizeByIndex(doc, pageIndex, out w, out h) != 0;
            widthPt = (float)w;
            heightPt = (float)h;
            return ok;
        }

        public static IntPtr LoadPage(IntPtr doc, int pageIndex)
        {
            if (doc == IntPtr.Zero) return IntPtr.Zero;
            return FPDF_LoadPage(doc, pageIndex);
        }

        public static void ClosePage(IntPtr page)
        {
            if (page != IntPtr.Zero) FPDF_ClosePage(page);
        }

        /// <summary>把整页渲染到 GDI+ 位图(白底不透明)。</summary>
        public static System.Drawing.Bitmap RenderPageToBitmap(IntPtr page, int widthPx, int heightPx)
        {
            return RenderRegionToBitmap(page, 0, 0, widthPx, heightPx, widthPx, heightPx);
        }

        /// <summary>
        /// 把页面局部区域渲染到位图(白底不透明)。
        /// 页面整图尺寸 = fullW×fullH 像素;只取 (startX,startY,wPx,hPx) 矩形。
        /// 用于:OCR 框选区域按任意分辨率高清重渲染(与显示缩放无关)。
        /// </summary>
        public static System.Drawing.Bitmap RenderRegionToBitmap(IntPtr page,
            int startX, int startY, int wPx, int hPx, int fullW, int fullH)
        {
            if (page == IntPtr.Zero || wPx <= 0 || hPx <= 0) return null;
            if (wPx > 16384 || hPx > 16384) return null;

            IntPtr bmp = FPDFBitmap_Create(wPx, hPx, 1);
            if (bmp == IntPtr.Zero) return null;
            try
            {
                // 白底不透明(0xAARRGGBB)
                FPDFBitmap_FillRect(bmp, 0, 0, wPx, hPx, 0xFFFFFFFF);
                // start_x/start_y 为负偏移:位图原点相对页面原点
                FPDF_RenderPageBitmap(bmp, page, -startX, -startY, fullW, fullH, 0, FPDF_ANNOT);

                IntPtr buffer = FPDFBitmap_GetBuffer(bmp);
                int stride = FPDFBitmap_GetStride(bmp);
                if (buffer == IntPtr.Zero || stride <= 0) return null;

                // pdfium BGRA(top-down) → GDI+ Format32bppArgb(BGRA) 逐行拷贝
                var result = new System.Drawing.Bitmap(wPx, hPx,
                    System.Drawing.Imaging.PixelFormat.Format32bppArgb);
                var rect = new System.Drawing.Rectangle(0, 0, wPx, hPx);
                var data = result.LockBits(rect,
                    System.Drawing.Imaging.ImageLockMode.WriteOnly,
                    System.Drawing.Imaging.PixelFormat.Format32bppArgb);
                try
                {
                    for (int y = 0; y < hPx; y++)
                    {
                        IntPtr src = new IntPtr(buffer.ToInt64() + (long)y * stride);
                        IntPtr dst = new IntPtr(data.Scan0.ToInt64() + (long)y * data.Stride);
                        NativeMethods.CopyMemory(dst, src, (uint)(wPx * 4));
                    }
                }
                finally
                {
                    result.UnlockBits(data);
                }
                return result;
            }
            finally
            {
                FPDFBitmap_Destroy(bmp);
            }
        }

        public static string LastErrorText()
        {
            uint err = FPDF_GetLastError();
            switch (err)
            {
                case FPDF_ERR_SUCCESS: return "成功";
                case FPDF_ERR_FILE: return "文件无法打开或读取";
                case FPDF_ERR_FORMAT: return "文件不是有效 PDF 或已损坏";
                case FPDF_ERR_PASSWORD: return "PDF 已加密,需要密码";
                case FPDF_ERR_SECURITY: return "不支持的安全方案";
                case FPDF_ERR_PAGE: return "页面内容无法解析";
                default: return "未知错误(" + err + ")";
            }
        }

        private static class NativeMethods
        {
            [DllImport("kernel32.dll", EntryPoint = "RtlMoveMemory", SetLastError = false)]
            public static extern void CopyMemory(IntPtr dest, IntPtr src, uint count);
        }
    }
}