// ============================================================
//  PdfDocument:PDF 文档封装(加载/页尺寸/按缩放渲染页位图)
//  坐标系:页面坐标 = PDF 点(1/72 英寸),原点左上(pdfium 渲染后
//  已翻转为屏幕方向,y 向下)。
// ============================================================
using System;
using System.Drawing;
using System.IO;

namespace pdfbt
{
    /// <summary>已打开的 PDF 文档。非线程安全,只在 UI 线程使用。</summary>
    internal sealed class PdfDocument : IDisposable
    {
        private IntPtr _doc = IntPtr.Zero;
        private IntPtr[] _pageHandles;   // 惰性加载的页句柄缓存
        // ★ FPDF_LoadMemDocument 要求后备缓冲在文档关闭前保持有效且不可移动——
        //   原来读入的 byte[] 是局部变量,打开后就没人引用;打开下一个 PDF 的大分配
        //   触发 GC 把它搬走/回收,文档内存变垃圾 → 第二个 PDF 打不开(实测用户报障)。
        //   钉住(GCHandleType.Pinned)+字段保引用,Close 时才释放。
        private byte[] _bytes;
        private System.Runtime.InteropServices.GCHandle _pin;

        public string FilePath { get; private set; }
        public int PageCount { get; private set; }
        public float[] PageWidthPt { get; private set; }
        public float[] PageHeightPt { get; private set; }

        public bool IsOpen
        {
            get { return _doc != IntPtr.Zero; }
        }

        /// <summary>打开 PDF(读入内存后走 FPDF_LoadMemDocument,免疫路径问题)。失败抛异常。</summary>
        public void Open(string path, string password)
        {
            Close();
            if (!File.Exists(path))
                throw new Exception("文件不存在: " + path);
            _bytes = File.ReadAllBytes(path);
            _pin = System.Runtime.InteropServices.GCHandle.Alloc(_bytes,
                System.Runtime.InteropServices.GCHandleType.Pinned);
            IntPtr doc = PdfiumNative.LoadDocumentFromBytes(_bytes, password);
            if (doc == IntPtr.Zero)
            {
                FreeBuffer();
                throw new Exception("PDF 打开失败:" + PdfiumNative.LastErrorText());
            }

            int count = PdfiumNative.GetPageCount(doc);
            if (count <= 0)
            {
                PdfiumNative.CloseDocument(doc);
                FreeBuffer();
                throw new Exception("PDF 没有任何页面。");
            }

            _doc = doc;
            FilePath = path;
            PageCount = count;
            _pageHandles = new IntPtr[count];
            PageWidthPt = new float[count];
            PageHeightPt = new float[count];
            for (int i = 0; i < count; i++)
            {
                float w, h;
                if (!PdfiumNative.GetPageSize(doc, i, out w, out h))
                {
                    w = 595f; h = 842f; // A4 兜底
                }
                PageWidthPt[i] = w;
                PageHeightPt[i] = h;
            }
        }

        /// <summary>释放文档后备缓冲(钉住句柄+字节数组)。</summary>
        private void FreeBuffer()
        {
            if (_pin.IsAllocated) _pin.Free();
            _bytes = null;
        }

        public void Close()
        {
            if (_pageHandles != null)
            {
                for (int i = 0; i < _pageHandles.Length; i++)
                    PdfiumNative.ClosePage(_pageHandles[i]);
                _pageHandles = null;
            }
            if (_doc != IntPtr.Zero)
            {
                PdfiumNative.CloseDocument(_doc);
                _doc = IntPtr.Zero;
            }
            FreeBuffer();
            FilePath = null;
            PageCount = 0;
            PageWidthPt = null;
            PageHeightPt = null;
        }

        /// <summary>渲染指定页。scale = 像素/PDF点。失败返回 null。</summary>
        public Bitmap RenderPage(int pageIndex, float scale)
        {
            if (!IsOpen) return null;
            if (pageIndex < 0 || pageIndex >= PageCount) return null;
            IntPtr page = GetPage(pageIndex);
            if (page == IntPtr.Zero) return null;

            int w = Math.Max(1, (int)Math.Round(PageWidthPt[pageIndex] * scale));
            int h = Math.Max(1, (int)Math.Round(PageHeightPt[pageIndex] * scale));
            return PdfiumNative.RenderPageToBitmap(page, w, h);
        }

        /// <summary>
        /// 高清渲染页面局部区域(OCR 用):与屏幕显示缩放无关,
        /// 用户任意缩放下框选,OCR 都拿到按 ocrScale 渲染的高清裁剪。
        /// 返回位图与 rectPt 一一对应(像素/pt = ocrScale)。
        /// </summary>
        public Bitmap RenderRegion(int pageIndex, RectangleF rectPt, float ocrScale)
        {
            if (!IsOpen) return null;
            if (pageIndex < 0 || pageIndex >= PageCount) return null;
            IntPtr page = GetPage(pageIndex);
            if (page == IntPtr.Zero) return null;

            // 整页渲染尺寸(控制缩放)
            int fullW = Math.Max(1, (int)Math.Round(PageWidthPt[pageIndex] * ocrScale));
            int fullH = Math.Max(1, (int)Math.Round(PageHeightPt[pageIndex] * ocrScale));
            // 区域矩形(裁到页面范围)
            float pw = PageWidthPt[pageIndex], ph = PageHeightPt[pageIndex];
            float l = Math.Max(0, rectPt.X), t = Math.Max(0, rectPt.Y);
            float r = Math.Min(pw, rectPt.Right), b = Math.Min(ph, rectPt.Bottom);
            if (r - l < 1 || b - t < 1) return null;
            int startX = (int)Math.Floor(l * ocrScale);
            int startY = (int)Math.Floor(t * ocrScale);
            int endX = (int)Math.Ceiling(r * ocrScale);
            int endY = (int)Math.Ceiling(b * ocrScale);
            return PdfiumNative.RenderRegionToBitmap(page, startX, startY,
                endX - startX, endY - startY, fullW, fullH);
        }

        private IntPtr GetPage(int pageIndex)
        {
            IntPtr page = _pageHandles[pageIndex];
            if (page == IntPtr.Zero)
            {
                page = PdfiumNative.LoadPage(_doc, pageIndex);
                _pageHandles[pageIndex] = page;
            }
            return page;
        }

        public void Dispose()
        {
            Close();
        }
    }
}