using Spire.Pdf;
using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Linq;

namespace ShenTun.Ecg.Common
{
    public class PdfHelper
    {
        /// <summary>
        /// 将pdf文件转换为图片文件
        /// </summary>
        /// <param name="stream">pdf文件流</param>
        /// <param name="pageIndex">要转换的pdf页索引（从0开始）</param>
        /// <param name="dpiX">dpi</param>
        /// <param name="dpiY">dpi</param>
        /// <param name="mimeType">mime类型</param>
        /// <returns></returns>
        public static Stream PdfToImage(Stream stream, int pageIndex = 0, int dpiX = 300, int dpiY = 300, string mimeType = "image/jpg")
        {
            using (PdfDocument document = new PdfDocument())
            {
                document.LoadFromStream(stream);

                // 图片类型选择为Bitmap
                Spire.Pdf.Graphics.PdfImageType pdfImageType = Spire.Pdf.Graphics.PdfImageType.Bitmap;
                // 将pdf中指定的页码转换为图片对象并返回
                using (Image image = document.SaveAsImage(pageIndex, pdfImageType, dpiX, dpiY))
                {
                    // 获取相应的编码器
                    ImageCodecInfo codecInfo = (
                        from item in ImageCodecInfo.GetImageEncoders()
                        where mimeType.Equals(item.MimeType)
                        select item
                    ).FirstOrDefault();

                    EncoderParameters encoderParams = new EncoderParameters(1);
                    encoderParams.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 100L);


                    MemoryStream result = new MemoryStream();
                    image.Save(result, codecInfo, encoderParams);
                    result.Position = 0;

                    return result;
                }
            }
        }
    }
}