PDFPatcher/App/Processor/ContentProcessors/RemoveFormProcessor.cs

using System;
using System.Collections.Generic;
using iTextSharp.text.pdf;
using PDFPatcher.Common;
using PDFPatcher.Model;

namespace PDFPatcher.Processor
{
	sealed class RemoveFormProcessor : IPageProcessor
	{
		int _processedPageCount;

		#region IPageProcessor 成员
		public string Name => "删除表单区域";

		public void BeginProcess(DocProcessorContext context) {
			_processedPageCount = 0;
		}
		public bool EndProcess(PdfReader pdf) {
			Tracker.TraceMessage(Tracker.Category.Notice, Name + "功能：");
			Tracker.TraceMessage($"　　删除了 {_processedPageCount} 页的表单区域。");
			return false;
		}

		public int EstimateWorkload(PdfReader pdf) {
			return pdf.NumberOfPages * 3;
		}

		public bool Process(PageProcessorContext context) {
			Tracker.IncrementProgress(3);
			var p = context.PageCommands;
			var r = false;
			var fl = ProcessFormContent(context);
			if (fl.HasContent()) {
				r = true;
				ProcessCommands(p.Commands, fl);
			}
			if (r) {
				context.IsPageContentModified = true;
				_processedPageCount++;
			}
			return r;
		}

		private static HashSet<PdfName> ProcessFormContent(PageProcessorContext context) {
			var fl = context.Page.Locate<PdfDictionary>(PdfName.RESOURCES, PdfName.XOBJECT);
			if (fl == null) {
				return null;
			}
			var r = new HashSet<PdfName>();
			foreach (var item in fl) {
				if (PdfReader.GetPdfObject(item.Value) is not PRStream f
					|| PdfName.FORM.Equals(f.GetAsName(PdfName.SUBTYPE)) == false) {
					continue;
				}
				r.Add(item.Key);
			}
			foreach (var item in r) {
				fl.Remove(item);
			}
			if (fl.Size == 0) {
				context.Page.Locate<PdfDictionary>(PdfName.RESOURCES).Remove(PdfName.XOBJECT);
			}
			return r;
		}

		#endregion

		static bool ProcessCommands(IList<Model.PdfPageCommand> parent, HashSet<PdfName> formNames) {
			var r = false;
			for (int i = parent.Count - 1; i >= 0; i--) {
				var cmd = parent[i];
				if (cmd is EnclosingCommand ec) {
					r |= ProcessCommands(ec.Commands, formNames);
				}
				if (cmd.Name.ToString() == "Do" && cmd.HasOperand && formNames.Contains(cmd.Operands[0] as PdfName)) {
					parent.RemoveAt(i);
					r = true;
				}
			}
			return r;
		}

	}
}