unipdf/model/appender.go

/*
 * This file is subject to the terms and conditions defined in
 * file 'LICENSE.md', which is part of this source code package.
 */

package model

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"os"
	"strconv"
	"strings"

	"github.com/unidoc/unipdf/v3/common"
	"github.com/unidoc/unipdf/v3/core"
)

// PdfAppender appends new PDF content to an existing PDF document via incremental updates.
type PdfAppender struct {
	rs       io.ReadSeeker
	parser   *core.PdfParser
	roReader *PdfReader
	Reader   *PdfReader
	pages    []*PdfPage
	acroForm *PdfAcroForm

	xrefs          core.XrefTable
	xrefOffset     int64
	greatestObjNum int

	// List of new objects and a map for quick lookups.
	newObjects     []core.PdfObject
	hasNewObject   map[core.PdfObject]struct{}
	replaceObjects map[core.PdfObject]int64

	// Used for skipping certain objects that are created (Pages etc).
	ignoreObjects map[core.PdfObject]struct{}

	// Map of objects traversed while resolving references. Set to that of the PdfReader on
	// creation (NewPdfAppender).
	traversed map[core.PdfObject]struct{}

	prevRevisionSize int64
	written          bool
}

func getPageResources(p *PdfPage) map[core.PdfObjectName]core.PdfObject {
	resources := make(map[core.PdfObjectName]core.PdfObject)
	if p.Resources == nil {
		return resources
	}
	if p.Resources.Font != nil {
		if dict, found := core.GetDict(p.Resources.Font); found {
			for _, key := range dict.Keys() {
				resources[key] = dict.Get(key)
			}
		}
	}
	if p.Resources.ExtGState != nil {
		if dict, found := core.GetDict(p.Resources.ExtGState); found {
			for _, key := range dict.Keys() {
				resources[key] = dict.Get(key)
			}
		}
	}
	if p.Resources.XObject != nil {
		if dict, found := core.GetDict(p.Resources.XObject); found {
			for _, key := range dict.Keys() {
				resources[key] = dict.Get(key)
			}
		}
	}
	if p.Resources.Pattern != nil {
		if dict, found := core.GetDict(p.Resources.Pattern); found {
			for _, key := range dict.Keys() {
				resources[key] = dict.Get(key)
			}
		}
	}
	if p.Resources.Shading != nil {
		if dict, found := core.GetDict(p.Resources.Shading); found {
			for _, key := range dict.Keys() {
				resources[key] = dict.Get(key)
			}
		}
	}
	if p.Resources.ProcSet != nil {
		if dict, found := core.GetDict(p.Resources.ProcSet); found {
			for _, key := range dict.Keys() {
				resources[key] = dict.Get(key)
			}
		}
	}
	if p.Resources.Properties != nil {
		if dict, found := core.GetDict(p.Resources.Properties); found {
			for _, key := range dict.Keys() {
				resources[key] = dict.Get(key)
			}
		}
	}

	return resources
}

// NewPdfAppender creates a new Pdf appender from a Pdf reader.
func NewPdfAppender(reader *PdfReader) (*PdfAppender, error) {
	a := &PdfAppender{
		rs:        reader.rs,
		Reader:    reader,
		parser:    reader.parser,
		traversed: reader.traversed,
	}
	if size, err := a.rs.Seek(0, io.SeekEnd); err != nil {
		return nil, err
	} else {
		a.prevRevisionSize = size
	}

	if _, err := a.rs.Seek(0, io.SeekStart); err != nil {
		return nil, err
	}

	var err error

	// Create a readonly (immutable) reader. It increases memory use but is necessary to be able
	// to detect changes in the original reader objects.
	//
	// In the case where an existing page is modified, the page contents are replaced upon merging
	// (appending). The new page will refer to objects from the read-only reader and new instances
	// of objects that have been changes. Objects from the original reader are not appended, only
	// new objects that modify the PDF. The change detection check is not resource demanding. It
	// only checks owners (source) of indirect objects.
	a.roReader, err = NewPdfReader(a.rs)
	if err != nil {
		return nil, err
	}
	for _, idx := range a.Reader.GetObjectNums() {
		if a.greatestObjNum < idx {
			a.greatestObjNum = idx
		}
	}
	a.xrefs = a.parser.GetXrefTable()
	a.xrefOffset = a.parser.GetXrefOffset()

	a.hasNewObject = make(map[core.PdfObject]struct{})
	for _, p := range a.roReader.PageList {
		a.pages = append(a.pages, p)
	}
	a.replaceObjects = make(map[core.PdfObject]int64)
	a.ignoreObjects = make(map[core.PdfObject]struct{})

	a.acroForm = a.roReader.AcroForm

	return a, nil
}

// updatesObjectsDeep recursively marks all objects under `obj` as updated appender (deep).
// Updated objects are appended to the new revision and keep their original object number.
func (a *PdfAppender) updateObjectsDeep(obj core.PdfObject, processed map[core.PdfObject]struct{}) {
	if processed == nil {
		processed = map[core.PdfObject]struct{}{}
	}
	if _, ok := processed[obj]; ok || obj == nil {
		return
	}
	processed[obj] = struct{}{}

	err := core.ResolveReferencesDeep(obj, a.traversed)
	if err != nil {
		common.Log.Debug("ERROR: %v", err)
	}

	switch v := obj.(type) {
	case *core.PdfIndirectObject:
		// Change detection:
		// - obj same as in read only reader (internal use by appender) - definately no change.
		// - obj is from original reader (derivative of original document) - mark for update if PdfObj WriteString has changed.
		// - obj is from another source (another file or new) - add as new object.
		switch {
		case v.GetParser() == a.roReader.parser:
			// obj same as in read only reader (internal use by appender) - definitely no change.
			return
		case v.GetParser() == a.Reader.parser:
			// obj is from original reader (derivative of original document) - mark for update if PdfObj WriteString has changed.
			origObj, _ := a.roReader.GetIndirectObjectByNumber(int(v.ObjectNumber))
			origInd, ok := origObj.(*core.PdfIndirectObject)
			if ok && origInd != nil {
				if origInd.PdfObject != v.PdfObject && origInd.PdfObject.WriteString() != v.PdfObject.WriteString() {
					a.addNewObject(obj)
					a.replaceObjects[obj] = v.ObjectNumber
				}
			}
		default:
			// obj is from another source (another file or new) - add as new object.
			a.addNewObject(obj)
		}
		a.updateObjectsDeep(v.PdfObject, processed)
	case *core.PdfObjectArray:
		for _, o := range v.Elements() {
			a.updateObjectsDeep(o, processed)
		}
	case *core.PdfObjectDictionary:
		for _, key := range v.Keys() {
			a.updateObjectsDeep(v.Get(key), processed)
		}
	case *core.PdfObjectStreams:
		// If the current parser is different from the read-only parser, then
		// the object has changed.
		if v.GetParser() != a.roReader.parser {
			for _, o := range v.Elements() {
				a.updateObjectsDeep(o, processed)
			}
		}
	case *core.PdfObjectStream:
		// If the current parser is different from the read-only parser, then
		// the object has changed.
		switch {
		case v.GetParser() == a.roReader.parser:
			// original roReader - no changes.
			return
		case v.GetParser() == a.Reader.parser:
			// same source document, potentially modified.
			// Check if data has changed.
			if streamObj, err := a.roReader.parser.LookupByReference(v.PdfObjectReference); err == nil {
				var isNotChanged bool
				if stream, ok := core.GetStream(streamObj); ok && bytes.Equal(stream.Stream, v.Stream) {
					isNotChanged = true
				}
				if dict, ok := core.GetDict(streamObj); isNotChanged && ok {
					isNotChanged = dict.WriteString() == v.PdfObjectDictionary.WriteString()
				}
				if isNotChanged {
					return
				}
			}
			if v.ObjectNumber != 0 {
				a.replaceObjects[obj] = v.ObjectNumber
			}
		default:
			// other source - add new.
			if _, has := a.hasNewObject[obj]; !has {
				a.addNewObject(obj)
			}
		}
		a.updateObjectsDeep(v.PdfObjectDictionary, processed)
	}
}

// addNewObject adds a new object to be written out in the new revision, either with as a new
// object or updating an older object (if replaceObjects entry set for obj).
func (a *PdfAppender) addNewObject(obj core.PdfObject) {
	if _, has := a.hasNewObject[obj]; !has {
		a.newObjects = append(a.newObjects, obj)
		a.hasNewObject[obj] = struct{}{}
	}
}

// mergeResources adds new named resources from src to dest. If the resources have the same name its will be renamed.
// The dest and src are resources dictionary. resourcesRenameMap is a rename map for resources.
func (a *PdfAppender) mergeResources(dest, src core.PdfObject, resourcesRenameMap map[core.PdfObjectName]core.PdfObjectName) core.PdfObject {
	if src == nil && dest == nil {
		return nil
	}
	if src == nil {
		return dest
	}

	srcDict, ok := core.GetDict(src)
	if !ok {
		return dest
	}
	if dest == nil {
		dict := core.MakeDict()
		dict.Merge(srcDict)
		return src
	}

	destDict, ok := core.GetDict(dest)
	if !ok {
		common.Log.Error("Error resource is not a dictionary")
		destDict = core.MakeDict()
	}

	for _, key := range srcDict.Keys() {
		if newKey, found := resourcesRenameMap[key]; found {
			destDict.Set(newKey, srcDict.Get(key))
		} else {
			destDict.Set(key, srcDict.Get(key))
		}
	}
	return destDict
}

// MergePageWith appends page content to source Pdf file page content.
func (a *PdfAppender) MergePageWith(pageNum int, page *PdfPage) error {
	pageIndex := pageNum - 1
	var srcPage *PdfPage
	for i, p := range a.pages {
		if i == pageIndex {
			srcPage = p
		}
	}
	if srcPage == nil {
		return fmt.Errorf("ERROR: Page dictionary %d not found in the source document", pageNum)
	}
	if srcPage.primitive != nil && srcPage.primitive.GetParser() == a.roReader.parser {
		srcPage = srcPage.Duplicate()
		a.pages[pageIndex] = srcPage
	}

	page = page.Duplicate()
	procPage(page)

	srcResources := getPageResources(srcPage)
	pageResources := getPageResources(page)
	resourcesRenameMap := make(map[core.PdfObjectName]core.PdfObjectName)

	for key := range pageResources {
		if _, found := srcResources[key]; found {
			for i := 1; true; i++ {
				newKey := core.PdfObjectName(string(key) + strconv.Itoa(i))
				if _, exists := srcResources[newKey]; !exists {
					resourcesRenameMap[key] = newKey
					break
				}
			}
		}
	}

	contentStreams, err := page.GetContentStreams()
	if err != nil {
		return err
	}

	srcContentStreams, err := srcPage.GetContentStreams()
	if err != nil {
		return err
	}

	for i, stream := range contentStreams {
		for oldName, newName := range resourcesRenameMap {
			// TODO: Not accurate, e.g. "/F1" could replace part of "/F12" etc.
			stream = strings.Replace(stream, "/"+string(oldName), "/"+string(newName), -1)
		}
		contentStreams[i] = stream
	}

	srcContentStreams = append(srcContentStreams, contentStreams...)
	if err := srcPage.SetContentStreams(srcContentStreams, core.NewFlateEncoder()); err != nil {
		return err
	}

	for _, a := range page.annotations {
		srcPage.annotations = append(srcPage.annotations, a)
	}

	if srcPage.Resources == nil {
		srcPage.Resources = NewPdfPageResources()
	}

	if page.Resources != nil {
		srcPage.Resources.Font = a.mergeResources(srcPage.Resources.Font, page.Resources.Font, resourcesRenameMap)
		srcPage.Resources.XObject = a.mergeResources(srcPage.Resources.XObject, page.Resources.XObject, resourcesRenameMap)
		srcPage.Resources.Properties = a.mergeResources(srcPage.Resources.Properties, page.Resources.Properties, resourcesRenameMap)
		if srcPage.Resources.ProcSet == nil {
			srcPage.Resources.ProcSet = page.Resources.ProcSet
		}
		srcPage.Resources.Shading = a.mergeResources(srcPage.Resources.Shading, page.Resources.Shading, resourcesRenameMap)
		srcPage.Resources.ExtGState = a.mergeResources(srcPage.Resources.ExtGState, page.Resources.ExtGState, resourcesRenameMap)
	}

	srcMediaBox, err := srcPage.GetMediaBox()
	if err != nil {
		return err
	}

	pageMediaBox, err := page.GetMediaBox()
	if err != nil {
		return err
	}
	var mediaBoxChanged bool

	if srcMediaBox.Llx > pageMediaBox.Llx {
		srcMediaBox.Llx = pageMediaBox.Llx
		mediaBoxChanged = true
	}
	if srcMediaBox.Lly > pageMediaBox.Lly {
		srcMediaBox.Lly = pageMediaBox.Lly
		mediaBoxChanged = true
	}
	if srcMediaBox.Urx < pageMediaBox.Urx {
		srcMediaBox.Urx = pageMediaBox.Urx
		mediaBoxChanged = true
	}
	if srcMediaBox.Ury < pageMediaBox.Ury {
		srcMediaBox.Ury = pageMediaBox.Ury
		mediaBoxChanged = true
	}

	if mediaBoxChanged {
		srcPage.MediaBox = srcMediaBox
	}

	return nil
}

// AddPages adds pages to be appended to the end of the source PDF.
func (a *PdfAppender) AddPages(pages ...*PdfPage) {
	for _, page := range pages {
		page = page.Duplicate()
		procPage(page)
		a.pages = append(a.pages, page)
	}
	return
}

// RemovePage removes a page by number.
func (a *PdfAppender) RemovePage(pageNum int) {
	pageIndex := pageNum - 1

	// Remove from the pages list.
	a.pages = append(a.pages[0:pageIndex], a.pages[pageNum:]...)
}

// replaceObject registers `replacement` as a replacement for `obj` in the appended revision.
// If an indirect object/stream it will maintain the same object number in the following
// revision.
func (a *PdfAppender) replaceObject(obj, replacement core.PdfObject) {
	switch t := obj.(type) {
	case *core.PdfIndirectObject:
		a.replaceObjects[replacement] = t.ObjectNumber
	case *core.PdfObjectStream:
		a.replaceObjects[replacement] = t.ObjectNumber
	}
}

// UpdateObject marks `obj` as updated and to be included in the following revision.
func (a *PdfAppender) UpdateObject(obj core.PdfObject) {
	a.replaceObject(obj, obj)
	if _, has := a.hasNewObject[obj]; !has {
		a.newObjects = append(a.newObjects, obj)
		a.hasNewObject[obj] = struct{}{}
	}
}

// UpdatePage updates the `page` in the new revision if it has changed.
func (a *PdfAppender) UpdatePage(page *PdfPage) {
	a.updateObjectsDeep(page.ToPdfObject(), nil)
}

// ReplacePage replaces the original page to a new page.
func (a *PdfAppender) ReplacePage(pageNum int, page *PdfPage) {
	pageIndex := pageNum - 1
	for i := range a.pages {
		if i == pageIndex {
			p := page.Duplicate()
			procPage(p)
			a.pages[i] = p
		}
	}
}

// Sign signs a specific page with a digital signature.
// The signature field parameter must have a valid signature dictionary
// specified by its V field.
func (a *PdfAppender) Sign(pageNum int, field *PdfFieldSignature) error {
	if field == nil {
		return errors.New("signature field cannot be nil")
	}

	signature := field.V
	if signature == nil {
		return errors.New("signature dictionary cannot be nil")
	}

	// Get a copy of the selected page.
	pageIndex := pageNum - 1
	if pageIndex < 0 || pageIndex > len(a.pages)-1 {
		return fmt.Errorf("page %d not found", pageNum)
	}
	page := a.Reader.PageList[pageIndex]

	// Add signature field annotations to the page annotations.
	field.P = page.ToPdfObject()
	if field.T == nil || field.T.String() == "" {
		field.T = core.MakeString(fmt.Sprintf("Signature %d", pageNum))
	}
	page.AddAnnotation(field.PdfAnnotationWidget.PdfAnnotation)

	// Add signature field to the form.
	if a.acroForm == a.roReader.AcroForm {
		a.acroForm = a.Reader.AcroForm
	}
	acroForm := a.acroForm
	if acroForm == nil {
		acroForm = NewPdfAcroForm()
	}
	acroForm.SigFlags = core.MakeInteger(3)

	fields := append(acroForm.AllFields(), field.PdfField)
	acroForm.Fields = &fields
	a.ReplaceAcroForm(acroForm)

	// Replace original page.
	a.UpdatePage(page)
	a.pages[pageIndex] = page

	return nil
}

// ReplaceAcroForm replaces the acrobat form. It appends a new form to the Pdf which
// replaces the original AcroForm.
func (a *PdfAppender) ReplaceAcroForm(acroForm *PdfAcroForm) {
	if acroForm != nil {
		a.updateObjectsDeep(acroForm.ToPdfObject(), nil)
	}
	a.acroForm = acroForm
}

// Write writes the Appender output to io.Writer.
// It can only be called once and further invocations will result in an error.
func (a *PdfAppender) Write(w io.Writer) error {
	if a.written {
		return errors.New("appender write can only be invoked once")
	}

	writer := NewPdfWriter()

	pagesDict, ok := core.GetDict(writer.pages)
	if !ok {
		return errors.New("invalid Pages obj (not a dict)")
	}
	kids, ok := pagesDict.Get("Kids").(*core.PdfObjectArray)
	if !ok {
		return errors.New("invalid Pages Kids obj (not an array)")
	}
	pageCount, ok := pagesDict.Get("Count").(*core.PdfObjectInteger)
	if !ok {
		return errors.New("invalid Pages Count object (not an integer)")
	}

	parser := a.roReader.parser
	trailer := parser.GetTrailer()
	if trailer == nil {
		return errors.New("missing trailer")
	}
	// Catalog.
	catalogContainer, ok := core.GetIndirect(trailer.Get("Root"))
	if !ok {
		return errors.New("catalog container not found")
	}
	catalog, ok := core.GetDict(catalogContainer)
	if !ok {
		common.Log.Debug("ERROR: Missing catalog: (root %q) (trailer %s)", catalogContainer, *trailer)
		return errors.New("missing catalog")
	}

	// Add the keys which are not set.
	for _, key := range catalog.Keys() {
		if writer.catalog.Get(key) == nil {
			obj := catalog.Get(key)
			writer.catalog.Set(key, obj)
		}
	}
	if a.acroForm != nil {
		writer.catalog.Set("AcroForm", a.acroForm.ToPdfObject())
		a.updateObjectsDeep(a.acroForm.ToPdfObject(), nil)
	}

	a.addNewObject(writer.infoObj)
	a.addNewObject(writer.root)

	// TODO: Represent the Pages as a model/object.  PdfPages should represent the Pages dictionary.
	pagesChanged := false
	if len(a.roReader.PageList) != len(a.pages) {
		pagesChanged = true
	} else {
		for i := range a.roReader.PageList {
			switch {
			case a.pages[i] == a.roReader.PageList[i]:
				// from ro reader - no change.
			case a.pages[i] == a.Reader.PageList[i]:
				// same as original file (possibly some modification of the page itself).
			default:
				// Different source.
				pagesChanged = true
			}
			if pagesChanged {
				break
			}
		}
	}
	if pagesChanged {
		a.updateObjectsDeep(writer.pages, nil)
	} else {
		a.ignoreObjects[writer.pages] = struct{}{}
	}
	// If pages unchanged, should not change the Pages.
	writer.pages.ObjectNumber = a.Reader.pagesContainer.ObjectNumber
	a.replaceObjects[writer.pages] = a.Reader.pagesContainer.ObjectNumber

	inheritedFields := []core.PdfObjectName{"Resources", "MediaBox", "CropBox", "Rotate"}
	for _, p := range a.pages {
		// Update the count.
		obj := p.ToPdfObject()

		*pageCount = *pageCount + 1
		// Check the object is not changing.
		// If the indirect object has the parser which equals to the readonly then the object is not changed.
		if ind, ok := obj.(*core.PdfIndirectObject); ok && ind.GetParser() == a.roReader.parser {
			kids.Append(&ind.PdfObjectReference)
			continue
		}
		if pDict, ok := core.GetDict(obj); ok {
			parent, hasParent := pDict.Get("Parent").(*core.PdfIndirectObject)
			for hasParent {
				common.Log.Trace("Page Parent: %T", parent)
				parentDict, ok := parent.PdfObject.(*core.PdfObjectDictionary)
				if !ok {
					return errors.New("invalid Parent object")
				}
				for _, field := range inheritedFields {
					common.Log.Trace("Field %s", field)
					if pDict.Get(field) != nil {
						common.Log.Trace("- page has already")
						continue
					}

					if obj := parentDict.Get(field); obj != nil {
						// Parent has the field.  Inherit, pass to the new page.
						common.Log.Trace("Inheriting field %s", field)
						pDict.Set(field, obj)
					}
				}
				parent, hasParent = parentDict.Get("Parent").(*core.PdfIndirectObject)
				common.Log.Trace("Next parent: %T", parentDict.Get("Parent"))
			}
			pDict.Set("Parent", writer.pages)
		}
		a.updateObjectsDeep(obj, nil)
		kids.Append(obj)
	}

	if _, err := a.rs.Seek(0, io.SeekStart); err != nil {
		return err
	}

	// Digital signature handling: Check if any of the new objects represent a signature dictionary.
	// The byte range is later updated dynamically based on the position of the actual signature
	// Contents.
	digestWriters := make(map[SignatureHandler]io.Writer)
	byteRange := core.MakeArray()
	for _, obj := range a.newObjects {
		if ind, found := core.GetIndirect(obj); found {
			if sigDict, found := ind.PdfObject.(*pdfSignDictionary); found {
				handler := *sigDict.handler
				var err error
				digestWriters[handler], err = handler.NewDigest(sigDict.signature)
				if err != nil {
					return err
				}
				byteRange.Append(core.MakeInteger(0xfffff), core.MakeInteger(0xfffff))
			}
		}
	}
	if byteRange.Len() > 0 {
		byteRange.Append(core.MakeInteger(0xfffff), core.MakeInteger(0xfffff))
	}
	for _, obj := range a.newObjects {
		if ind, found := core.GetIndirect(obj); found {
			if sigDict, found := ind.PdfObject.(*pdfSignDictionary); found {
				sigDict.Set("ByteRange", byteRange)
			}
		}
	}

	hasSigDict := len(digestWriters) > 0

	var reader io.Reader = a.rs
	if hasSigDict {
		writers := make([]io.Writer, 0, len(digestWriters))
		for _, hash := range digestWriters {
			writers = append(writers, hash)
		}
		reader = io.TeeReader(a.rs, io.MultiWriter(writers...))
	}

	// Write the original PDF.
	offset, err := io.Copy(w, reader)
	if err != nil {
		return err
	}

	if len(a.newObjects) == 0 {
		return nil
	}

	writer.writeOffset = offset
	writer.ObjNumOffset = a.greatestObjNum
	writer.appendMode = true
	writer.appendToXrefs = a.xrefs
	writer.appendXrefPrevOffset = a.xrefOffset
	writer.appendPrevRevisionSize = a.prevRevisionSize
	writer.minorVersion = a.roReader.PdfVersion().Minor
	writer.appendReplaceMap = a.replaceObjects

	xrefType := a.parser.GetXrefType()
	if xrefType != nil {
		v := *xrefType == core.XrefTypeObjectStream
		writer.useCrossReferenceStream = &v
	}

	// Reset the objects in the writer.
	writer.objectsMap = map[core.PdfObject]struct{}{}
	writer.objects = []core.PdfObject{}

	for _, obj := range a.newObjects {
		if _, ignore := a.ignoreObjects[obj]; ignore {
			continue
		}
		writer.addObject(obj)
	}

	writerW := w
	if hasSigDict {
		// For signatures, we need to write twice. First to find the byte offset
		// of the Contents and then dynamically update the file with the
		// signature and ByteRange.
		writerW = bytes.NewBuffer(nil)
	}

	// Perform the write. For signatures will do a mock write to a buffer.
	if err := writer.Write(writerW); err != nil {
		return err
	}

	// TODO(gunnsth): Consider whether the dynamic content can be handled efficiently with generic write hooks?
	// Logic is getting pretty complex here.
	if hasSigDict {
		// Update the byteRanges based on mock write.
		bufferData := writerW.(*bytes.Buffer).Bytes()
		byteRange := core.MakeArray()
		var sigDicts []*pdfSignDictionary
		var lastPosition int64
		for _, obj := range writer.objects {
			if ind, found := core.GetIndirect(obj); found {
				if sigDict, found := ind.PdfObject.(*pdfSignDictionary); found {
					sigDicts = append(sigDicts, sigDict)
					newPosition := sigDict.fileOffset + int64(sigDict.contentsOffsetStart)
					byteRange.Append(
						core.MakeInteger(lastPosition),
						core.MakeInteger(newPosition-lastPosition),
					)
					lastPosition = sigDict.fileOffset + int64(sigDict.contentsOffsetEnd)
				}
			}
		}
		byteRange.Append(
			core.MakeInteger(lastPosition),
			core.MakeInteger(offset+int64(len(bufferData))-lastPosition),
		)
		// set the ByteRange value
		byteRangeData := []byte(byteRange.WriteString())
		for _, sigDict := range sigDicts {
			bufferOffset := int(sigDict.fileOffset - offset)
			for i := sigDict.byteRangeOffsetStart; i < sigDict.byteRangeOffsetEnd; i++ {
				bufferData[bufferOffset+i] = ' '
			}
			dst := bufferData[bufferOffset+sigDict.byteRangeOffsetStart : bufferOffset+sigDict.byteRangeOffsetEnd]
			copy(dst, byteRangeData)
		}
		var prevOffset int
		for _, sigDict := range sigDicts {
			bufferOffset := int(sigDict.fileOffset - offset)
			data := bufferData[prevOffset : bufferOffset+sigDict.contentsOffsetStart]
			handler := *sigDict.handler
			digestWriters[handler].Write(data)
			prevOffset = bufferOffset + sigDict.contentsOffsetEnd
		}
		for _, sigDict := range sigDicts {
			data := bufferData[prevOffset:]
			handler := *sigDict.handler
			digestWriters[handler].Write(data)
		}
		for _, sigDict := range sigDicts {
			bufferOffset := int(sigDict.fileOffset - offset)
			handler := *sigDict.handler
			digest := digestWriters[handler]
			if err := handler.Sign(sigDict.signature, digest); err != nil {
				return err
			}
			sigDict.signature.ByteRange = byteRange
			contents := []byte(sigDict.signature.Contents.WriteString())

			// Empty out the ByteRange and Content data.
			// FIXME(gunnsth): Is this needed?  Seems like the correct data is copied below?  Prefer
			// to keep the rest space?
			for i := sigDict.byteRangeOffsetStart; i < sigDict.byteRangeOffsetEnd; i++ {
				bufferData[bufferOffset+i] = ' '
			}
			for i := sigDict.contentsOffsetStart; i < sigDict.contentsOffsetEnd; i++ {
				bufferData[bufferOffset+i] = ' '
			}

			// Copy the actual ByteRange and Contents data into the buffer prepared by first write.
			dst := bufferData[bufferOffset+sigDict.byteRangeOffsetStart : bufferOffset+sigDict.byteRangeOffsetEnd]
			copy(dst, byteRangeData)
			dst = bufferData[bufferOffset+sigDict.contentsOffsetStart : bufferOffset+sigDict.contentsOffsetEnd]
			copy(dst, contents)
		}

		buffer := bytes.NewBuffer(bufferData)
		_, err = io.Copy(w, buffer)
		if err != nil {
			return err
		}
	}

	a.written = true
	return nil
}

// WriteToFile writes the Appender output to file specified by path.
func (a *PdfAppender) WriteToFile(outputPath string) error {
	fWrite, err := os.Create(outputPath)
	if err != nil {
		return err
	}
	defer fWrite.Close()
	return a.Write(fWrite)
}