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[US-893] Accessibility code examples (#271)
* add example of adding image with alt text * add readme file * add comment * add example for adding language id * add copy page with a11y * fix typo
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‎accessibility/README.md‎

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## PDF Accessibility Examples.
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The examples in this section are showcasing how to work with accessibility features.
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## Examples
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- [pdf_add_image_alt_text.go](pdf_add_image_alt_text.go) showcases how to constuct a `StructTreeRoot` object and add alternate text for images.
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- [pdf_set_language_identifier.go](pdf_set_language_identifier.go) demonstrates how to set the language identifier for the document and its content.
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- [pdf_copy_page_with_accessibility.go](pdf_copy_page_with_accessibility.go) demonstrates how to copy pages from an existing PDF file to a new PDF file and preserve the structure tree information.

‎accessibility/logo.png‎

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‎accessibility/pdf_add_image_alt_text.go‎

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/*
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* Add image with alternate text to a PDF file.
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*
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* This example showcases how to add an image to a PDF file and set alternate text for the image.
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* Alternate text is useful for screen readers and other assistive technologies to provide a description of the image.
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*
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* The example demonstrates how to construct a `StructTreeRoot` object and add alternate text for images.
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*
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* Usage:
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* go run pdf_add_image_alt_text.go
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*/
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package main
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import (
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"fmt"
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"os"
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"github.com/unidoc/unipdf/v3/common/license"
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"github.com/unidoc/unipdf/v3/core"
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"github.com/unidoc/unipdf/v3/creator"
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"github.com/unidoc/unipdf/v3/model"
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)
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func init() {
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// Make sure to load your metered License API key prior to using the library.
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// If you need a key, you can sign up and create a free one at https://cloud.unidoc.io
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err := license.SetMeteredKey(os.Getenv(`UNIDOC_LICENSE_API_KEY`))
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if err != nil {
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panic(err)
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}
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}
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func main() {
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var (
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mcid int64 = 0
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structTreeRoot = model.NewStructTreeRoot()
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imageFile = "logo.png"
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kIds = []string{
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"86dfd8f4-b09b-41bc-981a-8b77de9aa251",
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"7c3ffc57-120a-4b44-827a-3f515ffa87b7",
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"b78b019d-cfb1-465f-b025-7dfda40d0b58",
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"06296b7a-818b-451a-9b59-5d4a20f59756",
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}
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outputPath = "image_alt_text.pdf"
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)
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c := creator.New()
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// Construct base K dictionary.
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docK := model.NewKDictionary()
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docK.S = core.MakeName(model.StructureTypeDocument)
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// Manually set optional ID for the K object
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docK.ID = core.MakeString(kIds[0])
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// Or generate the ID automatically using the following:
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// docK.GenerateRandomID()
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// Add K dictionary to the struct tree root.
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structTreeRoot.AddKDict(docK)
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// Create a child K dictionary.
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pageMarkedContentSection := model.NewKDictionary()
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// Set the structure type to Section.
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pageMarkedContentSection.S = core.MakeName(model.StructureTypeSection)
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pageMarkedContentSection.ID = core.MakeString(kIds[1])
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// Add as a child
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docK.AddKChild(pageMarkedContentSection)
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// Add first image
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err := addImage(c, imageFile, 0, 10, mcid, "An image alt text", kIds[2], pageMarkedContentSection)
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if err != nil {
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fmt.Printf("Error: %v\n", err)
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}
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// Update the MCID to be used for the next image.
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mcid++
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// Add second image.
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err = addImage(c, imageFile, 0, 400, mcid, "A second image alt text", kIds[3], pageMarkedContentSection)
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if err != nil {
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fmt.Printf("Error: %v\n", err)
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}
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// Set the struct tree root.
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c.SetStructTreeRoot(structTreeRoot)
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err = c.WriteToFile(outputPath)
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if err != nil {
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fmt.Printf("Error: %v\n", err)
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}
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}
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func addImage(c *creator.Creator, imageFile string, x, y float64, mcid int64, altText, kID string, pageMarkedContentSection *model.KDict) error {
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img, err := c.NewImageFromFile(imageFile)
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if err != nil {
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return err
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}
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img.SetPos(x, y)
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err = c.Draw(img)
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if err != nil {
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return err
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}
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// Add the image to the marked content section.
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altKdictEntry := img.SetMarkedContentID(mcid)
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// Set the alternate text.
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altKdictEntry.Alt = core.MakeString(altText)
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// Set the page number.
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altKdictEntry.SetPageNumber(int64(c.Context().Page))
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// Set the bounding box.
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altKdictEntry.SetBoundingBox(x, y, img.Width(), img.Height())
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// Set the ID.
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altKdictEntry.ID = core.MakeString(kID)
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// Add the K dictionary entry to the marked content section.
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pageMarkedContentSection.AddKChild(altKdictEntry)
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return nil
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}

‎accessibility/pdf_copy_page_with_accessibility.go‎

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/**
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* This example demonstrates how to copy pages from an existing PDF file to a new PDF file
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* and preserve the structure tree information.
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*
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* Usage:
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* go run pdf_copy_page_with_accessibility.go INPUT_PDF_PATH OUTPUT_PDF_PATH SPACE_SEPARATED_LIST_OF_PAGE_NUMBER_TO_COPY
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*/
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package main
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import (
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"fmt"
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"os"
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"strconv"
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"github.com/unidoc/unipdf/v3/common/license"
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"github.com/unidoc/unipdf/v3/core"
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"github.com/unidoc/unipdf/v3/creator"
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"github.com/unidoc/unipdf/v3/model"
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)
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func init() {
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// Make sure to load your metered License API key prior to using the library.
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// If you need a key, you can sign up and create a free one at https://cloud.unidoc.io
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err := license.SetMeteredKey(os.Getenv(`UNIDOC_LICENSE_API_KEY`))
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if err != nil {
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panic(err)
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}
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}
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func main() {
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args := os.Args
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if len(args) < 3 {
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fmt.Printf("Usage: %s INPUT_PDF_PATH OUTPUT_PDF_PATH SPACE_SEPARATED_LIST_OF_PAGE_NUMBER_TO_COPY\n", os.Args[0])
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return
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}
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inputPath := args[1]
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outputPath := args[2]
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pageNumbers := args[3:]
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c := creator.New()
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c.SetLanguage("en-US")
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c.SetPdfWriterAccessFunc(func(w *model.PdfWriter) error {
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w.SetCatalogMarkInfo(core.MakeDictMap(map[string]core.PdfObject{
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"Marked": core.MakeBool(true),
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}))
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w.SetVersion(1, 5)
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return nil
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})
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// Set the viewer preferences.
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vp := model.NewViewerPreferences()
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vp.SetDisplayDocTitle(true)
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c.SetViewerPreferences(vp)
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// Set PDF title.
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model.SetPdfTitle("Output Sample PDF")
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// Construct the StructTreeRoot.
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newStr := model.NewStructTreeRoot()
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// Construct base K dictionary.
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docK := model.NewKDictionary()
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docK.S = core.MakeName(model.StructureTypeDocument)
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newStr.AddKDict(docK)
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readerOpt := model.ReaderOpts{
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ComplianceMode: true,
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}
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r, _, err := model.NewPdfReaderFromFile(inputPath, &readerOpt)
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if err != nil {
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fmt.Printf("Error loading input file: %v\n", err)
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return
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}
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// Get the original `StructTreeRoot` object.
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strObj, found := r.GetCatalogStructTreeRoot()
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if !found {
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fmt.Printf("No StructTreeRoot found in the input PDF\n")
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return
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}
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orgStr, err := model.NewStructTreeRootFromPdfObject(strObj)
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if err != nil {
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fmt.Printf("Error parsing StructTreeRoot object: %v\n", err)
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return
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}
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orgK := orgStr.K[0].GetChildren()
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newPageIdx := 0
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for _, i := range pageNumbers {
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n, err := strconv.Atoi(i)
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if err != nil {
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fmt.Printf("Invalid page number: %s\n", i)
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continue
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}
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orgPage, err := r.GetPage(n)
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if err != nil {
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fmt.Printf("Error getting page %d: %v\n", n, err)
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continue
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}
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dupPage := orgPage.Duplicate()
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dupPage.SetStructParentsKey(newPageIdx)
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c.AddPage(dupPage)
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// Add section K object to store all original K objects from template page.
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sectK := model.NewKDictionary()
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sectK.S = core.MakeName(model.StructureTypeSection)
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sectK.T = core.MakeString(fmt.Sprintf("Page %d", n))
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sectK.GenerateRandomID()
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sectKv := model.KValue{}
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sectKv.SetKDict(sectK)
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// Copy all K objects from the original page to the new page.
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for _, k := range orgK {
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copyK := deepCopyKObject(k)
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if copyK != nil {
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sectK.AddChild(copyK)
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}
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}
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setKPageNumber(&sectKv, int64(n))
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docK.AddChild(&sectKv)
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newPageIdx++
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}
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c.SetStructTreeRoot(newStr)
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err = c.WriteToFile(outputPath)
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if err != nil {
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fmt.Printf("Error writing output file: %v\n", err)
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}
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}
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func setKPageNumber(kv *model.KValue, page int64) {
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if k := kv.GetKDict(); k != nil {
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k.SetPageNumber(page)
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for _, child := range k.GetChildren() {
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setKPageNumber(child, page)
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}
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}
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}
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func deepCopyKObject(origin *model.KValue) *model.KValue {
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copyKVal := model.NewKValue()
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if oKDict := origin.GetKDict(); oKDict != nil {
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copy := model.NewKDictionary()
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copy.S = oKDict.S
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copy.ID = oKDict.ID
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copy.Lang = oKDict.Lang
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copy.Alt = oKDict.Alt
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copy.T = oKDict.T
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copy.Pg = oKDict.Pg
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copy.C = oKDict.C
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for _, child := range oKDict.GetChildren() {
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copy.AddChild(deepCopyKObject(child))
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}
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copyKVal.SetKDict(copy)
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return copyKVal
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} else if refObj := origin.GetRefObject(); refObj != nil {
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copyKVal.SetRefObject(refObj)
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return copyKVal
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} else if mcid := origin.GetMCID(); mcid != nil {
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copyKVal.SetMCID(*mcid)
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return copyKVal
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}
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return nil
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}

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