PDF page labels in Go

//---------------------------------------------------------------------------------------
// Copyright (c) 2001-2021 by PDFTron Systems Inc. All Rights Reserved.
// Consult LICENSE.txt regarding license information.
//---------------------------------------------------------------------------------------

package main
import (
	"fmt"
    "strconv"
	. "pdftron"
)

import  "pdftron/Samples/LicenseKey/GO"

//-----------------------------------------------------------------------------------
// The sample illustrates how to work with PDF page labels.
//
// PDF page labels can be used to describe a page. This is used to 
// allow for non-sequential page numbering or the addition of arbitrary 
// labels for a page (such as the inclusion of Roman numerals at the 
// beginning of a book). PDFNet PageLabel object can be used to specify 
// the numbering style to use (for example, upper- or lower-case Roman, 
// decimal, and so forth), the starting number for the first page,
// and an arbitrary prefix to be pre-appended to each number (for 
// example, "A-" to generate "A-1", "A-2", "A-3", and so forth.)
//-----------------------------------------------------------------------------------

// Relative path to the folder containing the test files.
var inputPath = "../../TestFiles/"
var outputPath = "../../TestFiles/Output/"

func main(){
    // Initialize PDFNet
    PDFNetInitialize(PDFTronLicense.Key)
    
    //-----------------------------------------------------------
    // Example 1: Add page labels to an existing or newly created PDF
    // document.
    //-----------------------------------------------------------
    
    doc := NewPDFDoc(inputPath + "newsletter.pdf")
    doc.InitSecurityHandler()
    
    // Create a page labeling scheme that starts with the first page in 
    // the document (page 1) and is using uppercase roman numbering 
    // style. 
    L1 := PageLabelCreate(doc.GetSDFDoc(), PageLabelE_roman_uppercase, "My Prefix ", 1)
    doc.SetPageLabel(1, L1)
    
    // Create a page labeling scheme that starts with the fourth page in 
    // the document and is using decimal arabic numbering style. 
    // Also the numeric portion of the first label should start with number 
    // 4 (otherwise the first label would be "My Prefix 1").
    L2 := PageLabelCreate(doc.GetSDFDoc(), PageLabelE_decimal, "My Prefix ", 4)
    doc.SetPageLabel(4, L2)
    
    // Create a page labeling scheme that starts with the seventh page in 
    // the document and is using alphabetic numbering style. The numeric 
    // portion of the first label should start with number 1. 
    L3 := PageLabelCreate(doc.GetSDFDoc(), PageLabelE_alphabetic_uppercase, "My Prefix ", 1)
    doc.SetPageLabel(7, L3)
    
    doc.Save(outputPath + "newsletter_with_pagelabels.pdf", uint(SDFDocE_linearized))
    doc.Close()
    fmt.Println("Done. Result saved in newsletter_with_pagelabels.pdf...")
    
    //-----------------------------------------------------------
    // Example 2: Read page labels from an existing PDF document.
    //-----------------------------------------------------------
    
    doc = NewPDFDoc(outputPath + "newsletter_with_pagelabels.pdf")
    doc.InitSecurityHandler()
    
    label := NewPageLabel()
    pageNum := doc.GetPageCount()
    
    i := 1
    for i <= pageNum{
        fmt.Println("Page number: " + strconv.Itoa(i))
        label = doc.GetPageLabel(i)
        
        if label.IsValid(){
            fmt.Println("Label: " + label.GetLabelTitle(i))
        }else{
            fmt.Println("No Label.")
        }
        i = i + 1
    }

    doc.Close()
            
    //-----------------------------------------------------------
    // Example 3: Modify page labels from an existing PDF document.
    //-----------------------------------------------------------
    
    doc = NewPDFDoc(outputPath + "newsletter_with_pagelabels.pdf")
    doc.InitSecurityHandler()
    
    // Remove the alphabetic labels from example i.
    doc.RemovePageLabel(7)
    
    // Replace the Prefix in the decimal labels (from example 1).
    label = doc.GetPageLabel(4)
    if label.IsValid(){
        label.SetPrefix("A")
        label.SetStart(1)
    }   
    // Add a new label
    newLabel := PageLabelCreate(doc.GetSDFDoc(), PageLabelE_decimal, "B", 1)
    doc.SetPageLabel(10, newLabel) // starting from page 10
    
    doc.Save(outputPath + "newsletter_with_pagelabels_modified.pdf", uint(SDFDocE_linearized))
    fmt.Println("Done. Result saved in newsletter_with_pagelabels_modified.pdf...")
    
    pageNum = doc.GetPageCount()
    i = 1
    for i <= pageNum{
        fmt.Println("Page number: " + strconv.Itoa(i))
        label = doc.GetPageLabel(i)
        if label.IsValid(){
            fmt.Println("Label: " + label.GetLabelTitle(i))
        }else{
            fmt.Println("No Label.")
        }
        i = i + 1
    }

    doc.Close()
        
    //-----------------------------------------------------------
    // Example 4: Delete all page labels in an existing PDF document.
    //----------------------------------------------------------- 
    
    doc = NewPDFDoc(outputPath + "newsletter_with_pagelabels.pdf")
    doc.GetRoot().Erase("PageLabels")
    doc.Save(outputPath + "newsletter_with_pagelabels_removed.pdf", uint(SDFDocE_linearized))
    
    doc.Close()    
    PDFNetTerminate()
}