From 80c5811b6b15479b473e814cad0aae7de9920bb3 Mon Sep 17 00:00:00 2001
From: David Fish <dfish@plaid.com>
Date: Mon, 8 Jan 2018 11:19:41 -0800
Subject: Added generic alias-replacement function to enable Table of Contents
 functionality

---
 def.go       |  6 +++++-
 fpdf.go      | 32 +++++++++++++++++++++++---------
 fpdf_test.go | 31 +++++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+), 10 deletions(-)

diff --git a/def.go b/def.go
index 52e6474..936ca09 100644
--- a/def.go
+++ b/def.go
@@ -40,7 +40,10 @@ type gradientType struct {
 }
 
 const (
-	OrientationPortrait  = "portrait"
+	// OrientationPortrait represents the portrait orientation.
+	OrientationPortrait = "portrait"
+
+	// OrientationLandscape represents the landscape orientation.
 	OrientationLandscape = "landscape"
 )
 
@@ -243,6 +246,7 @@ type Fpdf struct {
 	fontSize         float64                   // current font size in user unit
 	ws               float64                   // word spacing
 	images           map[string]*ImageInfoType // array of used images
+	aliasMap         map[string]string         // map of alias->replacement
 	pageLinks        [][]linkType              // pageLinks[page][link], both 1-based
 	links            []intLinkType             // array of internal links
 	outlines         []outlineType             // array of outlines
diff --git a/fpdf.go b/fpdf.go
index 567311d..ad29d18 100644
--- a/fpdf.go
+++ b/fpdf.go
@@ -88,6 +88,7 @@ func fpdfNew(orientationStr, unitStr, sizeStr, fontDirStr string, size SizeType)
 	f.pageLinks = append(f.pageLinks, make([]linkType, 0, 0)) // pageLinks[0] is unused (1-based)
 	f.links = make([]intLinkType, 0, 8)
 	f.links = append(f.links, intLinkType{}) // links[0] is unused (1-based)
+	f.aliasMap = make(map[string]string)
 	f.inHeader = false
 	f.inFooter = false
 	f.lasth = 0
@@ -3071,6 +3072,26 @@ func (f *Fpdf) SetJavascript(script string) {
 	f.javascript = &script
 }
 
+// RegisterAlias adds an (alias, replacement) pair to the document so we can
+// replace all occurrences of that alias after writing but before the
+// document is closed.
+func (f *Fpdf) RegisterAlias(alias, replacement string) {
+	f.aliasMap[alias] = replacement
+}
+
+func (f *Fpdf) replaceAliases() {
+	for alias, replacement := range f.aliasMap {
+		for n := 1; n <= f.page; n++ {
+			s := f.pages[n].String()
+			if strings.Contains(s, alias) {
+				s = strings.Replace(s, alias, replacement, -1)
+				f.pages[n].Truncate(0)
+				f.pages[n].WriteString(s)
+			}
+		}
+	}
+}
+
 func (f *Fpdf) putpages() {
 	var wPt, hPt float64
 	var pageSize SizeType
@@ -3079,16 +3100,9 @@ func (f *Fpdf) putpages() {
 	nb := f.page
 	if len(f.aliasNbPagesStr) > 0 {
 		// Replace number of pages
-		nbStr := sprintf("%d", nb)
-		for n := 1; n <= nb; n++ {
-			s := f.pages[n].String()
-			if strings.Contains(s, f.aliasNbPagesStr) {
-				s = strings.Replace(s, f.aliasNbPagesStr, nbStr, -1)
-				f.pages[n].Truncate(0)
-				f.pages[n].WriteString(s)
-			}
-		}
+		f.RegisterAlias(f.aliasNbPagesStr, sprintf("%d", nb))
 	}
+	f.replaceAliases()
 	if f.defOrientation == "P" {
 		wPt = f.defPageSize.Wd * f.k
 		hPt = f.defPageSize.Ht * f.k
diff --git a/fpdf_test.go b/fpdf_test.go
index ff41fd2..c7d843a 100644
--- a/fpdf_test.go
+++ b/fpdf_test.go
@@ -2060,3 +2060,34 @@ func ExampleFpdf_AddSpotColor() {
 	// Output:
 	// Successfully generated pdf/Fpdf_AddSpotColor.pdf
 }
+
+// This example demonstrates how to use `RegisterAlias` to create a table of
+// contents.
+func ExampleFpdf_TableOfContents() {
+	pdf := gofpdf.New("P", "mm", "A4", "")
+	pdf.SetFont("Arial", "", 12)
+	pdf.AddPage()
+
+	// Write the table of contents. We use aliases instead of the page number
+	// because we don't know which page the section will begin on.
+	numSections := 3
+	for i := 1; i <= numSections; i++ {
+		pdf.Cell(0, 10, fmt.Sprintf("Section %d begins on page {%d}", i, i))
+		pdf.Ln(10)
+	}
+
+	// Write the sections. Before we start writing, we use `RegisterAlias` to
+	// ensure that the alias written in the table of contents will be replaced
+	// by the current page number.
+	for i := 1; i <= numSections; i++ {
+		pdf.AddPage()
+		pdf.RegisterAlias(fmt.Sprintf("{%d}", i), fmt.Sprintf("%d", pdf.PageNo()))
+		pdf.Write(10, fmt.Sprintf("Section %d", i))
+	}
+
+	fileStr := example.Filename("Fpdf_TableOfContents")
+	err := pdf.OutputFileAndClose(fileStr)
+	example.Summary(err, fileStr)
+	// Output:
+	// Successfully generated pdf/Fpdf_TableOfContents.pdf
+}
-- 
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