Split PDF and merge pages back in a reverse order.

pdf2reverse.go

package main

import (
	"fmt"
	"io/ioutil"
	"os"
	"path"
	"path/filepath"
	"strings"

	pdf "github.com/pdfcpu/pdfcpu/pkg/api"
)

func main() {
	if len(os.Args) < 3 {
		os.Exit(1)
	}
	in := os.Args[1]
	out := os.Args[2]

	var (
		tmp string
		err error
	)
	var pcount int
	if pcount, err = pdf.PageCount(in); err != nil {
		fmt.Printf("%v\n", err)
	}
	if pcount <= 1 {
		fmt.Printf("error: document has %d pages\n", pcount)
		os.Exit(1)
	}

	tmp, err = ioutil.TempDir("", "pdf2reverse-")
	if err != nil {
		os.Exit(1)
	}
	defer os.RemoveAll(tmp)

	// Create single page PDFs for in.pdf in outDir using the default configuration.
	pdf.SplitFile(in, tmp, 1, nil)

	var (
		ext     = filepath.Ext(in)
		base    = filepath.Base(strings.TrimRight(in, ext))
		infiles []string
	)
	for p := pcount; p >= 1; p-- {
		infiles = append(infiles, path.Join(tmp, fmt.Sprintf("%s_%d%s", base, p, ext)))
	}
	if err = pdf.MergeFile(infiles, out, nil); err != nil {
		fmt.Printf("%v\n", err)
	}
}