#!/bin/bash

# Check if pdftk and ghostscript are installed
if ! command -v pdftk &>/dev/null || ! command -v gs &>/dev/null; then
    echo "Error: pdftk and ghostscript are required but not installed."
    exit 1
fi

# Check for input arguments
if [ "$#" -ne 3 ]; then
    echo "Replaces the last page of a pdf file (input) with another (insert) and saves the file (output)."
    echo "Usage: $0 input.pdf insert.pdf output.pdf"
    exit 1
fi

input_pdf="$1"
insert_pdf="$2"
output_pdf="$3"

# Get the number of pages in the input PDF
num_pages=$(pdftk "$input_pdf" dump_data | grep NumberOfPages | awk '{print $2}')

if [ -z "$num_pages" ]; then
    echo "Error: Unable to determine the number of pages in the input PDF."
    exit 1
fi

# Extract all pages except the last one
pdftk "$input_pdf" cat 1-$(($num_pages - 1)) output temp_removed_last.pdf

# Merge the modified PDF with the insert PDF
pdftk temp_removed_last.pdf "$insert_pdf" cat output "$output_pdf"

# Clean up temporary files
rm -f temp_removed_last.pdf

echo "Successfully created $output_pdf by replacing the last page with $insert_pdf."