#! /usr/bin/env nix-shell
#! nix-shell -i bash -p pdftk gnugrep
set -efu

INPUT_FILE="${2:?Pass the PDF path as second argument.}"
PAGES_PER_REPORT="${1:?Pass the chunk size as first argument.}"

if [ ! -f "$INPUT_FILE" ]; then
  echo >&2 "File $INPUT_FILE does not exist."
  exit 1
fi

TOTAL_PAGES="$(pdftk "$INPUT_FILE" dump_data | grep NumberOfPages | cut -f2 -d' ')"

RUNS=$((TOTAL_PAGES/PAGES_PER_REPORT))

for run in $(seq 0 "$((RUNS-1))"); do
  start_page=$((run*PAGES_PER_REPORT+1))
  end_page=$(((run+1)*PAGES_PER_REPORT))
  output_file="chunk_$((run+1)).pdf"
  echo "splitting $INPUT_FILE from $start_page to $end_page into $output_file"
  pdftk "$INPUT_FILE" cat "$start_page-$end_page" output "$output_file"
done