#!/bin/bash

set -e

tmp_dir="$(mktemp -d)"
trap 'rm -rf --one-file-system "${tmp_dir}"' EXIT

if [ $# -ne 3 ]; then
  echo 'Verwendung: combine-images Geometrie Dateistamm_ Endung'
  echo ' Geometrie hat die Form "Breite"x"Hoehe"+"x-Offset"+"y-Offset"'
  exit 1
fi

geometry="$1"
stem="$2"
ending="$3"

files="$(
  ls "$(dirname "${stem}")" | \
    grep "^$(basename "${stem}")[0-9]\+_[0-9]\+\.${ending}\$"
)"

numbers="$(
  echo "${files}" | \
    sed "
      s|^$(basename "${stem}")||
      s|\.${ending}\$||
    " | \
    sort
)"

min_x="$(
  echo "${numbers}" | \
    sed 's|_[0-9]\+$||' | \
    sort -nr | \
    tail -n1
)"

max_x="$(
  echo "${numbers}" | \
    sed 's|_[0-9]\+$||' | \
    sort -n | \
    tail -n1
)"

min_y="$(
  echo "${numbers}" | \
    sed 's|^[0-9]\+_||' | \
    sort -nr | \
    tail -n1
)"

max_y="$(
  echo "${numbers}" | \
    sed 's|^[0-9]\+_||' | \
    sort -n | \
    tail -n1
)"

if ! [ "${numbers}" = "$(
  for ((x=${min_x}; x<=${max_x}; x++)); do
    for ((y=${min_y}; y<=${max_y}; y++)); do
      echo "${x}_${y}"
    done
  done
  )" ]; then
  echo 'Die angegebenen Bilder ergeben kein Rechteck!'
  exit 1
fi

for ((x=${min_x}; x<=${max_x}; x++)); do
  for ((y=${min_y}; y<=${max_y}; y++)); do
    convert "${stem}${x}_${y}.${ending}" -crop "${geometry}" "${tmp_dir}/C${x}_${y}.bmp"
    printf '.'
  done
  convert $(
    for ((y=${max_y}; y>=${min_y}; y--)); do
      printf '%s ' "${tmp_dir}/C${x}_${y}.bmp"
    done
  ) -append "${tmp_dir}/C${x}.bmp"
  printf '.'
done

convert $(
  for ((x=${min_x}; x<=${max_x}; x++)); do
    printf '%s ' "${tmp_dir}/C${x}.bmp"
  done
) +append "${stem%_}.${ending}"
printf '.\n'