#!/bin/bash

# Resizes files to A4 (or other size - change PaperWdthMetr and PaperHghtMetr below) and merges into a PDF

# by Mikher and user173283 on StackExchange
# https://unix.stackexchange.com/questions/20026/convert-images-to-pdf-how-to-make-pdf-pages-same-size

export LOCALE=C

[[ "${2}x" == "x" ]] && \
 { echo "Usage: $( basename $0 ) output.pdf extension"
   echo "       merges all files (*.extension) into a single PDF"
   echo "If files z_merged.pdf, z_temp.pdf or $1 exist, they will be overwritten"
 exit 1
 } || \
 OutName="$1"
 ext="$2"

# Set basic variables
unset Debug #; Debug="yes" # print extra messages
IMBackground="white"      # what colour for paper
IMQuality="91"            # JPEG compression level
PaperHghtMetr="279.4"     # milimeters, 297 for ISO A4
PaperWdthMetr="215.9"     # milimeters, 210 for ISO A4
PaperDens="300"           # maximum (wanted) dpi for a page
PaperHInch=$( echo scale=5\; $PaperHghtMetr / 2.54 / 10      | bc -l ) # Inch
PaperWInch=$( echo scale=5\; $PaperWdthMetr / 2.54 / 10      | bc -l ) # Inch
PaperRtio=$(     echo scale=5\; $PaperWdthMetr / $PaperHghtMetr | bc -l )

# Remove temporary files from prior run
rm -rf z_merged.pdf z_temp.pdf 2>/dev/null

# Process any $ext file in the current directory
find . -maxdepth 1 -name "*.${ext}" -print0 | sort -z | while read -d '' -r FName
do
  echo "Converting $FName"
  ImgIdentify=$( identify -format "%w %h" "$FName" )
  ImgWdthOrig=$( echo $ImgIdentify | cut -d" " -f1  )
  ImgHghtOrig=$( echo $ImgIdentify | cut -d" " -f2  )
  ImgRtio=$( echo "scale=5; $ImgWdthOrig / $ImgHghtOrig"  | bc -l )


# Match output page layout - Landscape or Portrait - to input file
  if (( $(echo "$ImgRtio > 1 && $PaperRtio > 1 || $ImgRtio < 1 && $PaperRtio < 1" |bc -l) )); then
    echo "Portrait"
    PaperHghtInch=$PaperHInch
    PaperWdthInch=$PaperWInch
  else
    echo "Landscape"
    PaperHghtInch=$PaperWInch
    PaperWdthInch=$PaperHInch
  fi


  [[ $( echo $ImgRtio'>'$PaperRtio | bc -l ) == 1 ]] \
    && ImgDens=$( echo scale=0\; $ImgWdthOrig / $PaperWdthInch | bc -l ) \
    || ImgDens=$( echo scale=0\; $ImgHghtOrig / $PaperHghtInch | bc -l )
  [[ $Debug ]] && echo "ImgDens1: $ImgDens"
  [[ $( echo $ImgDens'>'$PaperDens | bc -l ) == 1 ]] \
    && ImgDens=$PaperDens
  [[ $Debug ]] && echo "ImgDens2: $ImgDens"

  ImgWdth=$( echo $PaperWdthInch \* $ImgDens | bc -l ) # pixels
  ImgHght=$( echo $PaperHghtInch \* $ImgDens | bc -l ) # pixels

  [[ $Debug ]] && echo "ImgWdth: $ImgWdth".
  [[ $Debug ]] && echo "ImgHght: $ImgHght".

  convert "${FName}"                                 \
          -resize ${ImgWdth}x${ImgHght}              \
          -background $IMBackground -gravity center  \
          -extent ${ImgWdth}x${ImgHght}              \
          -units PixelsPerInch -set density $ImgDens \
          -repage ${ImgWdth}x${ImgHght}+0+0          \
          -compress JPEG                             \
          -quality $IMQuality                        \
          "${FName%.$ext}.pdf"

  # Merge new PDF page with prior pages
  [[ -f z_merged.pdf ]] && \
   { pdftk z_merged.pdf "${FName%.$ext}.pdf" cat output z_temp.pdf
     mv z_temp.pdf z_merged.pdf
   } || \
     cp "${FName%.$ext}.pdf" z_merged.pdf
  [[ $Debug ]] || rm -rf "${FName%.$ext}.pdf"
done

[[ -f z_merged.pdf ]] && mv z_merged.pdf "$OutName"
echo "Done."