#!/bin/bash
#
#    djvuocr.sh is free software. You can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, either version 3 of the License, or
#    (at your option) any later version.
#
#    djvuocr.sh is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with djvuocr.sh.  If not, see <http://www.gnu.org/licenses/>.
#
#
# This is script is meant to automate the process of converting
# image-based PDF files into searchable DJVU files by means of OCR.
#
# It was inspired by:
# http://superuser.com/questions/641899/how-to-automatically-find-non-searchable-pdfs
# http://jwilk.net/software/ocrodjvu
#
# It is required to have the following installed:
#   ocrodjvu (tested with 0.7.18 from Debian packages.debian.org)
#   pdftoppm, pdfinfo and pdffonts (from poppler-utils 0.24.5)
#   scantailor (tested with 0.9.11.1)
#   djvm and cjb2 (from djvulibre; djvulibre-bin 3.5.25.4-3)
#
# Save this script to a file and make it executable:
#   chmod +x djvuocr.sh
#
# Then run it on a terminal with the name of the PDF that you want to
# OCR:
#   djvuocr.sh /directory/MyPdfFile.pdf
#
# Good luck!

function check_use() {
    if [[ ! "$#" = "1" ]]; then
	printf "Usage: $0 /path/to/directory\n";
	exit 1;
    fi;
}

function check_apps() {
    [[ -z $(which "scantailor") ]] && inst="$inst scantailor";
    [[ -z $(which "pdf2djvu") ]] && inst="$inst pdf2djvu";
    [[ -z $(which "ocrodjvu") ]] && inst="$inst ocrodjvu";
    [[ -z $(which "pdftoppm") || -z $(which "pdfinfo") || -z $(which "pdffonts") ]] && inst="$inst poppler-utils";
    [[ -z $(which "djvm") || -z $(which "cjb2") ]] && inst="$inst djvulibre-bin";
    if [[ -n $inst ]]; then
	printf "The following utilities need to be installed:\n$inst\n\n"
	printf "Do you want to continue? [Y/n]"
	read bol_inst;
	case $bol_inst in
	    [yY] | [yY][eE][sS] | "")
		sudo aptitude install "$inst";
		;;
	    [nN] | [Nn][Oo])
		printf "Aborting. Have a nice day.\n"
		exit 1;
		;;
	esac;
    fi;
}

function DjVuOCR() {
    [[ -z $nomTmp ]] && nomTmp="$(uuidgen)";
    OCRdir="/tmp/OCR/$nomTmp";
    mkdir -p "$OCRdir";
    printf "\nCreated working directory $OCRdir";

    printf "\nConverting pages to TIFF: ";
    for i in $pags; do
	printf "$i ";
	pdftoppm -tiffcompression none -r 300 -tiff -f "$i" -l "$i" "$arch_pdf" "$OCRdir/$nomTmp";
    done;
    printf "\n";
    printf "Do you want to use scantailor to improve the OCR? [y/N] "
    read bol_tailor </dev/tty;
    case $bol_tailor in
	[yY] | [yY][eE][sS])
	    printf "When scantailor is opened,\
1) click \"New Project\";
2) choose $OCRdir as \"Input Directory\";
3) don't change the \"Output Directory\";
4) fullfil the tasks to the left;
5) in the last task select black and white (not mixed nor grayscale);
6) when done, click on the play symbol (an arrow within a circle), and
7) close scantailor. You don't need to save the project if you don't want to.

You'll be brought back to this terminal when finished. Hit ENTER now."
	    read </dev/tty;
	    scantailor;
	    out_dir="out";
	    ;;
	[nN] | [Nn][Oo] | "")
	    printf "Skipping scantailor";
	    ;;
    esac;
    out_dir="$OCRdir/$out_dir";

    printf "\nConverting pages to DJVU: \n";
    djvu_dir="$OCRdir/djvu";
    mkdir -p "$djvu_dir"
    # Check if tesseract is working
    if [[ "$(ocrodjvu --list-engines)" =~ "tesseract" ]]; then
	printf "Using tesseract OCR\n";
	ocr="tesseract";
    else
	printf "Not using tesseract. The results will be sub-optimal\n";
    fi;

    for i in "$out_dir"/*.tif; do
	if [[ -f "$i" ]]; then
	    # http://jwilk.net/software/ocrodjvu
	    djvu_arch="$djvu_dir/$(basename -s .tif "$i")".djvu;
	    cjb2 "$i" "$djvu_arch";
	    if [[ -n "$ocr" ]]; then
		ocrodjvu --in-place -e "$ocr" "$djvu_arch";
	    else
		ocrodjvu --in-place "$djvu_arch";
	    fi;
	fi;
    done;

    printf "\nExtracting remaining pages from PDF: \n"
    for (( i=1; i<=$num_pag; i++ )); do
	if [[ ! -f "$djvu_dir/$nomTmp-$i.djvu" ]]; then
	    pdf2djvu -j0 --lines -p "$i" -o "$djvu_dir/$nomTmp-$i".djvu "$arch_pdf";
	fi;
    done;

    printf "\nJoining to DJVU: \n";
    djvm -c "$OCRdir/$(basename -s .pdf "$arch_pdf")"-OCR.djvu "$djvu_dir/$nomTmp-"*.djvu;

    printf "\n***** Success! *****\n";
    printf "The original file was\n";
    printf "$arch_pdf\n";
    printf "Your new file is located at $OCRdir\n";

    printf "\nDo you want to clean the temporary files and ";
    printf "move your new file to the original location? [Y/n] ";
    read fin </dev/tty;
    case "$fin" in
	[yY] | [yY][eE][sS] | "")
	    rm -fr "$djvu_dir" "$out_dir" "$OCRdir/$nomTmp*.tif";
	    mv "$OCRdir/$(basename -s .pdf "$arch_pdf")"-OCR.djvu "$(dirname "$arch_pdf")"
	    ;;
	[nN] | [nN][oO])
	    printf "\n"
	    du -h "$OCRdir";
	    ;;
    esac;
}

function main() {
    # Go page by page trying to see which ones are searchable
    # (searchable pages should have a font)
    num_pag=$(printf "$PDFINFO_OUT" | grep '^Pages' | awk '{print $2}');
    pags="";
    i=0;
    for ((i=1; i<=$num_pag; i++)); do
	# Count the number of fonts (get rid of pdffonts header)
	font=$(pdffonts -f "$i" -l "$i" "$arch_pdf" | wc -l);
	font=$(( $font - 2 ));
	# If there are no fonts, this page is not searchable, and I want
	# to store it
	if [[ "$font" == "0" ]]; then
    	    pags="$pags $i";
	fi;
    done;

    # Start the conversion
    if [[ -n "$pags" ]]; then
	printf "***** It has non-searchable pages $pags *****\n";
	printf "Do you want to run OCR on this document? [Y/n]\n";
	read OCR_bol </dev/tty;
	case $OCR_bol in
	    [yY] | [yY][eE][sS] | "")
		DjVuOCR
		;;
	    [nN] | [Nn][Oo])
		printf "Not working on this file.\n"
		;;
	esac;
    fi;
}

check_use "$@";
check_apps;
dir="$1"

# http://mywiki.wooledge.org/BashFAQ/020
while IFS= read -r -d '' arch_pdf; do
# # http://linuxconfig.org/bash-scripting-tutorial
# find "$dir" -type f -iname '*.pdf' -print0 | while read file; do
# done;
    # Check if the file is readable with pdfinfo
    printf "\nChecking $(basename "$arch_pdf")\n";
    # Run pdfinfo on the file and send any STDERR (file descriptor 2)
    # to /dev/null (make it disappear)
    PDFINFO_OUT="$(pdfinfo "$arch_pdf" 2>/dev/null)";
    # Catch the exit code
    RET_PDFINFO="$?";
    # Check if there was an error (0 if there is no error)
    if [[ ! "$RET_PDFINFO" = "0" ]]; then
	READ_ERROR=1;
	printf "Error while reading $FILE. Skipping...\n";
	# stop this loop and start the next one
	continue;
    fi;
    main;
done < <(find "$dir" -type f -iname '*pdf' -print0)