#!/bin/bash
###############################################################################
#
# pdf-optimize: compress pdf using Ghostscript
#
# Copyright (C) 2020
# Author: Solal "Otthorn" Nathan <otthorn@crans.org>
# SPDX-License-Identifier: GPL-3.0-or-later
#
###############################################################################
#
# This program comes with ABSOLUTELY NO WARRANTY; This is free software, and
# you are welcome to redistribute it under certain conditions; See licence for
# more details.
#
###############################################################################

function usage
{
	echo "usage: pdf-optimize [options] input.pdf"
	echo "    ";
	echo "  -o | --output           : output filename";
	echo "  -q | --quiet            : run quietly";
	echo "  -v | --verbose          : run verbosly";
	echo "  -y | --yes-to-replace   : yes to replace existing files";
	echo "  -h | --help             : print this message";
	echo "    ";
	echo "If no output path is specified, given input.pdf as input will output
input_compressed.pdf"
}

function arg_parse
{
	# if no argument is given print help
	if [[ -z "$1" ]]; then
		usage; exit;
	fi

	# positional arguments
	args=()

	while [ "$1" != "" ]; do
		case "$1" in
			-o | --output )           output_path="$2";  shift;;
			-q | --quiet )            quiet=1;;
			-v | --verbose )          verbose=1;;
			-y | --yes-to-replace )   replace=1;;
			-h | --help )             usage;             exit;;
			* )                       args+=("$1")
		esac
		shift
	done

	# restore positional argument
	set -- "${args[@]}"

	# only the first one should be used
	input_path="${args[0]}"

	# add default output path if none is given
	if [[ -z "$output_path" ]]; then
		output_path="${input_path%.*}_compressed.pdf";
	fi

	# check if the output file already exists before writting to it
	if [[ -f "$output_path" && "$replace" == 0 ]]; then
		yes_or_no "$output_path already exists, do you want to replace it?" ||
			exit 1;
	fi

	# check if the input file exists
	if [[ ! -f "$input_path" ]]; then
		echo "$input_path does not exist."
		echo "Aborting";
		exit 1;
	fi
}

function yes_or_no
{
	read -pr "$* [y/N]: " ans
	case "$ans" in
		[yY] | [yY]es )     return 0;;
		* )                 echo "Aborting"; return 1;;
	esac
}

function run
{
	arg_parse "$@";
	
	# print general information
	if [[ "$quiet" != 1 ]]; then
		echo "Compressing from ${bold}$input_path${normal} into \
${bold}$output_path${normal}."
	fi

	# run the compression using ghostscript
	if [[ "$verbose" != 1 ]]; then
		ghostscript -sDEVICE=pdfwrite \
		   -dCompatibilityLevel=1.4 \
		   -dPDFSETTINGS=/prepress \
		   -dNOPAUSE \
		   -dQUIET \
		   -dBATCH \
		   -sOutputFile="$output_path" \
		   "$input_path"
	else
		echo "input_path=$input_path";
		echo "output_path=$output_path";
		echo "quiet=$quiet";
		echo "verbose=$verbose";
		echo "replace=$replace";
		echo "    ";
		ghostscript -sDEVICE=pdfwrite \
		   -dCompatibilityLevel=1.4 \
		   -dPDFSETTINGS=/prepress \
		   -dNOPAUSE \
		   -dBATCH \
		   -sOutputFile="$output_path" \
		   "$input_path" 
	fi
	
	# catching errors
	if [[ "$?" != 0 ]]; then
		echo "Something went wrong with ghostscript.";
		echo "Aborting.";
		exit 1;
	fi

	# compute the compresion rate
	if [[ "$quiet" != 1 ]]; then
		compute_compression;
	fi
}

function compute_compression
{
	input_size=$(du "$input_path" | cut -f1)
	output_size=$(du "$output_path" | cut -f1)
	percentage=$(echo "scale=1;$output_size / $input_size * 100" | bc -l)
	input_size_h=$(du -h "$input_path" | cut -f1)
	output_size_h=$(du -h "$output_path" | cut -f1)

	echo "Size reduced from ${bold}$input_size_h${normal} to \
${bold}$output_size_h${normal} [$percentage %]"
}

# font settings
bold=$(tput bold)
normal=$(tput sgr0)

# default values
quiet=0;   # do not be quiet
verbose=0; # do not be verbose
replace=0; # do not replace existing files

# execute main function
run "$@";