#!/usr/bin/env bash

## This script is used to collate many pictures into a single PDF
## document. It is useful for book scanning. This assumes you are
## in the directory already

# This assumes all the pictures have been converted and deposited
# into a pdf/ directory, with a "pdf/0-XX.pdf" filename.
# do this to kick off --> \ls | sort -n | parallel -j12 --eta convert {} -monochrome -compress lzw ../pdf/0-{/.}.pdf

PDFLOC="pdf"
BATCHSIZE=10
PROCSIZE=12

passcount=0

oIFS="$IFS"
IFS=$'\n'

function process_files_at_location {
	# Pass this one argument--which directory to pull the file list from

	filelist=($(find $1 -type f -name "$passcount-*" | sort -n -t'-' -k2))
	batch=()
	commands=()

	passcount=$(($passcount+1))

	echo $passcount

	function cut_batch {
		first=$(echo ${batch[0]} | cut -d'/' -f2 | cut -d'-' -f2)
		cmd="gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile=pdf/$passcount-$first ${batch[@]}"
		commands+=("$cmd")
		batch=()
	}

	for file in ${filelist[@]}
	do
		batch+=($file)

		if [ ${#batch[@]} -ge $BATCHSIZE ] || [  ]
		then
			cut_batch
		fi
	done
	cut_batch

	# Run commands
	printf '%s\n' "${commands[@]}" | parallel -j$PROCSIZE


	# Repeat as necessary, until one pdf remains
	if [ `find $PDFLOC -type f -name "$passcount-*" | wc -l` -gt 1 ]
	then
		echo "### repeating process"
		process_files_at_location "$1"
	fi
}

process_files_at_location "$PDFLOC"

IFS="$oIFS"