#!/bin/bash
# copyright 2007 Gilbert Ashley <amigo@ibiblio.org>
# minimal implementation similar to the 'cut' command
show_usage() {
echo
echo ${0##/*}" Usage:"
echo "  Cut FIELDS from STRING using separator delimiter SEP"
echo "${0##/} -[fFIELDS|f FIELDS|--fields=] -[dSEP|d SEP] STRING"
echo "Using --output-delimiter= replaces the delimiter in the output."
echo "Fields can be given using one of these forms: single field '2'"
echo "open range '4-', closed range '2-5', or comma-separated list '2,3,4'"
exit
}

case $1 in
	""|"-h"|"--help") show_usage ;;
esac

# Minimum number of arguments needed by this program
MINARGS=3

# count the number of arguments given
COUNT=0
for ARGV in "$@" ; do (( COUNT++ )) ; done
ARGC=$COUNT

# check to make sure enough arguments were given
if [[ $ARGC -lt $MINARGS ]] ; then
 echo "Too few arguments given (Minimum:$MINARGS)"
 echo
 show_usage
fi

# process command-line arguments
for WORD in "$@" ; do
	case $WORD in
		-*)  true ;
			case $WORD in
				--fields=*) [[ $DEBUG ]] && echo "Short range FIELD Option using '='"
					FIELDS=${WORD##*=}
					shift ;;
				-f?) [[ $DEBUG ]] && echo "Short single FIELD Option"
					FIELDS=${WORD##*f}
					shift ;;
				-f) [[ $DEBUG ]] && echo "Short split FIELD Option"
					if [[ ${2:0:1} != "-" ]] ; then
					 FIELDS=$2
					 [[ $DEBUG ]] && echo FIELDS=$FIELDS
					 shift 2
					else
					 echo "Missing argument"
					 show_usage
					fi ;;
				-f*) [[ $DEBUG ]] && echo "Short FIELD Option range"
					FIELDS=${WORD##*f}
					[[ $DEBUG ]] && echo FIELDS=$FIELDS
					shift ;;
				-d?) [[ $DEBUG ]] && echo "Short single DEL Option"
					SEP=${WORD##*d}
					[[ $DEBUG ]] && echo FIELDS=$FIELDS
					shift ;;
				-d) [[ $DEBUG ]] && echo "Short split FIELD Option"
					if [[ ${2:0:1} != "-" ]] ; then
					 SEP=$2
					 [[ $DEBUG ]] && echo FIELDS=$FIELDS
					 shift 2
					else
					 echo "Missing argument"
					 show_usage
					fi ;;
				-d*) [[ $DEBUG ]] && echo "Short-short DEL Option"
					SEP=${WORD##*d}
					[[ $DEBUG ]] && echo SEP=$SEP
					shift ;;
				--output-delimiter=*) [[ $DEBUG ]] && echo "Long NEW_SEP Option"
					NEW_SEP=${WORD##*=}
					[[ $DEBUG ]] && echo NEW_SEP=$NEW_SEP
					shift
				;;
			esac
		;;
	esac
done

# we've munched our way through the options arguments with shift
# the remainder of the command-line is the INPUT_STREAM
STRING="$@"

# set the NEW_SEP to SEP unless  --output-delimiter was given
! [[ $NEW_SEP ]] && NEW_SEP=$SEP

# function _freq counts the number of matches
# of PATTERN in PARSESTRING and returns FREQ
# example usage: _freq $PATTERN $PARSESTRING
function _freq() { FREQ=0
! [[ $PATTERN ]] && PATTERN=$1
! [[ $PARSESTRING ]] && PARSESTRING=$2
while [[ $PARSESTRING != "" ]] ; do
	case $PARSESTRING in
		*$PATTERN*) FREQ=$(( FREQ + 1 )) ;
			PARSESTRING=${PARSESTRING#*${PATTERN}} ;;
		*) PARSESTRING="" ;;
	esac
done
echo $FREQ
}

# _get_one_field returns the contents of a FIELD in STRING
# fields are determined by a dividing separator SEP 
# STRING, FIELD and SEP must be supplied to this function
function _get_one_field() {
if [[ $FIELD = 1 ]] ; then
	# output the contents to the left of the first SEP
	OUTPUT=${STRING%%${SEP}*}
else
	# Chop off the first match and cheat on the count
	STUB=${STRING#*$SEP}
	COUNT=1
	# skip over any matches before the requested one
	while [[ $COUNT -lt $(( $FIELD - 1 )) ]] ; do
		# ROF Chop off leading FIELD and/or SEP
		STUB=${STUB#*$SEP}
		[[ $DEBUG ]] && echo $STUB
		(( COUNT++ ))
	done
	# LOF Chop off trailing SEP and/or rest of STUB
	OUTPUT=${STUB%%${SEP}*}
fi
echo $OUTPUT
}

# the command-line  FIELDS variable takes one of these  forms:
# single field '2', open range '4-', closed range '2-5', or comma-separated list '2,3,4'
# We examine the FIELDS variable with if's and convert everything to a LIST

# the first character is always the START or HEAD
HEAD=${FIELDS:0:1}
	
# if the second character is a '-' then this is a range like: 2-  or  3-5
if [[ ${FIELDS:1:1} = "-" ]] ; then
	# if the third character is null, range goes to end of STRING
	if [[ ${FIELDS:2:1} = "" ]] ; then
		# this is an open START to END range like: 2-
		#echo "START to END range"
		START=${FIELDS:0:1}
		# _freq counts the number of SEP's in STRING
		FINISH=$(_freq $SEP $STRING)
		# there are always one more TOTAL_FIELDS then SEP's
		FINISH=$(( FINISH + 1 ))
	else
		# this is a closed range like: 3-5
		START=${FIELDS:0:1}
		FINISH=${FIELDS:2:1}
	fi
	# translate the RANGE values to a comma-separated LIST
	LIST="$START,"
	COUNT=$START
	while [[ $COUNT -lt $(( $FINISH - 1 )) ]] ; do
		(( COUNT++ ))
		LIST=$LIST$COUNT","
	done
	LIST=$LIST$FINISH
elif [[ ${FIELDS:1:1} = "," ]] ; then
	# this is already a list
	# TODO? support a list like this:2,3,5-
	LIST=$FIELDS
elif [[ ${FIELDS:1:1} = "" ]] ; then
	# single argument given
	LIST=${FIELDS:0:1}
fi

# read first character of FIELDS variable
HEAD=${LIST:0:1}
# increment the LIST by chopping the first 2 digits
LIST=${LIST:2}

# set the FIELD to the HEAD
FIELD=$HEAD
# read the contents of the START or HEAD FIELD
OUTPUT="$(_get_one_field)"
# start the OUTPUT_STACK with the first OUTPUT
OUTPUT_STACK="$OUTPUT"

# read the *rest* of the LIST of fields
while [[ $LIST != "" ]] ; do
	# readfirst character
	FIELD=${LIST:0:1}
	# increment LIST
	LIST=${LIST:2}
	#  the OUTPUT of the current FIELD
	OUTPUT="$(_get_one_field)"
	# add the OUTPUT to OUTPUT_STACK with a NEW_SEP between
	OUTPUT_STACK=$OUTPUT_STACK$NEW_SEP$OUTPUT
done

# this the final ouput
FINAL_OUTPUT=$OUTPUT_STACK
# official program FINAL_OUTPUT
echo $FINAL_OUTPUT
exit