#!/bin/bash
# copyright 2007 Gilbert Ashley <amigo@ibiblio.org>
# BashTrix grepis an implementation of the 'grep' command
# written in pure shell. Very few grep options are supported.
VERSION=0.1

ERROR=0
# show program usage
show_usage() {
echo "Usage: ${0##/*} [OPTION]... [PATTERN] [FILE]..."
echo "Try '${0##/*} --help' for more information."
exit $ERROR
}
# show program help
show_help() {
echo
echo "Usage: ${0##/*} [OPTION]... [PATTERN] [FILE]..."
echo "${0##/} -[v] PATTERN FILE"
echo "  or: (cat|echo) | ${0##/*} [OPTION]... [PATTERN]"
echo "Print lines of each FILE to standard output which contain matches of PATTERN."
echo "With more than one FILE, precede each with a header giving the file name."
echo "With no FILE, read standard input."
echo "  -q, --quiet, --silent  never print headers giving file names"
echo "  -v, --reverse	Reverse the match"
echo "  --verbose          always print headers giving file names"
echo "      --help     display this help and exit"
echo "      --version  output version information and exit"
exit $ERROR
}

show_version() {
echo ${0##/*}" (BashTrix) $VERSION"
echo "Copyright 2007 Gilbert Ashley <amigo@ibiblio.org>"
echo "This is free software written in pure shell."
exit $ERROR
}

# show usage if '-h' or  '--help' is the first argument or no argument is given
case $1 in
	"") show_usage ;;
	"-h"|"--help") show_help ;;
	"--version") show_version ;;
esac

# get the - options
for WORD in "$@" ; do
	case $WORD in
		-*)  true ;
			case $WORD in
				-v) REVERSE_MATCH=1 ; shift ;;
				-n) PRINT_LINE_NUMBERS=1 ; shift ;;
				-H) PRINT_FILE_NAMES=1 ; shift ;;
				--help) show_usage ;;
				--version) show_version ;;
				-) READ_STDIN=1 ; shift ;;
			esac
		;;
	esac
done

# get the search PATTERN and advance
# these patterns are processed by a case statement which can't deal with
# regular expresions. We identify regex anchors (beginning '^' and ending '$' characters,
# which denote line begins with or line ends with), and strip off the character
# so case can deal with it directly. case handles bracket-enclosed expressions
# mostly the same. However this routine does not deal with '[^sometext]' or '[sometext$]' -yet.
PATTERN=$1
if [[ "${PATTERN:0:1}" = "^" ]] ; then
 MATCH_BEGINNING=1
 PATTERN=${PATTERN:1}
 #PATTERN=${PATTERN/^/}
else
	OFFSET=$(( ${#PATTERN} - 1 ))
	if [[ "${PATTERN:$OFFSET:1}" = "$" ]] ; then
	MATCH_ENDING=1
	PATTERN=${PATTERN:0:$OFFSET}
	fi
fi

if [[ "${PATTERN:0:1}" = "[" ]] ; then
	if [[ "${PATTERN:1:1}" = "^" ]] ; then
		REVERSE_MATCH=1
		PATTERN="[${PATTERN:2}"
	else
		OFFSET=$(( ${#PATTERN} - 2 ))
		if [[ "${PATTERN:$OFFSET:1}" = "$" ]] ; then
		MATCH_ENDING=1
		PATTERN="${PATTERN:0:$OFFSET}]"
		fi
		
	fi
fi

 echo $PATTERN

# move to the next argument in the command line
shift

if [[ $# -gt 0 ]] ; then
	while [[ $# -gt 0 ]] ; do
		FILE_NAME="$1"
		if [ ! -r "$1" ] ; then
			echo "Cannot find file $1" 1>&2
			ERROR=1
			break
		else
			# write the header output if requested
			if [[ $SHOW_HEADERS ]] ; then
			 echo "==> $FILE_NAME <=="
			fi
			# reset to the start and print the requested lines
			FILE_LINE_COUNT=0
			LINE=
			IFS=
			while read LINE ; do
				# add the curent line to the line counter
				(( FILE_LINE_COUNT++ ))
				STRING=$LINE
				if [[ $PRINT_LINE_NUMBERS ]] ; then
				 OUTPUT_HEADER="$FILE_LINE_COUNT:"
				fi
				if [[ $PRINT_FILE_NAMES ]] ; then
				 OUTPUT_HEADER="$FILE_NAME:$OUTPUT_HEADER"
				fi
				case $STRING in
					$PATTERN*)
						if [[ ! $REVERSE_MATCH ]] ; then
						 echo $OUTPUT_HEADER$STRING
						fi
						;;
					*$PATTERN)
						if [[ ! $REVERSE_MATCH ]] && [[ ! $MATCH_BEGINNING ]] ; then
						 echo $OUTPUT_HEADER$STRING
						fi
						;;
					*$PATTERN*)
						if [[ ! $REVERSE_MATCH ]] ; then 
							if [[ ! $MATCH_BEGINNING ]] && [[ ! $MATCH_ENDING ]] ; then
								 echo $OUTPUT_HEADER$STRING
							fi
						fi
						;;
						*)
						if [[ $REVERSE_MATCH ]] ; then
							if [[ "$STRING" != "" ]] ; then
							  echo $OUTPUT_HEADER$STRING
							fi
						fi
						;;
				
				esac
				# go to next LINE
			done <"$1"
		fi
	# go to next FILE in $@
	shift
	done
else
	# piped input is presumed to be separated into lines already
	FILE_NAME="STDIN"
	
	# write the header output if requested
	if [[ $SHOW_HEADERS ]] ; then
		echo "==> $FILE_NAME <=="
	fi
	
	# output the requested lines in the file
	FILE_LINE_COUNT=0
	LINE=
	IFS=
	while read LINE ; do
		# add the curent line to the line counter
		(( FILE_LINE_COUNT++ ))
		STRING=$LINE
		case $STRING in
			$PATTERN*)
				if [[ $MATCH_BEGINNING ]] && [[ ! $REVERSE_MATCH ]] ; then
					echo $STRING
				fi
				#break
				;;
			*$PATTERN)
				if [[ $MATCH_ENDING ]] && [[ ! $REVERSE_MATCH ]] ; then
					echo $STRING
				fi
				;;
			*$PATTERN*)
				if [[ ! $REVERSE_MATCH ]] ; then
					if [[ ! $MATCH_BEGINNING ]] &&  [[ ! $MATCH_ENDING ]] ; then
						echo $STRING
					fi
				fi
				;;
				*)
				if [[ $REVERSE_MATCH ]] ; then
					if [[ "$STRING" != "" ]] ; then
						echo $STRING
					fi
				fi
				;;
				
		esac
		# go to next LINE
		shift
	done
fi

exit $ERROR