#!/bin/sh

### Initialize
# init buffers
buff="$(mktemp)"
lbuf="$(mktemp)"
trap 'rm "$buff" "$lbuf"' EXIT INT KILL

# init state
prev=
curr=
verbatim=false
# (tuneables)
nl='::NL::'
sp='::SP::'
to=html

### Formats
## HTML and GMI are given here. Other formats can be defined in their
## own files and they'll be sourced.

## NOTES
# should we allow modifying variables from the environment ?

html() {
	fmtbuff_hd_1="<h1>%s</h1>$nl"
	fmtline_hd_1="%s"
	fmtbuff_hd_2="<h2>%s</h2>$nl"
	fmtline_hd_2="%s"
	fmtbuff_hd_3="<h3>%s</h3>$nl"
	fmtline_hd_3="%s"
	fmtbuff_quot="<blockquote>$nl%s</blockquote>$nl"
	fmtline_quot="%s$nl"
	fmtbuff_list="<ul>$nl%s</ul>$nl"
	fmtline_list="<li>%s</li>$nl"
	fmtbuff_para="<p>%s</p>$nl"
	fmtline_para="%s$nl"
	fmtline_plnk="<a href=\"%s\">%s</a>$nl"
	fmtbuff_link="<ul class=\"links\">$nl%s</ul>$nl"
	fmtline_link="<li><a href=\"%s\">%s</li>$nl"
	fmtbuff_verb="<pre><code>%s</code></pre>$nl"
	fmtline_verb="%s$nl"
	fmtbuff_blank="$nl"
	fmtline_blank="$nl"
}

gmi() {
	fmtbuff_hd_1="# %s$nl"
	fmtline_hd_1="%s"
	fmtbuff_hd_2="## %s$nl"
	fmtline_hd_2="%s"
	fmtbuff_hd_3="### %s$nl"
	fmtline_hd_3="%s"
	fmtbuff_quot="> %s$nl"
	fmtline_quot="%s$sp"
	fmtbuff_list="%s$nl"
	fmtline_list="* %s$nl"
	fmtbuff_para="%s$nl"
	fmtline_para="%s$sp"
	fmtline_plnk="$nl=> %s %s$nl"
	fmtbuff_link="%s$nl"
	fmtline_link="=> %s %s"
	fmtbuff_verb="\`\`\`$nl%s\`\`\`$nl"
	fmtline_verb="%s$nl"
	fmtbuff_blank="$nl"
	fmtline_blank="$nl"
}

### Filters

filter_buff_html(){ cat; }

filter_buff() {
	f="filter_buff_$to"
	if type "$f" | grep -q function
	then "$f"
	else cat
	fi | sed -e "s/$nl/\n/g" -e "s/$sp/ /g" # fix whitespace
}

filter_line() {
	f="filter_line_$to"
	if type "$f" | grep -q function
	then printf '%s\n' "$*" | "$f"
	else printf '%s\n' "$*"
	fi
}

filter_line_html() {
	# s/// : escape <, >, & from html
	# s### : *bold*, _italic_, `code`
	sed -e 's/&/\&amp;/g' \
	    -e 's/</\&lt;/g' \
	    -e 's/>/\&gt;/g' \
	    -e 's#\*\([^*]*\)\*#<b>\1</b>#g' \
	    -e 's#_\([^_]*\)_#<i>\1</i>#g' \
	    -e 's#`\([^`]*\)`#<code>\1</code>#'

}

### Processing

## Utility functions

pushline() {
	tag="$1"; shift
	printf "$(eval echo "\$fmtline_$tag")" "$@" >> "$buff"
}

bufprint() {
	b="$(cat<"$buff")"
	printf "$(eval echo "\$fmtbuff_$1")" "$b" | filter_buff
	: > "$buff"
}

## Where the magic happens
process() {
	set -f
	while read -r sigil line
	do
		if $verbatim && test "$sigil" != '```'
		then
			pushline verb "$(filter_line "$sigil $line")"
			continue
		fi

		case "$sigil" in
			('```')
				if $verbatim
				then
					bufprint verb
					verbatim=false
					prev=
				else
					# CONSIDER: "types" of verbatim
					# designated by extra fields after the
					# sigil
					## ``` class_of_content
					# ^- change the class of the content,
					# eg. in html do <pre class="type">
					# other formats might do other things
					## ``` | some_program
					# ^- pipe the buffer to some_program
					## others?
					bufprint "$prev"
					verbatim=true
				fi
				continue
				;;
			('=>')
				printf '%s\n' "$line" > "$lbuf"
				read -r url title < "$lbuf"
				if test "$curr" = para
				then
					pushline plnk "$url" "$title"
					continue
				else curr=link
				fi
				;;
			('#'*) curr=hd_${#sigil} ;;
			('>') curr=quot ;;
			('*') curr=list ;;
			('') curr=blank ;;
			(*)
				curr=para
				line="$sigil $line"
				;;
		esac

		test "$curr" = "$prev" || bufprint "$prev"
		prev="$curr"

		if test "$curr" = verb
		then
			pushline "$curr" "$line"
			continue
		fi

		if test "$curr" = link
		then pushline "$curr" "$url" "$(filter_line "$title")"
		else pushline "$curr" "$(filter_line "$line")"
		fi
	done

	bufprint "$curr"
}

### Entry point

usage() {
	cat <<EOF >&2
jimmy: convert gmi to other formats
usage: jimmy [-h] [-t FORMAT] [FILE...]
If no FILE is given on the command line, jimmy reads standard input.
options:
 -h	show this help and exit
 -t FORMAT
	convert gmi to FORMAT. html is default, gmi is built-in.
	you can also pass the name of a file that will be sourced.
EOF
}

main() {
	while getopts ht:x OPT
	do
		case "$OPT" in
			(h) usage 0 ;;
			(t) to="$OPTARG" ;;
			(x) set -x ;;
			(*) usage 1 ;;
		esac
	done
	shift $((OPTIND - 1))

	case "$to" in
		(html|gmi) "$to" ;;
		(*) . "$to" || {
				  echo >&2 "Can't find file: '$to'"
				  exit 2
			  }
		    ;;
	esac

	# while read requires a final newline
	(cat "${@:--}"; echo) | process
}

main "$@"