# subtext -- text substitutor -*- awk -*-
# (C) C Duckworth <acdw@acdw.net>

BEGIN {
	## Tuneables
	postproc = get_value(postproc, "ST_POSTPROC", "shexpand")
	bodyfunc = get_value(bodyfunc, "ST_BODYFUNC", "sub_text")
	sopath = get_value(sopath, "ST_SOPATH", ".:"ENVIRON["HOME"]"/.subtext")
	split(sopath, asopath, ":")
	# postproc = postproc ? postproc : "shexpand"
	# bodyfunc = bodyfunc ? bodyfunc : "sub_text"
	## Globals
	# Booleans
	true = 1
	false = 0
	## Wrap the text in a function
	pretext = "### begin text\n"bodyfunc"(){\n"
	posttext = "}\n### end text"
	## Prelude function strings
	# Ask sed to do these b/c awk has no capture groups ;_;
	shellfix = "sed -E" \
		" -e 's/`/\\\\`/g'" \
		" -e 's/(^|[^\\$])\\$([^\\$]|$)/\\1\\\\$\\2/g'" \
		" -e 's/(^|[^\\$])\\$(\\$+)([^\\$]|$)/\\1\\2\\3/g'"
	shxwrap = " -e 's/^/:/'"
	htmlfix = "sed -E" \
		" -e 's#([^\\\\]|^)&#\\1\\&amp;#g'" \
		" -e 's#([^\\\\]|^)<#\\1\\&lt;#g'" \
		" -e 's#([^\\\\]|^)>#\\1\\&gt;#g'" \
		" -e 's#\\\\([&<>])#\\1#g'";
	## Prelude
	par = "#!/bin/sh\n### kernel\n" \
		"preface()(sed \"s/^/$1/\")\n" \
		"unpreface()(sed \"s/^$1//\")\n" \
		"shexpand()(eval \"$( (echo 'cat<<.';preface +;echo .)" \
		" | unpreface + )\")\n" \
		"### library\n" \
		"shellfix()(" shellfix ")\n" \
		"htmlfix()(" htmlfix ")\n" \
		"### variables\n" \
		"ST_POSTPROC=" postproc "\n" \
		"ST_BODYFUNC=" bodyfunc "\n" \
		"ST_SOPATH=" sopath "\n" \
		"### header\n"
}

### End a block

end[endn] && $0 == end[endn] {
	par = par "\n" end[endn--] "\n)"
	printpar()
	subdocp = false
	next
}

### Line continuation

/\\$/ {
	getline nl
	sub(/\\$/,"")
	$0 = $0 " " nl
}

### Special commands
## These call subtext-internal functions

/^\.so/ {			# Insert $2 verbatim (if in sopath), else error
	source($2)
	next
}

### Escape sequences

/^\.\.\./ {			# Delimit document (end is optional)
	printpar()
	docp = !docp
	if (docp) print pretext "unpreface ':'<<'_'|eval \"$ST_POSTPROC\""
	else end_text()
	next
}

/^\.\./ && docp {		# Begin a heredoc
	# ..[<command>] [<options>] [<<delim]
	## ends with DELIM or '..'
	subdocp = true
	end[++endn] = (match($0,"<<") ? substr($0,RSTART+RLENGTH) : "..")
	command = substr($0, 3, RSTART ? RSTART - 2 : length)
	$0 = "$$(" (command ? command : "cat") "<<" end[endn]
}

/^\./ && docp {			# One-line command
	# .<command> [<parameters>]
	## wraps the line in $( ... ), basically (also quotes)
	specialp = 2
	gsub(/"/,"\\\\&")
	ln = "$$(" substr($1, 2)
	for (f=2;f<=NF;f++) ln = ln " \"" $f "\""
	ln = ln ")"
	$0 = ln
}

/^\\/ && docp { # \ at the beginning of a line escapes the next character
	$0 = substr($0, 2)
}

### Book-keeping

/^$/ {
	if (!par) next
	printpar()
}

{ par = par (par?"\n":"") $0 }
{ if (--specialp < 0) specialp = 0 }

END {
	if (dead) exit dead
	if (par) printpar()
	while (endn > 0)
		print "\n" end[endn--] "\n)"
	if (docp) end_text()
}

function end_text() {
	print "_\n" posttext
}

function printpar() {
	specialp = specialp || (match(par, /^[ 	]*</))
	if (docp) {
		if (!subdocp && !specialp) par = "<p>" par "</p>"
		shx = shellfix shxwrap
		print par | shx
		close(shx)
	} else print par
	par = ""
}

function get_value(var, env_var, default) {
	if (var) return var
	else if (ENVIRON[env_var]) return ENVIRON[env_var]
	else return default
}

function source(name) {
	found = false
	sp = ""
	for (dir in asopath) {
		fn = asopath[dir] "/" name
		sp = asopath[dir] "\n\t" sp
		while ((getline ln < fn) > 0) {
			found = true
			par = par (par?"\n":"") ln
		}
		if (found) break
	}
	if (!found)
		die("Couldn't source " name "; looked in:\n\t" sp, 9)
}

function die(message, code) {
	dead = code
	print "!!" FILENAME ":" NR ": " message > "/dev/stderr"
	exit
}