#!/usr/bin/awk -f

# md2html.awk
# Usage:
# 	md2html file.md > file.html
# Options: -v esc=false to not escape html

function newblock(nblock) {
	if (text)
		print "<" block ">" text "</" block ">"
	text = ""
	block = nblock ? nblock : "p"
}

function subinline(tgl, inl) {
	while (match($0, tgl)){
		if (inline[ni] == inl)
			ni -= sub(tgl, "</" inl ">")
		else if (sub(tgl, "<" inl ">"))
			inline[++ni] = inl
	}
}

function dolink(href, lnk) {
	# Undo escaped html in uris
	gsub(/&amp;/, "\\&", href)
	gsub(/&lt;/, "<", href)
	gsub(/&gt;/, ">", href)
	# & can be tricky, and not standard:
	gsub(/&/, "\\\\\\&", href)
	gsub(/&/, "\\\\\\&", lnk)
	return "<a href=\"" href "\">" lnk "</a>"
}

BEGIN {
	ni = 0;	# inlines
	nl = 0;	# nested lists
	text = ""
	block = "p"
}

# Escape html
esc != "false" {
	gsub("&", "\\&amp;")
	gsub("<", "\\&lt;")
	gsub(">", "\\&gt;")
}

# Horizontal rules (_ is not in markdown)
/^[ 	]*([-*_] ?)+[ 	]*$/ && text == "" {
	print "<hr>"
	next
}

# Tables (not in markdown)
# Syntax:
# 		Right Align| 	Center Align	|Left Align
/([ 	]\|)|(\|[ 	])/ {
	if (block != "table")
		newblock("table")
	nc = split($0, cells, "|")
	$0 = "<tr>\n"
	for (i = 1; i <= nc; i++){
		align = "left"
		if (sub(/^[ 	]+/, "", cells[i])){
			if (sub(/[ 	]+$/, "", cells[i]))
				align = "center"
			else
				align = "right"
		}
		sub(/[ 	]+$/,"", cells[i])
		$0 = $0 "<td align=\"" align "\">" cells[i] "</td>\n"
	}
	$0 = $0 "</tr>"
}

# Ordered and unordered (possibly nested) lists
/^[ 	]*([*+-]|(([0-9]+[\.-]?)+))[ 	]/ {
	newblock("li")
	nnl = 1
	while (match($0, /^[ 	]/)){
		sub(/^[ 	]/,"")
		nnl++
	}
	while (nl > nnl)
		print "</" list[nl--] ">"
	while (nl < nnl){
		list[++nl] = "ol"
		if (match($0, /^[*+-]/))
			list[nl] = "ul"
		print "<" list[nl] ">"
	}
	sub(/^([*+-]|(([0-9]+[\.-]?)+))[ 	]/,"")
}

# Multi line list items
block == "li" {
	sub(/^( *)|(	*)/,"")
}

# Code blocks
/^(    |	)/ {
	if (block != "code")
		newblock("code")
	sub(/^(    |	)/, "")
	text = text $0 "\n"
	next
}

# Paragraphs
/^$/ {
	newblock()
	while (nl > 0)
		print "</" list[nl--] ">"
}

# Headers
/^#/ {
	newblock()
	match($0, /#+/)
	n = RLENGTH
	if (n > 6)
		n = 6
	text = substr($0, RLENGTH + 1)
	block = "h" n
	next
}

# Alternate headers (underlined)
/^=+$/ {
	block = "h" 1
	next
}

/^-+$/ {
	block = "h" 2
	next
}

{
	# Images
	while (match($0, /!\[[^\]]+\]\([^\)]+\)/)){
		split(substr($0, RSTART, RLENGTH), a, /(!\[)|\)|(\]\()/)
		sub(/!\[[^\]]+\]\([^\)]+\)/, "<img src=\"" a[3] "\" alt=\"" a[2] "\">")
	}
	# Links
	while (match($0, /\[[^\]]+\]\([^\)]+\)/)){
		split(substr($0, RSTART, RLENGTH), a, /[\[\)]|(\]\()/)
		sub(/\[[^\]]+\]\([^\)]+\)/, dolink(a[3], a[2]))
	}
	# Auto links (uri matching is poor)
	na = split($0, a, /(^\()|[ 	]|([,\.\)]([ 	]|$))/)
	for (i = 1; i <= na; i++)
		if (match(a[i], /^(((https?|ftp|file|news|irc):\/\/)|(mailto:)).+$/))
			sub(a[i], dolink(a[i], a[i]))
	# Inline
	subinline("(\\*\\*)|(__)", "strong")
	subinline("\\*", "em")
	subinline("`", "code")
	text = text (text ? " " : "") $0
}

END {
	while (ni > 0)
		text = text "</" inline[ni--] ">"
	newblock()
	while (nl > 0)
		print "</" list[nl--] ">"
}