#!/usr/bin/perl

use v5.12;
use warnings;

use Text::ParseWords qw/quotewords/;


# 1  Definitions


# 1.1  Global program state

my $empty = ''; # currently buffered empty lines
my $opel = ''; # currently opened element


# 1.2  Elements

# 1.2.1  Block elements
my %blels = (
	Pp_0 => '<p>%</p>',
	Qp_0 => '<blockquote><p>%</p></blockquote>',
	Pr_0 => '<pre>%</pre>',
	Sh_0 => '<h3>%</h3>',
	Sh_1 => '<h\\$1>%</h\\$1>',
	Ti_0 => '<title>%</title>',
);

# 1.2.2  Inline elements
my %inels = (
	Au_1 => '<meta name="author" content="\\$1"/>',
	Bd_0 => '\\$3<b>\\$1</b>\\$2',
	br_0 => '<br/>',
	Cd_0 => '\\$3<code>\\$1</code>\\$2',
	Cs_1 => '<meta http-equiv="Content-Type" content="text/html; charset=\\$1"/>',
	Em_0 => '\\$3<em>\\$1</em>\\$2',
	Hy_0 => '<a href="\\$2">\\$1</a>',
	Im_0 => '<img src="\\$1" alt="\\$2"/>',
	It_0 => '\\$3<i>\\$1</i>\\$2',
	St_0 => '\\$3<strong>\\$1</strong>\\$2',
	Tt_0 => '\\$3<tt>\\$1</tt>\\$2',
	Ul_0 => '\\$3<u>\\$1</u>\\$2',
);


# 1.3  Subroutines

# 1.3.1  Handle element request
sub request {
	my ($el, $args) = @_;
	my @argv = quotewords('\s+', 0, $args);
	my $n = @argv;
	my $elkey = "${el}_$n";

	if (exists $blels{$elkey}) {
		# Clear empty line buffer
		$empty = '';

		# Close currently open block element, open new
		if (exists $blels{$opel}) {
			print end($blels{$opel}) . "\n";
			$opel = '';
		}
		$opel = $elkey;

		print interpol(start($blels{$elkey}), @argv) . "\n";
	} elsif (exists $inels{$elkey}) {
		print interpol($inels{$elkey}, @argv) . "\n";
	} else {
		print STDERR "Error: $el/$n not implemented\n";
		exit 1;
	}
}

# 1.3.2  Interpolate \$n parameters
sub interpol {
	my $s = shift;
	my $i = 1;
	my $arg;
	while ($arg = shift) {
		$s =~ s/\\\$$i/$arg/g;
		$i++;
	}
	return $s;
}

# 1.3.3  Retrieve first portion of block element string
sub start {
	return (split '%', shift)[0];
}

# 1.3.4  Retrieve second portion of block element string
sub end {
	return (split '%', shift)[1];
}


# 2  Program


# 2.1  Translate mh source text to HTML
while (<>) {
	chomp;
	if (/^\.([A-Za-z][a-z])\s*(.*)/) {
		request($1, $2);
	} elsif ($_ eq '') {
		$empty .= "\n";
	} else {
		print $empty; $empty = '';
		print "$_\n";
	}
}

# 2.2  Close currently open block element
if (exists $blels{$opel}) {
	print end($blels{$opel}) . "\n";
	$opel = '';
}