#! /usr/bin/perl

# LaTeX Watch, version 1.0
#	- by Robin Houston, March 2007.

use strict;
use warnings;
use POSIX;
use File::Copy 'copy';

# Debugging flag (currently 0 to disable, or 1 to enable)
use constant DEBUG => 0;

# Add teTeX path
$ENV{PATH} .= ":/usr/local/teTeX/bin/".`/usr/local/teTeX/bin/highesttexbin.pl`;

# PostScript viewer
my @ps_viewer = qw(gv -spartan -scale 2 -nocenter -antialias -nowatch);

# Location of CocoaDialog binary
my $CocoaDialog = "$ENV{TM_SUPPORT_PATH}/bin/CocoaDialog.app/Contents/MacOS/CocoaDialog";

# Explain what's happening (if we're debugging)
sub debug_msg {
	system($CocoaDialog, "msgbox",
		"--button1" => "OK",
		"--text" => $_[0])
	if DEBUG;
}

# Display an error dialog and exit with exit-code 1
sub fail {
	my ($message, $explanation) = @_;
	system($CocoaDialog, "msgbox",
		"--button1" => "Cancel",
		"--title" => "LaTeX Watch error",
		"--text" => "Error: $message",
		"--informative-text" => "$explanation.");
	exit(1)
}

sub fail_unless_system {
	system(@_);
	if ($? == -1) {
		fail("Failed to execute $_[0]",
			"The command '@_' failed to execute: $!");
	}
	elsif ($? & 127) {
		fail("Command failed",
			"The command '@_' caused $_[0] to die with signal ".($? & 127));
	}
	elsif ($? >>= 8) {
		fail("Command failed",
			"The command '@_' failed (error code $?)");
	}
}

my $filepath = $ENV{TM_FILEPATH};
fail("File not saved", "You must save the file before it can be watched")
	if !defined($filepath);

my ($wd, $name);
if ($filepath =~ m!(.*)/!) {
	$wd = $1;
	my $fullname = $';
	if ($fullname =~ /\.tex$/) {
		$name = $`;
	}
	else {
		fail("Filename doesn't end in .tex",
			"The filename ($fullname) does not end with the .tex extension");
	}
}
else {
	fail("Path does not contain /", "The file path ($filepath) does not contain a '/'");
}
if (! -W $wd) {
	fail("Directory not writeable", "I can't write to the directory $wd");
}

my ($preamble, $viewer_pid);

# Clean up if we're interrupted or die
sub clean_up {
	debug_msg("Cleaning up");
	unlink(map("$wd/.$name.$_", qw(ini fmt tex dvi ps bbl log watcher_pid)));
	kill (2, $viewer_pid) if defined $viewer_pid;
}
END { clean_up() }
$SIG{INT} = $SIG{TERM} = sub { exit(0) };

my $mtime;
while(1) {
	my $current_mtime = -M $filepath;
	if (!defined($current_mtime)) {
		fail("Failed to get modification time",
			"I failed to find the modification time of the file '$filepath': $!");
	}
	if (!defined($mtime) or $current_mtime < $mtime) {
		debug_msg("Reloading file");
		$mtime = $current_mtime;
		reload();
		compile();
		view();
	}
	if (defined($viewer_pid) and waitpid($viewer_pid, POSIX::WNOHANG)) {
		my $r = $?;
		debug_msg("Viewer appears to have been closed ($r). Exiting.");
		if ($r & 127) {
			fail("Viewer failed",
				"The PostScript viewer died with signal ".($r & 127));
		}
		elsif ($r >>= 8) {
			fail("Viewer failed",
				"The PostScript viewer exited with an error (error code $r)");
		}
		exit;
	}
	sleep(1);
}

sub reload {
	open (my $f, "<", $filepath)
		or fail ("Failed to open file",
			"I couldn't open the file '$filepath' for reading: $!");

	local $/ = "\\begin{document}";
	my $new_preamble = <$f>;
	chomp ($new_preamble)
		or fail ("No \\begin{document} found",
			"I couldn't find the command \\begin{document} in your file");

	if ($new_preamble ne $preamble) {
		debug_msg("Preamble has changed. Regenerating format.");
		regenerate_format($new_preamble);
	}

	undef $/;
	save_body(<$f>);

	close $f
		or fail ("Failed to close file",
			"I got an error closing the file '$filepath': $!");
}

sub regenerate_format {
	($preamble) = @_;
	open (my $ini, ">", "$wd/.$name.ini")
		or fail("Failed to create file",
			"The file '$wd/.$name.ini' could not be opened for writing: $!");
	print $ini ($preamble, "\n\\dump\n");
	close $ini
		or fail("Failed to close file",
			"The file '$wd/.$name.ini' gave an error on closing: $!");

	copy("$wd/$name.bbl", "$wd/.$name.bbl"); # Ignore errors
	fail_unless_system("etex", "-ini", "&latex", "$wd/.$name.ini");
}

sub save_body {
	open (my $f, ">", "$wd/.$name.tex")
		or fail("Failed to create file",
			"I couldn't create the file '$wd/.$name.tex': $!");

	print $f ("\\begin{document}\n", @_);

	close($f)
		or fail("Failed to close file",
			"I got an error on closing the file '$wd/.$name.tex': $!");
}

sub compile {
	copy("$wd/$name.bbl", "$wd/.$name.bbl"); # Ignore errors
	copy("$wd/$name.aux", "$wd/.$name.aux"); # Ignore errors
	fail_unless_system("etex", "&.$name", "$wd/.$name.tex");
	rename("$wd/.$name.aux", "$wd/$name.aux");
	fail_unless_system("dvips", "$wd/.$name.dvi", "-o");
}

sub view {
	if (defined($viewer_pid)) {
		kill(1, $viewer_pid)
			or fail("Failed to signal viewer",
				"I failed to signal the PostScript viewer (PID $viewer_pid) to reload: $!");
	}
	else {
		$viewer_pid = start_viewer("$wd/.$name.ps");
	}
}

sub start_viewer {
	my ($ps_file) = @_;
	my $pid = fork();
	if ($pid) {
		# In parent
		return $pid;
	}
	else {
		# In child
		POSIX::setsid(); # detach from terminal
		close STDOUT; open(STDOUT, ">", "/dev/null");
		close STDERR; open(STDERR, ">", "/dev/null");
		
		debug_msg("Starting PostScript viewer ($$)");
		exec(@ps_viewer, $ps_file);
		fail("Failed to start PostScript viewer",
			"I failed to run the PostScript viewer: @ps_viewer");
	}
}