#!/usr/bin/perl

use strict;

use warnings;

use IPC::Open2;

# An example hook script to integrate Watchman

# (https://facebook.github.io/watchman/) with git to speed up detecting

# new and modified files.

#

# The hook is passed a version (currently 2) and last update token

# formatted as a string and outputs to stdout a new update token and

# all files that have been modified since the update token. Paths must

# be relative to the root of the working tree and separated by a single NUL.

#

# To enable this hook, rename this file to "query-watchman" and set

# 'git config core.fsmonitor .git/hooks/query-watchman'

#

my ($version, $last_update_token) = @ARGV;

# Uncomment for debugging

# print STDERR "$0 $version $last_update_token\n";

# Check the hook interface version

if ($version ne 2) {

	die "Unsupported query-fsmonitor hook version '$version'.\n" .

	    "Falling back to scanning...\n";

}

my $git_work_tree = get_working_dir();

my $retry = 1;

my $json_pkg;

eval {

	require JSON::XS;

	$json_pkg = "JSON::XS";

	1;

} or do {

	require JSON::PP;

	$json_pkg = "JSON::PP";

};

launch_watchman();

sub launch_watchman {

	my $o = watchman_query();

	if (is_work_tree_watched($o)) {

		output_result($o->{clock}, @{$o->{files}});

	}

}

sub output_result {

	my ($clockid, @files) = @_;

	# Uncomment for debugging watchman output

	# open (my $fh, ">", ".git/watchman-output.out");

	# binmode $fh, ":utf8";

	# print $fh "$clockid\n@files\n";

	# close $fh;

	binmode STDOUT, ":utf8";

	print $clockid;

	print "\0";

	local $, = "\0";

	print @files;

}

sub watchman_clock {

	my $response = qx/watchman clock "$git_work_tree"/;

	die "Failed to get clock id on '$git_work_tree'.\n" .

		"Falling back to scanning...\n" if $? != 0;

	return $json_pkg->new->utf8->decode($response);

}

sub watchman_query {

	my $pid = open2(\*CHLD_OUT, \*CHLD_IN, 'watchman -j --no-pretty')

	or die "open2() failed: $!\n" .

	"Falling back to scanning...\n";

	# In the query expression below we're asking for names of files that

	# changed since $last_update_token but not from the .git folder.

	#

	# To accomplish this, we're using the "since" generator to use the

	# recency index to select candidate nodes and "fields" to limit the

	# output to file names only. Then we're using the "expression" term to

	# further constrain the results.

	if (substr($last_update_token, 0, 1) eq "c") {

		$last_update_token = "\"$last_update_token\"";

	}

	my $query = <<"	END";

		["query", "$git_work_tree", {

			"since": $last_update_token,

			"fields": ["name"],

			"expression": ["not", ["dirname", ".git"]]

		}]

	END

	# Uncomment for debugging the watchman query

	# open (my $fh, ">", ".git/watchman-query.json");

	# print $fh $query;

	# close $fh;

	print CHLD_IN $query;

	close CHLD_IN;

	my $response = do {local $/; <CHLD_OUT>};

	# Uncomment for debugging the watch response

	# open ($fh, ">", ".git/watchman-response.json");

	# print $fh $response;

	# close $fh;

	die "Watchman: command returned no output.\n" .

	"Falling back to scanning...\n" if $response eq "";

	die "Watchman: command returned invalid output: $response\n" .

	"Falling back to scanning...\n" unless $response =~ /^\{/;

	return $json_pkg->new->utf8->decode($response);

}

sub is_work_tree_watched {

	my ($output) = @_;

	my $error = $output->{error};

	if ($retry > 0 and $error and $error =~ m/unable to resolve root .* directory (.*) is not watched/) {

		$retry--;

		my $response = qx/watchman watch "$git_work_tree"/;

		die "Failed to make watchman watch '$git_work_tree'.\n" .

		    "Falling back to scanning...\n" if $? != 0;

		$output = $json_pkg->new->utf8->decode($response);

		$error = $output->{error};

		die "Watchman: $error.\n" .

		"Falling back to scanning...\n" if $error;

		# Uncomment for debugging watchman output

		# open (my $fh, ">", ".git/watchman-output.out");

		# close $fh;

		# Watchman will always return all files on the first query so

		# return the fast "everything is dirty" flag to git and do the

		# Watchman query just to get it over with now so we won't pay

		# the cost in git to look up each individual file.

		my $o = watchman_clock();

		$error = $output->{error};

		die "Watchman: $error.\n" .

		"Falling back to scanning...\n" if $error;

		output_result($o->{clock}, ("/"));

		$last_update_token = $o->{clock};

		eval { launch_watchman() };

		return 0;

	}

	die "Watchman: $error.\n" .

	"Falling back to scanning...\n" if $error;

	return 1;

}

sub get_working_dir {

	my $working_dir;

	if ($^O =~ 'msys' || $^O =~ 'cygwin') {

		$working_dir = Win32::GetCwd();

		$working_dir =~ tr/\\/\//;

	} else {

		require Cwd;

		$working_dir = Cwd::cwd();

	}

	return $working_dir;

}