#!/usr/bin/perl -w
# This script is used to turn one or more of the "patch/*" branches
# into one or more diffs in the "patches" directory.  Pass the option
# --gen if you want generated files in the diffs.  Pass the name of
# one or more diffs if you want to just update a subset of all the
# diffs.

use strict;
use Getopt::Long;

my $patches_dir = 'patches';
my $tmp_dir = "patches.$$";

&Getopt::Long::Configure('bundling');
&usage if !&GetOptions(
    'skip-check' => \( my $skip_branch_check ),
    'shell|s' => \( my $launch_shell ),
    'gen:s' => \( my $incl_generated_files ),
    'help|h' => \( my $help_opt ),
);
&usage if $help_opt;

if (defined $incl_generated_files) {
    $patches_dir = $incl_generated_files if $incl_generated_files ne '';
    $incl_generated_files = 1;
}

die "No '$patches_dir' directory was found.\n" unless -d $patches_dir;
die "No '.git' directory present in the current dir.\n" unless -d '.git';

my($status, $is_clean, $starting_branch) = &check_git_status;
if (!$skip_branch_check && !$is_clean) {
    die "The checkout is not clean:\n", $status;
}

my @extra_files;
open(IN, '<', 'Makefile.in') or die "Couldn't open Makefile.in: $!\n";
while (<IN>) {
    if (s/^GENFILES=//) {
	while (s/\\$//) {
	    $_ .= <IN>;
	}
	@extra_files = split(' ', $_);
	last;
    }
}
close IN;

if ($incl_generated_files) {
    die "'$tmp_dir' must not exist in the current directory.\n" if -e $tmp_dir;
    mkdir($tmp_dir, 0700) or die "Unable to mkdir($tmp_dir): $!\n";
    system "./config.status Makefile && make gen && rsync -a @extra_files $tmp_dir/master/" and exit 1;
}
our $last_touch = time;

my(%patches, %local_patch);

# Start by finding all patches so that we can load all possible parents.
open(PIPE, '-|', 'git', 'branch', '-a') or die $!;
while (<PIPE>) {
    if (m# origin/patch/(.*)#) {
	$patches{$1} = 1;
    } elsif (m# patch/(.*)#) {
	$patches{$1} = $local_patch{$1} = 1;
    }
}
close PIPE;

my @patches = sort keys %patches;

my(%parent, %description);
foreach my $patch (@patches) {
    my $branch = ($local_patch{$patch} ? '' : 'origin/') . "patch/$patch";
    my $desc = '';
    open(PIPE, '-|', 'git', 'diff', '-U1000', "master...$branch", '--', "PATCH.$patch") or die $!;
    while (<PIPE>) {
	last if /^@@ /;
    }
    while (<PIPE>) {
	next unless s/^[ +]//;
	if (m#patch -p1 <patches/(\S+)\.diff# && $1 ne $patch) {
	    $parent{$patch} = $1;
	}
	$desc .= $_;
    }
    $description{$patch} = $desc;
}

if (@ARGV) {
    # Limit the list of patches to actually process based on @ARGV.
    @patches = ( );
    foreach (@ARGV) {
	s{^(patches|patch|origin/patch)/} {};
	s{\.diff$} {};
	push(@patches, $_);
    }
}

my %completed;
foreach my $patch (@patches) {
    next if $completed{$patch}++;
    last unless update_patch($patch);
}

if ($incl_generated_files) {
    system "rm -rf $tmp_dir";
}

sleep 1 while $last_touch >= time;
system "git checkout $starting_branch" and exit 1;

exit;


sub update_patch
{
    my($patch) = @_;

    my $parent = $parent{$patch};
    if (defined $parent) {
	unless ($completed{$parent}++) {
	    update_patch($parent);
	}
	$parent = "patch/$parent";
    } else {
	$parent = 'master';
    }

    print "======== $patch ========\n";

    sleep 1 while $incl_generated_files && $last_touch >= time;
    if ($local_patch{$patch}) {
	system "git checkout patch/$patch" and return 0;
    } else {
	system "git checkout --track -b patch/$patch origin/patch/$patch" and return 0;
    }

    my $ok = system("git merge $parent") == 0;
    if (!$ok || $launch_shell) {
	print qq|"git merge $parent" incomplete -- please fix.\n| if !$ok;
	$ENV{PS1} = "[$parent] patch/$patch: ";
	while (1) {
	    if (system($ENV{SHELL}) != 0) {
		print "Abort? [n/y] ";
		$_ = <STDIN>;
		next unless /^y/i;
		return 0;
	    }
	    ($status, $is_clean) = &check_git_status;
	    last if $is_clean;
	    print $status;
	}
    }

    open(OUT, '>', "$patches_dir/$patch.diff") or die $!;
    print OUT $description{$patch}, "\n";

    if ($incl_generated_files) {
	system "./config.status Makefile && make gen && rsync -a @extra_files $tmp_dir/$patch/" and exit 1;
    }
    $last_touch = time;

    open(PIPE, '-|', 'git', 'diff', $parent) or die $!;
    DIFF: while (<PIPE>) {
	while (m{^diff --git a/PATCH}) {
	    while (<PIPE>) {
		last if m{^diff --git a/};
	    }
	    last DIFF if !defined $_;
	}
	next if /^index /;
	print OUT $_;
    }
    close PIPE;

    if ($incl_generated_files) {
	$parent =~ s#.*/##;
	open(PIPE, '-|', 'diff', '-up', "$tmp_dir/$parent", "$tmp_dir/$patch") or die $!;
	while (<PIPE>) {
	    s#^(diff -up) $tmp_dir/[^/]+/(.*?) $tmp_dir/[^/]+/(.*)#$1 a/$2 b/$3#o;
	    s#^\Q---\E $tmp_dir/[^/]+/([^\t]+)\t.*#--- a/$1#o;
	    s#^\Q+++\E $tmp_dir/[^/]+/([^\t]+)\t.*#+++ b/$1#o;
	    print OUT $_;
	}
	close PIPE;
    }

    close OUT;

    1;
}

exit;

sub check_git_status
{
    open(IN, '-|', 'git status') or die $!;
    my $status = join('', <IN>);
    close IN;
    my $is_clean = $status =~ /\nnothing to commit \(working directory clean\)/;
    my($starting_branch) = $status =~ /^# On branch (.+)\n/;
    ($status, $is_clean, $starting_branch);
}

sub usage
{
    die <<EOT;
Usage: patch-update [OPTIONS]

--gen[=DIR]   Include generated files.  Optional dest DIR overrides "patches".
--skip-check  Skip the check that ensures starting with a clean branch.
EOT
}