#!/usr/bin/perl

use 5.008;
use strict;
use warnings;
use Git;

binmode(STDOUT, ":raw");

my $repo = Git->repository();

my $menu_use_color = $repo->get_colorbool('color.interactive');
my ($prompt_color, $header_color, $help_color) =
	$menu_use_color ? (
		$repo->get_color('color.interactive.prompt', 'bold blue'),
		$repo->get_color('color.interactive.header', 'bold'),
		$repo->get_color('color.interactive.help', 'red bold'),
	) : ();
my $error_color = ();
if ($menu_use_color) {
	my $help_color_spec = ($repo->config('color.interactive.help') or
				'red bold');
	$error_color = $repo->get_color('color.interactive.error',
					$help_color_spec);
}

my $diff_use_color = $repo->get_colorbool('color.diff');
my ($fraginfo_color) =
	$diff_use_color ? (
		$repo->get_color('color.diff.frag', 'cyan'),
	) : ();
my ($diff_plain_color) =
	$diff_use_color ? (
		$repo->get_color('color.diff.plain', ''),
	) : ();
my ($diff_old_color) =
	$diff_use_color ? (
		$repo->get_color('color.diff.old', 'red'),
	) : ();
my ($diff_new_color) =
	$diff_use_color ? (
		$repo->get_color('color.diff.new', 'green'),
	) : ();

my $normal_color = $repo->get_color("", "reset");

my $use_readkey = 0;
sub ReadMode;
sub ReadKey;
if ($repo->config_bool("interactive.singlekey")) {
	eval {
		require Term::ReadKey;
		Term::ReadKey->import;
		$use_readkey = 1;
	};
}

sub colored {
	my $color = shift;
	my $string = join("", @_);

	if (defined $color) {
		# Put a color code at the beginning of each line, a reset at the end
		# color after newlines that are not at the end of the string
		$string =~ s/(\n+)(.)/$1$color$2/g;
		# reset before newlines
		$string =~ s/(\n+)/$normal_color$1/g;
		# codes at beginning and end (if necessary):
		$string =~ s/^/$color/;
		$string =~ s/$/$normal_color/ unless $string =~ /\n$/;
	}
	return $string;
}

# command line options
my $patch_mode;
my $patch_mode_revision;

sub apply_patch;
sub apply_patch_for_checkout_commit;
sub apply_patch_for_stash;

my %patch_modes = (
	'stage' => {
		DIFF => 'diff-files -p',
		APPLY => sub { apply_patch 'apply --cached', @_; },
		APPLY_CHECK => 'apply --cached',
		VERB => 'Stage',
		TARGET => '',
		PARTICIPLE => 'staging',
		FILTER => 'file-only',
		IS_REVERSE => 0,
	},
	'stash' => {
		DIFF => 'diff-index -p HEAD',
		APPLY => sub { apply_patch 'apply --cached', @_; },
		APPLY_CHECK => 'apply --cached',
		VERB => 'Stash',
		TARGET => '',
		PARTICIPLE => 'stashing',
		FILTER => undef,
		IS_REVERSE => 0,
	},
	'reset_head' => {
		DIFF => 'diff-index -p --cached',
		APPLY => sub { apply_patch 'apply -R --cached', @_; },
		APPLY_CHECK => 'apply -R --cached',
		VERB => 'Unstage',
		TARGET => '',
		PARTICIPLE => 'unstaging',
		FILTER => 'index-only',
		IS_REVERSE => 1,
	},
	'reset_nothead' => {
		DIFF => 'diff-index -R -p --cached',
		APPLY => sub { apply_patch 'apply --cached', @_; },
		APPLY_CHECK => 'apply --cached',
		VERB => 'Apply',
		TARGET => ' to index',
		PARTICIPLE => 'applying',
		FILTER => 'index-only',
		IS_REVERSE => 0,
	},
	'checkout_index' => {
		DIFF => 'diff-files -p',
		APPLY => sub { apply_patch 'apply -R', @_; },
		APPLY_CHECK => 'apply -R',
		VERB => 'Discard',
		TARGET => ' from worktree',
		PARTICIPLE => 'discarding',
		FILTER => 'file-only',
		IS_REVERSE => 1,
	},
	'checkout_head' => {
		DIFF => 'diff-index -p',
		APPLY => sub { apply_patch_for_checkout_commit '-R', @_ },
		APPLY_CHECK => 'apply -R',
		VERB => 'Discard',
		TARGET => ' from index and worktree',
		PARTICIPLE => 'discarding',
		FILTER => undef,
		IS_REVERSE => 1,
	},
	'checkout_nothead' => {
		DIFF => 'diff-index -R -p',
		APPLY => sub { apply_patch_for_checkout_commit '', @_ },
		APPLY_CHECK => 'apply',
		VERB => 'Apply',
		TARGET => ' to index and worktree',
		PARTICIPLE => 'applying',
		FILTER => undef,
		IS_REVERSE => 0,
	},
);

my %patch_mode_flavour = %{$patch_modes{stage}};

sub run_cmd_pipe {
	if ($^O eq 'MSWin32' || $^O eq 'msys') {
		my @invalid = grep {m/[":*]/} @_;
		die "$^O does not support: @invalid\n" if @invalid;
		my @args = map { m/ /o ? "\"$_\"": $_ } @_;
		return qx{@args};
	} else {
		my $fh = undef;
		open($fh, '-|', @_) or die;
		return <$fh>;
	}
}

my ($GIT_DIR) = run_cmd_pipe(qw(git rev-parse --git-dir));

if (!defined $GIT_DIR) {
	exit(1); # rev-parse would have already said "not a git repo"
}
chomp($GIT_DIR);

my %cquote_map = (
 "b" => chr(8),
 "t" => chr(9),
 "n" => chr(10),
 "v" => chr(11),
 "f" => chr(12),
 "r" => chr(13),
 "\\" => "\\",
 "\042" => "\042",
);

sub unquote_path {
	local ($_) = @_;
	my ($retval, $remainder);
	if (!/^\042(.*)\042$/) {
		return $_;
	}
	($_, $retval) = ($1, "");
	while (/^([^\\]*)\\(.*)$/) {
		$remainder = $2;
		$retval .= $1;
		for ($remainder) {
			if (/^([0-3][0-7][0-7])(.*)$/) {
				$retval .= chr(oct($1));
				$_ = $2;
				last;
			}
			if (/^([\\\042btnvfr])(.*)$/) {
				$retval .= $cquote_map{$1};
				$_ = $2;
				last;
			}
			# This is malformed -- just return it as-is for now.
			return $_[0];
		}
		$_ = $remainder;
	}
	$retval .= $_;
	return $retval;
}

sub refresh {
	my $fh;
	open $fh, 'git update-index --refresh |'
	    or die;
	while (<$fh>) {
		;# ignore 'needs update'
	}
	close $fh;
}

sub list_untracked {
	map {
		chomp $_;
		unquote_path($_);
	}
	run_cmd_pipe(qw(git ls-files --others --exclude-standard --), @ARGV);
}

my $status_fmt = '%12s %12s %s';
my $status_head = sprintf($status_fmt, 'staged', 'unstaged', 'path');

{
	my $initial;
	sub is_initial_commit {
		$initial = system('git rev-parse HEAD -- >/dev/null 2>&1') != 0
			unless defined $initial;
		return $initial;
	}
}

sub get_empty_tree {
	return '4b825dc642cb6eb9a060e54bf8d69288fbee4904';
}

# Returns list of hashes, contents of each of which are:
# VALUE:	pathname
# BINARY:	is a binary path
# INDEX:	is index different from HEAD?
# FILE:		is file different from index?
# INDEX_ADDDEL:	is it add/delete between HEAD and index?
# FILE_ADDDEL:	is it add/delete between index and file?

sub list_modified {
	my ($only) = @_;
	my (%data, @return);
	my ($add, $del, $adddel, $file);
	my @tracked = ();

	if (@ARGV) {
		@tracked = map {
			chomp $_;
			unquote_path($_);
		} run_cmd_pipe(qw(git ls-files --), @ARGV);
		return if (!@tracked);
	}

	my $reference;
	if (defined $patch_mode_revision and $patch_mode_revision ne 'HEAD') {
		$reference = $patch_mode_revision;
	} elsif (is_initial_commit()) {
		$reference = get_empty_tree();
	} else {
		$reference = 'HEAD';
	}
	for (run_cmd_pipe(qw(git diff-index --cached
			     --numstat --summary), $reference,
			     '--', @tracked)) {
		if (($add, $del, $file) =
		    /^([-\d]+)	([-\d]+)	(.*)/) {
			my ($change, $bin);
			$file = unquote_path($file);
			if ($add eq '-' && $del eq '-') {
				$change = 'binary';
				$bin = 1;
			}
			else {
				$change = "+$add/-$del";
			}
			$data{$file} = {
				INDEX => $change,
				BINARY => $bin,
				FILE => 'nothing',
			}
		}
		elsif (($adddel, $file) =
		       /^ (create|delete) mode [0-7]+ (.*)$/) {
			$file = unquote_path($file);
			$data{$file}{INDEX_ADDDEL} = $adddel;
		}
	}

	for (run_cmd_pipe(qw(git diff-files --numstat --summary --), @tracked)) {
		if (($add, $del, $file) =
		    /^([-\d]+)	([-\d]+)	(.*)/) {
			$file = unquote_path($file);
			if (!exists $data{$file}) {
				$data{$file} = +{
					INDEX => 'unchanged',
					BINARY => 0,
				};
			}
			my ($change, $bin);
			if ($add eq '-' && $del eq '-') {
				$change = 'binary';
				$bin = 1;
			}
			else {
				$change = "+$add/-$del";
			}
			$data{$file}{FILE} = $change;
			if ($bin) {
				$data{$file}{BINARY} = 1;
			}
		}
		elsif (($adddel, $file) =
		       /^ (create|delete) mode [0-7]+ (.*)$/) {
			$file = unquote_path($file);
			$data{$file}{FILE_ADDDEL} = $adddel;
		}
	}

	for (sort keys %data) {
		my $it = $data{$_};

		if ($only) {
			if ($only eq 'index-only') {
				next if ($it->{INDEX} eq 'unchanged');
			}
			if ($only eq 'file-only') {
				next if ($it->{FILE} eq 'nothing');
			}
		}
		push @return, +{
			VALUE => $_,
			%$it,
		};
	}
	return @return;
}

sub find_unique {
	my ($string, @stuff) = @_;
	my $found = undef;
	for (my $i = 0; $i < @stuff; $i++) {
		my $it = $stuff[$i];
		my $hit = undef;
		if (ref $it) {
			if ((ref $it) eq 'ARRAY') {
				$it = $it->[0];
			}
			else {
				$it = $it->{VALUE};
			}
		}
		eval {
			if ($it =~ /^$string/) {
				$hit = 1;
			};
		};
		if (defined $hit && defined $found) {
			return undef;
		}
		if ($hit) {
			$found = $i + 1;
		}
	}
	return $found;
}

# inserts string into trie and updates count for each character
sub update_trie {
	my ($trie, $string) = @_;
	foreach (split //, $string) {
		$trie = $trie->{$_} ||= {COUNT => 0};
		$trie->{COUNT}++;
	}
}

# returns an array of tuples (prefix, remainder)
sub find_unique_prefixes {
	my @stuff = @_;
	my @return = ();

	# any single prefix exceeding the soft limit is omitted
	# if any prefix exceeds the hard limit all are omitted
	# 0 indicates no limit
	my $soft_limit = 0;
	my $hard_limit = 3;

	# build a trie modelling all possible options
	my %trie;
	foreach my $print (@stuff) {
		if ((ref $print) eq 'ARRAY') {
			$print = $print->[0];
		}
		elsif ((ref $print) eq 'HASH') {
			$print = $print->{VALUE};
		}
		update_trie(\%trie, $print);
		push @return, $print;
	}

	# use the trie to find the unique prefixes
	for (my $i = 0; $i < @return; $i++) {
		my $ret = $return[$i];
		my @letters = split //, $ret;
		my %search = %trie;
		my ($prefix, $remainder);
		my $j;
		for ($j = 0; $j < @letters; $j++) {
			my $letter = $letters[$j];
			if ($search{$letter}{COUNT} == 1) {
				$prefix = substr $ret, 0, $j + 1;
				$remainder = substr $ret, $j + 1;
				last;
			}
			else {
				my $prefix = substr $ret, 0, $j;
				return ()
				    if ($hard_limit && $j + 1 > $hard_limit);
			}
			%search = %{$search{$letter}};
		}
		if (ord($letters[0]) > 127 ||
		    ($soft_limit && $j + 1 > $soft_limit)) {
			$prefix = undef;
			$remainder = $ret;
		}
		$return[$i] = [$prefix, $remainder];
	}
	return @return;
}

# filters out prefixes which have special meaning to list_and_choose()
sub is_valid_prefix {
	my $prefix = shift;
	return (defined $prefix) &&
	    !($prefix =~ /[\s,]/) && # separators
	    !($prefix =~ /^-/) &&    # deselection
	    !($prefix =~ /^\d+/) &&  # selection
	    ($prefix ne '*') &&      # "all" wildcard
	    ($prefix ne '?');        # prompt help
}

# given a prefix/remainder tuple return a string with the prefix highlighted
# for now use square brackets; later might use ANSI colors (underline, bold)
sub highlight_prefix {
	my $prefix = shift;
	my $remainder = shift;

	if (!defined $prefix) {
		return $remainder;
	}

	if (!is_valid_prefix($prefix)) {
		return "$prefix$remainder";
	}

	if (!$menu_use_color) {
		return "[$prefix]$remainder";
	}

	return "$prompt_color$prefix$normal_color$remainder";
}

sub error_msg {
	print STDERR colored $error_color, @_;
}

sub list_and_choose {
	my ($opts, @stuff) = @_;
	my (@chosen, @return);
	my $i;
	my @prefixes = find_unique_prefixes(@stuff) unless $opts->{LIST_ONLY};

      TOPLOOP:
	while (1) {
		my $last_lf = 0;

		if ($opts->{HEADER}) {
			if (!$opts->{LIST_FLAT}) {
				print "     ";
			}
			print colored $header_color, "$opts->{HEADER}\n";
		}
		for ($i = 0; $i < @stuff; $i++) {
			my $chosen = $chosen[$i] ? '*' : ' ';
			my $print = $stuff[$i];
			my $ref = ref $print;
			my $highlighted = highlight_prefix(@{$prefixes[$i]})
			    if @prefixes;
			if ($ref eq 'ARRAY') {
				$print = $highlighted || $print->[0];
			}
			elsif ($ref eq 'HASH') {
				my $value = $highlighted || $print->{VALUE};
				$print = sprintf($status_fmt,
				    $print->{INDEX},
				    $print->{FILE},
				    $value);
			}
			else {
				$print = $highlighted || $print;
			}
			printf("%s%2d: %s", $chosen, $i+1, $print);
			if (($opts->{LIST_FLAT}) &&
			    (($i + 1) % ($opts->{LIST_FLAT}))) {
				print "\t";
				$last_lf = 0;
			}
			else {
				print "\n";
				$last_lf = 1;
			}
		}
		if (!$last_lf) {
			print "\n";
		}

		return if ($opts->{LIST_ONLY});

		print colored $prompt_color, $opts->{PROMPT};
		if ($opts->{SINGLETON}) {
			print "> ";
		}
		else {
			print ">> ";
		}
		my $line = <STDIN>;
		if (!$line) {
			print "\n";
			$opts->{ON_EOF}->() if $opts->{ON_EOF};
			last;
		}
		chomp $line;
		last if $line eq '';
		if ($line eq '?') {
			$opts->{SINGLETON} ?
			    singleton_prompt_help_cmd() :
			    prompt_help_cmd();
			next TOPLOOP;
		}
		for my $choice (split(/[\s,]+/, $line)) {
			my $choose = 1;
			my ($bottom, $top);

			# Input that begins with '-'; unchoose
			if ($choice =~ s/^-//) {
				$choose = 0;
			}
			# A range can be specified like 5-7 or 5-.
			if ($choice =~ /^(\d+)-(\d*)$/) {
				($bottom, $top) = ($1, length($2) ? $2 : 1 + @stuff);
			}
			elsif ($choice =~ /^\d+$/) {
				$bottom = $top = $choice;
			}
			elsif ($choice eq '*') {
				$bottom = 1;
				$top = 1 + @stuff;
			}
			else {
				$bottom = $top = find_unique($choice, @stuff);
				if (!defined $bottom) {
					error_msg "Huh ($choice)?\n";
					next TOPLOOP;
				}
			}
			if ($opts->{SINGLETON} && $bottom != $top) {
				error_msg "Huh ($choice)?\n";
				next TOPLOOP;
			}
			for ($i = $bottom-1; $i <= $top-1; $i++) {
				next if (@stuff <= $i || $i < 0);
				$chosen[$i] = $choose;
			}
		}
		last if ($opts->{IMMEDIATE} || $line eq '*');
	}
	for ($i = 0; $i < @stuff; $i++) {
		if ($chosen[$i]) {
			push @return, $stuff[$i];
		}
	}
	return @return;
}

sub singleton_prompt_help_cmd {
	print colored $help_color, <<\EOF ;
Prompt help:
1          - select a numbered item
foo        - select item based on unique prefix
           - (empty) select nothing
EOF
}

sub prompt_help_cmd {
	print colored $help_color, <<\EOF ;
Prompt help:
1          - select a single item
3-5        - select a range of items
2-3,6-9    - select multiple ranges
foo        - select item based on unique prefix
-...       - unselect specified items
*          - choose all items
           - (empty) finish selecting
EOF
}

sub status_cmd {
	list_and_choose({ LIST_ONLY => 1, HEADER => $status_head },
			list_modified());
	print "\n";
}

sub say_n_paths {
	my $did = shift @_;
	my $cnt = scalar @_;
	print "$did ";
	if (1 < $cnt) {
		print "$cnt paths\n";
	}
	else {
		print "one path\n";
	}
}

sub update_cmd {
	my @mods = list_modified('file-only');
	return if (!@mods);

	my @update = list_and_choose({ PROMPT => 'Update',
				       HEADER => $status_head, },
				     @mods);
	if (@update) {
		system(qw(git update-index --add --remove --),
		       map { $_->{VALUE} } @update);
		say_n_paths('updated', @update);
	}
	print "\n";
}

sub revert_cmd {
	my @update = list_and_choose({ PROMPT => 'Revert',
				       HEADER => $status_head, },
				     list_modified());
	if (@update) {
		if (is_initial_commit()) {
			system(qw(git rm --cached),
				map { $_->{VALUE} } @update);
		}
		else {
			my @lines = run_cmd_pipe(qw(git ls-tree HEAD --),
						 map { $_->{VALUE} } @update);
			my $fh;
			open $fh, '| git update-index --index-info'
			    or die;
			for (@lines) {
				print $fh $_;
			}
			close($fh);
			for (@update) {
				if ($_->{INDEX_ADDDEL} &&
				    $_->{INDEX_ADDDEL} eq 'create') {
					system(qw(git update-index --force-remove --),
					       $_->{VALUE});
					print "note: $_->{VALUE} is untracked now.\n";
				}
			}
		}
		refresh();
		say_n_paths('reverted', @update);
	}
	print "\n";
}

sub add_untracked_cmd {
	my @add = list_and_choose({ PROMPT => 'Add untracked' },
				  list_untracked());
	if (@add) {
		system(qw(git update-index --add --), @add);
		say_n_paths('added', @add);
	}
	print "\n";
}

sub run_git_apply {
	my $cmd = shift;
	my $fh;
	open $fh, '| git ' . $cmd . " --recount --allow-overlap";
	print $fh @_;
	return close $fh;
}

sub parse_diff {
	my ($path) = @_;
	my @diff_cmd = split(" ", $patch_mode_flavour{DIFF});
	if (defined $patch_mode_revision) {
		push @diff_cmd, $patch_mode_revision;
	}
	my @diff = run_cmd_pipe("git", @diff_cmd, "--", $path);
	my @colored = ();
	if ($diff_use_color) {
		@colored = run_cmd_pipe("git", @diff_cmd, qw(--color --), $path);
	}
	my (@hunk) = { TEXT => [], DISPLAY => [], TYPE => 'header' };

	for (my $i = 0; $i < @diff; $i++) {
		if ($diff[$i] =~ /^@@ /) {
			push @hunk, { TEXT => [], DISPLAY => [],
				TYPE => 'hunk' };
		}
		push @{$hunk[-1]{TEXT}}, $diff[$i];
		push @{$hunk[-1]{DISPLAY}},
			($diff_use_color ? $colored[$i] : $diff[$i]);
	}
	return @hunk;
}

sub parse_diff_header {
	my $src = shift;

	my $head = { TEXT => [], DISPLAY => [], TYPE => 'header' };
	my $mode = { TEXT => [], DISPLAY => [], TYPE => 'mode' };
	my $deletion = { TEXT => [], DISPLAY => [], TYPE => 'deletion' };

	for (my $i = 0; $i < @{$src->{TEXT}}; $i++) {
		my $dest =
		   $src->{TEXT}->[$i] =~ /^(old|new) mode (\d+)$/ ? $mode :
		   $src->{TEXT}->[$i] =~ /^deleted file/ ? $deletion :
		   $head;
		push @{$dest->{TEXT}}, $src->{TEXT}->[$i];
		push @{$dest->{DISPLAY}}, $src->{DISPLAY}->[$i];
	}
	return ($head, $mode, $deletion);
}

sub hunk_splittable {
	my ($text) = @_;

	my @s = split_hunk($text);
	return (1 < @s);
}

sub parse_hunk_header {
	my ($line) = @_;
	my ($o_ofs, $o_cnt, $n_ofs, $n_cnt) =
	    $line =~ /^@@ -(\d+)(?:,(\d+))? \+(\d+)(?:,(\d+))? @@/;
	$o_cnt = 1 unless defined $o_cnt;
	$n_cnt = 1 unless defined $n_cnt;
	return ($o_ofs, $o_cnt, $n_ofs, $n_cnt);
}

sub split_hunk {
	my ($text, $display) = @_;
	my @split = ();
	if (!defined $display) {
		$display = $text;
	}
	# If there are context lines in the middle of a hunk,
	# it can be split, but we would need to take care of
	# overlaps later.

	my ($o_ofs, undef, $n_ofs) = parse_hunk_header($text->[0]);
	my $hunk_start = 1;

      OUTER:
	while (1) {
		my $next_hunk_start = undef;
		my $i = $hunk_start - 1;
		my $this = +{
			TEXT => [],
			DISPLAY => [],
			TYPE => 'hunk',
			OLD => $o_ofs,
			NEW => $n_ofs,
			OCNT => 0,
			NCNT => 0,
			ADDDEL => 0,
			POSTCTX => 0,
			USE => undef,
		};

		while (++$i < @$text) {
			my $line = $text->[$i];
			my $display = $display->[$i];
			if ($line =~ /^ /) {
				if ($this->{ADDDEL} &&
				    !defined $next_hunk_start) {
					# We have seen leading context and
					# adds/dels and then here is another
					# context, which is trailing for this
					# split hunk and leading for the next
					# one.
					$next_hunk_start = $i;
				}
				push @{$this->{TEXT}}, $line;
				push @{$this->{DISPLAY}}, $display;
				$this->{OCNT}++;
				$this->{NCNT}++;
				if (defined $next_hunk_start) {
					$this->{POSTCTX}++;
				}
				next;
			}

			# add/del
			if (defined $next_hunk_start) {
				# We are done with the current hunk and
				# this is the first real change for the
				# next split one.
				$hunk_start = $next_hunk_start;
				$o_ofs = $this->{OLD} + $this->{OCNT};
				$n_ofs = $this->{NEW} + $this->{NCNT};
				$o_ofs -= $this->{POSTCTX};
				$n_ofs -= $this->{POSTCTX};
				push @split, $this;
				redo OUTER;
			}
			push @{$this->{TEXT}}, $line;
			push @{$this->{DISPLAY}}, $display;
			$this->{ADDDEL}++;
			if ($line =~ /^-/) {
				$this->{OCNT}++;
			}
			else {
				$this->{NCNT}++;
			}
		}

		push @split, $this;
		last;
	}

	for my $hunk (@split) {
		$o_ofs = $hunk->{OLD};
		$n_ofs = $hunk->{NEW};
		my $o_cnt = $hunk->{OCNT};
		my $n_cnt = $hunk->{NCNT};

		my $head = ("@@ -$o_ofs" .
			    (($o_cnt != 1) ? ",$o_cnt" : '') .
			    " +$n_ofs" .
			    (($n_cnt != 1) ? ",$n_cnt" : '') .
			    " @@\n");
		my $display_head = $head;
		unshift @{$hunk->{TEXT}}, $head;
		if ($diff_use_color) {
			$display_head = colored($fraginfo_color, $head);
		}
		unshift @{$hunk->{DISPLAY}}, $display_head;
	}
	return @split;
}

sub find_last_o_ctx {
	my ($it) = @_;
	my $text = $it->{TEXT};
	my ($o_ofs, $o_cnt) = parse_hunk_header($text->[0]);
	my $i = @{$text};
	my $last_o_ctx = $o_ofs + $o_cnt;
	while (0 < --$i) {
		my $line = $text->[$i];
		if ($line =~ /^ /) {
			$last_o_ctx--;
			next;
		}
		last;
	}
	return $last_o_ctx;
}

sub merge_hunk {
	my ($prev, $this) = @_;
	my ($o0_ofs, $o0_cnt, $n0_ofs, $n0_cnt) =
	    parse_hunk_header($prev->{TEXT}[0]);
	my ($o1_ofs, $o1_cnt, $n1_ofs, $n1_cnt) =
	    parse_hunk_header($this->{TEXT}[0]);

	my (@line, $i, $ofs, $o_cnt, $n_cnt);
	$ofs = $o0_ofs;
	$o_cnt = $n_cnt = 0;
	for ($i = 1; $i < @{$prev->{TEXT}}; $i++) {
		my $line = $prev->{TEXT}[$i];
		if ($line =~ /^\+/) {
			$n_cnt++;
			push @line, $line;
			next;
		}

		last if ($o1_ofs <= $ofs);

		$o_cnt++;
		$ofs++;
		if ($line =~ /^ /) {
			$n_cnt++;
		}
		push @line, $line;
	}

	for ($i = 1; $i < @{$this->{TEXT}}; $i++) {
		my $line = $this->{TEXT}[$i];
		if ($line =~ /^\+/) {
			$n_cnt++;
			push @line, $line;
			next;
		}
		$ofs++;
		$o_cnt++;
		if ($line =~ /^ /) {
			$n_cnt++;
		}
		push @line, $line;
	}
	my $head = ("@@ -$o0_ofs" .
		    (($o_cnt != 1) ? ",$o_cnt" : '') .
		    " +$n0_ofs" .
		    (($n_cnt != 1) ? ",$n_cnt" : '') .
		    " @@\n");
	@{$prev->{TEXT}} = ($head, @line);
}

sub coalesce_overlapping_hunks {
	my (@in) = @_;
	my @out = ();

	my ($last_o_ctx, $last_was_dirty);

	for (grep { $_->{USE} } @in) {
		if ($_->{TYPE} ne 'hunk') {
			push @out, $_;
			next;
		}
		my $text = $_->{TEXT};
		my ($o_ofs) = parse_hunk_header($text->[0]);
		if (defined $last_o_ctx &&
		    $o_ofs <= $last_o_ctx &&
		    !$_->{DIRTY} &&
		    !$last_was_dirty) {
			merge_hunk($out[-1], $_);
		}
		else {
			push @out, $_;
		}
		$last_o_ctx = find_last_o_ctx($out[-1]);
		$last_was_dirty = $_->{DIRTY};
	}
	return @out;
}

sub reassemble_patch {
	my $head = shift;
	my @patch;

	# Include everything in the header except the beginning of the diff.
	push @patch, (grep { !/^[-+]{3}/ } @$head);

	# Then include any headers from the hunk lines, which must
	# come before any actual hunk.
	while (@_ && $_[0] !~ /^@/) {
		push @patch, shift;
	}

	# Then begin the diff.
	push @patch, grep { /^[-+]{3}/ } @$head;

	# And then the actual hunks.
	push @patch, @_;

	return @patch;
}

sub color_diff {
	return map {
		colored((/^@/  ? $fraginfo_color :
			 /^\+/ ? $diff_new_color :
			 /^-/  ? $diff_old_color :
			 $diff_plain_color),
			$_);
	} @_;
}

sub edit_hunk_manually {
	my ($oldtext) = @_;

	my $hunkfile = $repo->repo_path . "/addp-hunk-edit.diff";
	my $fh;
	open $fh, '>', $hunkfile
		or die "failed to open hunk edit file for writing: " . $!;
	print $fh "# Manual hunk edit mode -- see bottom for a quick guide\n";
	print $fh @$oldtext;
	my $participle = $patch_mode_flavour{PARTICIPLE};
	my $is_reverse = $patch_mode_flavour{IS_REVERSE};
	my ($remove_plus, $remove_minus) = $is_reverse ? ('-', '+') : ('+', '-');
	print $fh <<EOF;
# ---
# To remove '$remove_minus' lines, make them ' ' lines (context).
# To remove '$remove_plus' lines, delete them.
# Lines starting with # will be removed.
#
# If the patch applies cleanly, the edited hunk will immediately be
# marked for $participle. If it does not apply cleanly, you will be given
# an opportunity to edit again. If all lines of the hunk are removed,
# then the edit is aborted and the hunk is left unchanged.
EOF
	close $fh;

	chomp(my $editor = run_cmd_pipe(qw(git var GIT_EDITOR)));
	system('sh', '-c', $editor.' "$@"', $editor, $hunkfile);

	if ($? != 0) {
		return undef;
	}

	open $fh, '<', $hunkfile
		or die "failed to open hunk edit file for reading: " . $!;
	my @newtext = grep { !/^#/ } <$fh>;
	close $fh;
	unlink $hunkfile;

	# Abort if nothing remains
	if (!grep { /\S/ } @newtext) {
		return undef;
	}

	# Reinsert the first hunk header if the user accidentally deleted it
	if ($newtext[0] !~ /^@/) {
		unshift @newtext, $oldtext->[0];
	}
	return \@newtext;
}

sub diff_applies {
	my $fh;
	return run_git_apply($patch_mode_flavour{APPLY_CHECK} . ' --check',
			     map { @{$_->{TEXT}} } @_);
}

sub _restore_terminal_and_die {
	ReadMode 'restore';
	print "\n";
	exit 1;
}

sub prompt_single_character {
	if ($use_readkey) {
		local $SIG{TERM} = \&_restore_terminal_and_die;
		local $SIG{INT} = \&_restore_terminal_and_die;
		ReadMode 'cbreak';
		my $key = ReadKey 0;
		ReadMode 'restore';
		print "$key" if defined $key;
		print "\n";
		return $key;
	} else {
		return <STDIN>;
	}
}

sub prompt_yesno {
	my ($prompt) = @_;
	while (1) {
		print colored $prompt_color, $prompt;
		my $line = prompt_single_character;
		return 0 if $line =~ /^n/i;
		return 1 if $line =~ /^y/i;
	}
}

sub edit_hunk_loop {
	my ($head, $hunk, $ix) = @_;
	my $text = $hunk->[$ix]->{TEXT};

	while (1) {
		$text = edit_hunk_manually($text);
		if (!defined $text) {
			return undef;
		}
		my $newhunk = {
			TEXT => $text,
			TYPE => $hunk->[$ix]->{TYPE},
			USE => 1,
			DIRTY => 1,
		};
		if (diff_applies($head,
				 @{$hunk}[0..$ix-1],
				 $newhunk,
				 @{$hunk}[$ix+1..$#{$hunk}])) {
			$newhunk->{DISPLAY} = [color_diff(@{$text})];
			return $newhunk;
		}
		else {
			prompt_yesno(
				'Your edited hunk does not apply. Edit again '
				. '(saying "no" discards!) [y/n]? '
				) or return undef;
		}
	}
}

sub help_patch_cmd {
	my $verb = lc $patch_mode_flavour{VERB};
	my $target = $patch_mode_flavour{TARGET};
	print colored $help_color, <<EOF ;
y - $verb this hunk$target
n - do not $verb this hunk$target
q - quit; do not $verb this hunk nor any of the remaining ones
a - $verb this hunk and all later hunks in the file
d - do not $verb this hunk nor any of the later hunks in the file
g - select a hunk to go to
/ - search for a hunk matching the given regex
j - leave this hunk undecided, see next undecided hunk
J - leave this hunk undecided, see next hunk
k - leave this hunk undecided, see previous undecided hunk
K - leave this hunk undecided, see previous hunk
s - split the current hunk into smaller hunks
e - manually edit the current hunk
? - print help
EOF
}

sub apply_patch {
	my $cmd = shift;
	my $ret = run_git_apply $cmd, @_;
	if (!$ret) {
		print STDERR @_;
	}
	return $ret;
}

sub apply_patch_for_checkout_commit {
	my $reverse = shift;
	my $applies_index = run_git_apply 'apply '.$reverse.' --cached --check', @_;
	my $applies_worktree = run_git_apply 'apply '.$reverse.' --check', @_;

	if ($applies_worktree && $applies_index) {
		run_git_apply 'apply '.$reverse.' --cached', @_;
		run_git_apply 'apply '.$reverse, @_;
		return 1;
	} elsif (!$applies_index) {
		print colored $error_color, "The selected hunks do not apply to the index!\n";
		if (prompt_yesno "Apply them to the worktree anyway? ") {
			return run_git_apply 'apply '.$reverse, @_;
		} else {
			print colored $error_color, "Nothing was applied.\n";
			return 0;
		}
	} else {
		print STDERR @_;
		return 0;
	}
}

sub patch_update_cmd {
	my @all_mods = list_modified($patch_mode_flavour{FILTER});
	my @mods = grep { !($_->{BINARY}) } @all_mods;
	my @them;

	if (!@mods) {
		if (@all_mods) {
			print STDERR "Only binary files changed.\n";
		} else {
			print STDERR "No changes.\n";
		}
		return 0;
	}
	if ($patch_mode) {
		@them = @mods;
	}
	else {
		@them = list_and_choose({ PROMPT => 'Patch update',
					  HEADER => $status_head, },
					@mods);
	}
	for (@them) {
		return 0 if patch_update_file($_->{VALUE});
	}
}

# Generate a one line summary of a hunk.
sub summarize_hunk {
	my $rhunk = shift;
	my $summary = $rhunk->{TEXT}[0];

	# Keep the line numbers, discard extra context.
	$summary =~ s/@@(.*?)@@.*/$1 /s;
	$summary .= " " x (20 - length $summary);

	# Add some user context.
	for my $line (@{$rhunk->{TEXT}}) {
		if ($line =~ m/^[+-].*\w/) {
			$summary .= $line;
			last;
		}
	}

	chomp $summary;
	return substr($summary, 0, 80) . "\n";
}


# Print a one-line summary of each hunk in the array ref in
# the first argument, starting wih the index in the 2nd.
sub display_hunks {
	my ($hunks, $i) = @_;
	my $ctr = 0;
	$i ||= 0;
	for (; $i < @$hunks && $ctr < 20; $i++, $ctr++) {
		my $status = " ";
		if (defined $hunks->[$i]{USE}) {
			$status = $hunks->[$i]{USE} ? "+" : "-";
		}
		printf "%s%2d: %s",
			$status,
			$i + 1,
			summarize_hunk($hunks->[$i]);
	}
	return $i;
}

sub patch_update_file {
	my $quit = 0;
	my ($ix, $num);
	my $path = shift;
	my ($head, @hunk) = parse_diff($path);
	($head, my $mode, my $deletion) = parse_diff_header($head);
	for (@{$head->{DISPLAY}}) {
		print;
	}

	if (@{$mode->{TEXT}}) {
		unshift @hunk, $mode;
	}
	if (@{$deletion->{TEXT}}) {
		foreach my $hunk (@hunk) {
			push @{$deletion->{TEXT}}, @{$hunk->{TEXT}};
			push @{$deletion->{DISPLAY}}, @{$hunk->{DISPLAY}};
		}
		@hunk = ($deletion);
	}

	$num = scalar @hunk;
	$ix = 0;

	while (1) {
		my ($prev, $next, $other, $undecided, $i);
		$other = '';

		if ($num <= $ix) {
			$ix = 0;
		}
		for ($i = 0; $i < $ix; $i++) {
			if (!defined $hunk[$i]{USE}) {
				$prev = 1;
				$other .= ',k';
				last;
			}
		}
		if ($ix) {
			$other .= ',K';
		}
		for ($i = $ix + 1; $i < $num; $i++) {
			if (!defined $hunk[$i]{USE}) {
				$next = 1;
				$other .= ',j';
				last;
			}
		}
		if ($ix < $num - 1) {
			$other .= ',J';
		}
		if ($num > 1) {
			$other .= ',g';
		}
		for ($i = 0; $i < $num; $i++) {
			if (!defined $hunk[$i]{USE}) {
				$undecided = 1;
				last;
			}
		}
		last if (!$undecided);

		if ($hunk[$ix]{TYPE} eq 'hunk' &&
		    hunk_splittable($hunk[$ix]{TEXT})) {
			$other .= ',s';
		}
		if ($hunk[$ix]{TYPE} eq 'hunk') {
			$other .= ',e';
		}
		for (@{$hunk[$ix]{DISPLAY}}) {
			print;
		}
		print colored $prompt_color, $patch_mode_flavour{VERB},
		  ($hunk[$ix]{TYPE} eq 'mode' ? ' mode change' :
		   $hunk[$ix]{TYPE} eq 'deletion' ? ' deletion' :
		   ' this hunk'),
		  $patch_mode_flavour{TARGET},
		  " [y,n,q,a,d,/$other,?]? ";
		my $line = prompt_single_character;
		if ($line) {
			if ($line =~ /^y/i) {
				$hunk[$ix]{USE} = 1;
			}
			elsif ($line =~ /^n/i) {
				$hunk[$ix]{USE} = 0;
			}
			elsif ($line =~ /^a/i) {
				while ($ix < $num) {
					if (!defined $hunk[$ix]{USE}) {
						$hunk[$ix]{USE} = 1;
					}
					$ix++;
				}
				next;
			}
			elsif ($other =~ /g/ && $line =~ /^g(.*)/) {
				my $response = $1;
				my $no = $ix > 10 ? $ix - 10 : 0;
				while ($response eq '') {
					my $extra = "";
					$no = display_hunks(\@hunk, $no);
					if ($no < $num) {
						$extra = " (<ret> to see more)";
					}
					print "go to which hunk$extra? ";
					$response = <STDIN>;
					if (!defined $response) {
						$response = '';
					}
					chomp $response;
				}
				if ($response !~ /^\s*\d+\s*$/) {
					error_msg "Invalid number: '$response'\n";
				} elsif (0 < $response && $response <= $num) {
					$ix = $response - 1;
				} else {
					error_msg "Sorry, only $num hunks available.\n";
				}
				next;
			}
			elsif ($line =~ /^d/i) {
				while ($ix < $num) {
					if (!defined $hunk[$ix]{USE}) {
						$hunk[$ix]{USE} = 0;
					}
					$ix++;
				}
				next;
			}
			elsif ($line =~ /^q/i) {
				for ($i = 0; $i < $num; $i++) {
					if (!defined $hunk[$i]{USE}) {
						$hunk[$i]{USE} = 0;
					}
				}
				$quit = 1;
				last;
			}
			elsif ($line =~ m|^/(.*)|) {
				my $regex = $1;
				if ($1 eq "") {
					print colored $prompt_color, "search for regex? ";
					$regex = <STDIN>;
					if (defined $regex) {
						chomp $regex;
					}
				}
				my $search_string;
				eval {
					$search_string = qr{$regex}m;
				};
				if ($@) {
					my ($err,$exp) = ($@, $1);
					$err =~ s/ at .*git-add--interactive line \d+, <STDIN> line \d+.*$//;
					error_msg "Malformed search regexp $exp: $err\n";
					next;
				}
				my $iy = $ix;
				while (1) {
					my $text = join ("", @{$hunk[$iy]{TEXT}});
					last if ($text =~ $search_string);
					$iy++;
					$iy = 0 if ($iy >= $num);
					if ($ix == $iy) {
						error_msg "No hunk matches the given pattern\n";
						last;
					}
				}
				$ix = $iy;
				next;
			}
			elsif ($line =~ /^K/) {
				if ($other =~ /K/) {
					$ix--;
				}
				else {
					error_msg "No previous hunk\n";
				}
				next;
			}
			elsif ($line =~ /^J/) {
				if ($other =~ /J/) {
					$ix++;
				}
				else {
					error_msg "No next hunk\n";
				}
				next;
			}
			elsif ($line =~ /^k/) {
				if ($other =~ /k/) {
					while (1) {
						$ix--;
						last if (!$ix ||
							 !defined $hunk[$ix]{USE});
					}
				}
				else {
					error_msg "No previous hunk\n";
				}
				next;
			}
			elsif ($line =~ /^j/) {
				if ($other !~ /j/) {
					error_msg "No next hunk\n";
					next;
				}
			}
			elsif ($other =~ /s/ && $line =~ /^s/) {
				my @split = split_hunk($hunk[$ix]{TEXT}, $hunk[$ix]{DISPLAY});
				if (1 < @split) {
					print colored $header_color, "Split into ",
					scalar(@split), " hunks.\n";
				}
				splice (@hunk, $ix, 1, @split);
				$num = scalar @hunk;
				next;
			}
			elsif ($other =~ /e/ && $line =~ /^e/) {
				my $newhunk = edit_hunk_loop($head, \@hunk, $ix);
				if (defined $newhunk) {
					splice @hunk, $ix, 1, $newhunk;
				}
			}
			else {
				help_patch_cmd($other);
				next;
			}
			# soft increment
			while (1) {
				$ix++;
				last if ($ix >= $num ||
					 !defined $hunk[$ix]{USE});
			}
		}
	}

	@hunk = coalesce_overlapping_hunks(@hunk);

	my $n_lofs = 0;
	my @result = ();
	for (@hunk) {
		if ($_->{USE}) {
			push @result, @{$_->{TEXT}};
		}
	}

	if (@result) {
		my $fh;
		my @patch = reassemble_patch($head->{TEXT}, @result);
		my $apply_routine = $patch_mode_flavour{APPLY};
		&$apply_routine(@patch);
		refresh();
	}

	print "\n";
	return $quit;
}

sub diff_cmd {
	my @mods = list_modified('index-only');
	@mods = grep { !($_->{BINARY}) } @mods;
	return if (!@mods);
	my (@them) = list_and_choose({ PROMPT => 'Review diff',
				     IMMEDIATE => 1,
				     HEADER => $status_head, },
				   @mods);
	return if (!@them);
	my $reference = is_initial_commit() ? get_empty_tree() : 'HEAD';
	system(qw(git diff -p --cached), $reference, '--',
		map { $_->{VALUE} } @them);
}

sub quit_cmd {
	print "Bye.\n";
	exit(0);
}

sub help_cmd {
	print colored $help_color, <<\EOF ;
status        - show paths with changes
update        - add working tree state to the staged set of changes
revert        - revert staged set of changes back to the HEAD version
patch         - pick hunks and update selectively
diff	      - view diff between HEAD and index
add untracked - add contents of untracked files to the staged set of changes
EOF
}

sub process_args {
	return unless @ARGV;
	my $arg = shift @ARGV;
	if ($arg =~ /--patch(?:=(.*))?/) {
		if (defined $1) {
			if ($1 eq 'reset') {
				$patch_mode = 'reset_head';
				$patch_mode_revision = 'HEAD';
				$arg = shift @ARGV or die "missing --";
				if ($arg ne '--') {
					$patch_mode_revision = $arg;
					$patch_mode = ($arg eq 'HEAD' ?
						       'reset_head' : 'reset_nothead');
					$arg = shift @ARGV or die "missing --";
				}
			} elsif ($1 eq 'checkout') {
				$arg = shift @ARGV or die "missing --";
				if ($arg eq '--') {
					$patch_mode = 'checkout_index';
				} else {
					$patch_mode_revision = $arg;
					$patch_mode = ($arg eq 'HEAD' ?
						       'checkout_head' : 'checkout_nothead');
					$arg = shift @ARGV or die "missing --";
				}
			} elsif ($1 eq 'stage' or $1 eq 'stash') {
				$patch_mode = $1;
				$arg = shift @ARGV or die "missing --";
			} else {
				die "unknown --patch mode: $1";
			}
		} else {
			$patch_mode = 'stage';
			$arg = shift @ARGV or die "missing --";
		}
		die "invalid argument $arg, expecting --"
		    unless $arg eq "--";
		%patch_mode_flavour = %{$patch_modes{$patch_mode}};
	}
	elsif ($arg ne "--") {
		die "invalid argument $arg, expecting --";
	}
}

sub main_loop {
	my @cmd = ([ 'status', \&status_cmd, ],
		   [ 'update', \&update_cmd, ],
		   [ 'revert', \&revert_cmd, ],
		   [ 'add untracked', \&add_untracked_cmd, ],
		   [ 'patch', \&patch_update_cmd, ],
		   [ 'diff', \&diff_cmd, ],
		   [ 'quit', \&quit_cmd, ],
		   [ 'help', \&help_cmd, ],
	);
	while (1) {
		my ($it) = list_and_choose({ PROMPT => 'What now',
					     SINGLETON => 1,
					     LIST_FLAT => 4,
					     HEADER => '*** Commands ***',
					     ON_EOF => \&quit_cmd,
					     IMMEDIATE => 1 }, @cmd);
		if ($it) {
			eval {
				$it->[1]->();
			};
			if ($@) {
				print "$@";
			}
		}
	}
}

process_args();
refresh();
if ($patch_mode) {
	patch_update_cmd();
}
else {
	status_cmd();
	main_loop();
}