#!/usr/bin/perl -w

use strict;
use Git;

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 $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");

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;

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);

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

sub list_untracked {
        map {
                chomp $_;
                $_;
        }
        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 $_; $_;
                } run_cmd_pipe(qw(git ls-files --exclude-standard --), @ARGV);
                return if (!@tracked);
        }

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

        for (run_cmd_pipe(qw(git diff-files --numstat --summary --), @tracked)) {
                if (($add, $del, $file) =
                    /^([-\d]+)  ([-\d]+)        (.*)/) {
                        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, $file) =
                       /^ (create|delete) mode [0-7]+ (.*)$/) {
                        $data{$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{$letter}};
                }
                if ($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 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 $bottom) {
                                        print "Huh ($choice)?\n";
                                        next TOPLOOP;
                                }
                        }
                        if ($opts->{SINGLETON} && $bottom != $top) {
                                print "Huh ($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 parse_diff {
        my ($path) = @_;
        my @diff = run_cmd_pipe(qw(git diff-files -p --), $path);
        my @colored = ();
        if ($diff_use_color) {
                @colored = run_cmd_pipe(qw(git diff-files -p --color --), $path);
        }
        my (@hunk) = { TEXT => [], DISPLAY => [] };

        for (my $i = 0; $i < @diff; $i++) {
                if ($diff[$i] =~ /^@@ /) {
                        push @hunk, { TEXT => [], DISPLAY => [] };
                }
                push @{$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 => [] };
        my $mode = { TEXT => [], DISPLAY => [] };

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

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 => [],
                        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 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;
        print $fh <<EOF;
# ---
# To remove '-' lines, make them ' ' lines (context).
# To remove '+' lines, delete them.
# Lines starting with # will be removed.
#
# If the patch applies cleanly, the edited hunk will immediately be
# marked for staging. 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;

        my $editor = $ENV{GIT_EDITOR} || $repo->config("core.editor")
                || $ENV{VISUAL} || $ENV{EDITOR} || "vi";
        system('sh', '-c', $editor.' "$@"', $editor, $hunkfile);

        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;
        open $fh, '| git apply --recount --cached --check';
        for my $h (@_) {
                print $fh @{$h->{TEXT}};
        }
        return close $fh;
}

sub prompt_yesno {
        my ($prompt) = @_;
        while (1) {
                print colored $prompt_color, $prompt;
                my $line = <STDIN>;
                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 => $text, USE => 1 };
                if (diff_applies($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 {
        print colored $help_color, <<\EOF ;
y - stage this hunk
n - do not stage this hunk
a - stage this and all the remaining hunks in the file
d - do not stage this hunk nor any of the remaining hunks in the file
g - select a hunk to go to
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 patch_update_cmd {
        my @all_mods = list_modified('file-only');
        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 => $status_head, },
                                        @mods);
        }
        for (@them) {
                patch_update_file($_->{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 ($ix, $num);
        my $path = shift;
        my ($head, @hunk) = parse_diff($path);
        ($head, my $mode) = parse_diff_header($head);
        for (@{$head->{DISPLAY}}) {
                print;
        }

        if (@{$mode->{TEXT}}) {
                while (1) {
                        print @{$mode->{DISPLAY}};
                        print colored $prompt_color,
                                "Stage mode change [y/n/a/d/?]? ";
                        my $line = <STDIN>;
                        if ($line =~ /^y/i) {
                                $mode->{USE} = 1;
                                last;
                        }
                        elsif ($line =~ /^n/i) {
                                $mode->{USE} = 0;
                                last;
                        }
                        elsif ($line =~ /^a/i) {
                                $_->{USE} = 1 foreach ($mode, @hunk);
                                last;
                        }
                        elsif ($line =~ /^d/i) {
                                $_->{USE} = 0 foreach ($mode, @hunk);
                                last;
                        }
                        else {
                                help_patch_cmd('');
                                next;
                        }
                }
        }

        $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_splittable($hunk[$ix]{TEXT})) {
                        $other .= '/s';
                }
                $other .= '/e';
                for (@{$hunk[$ix]{DISPLAY}}) {
                        print;
                }
                print colored $prompt_color, "Stage this hunk [y/n/a/d$other/?]? ";
                my $line = <STDIN>;
                if ($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>;
                                        chomp $response;
                                }
                                if ($response !~ /^\s*\d+\s*$/) {
                                        print STDERR "Invalid number: '$response'\n";
                                } elsif (0 < $response && $response <= $num) {
                                        $ix = $response - 1;
                                } else {
                                        print STDERR "Sorry, only $num hunks available.\n";
                                }
                                next;
                        }
                        elsif ($line =~ /^d/i) {
                                while ($ix < $num) {
                                        if (!defined $hunk[$ix]{USE}) {
                                                $hunk[$ix]{USE} = 0;
                                        }
                                        $ix++;
                                }
                                next;
                        }
                        elsif ($other =~ /K/ && $line =~ /^K/) {
                                $ix--;
                                next;
                        }
                        elsif ($other =~ /J/ && $line =~ /^J/) {
                                $ix++;
                                next;
                        }
                        elsif ($other =~ /k/ && $line =~ /^k/) {
                                while (1) {
                                        $ix--;
                                        last if (!$ix ||
                                                 !defined $hunk[$ix]{USE});
                                }
                                next;
                        }
                        elsif ($other =~ /j/ && $line =~ /^j/) {
                                while (1) {
                                        $ix++;
                                        last if ($ix >= $num ||
                                                 !defined $hunk[$ix]{USE});
                                }
                                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);
                                $num = scalar @hunk;
                                next;
                        }
                        elsif ($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});
                        }
                }
        }

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

        if (@result) {
                my $fh;

                open $fh, '| git apply --cached --recount';
                for (@{$head->{TEXT}}, @result) {
                        print $fh $_;
                }
                if (!close $fh) {
                        for (@{$head->{TEXT}}, @result) {
                                print STDERR $_;
                        }
                }
                refresh();
        }

        print "\n";
}

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 eq "--patch") {
                $patch_mode = 1;
                $arg = shift @ARGV or die "missing --";
                die "invalid argument $arg, expecting --"
                    unless $arg eq "--";
        }
        elsif ($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();
}