#!/usr/bin/perl

use strict;
use warnings;
use File::Path qw(make_path);
use File::Copy qw(copy);
use File::Find;
use File::Compare;
use File::Basename;
use File::Glob qw(:bsd_glob);
use File::Spec;
use Getopt::Long;
use Archive::Tar;
use Compress::Zlib;
use POSIX qw(strftime);
use Digest::SHA qw(sha1_hex);

use constant VCX_DIR	=> '.vcx';
use constant HEAD       => VCX_DIR . '/head';  # Current commit ID
use constant OBJ_DIR	=> VCX_DIR . '/obj';   # Latest version of a file
use constant REV_DIR	=> VCX_DIR . '/rev';   # Commits

# Staging area
use constant TMP_DIR	=> VCX_DIR . '/index';
use constant TMP_TREE   => TMP_DIR . '/tree';
use constant TMP_META   => TMP_DIR . '/meta';
use constant TMP_DIFF   => TMP_DIR . '/delta.tar.gz';

Getopt::Long::Configure("bundling");

my $cmd = shift @ARGV // '';
my @args = @ARGV;

if ($cmd eq 'init') {
	run_init();
} elsif ($cmd eq 'status') {
	run_status();
} elsif ($cmd eq 'add') {
	die "Usage: $0 add [path1] [path2] ...\n" unless @args;
	run_add(@args); 
} elsif ($cmd eq 'commit') {
	my ($m, $a);
	GetOptions('m=s' => \$m, 'a' => \$a);
	if ($a) { run_add("."); }
	run_commit($m);
} elsif ($cmd eq 'log') {
	run_log();
} else {
	print "Usage: $0 [init|status|add|commit|log]\n";
	exit 1;
}

sub run_init {
	make_path(OBJ_DIR, REV_DIR);

	my $initial_hex = to_hex_id(0);
	my $rev0_dir = File::Spec->catfile(REV_DIR, $initial_hex);
	make_path($rev0_dir);

	write_file(HEAD, "$initial_hex\n");

	# Baseline tree (empty)
	my $empty_tree_hash = sha1_hex(""); 
	my $empty_tree_file = File::Spec->catfile($rev0_dir, "tree-$empty_tree_hash");
	open my $fh, '>', $empty_tree_file or die $!; close $fh;
	make_path(File::Spec->catdir(OBJ_DIR, $empty_tree_hash));

	open my $mfh, '>', File::Spec->catfile($rev0_dir, "message"); close $mfh;
	print "Initialized repository.\n";
}

sub run_status {
	open my $fh, '<', HEAD or die "VCX not initialized.\n";
	my $head = <$fh>; chomp $head; close $fh;
	print "On revision [$head]\n";

	my %staged_diffs;
	my $staged_diff_bundle = TMP_DIFF;
	if (-e TMP_DIFF) {
		my @list = qx(tar -tf '$staged_diff_bundle');
		foreach (@list) {
			chomp;
			if (/(.+)\.patch$/) { $staged_diffs{$1} = 1; }
		}
	}

	my ($tree_ptr) = bsd_glob(File::Spec->catfile(REV_DIR, $head, "tree-*"));
	my ($tree_hash) = $tree_ptr =~ /tree-([a-f0-9]{40})$/;
	my $latest_tree_dir = File::Spec->catdir(OBJ_DIR, $tree_hash);

	# Pass 1: Workspace -> History (Detects New and Modified)
	find({
		wanted => sub {
			return if $File::Find::name =~ /^\.\/\Q${\VCX_DIR}\E/;
			return if -d $File::Find::name;

			my $rel = File::Spec->abs2rel($File::Find::name, '.');
			$rel =~ s|^\./||;
			
			my $base_in_tree = File::Spec->catfile($latest_tree_dir, $rel);
			my $path_hash = sha1_hex($rel);

			if (-e $base_in_tree || -l $base_in_tree) {
				my $obj_in_store = readlink($base_in_tree);
				if (compare($_, $obj_in_store) != 0) {
					my $staged = $staged_diffs{$path_hash} ? " (staged)" : "";
					print "[M] $rel$staged\n";
				}
			} else {
				my $tmp_link = File::Spec->catfile(TMP_TREE, $rel);
				my $staged = (-e $tmp_link || -l $tmp_link) ? " (staged)" : "";
				print "[N] $rel$staged\n";
			}
		},
		no_chdir => 1
	}, '.');

	# Pass 2: History -> Workspace (Detects Deletions)
	if (-d $latest_tree_dir) {
		find({
			wanted => sub {
				return if -d $_;
				my $rel = File::Spec->abs2rel($_, $latest_tree_dir);
				
				# If it's in the commit tree but GONE from the workspace
				if (!-e $rel && !-l $rel) {
					my $tmp_link = File::Spec->catfile(TMP_TREE, $rel);
					my $staged = (!-e $tmp_link && !-l $tmp_link) ? " (staged)" : "";
					print "[D] $rel$staged\n";
				}
			},
			no_chdir => 1
		}, $latest_tree_dir);
	}
}

sub run_add {
	my @targets = @_;
	my %patches;

	make_path(TMP_TREE);

	open my $fh_h, '<', HEAD or die $!;
	my $head = <$fh_h>; chomp $head; close $fh_h;

	my ($latest_tree_ptr) = bsd_glob(File::Spec->catfile(REV_DIR, $head, "tree-*"));
	my ($latest_tree_hash) = $latest_tree_ptr =~ /tree-([a-f0-9]{40})$/;
	my $latest_tree_dir = File::Spec->catdir(OBJ_DIR, $latest_tree_hash);

	my $next_id_hex = to_hex_id(from_hex_id($head) + 1);

	my %entries;
	open my $afh, '>>', TMP_META or die $!;

	init_stage($latest_tree_dir, \%entries);

	foreach my $input (@targets) {
		my @expanded = bsd_glob($input);
		foreach my $t (@expanded) {
			find({
				wanted => sub {
					if ($File::Find::name =~ /\/\Q${\VCX_DIR}\E$/ || $_ eq VCX_DIR) {
						$File::Find::prune = 1;
						return;
					}
					
					return if -d $_;

					my $rel = $File::Find::name =~ s|^\./||r;
					$entries{$rel} = 1;

					my $staged_path = File::Spec->catfile(TMP_TREE, $rel);
					my $prev_link = File::Spec->catfile($latest_tree_dir, $rel);

					# CASE 1: Regular File
					if (-f $_ && !-l $_) {
						return if -e $staged_path; # Already staged

						if (-l $prev_link) {
							my $obj_in_head = readlink($prev_link);
							return if compare($_, $obj_in_head) == 0;
						}

						my $obj_name = sha1_hex($rel);
						my $obj_path = File::Spec->catfile(OBJ_DIR, $obj_name);

						# Prepare patches in memory and save to disk in one write.
						make_patch($File::Find::name, $obj_name, $obj_path, \%patches);
						stage_file($File::Find::name, $obj_path, $staged_path);
						print $afh "$rel\n"; # Record in meta file for the commit command
					} 
					
					# CASE 2: Symlink
					elsif (-l _) {
						my $target = readlink($File::Find::name);
						if (-l $prev_link) {
							return if readlink($prev_link) eq $target;
						}
						if (-l $staged_path) {
							return if readlink($staged_path) eq $target;
						}
						stage_link($File::Find::name, $staged_path);
					}
				},
				no_chdir => 1,
			}, $t);
		}
	}

	save_patches(\%patches);

	# Pass 2: History -> Workspace (Detects Deletions)	
	foreach my $path (keys %entries) {
		if (!-e $path && !-l $path) {
			delete $entries{$path};
			my $staged_path = File::Spec->catfile(TMP_TREE, $path);
			if (-e $staged_path || -l $staged_path) {
				unlink($staged_path) or die "Could not unlink staged $path: $!";
				my $parent = dirname($staged_path);
				while ($parent ne TMP_TREE && -d $parent) {
					last if bsd_glob("$parent/*"); # Stop if not empty
					rmdir($parent);
					$parent = dirname($parent);
				}
			}
			print "[D] $path (staged for deletion)\n";
		}
	}

	close $afh;

	my @sorted_paths = sort keys %entries;
	my $tree_ents    = join("\n", @sorted_paths);	
	my $tree_header  = "tree " . scalar(@sorted_paths) . "\n";
	my $tree_data    = $tree_header . $tree_ents;

	my $tree_hash = sha1_hex($tree_data);
	my $tree_file = File::Spec->catfile(TMP_DIR, "tree-$tree_hash");
	open my $fh, '>', $tree_file or die $!; close $fh;
}

sub run_commit {
	my ($msg) = @_;

	my ($staged_tree_ptr) = bsd_glob(File::Spec->catfile(TMP_DIR, "tree-*"));
	my ($tree_hash) = $staged_tree_ptr =~ /tree-([a-f0-9]{40})$/;
	my $tree_path = File::Spec->catdir(OBJ_DIR, $tree_hash);
	my $tree_exists = -d $tree_path;

	my $content_changed = (-e TMP_META || -e TMP_DIFF);

	if ($tree_exists && !$content_changed) {
		print "Nothing to commit.";
		File::Path::remove_tree(TMP_DIR) if -d TMP_DIR;
		return;
	}

	if (!$msg || $msg eq "") {
		$msg = launch_editor();
		die "Commit aborted: empty message.\n" unless $msg =~ /\S/;
	}

	# Prepare IDs
	open my $fh_h, '<', HEAD or die "Not a repository.\n";
	my $old_head = <$fh_h>; chomp $old_head; close $fh_h;
	my $next_id_hex = to_hex_id(from_hex_id($old_head) + 1);
	my $rev_dir = File::Spec->catfile(REV_DIR, $next_id_hex);
	make_path($rev_dir);

	# Save file to store
	if (-e TMP_META) {
		open my $mfh, '<', TMP_META or die $!;
		while (my $rel = <$mfh>) {
			chomp $rel;
			my $obj_name = sha1_hex($rel);
			my $obj_path  = File::Spec->catfile(OBJ_DIR, $obj_name);
			copy($rel, $obj_path) or die "Failed to update store for $rel: $!";
		}
		close $mfh;
	}

	# Save tree (snapshots the structure)
	if (!$tree_exists) {
		make_path($tree_path);
		rename(TMP_TREE, $tree_path) or die "Failed to save directories: $!";
	}

	rename($staged_tree_ptr, File::Spec->catfile($rev_dir, "tree-$tree_hash")) 
		or die "Failed to save tree pointer to revision: $!";	

	# Move deltas
	if (-e TMP_DIFF) {
		my $dest_diff = File::Spec->catfile($rev_dir, "delta.tar.gz");
		rename(TMP_DIFF, $dest_diff)
			or die "Failed to move delta to $dest_diff: $!";
	}

	write_file(File::Spec->catfile($rev_dir, "message"), "$msg\n");
	write_file(HEAD, "$next_id_hex\n"); # Update head

	File::Path::remove_tree(TMP_DIR) if -d TMP_DIR;
	
	my ($subject) = split(/\n/, $msg);
	print "Committed revision [$next_id_hex]: $subject\n";
}

sub run_log {
	open my $fh_h, '<', HEAD or die "Not a repository.\n";
	my $head = <$fh_h>; chomp $head; close $fh_h;

	# Setup pager
	my $pager = $ENV{PAGER} || 'less -R';
	open(my $pipe, "| $pager") or die "Can't pipe to $pager: $!";
	my $old_fh = select($pipe); 

	print "Revision History (HEAD: $head)\n\n";

	my $rev_num = from_hex_id($head);
	while ($rev_num > 0) {
		my $hex_id  = to_hex_id($rev_num);
		my $rev_dir = File::Spec->catfile(REV_DIR, $hex_id);
		
		# Stop if we hit a gap in history or the beginning
		last unless -d $rev_dir;

		# Stat index 9 is the last modification time
		my $mtime = (stat($rev_dir))[9];
		my $date_str = strftime("%a %b %e %H:%M:%S %Y", localtime($mtime));

		my $msg_file = File::Spec->catfile($rev_dir, "message");
		my $message  = "[No message]";

		if (-e $msg_file) {
			open my $mfh, '<', $msg_file;
			$message = do { local $/; <$mfh> } // "[Empty message]";
			$message =~ s/^\s+|\s+$//g; # Trim whitespace
			close $mfh;
		}

		print "commit $hex_id\n";
		print "Date:  $date_str\n";
		print "\n	$message\n\n";

		$rev_num--;
	}

	close $pipe;
	select($old_fh);
}

sub stage_file {
	my ($src, $obj, $tmp) = @_;
	make_path(dirname($tmp));
	
	# We want the link inside tmp/ to point to "obj/HASH"
	# relative to project root.
	my $rel_target = $obj; 
	
	unlink($tmp) if -e $tmp || -l $tmp;
	symlink($rel_target, $tmp) or die "Failed to symlink $tmp: $!";
	print "[Staged File] $src\n";
}

sub stage_link {
	my ($src, $tmp) = @_;
	my $target = readlink($src); 
	
	make_path(dirname($tmp));
	unlink($tmp) if -e $tmp || -l $tmp;
	# For workspace symlinks, we clone the target
	symlink($target, $tmp) or die "Failed to symlink $tmp: $!";
	print "[Staged link] $src -> $target\n";
}

sub make_patch {
	my ($src, $obj_name, $obj_path, $patches) = @_;

	return unless -e $obj_path;

	my $patch;

	# TODO: implement a disk-based diff for large files, esp bin files
	if (-T $src) {
		if (compare($src, $obj_path) != 0) {
			$patch = qx(diff -u '$obj_path' '$src');
		}
	} else {
		$patch = make_bin_patch($src, $obj_path);
	}

	if ($patch) { $patches->{$obj_name} = $patch; }
}

sub make_bin_patch {
	my ($new_file, $old_file) = @_;
	
	open my $f_new, '<:raw', $new_file or die "Cannot open file: $!";
	open my $f_old, '<:raw', $old_file or die "Cannot open object file: $!";
	my $f_out;

	my $patch = "";
	my $offset   = 0;
	my $blk_size = 4096;

	while (1) {
		my $read_new = sysread($f_new, my $buf_new, $blk_size);
		my $read_old = sysread($f_old, my $buf_old, $blk_size);

		# Stop when we've processed the entire new file
		last if $read_new == 0 && $read_old == 0;

		# Handle file size differences (pad with nulls if one is shorter)
		$buf_new .= "\0" x ($blk_size - length($buf_new)) if length($buf_new) < $blk_size;
		$buf_old .= "\0" x ($blk_size - length($buf_old)) if length($buf_old) < $blk_size;

		# If they differ, we save the OLD buffer (reverse delta)
		if ($buf_new ne $buf_old) {
			# Header: [64-bit offset][32-bit length][data]
			# 'Q' is 64-bit unsigned (quad), 'L' is 32-bit unsigned (long)
			$patch .= pack("QL", $offset, length($buf_old)) . $buf_old;
		}

		$offset += $blk_size;
	}
	close $f_new; close $f_old;
	close $f_out if $f_out;

	return length($patch) > 0 ? $patch : undef;
}

sub save_patches {
	my ($patches) = @_;

	return unless keys %$patches;

	my $tar = Archive::Tar->new;
	while (my ($obj_name, $patch) = each %$patches) {
		$tar->add_data("$obj_name.patch", $patch);
	}

	$tar->write(TMP_DIFF, 1); # gzip
}

sub apply_bin_patch {
	my ($obj_file, $patch_file) = @_;

	open my $obj_fh, '+<:raw', $obj_file or die "Cannot open object: $!";
	open my $ptch_fh, '<:raw', $patch_file or die "Cannot open patch: $!";

	# Header is 12 bytes (Q + L)
	while (sysread($ptch_fh, my $header, 12)) {
		my ($offset, $len) = unpack("QL", $header);
		
		# sysread/syswrite to avoid read()'s internal buffers. 
		sysread($ptch_fh, my $payload, $len);
		sysseek($obj_fh, $offset, 0);
		syswrite($obj_fh, $payload, $len);
	}

	close $obj_fh;
	close $ptch_fh;
}

# Convert decimal to a padded 7-char hex string
sub to_hex_id { sprintf("%07x", $_[0]) }

# Convert hex back to decimal
sub from_hex_id { hex($_[0]) }

sub launch_editor {
	my $editor = $ENV{EDITOR} || $ENV{VISUAL} || 'vi';
	my $temp_msg_file = File::Spec->catfile(VCX_DIR, "COMMIT_EDITMSG");
	
	open my $fh, '>', $temp_msg_file or die "Cannot create temp message file: $!";
	print $fh "\n# Enter the commit message for your changes.\n";
	print $fh "# Lines starting with '#' will be ignored.\n";
	close $fh;

	system("$editor \"$temp_msg_file\"");

	my $final_msg = "";
	if (-e $temp_msg_file) {
		open my $rfh, '<', $temp_msg_file or die $!;
		while (my $line = <$rfh>) {
			next if $line =~ /^#/; # Strip out the helper comments
			$final_msg .= $line;
		}
		close $rfh;
		unlink($temp_msg_file); # Clean up
	}

	$final_msg =~ s/^\s+|\s+$//g; # Trim whitespace
	return $final_msg;
}

sub write_file {
	my ($path, $content) = @_;
	open my $fh, '>', $path or die "Could not open '$path' for writing: $!";
	print $fh $content;
	close $fh or die "Could not close '$path' after writing: $!";
}

sub init_stage {
	my ($latest_tree_dir, $entries_ref) = @_;

	find({
		wanted => sub {
			return if -d _;

			my $rel = File::Spec->abs2rel($_, $latest_tree_dir);
			my $staged_path = File::Spec->catfile(TMP_TREE, $rel);
			make_path(dirname($staged_path));
			
			my $target = readlink($_);
			symlink($target, $staged_path) or die "Failed to link $rel: $!";
			
			$entries_ref->{$rel} = 1;
		},
		no_chdir => 1
	}, $latest_tree_dir);
}