#!/usr/bin/perl -w
####################################################################################################
#
# git-qt-grafts
#
# Sets up the proper grafts for a Qt repository
#
# Copyright (C) 2015 The Qt Company Ltd.
# Contact: http://www.qt.io/licensing/
#
####################################################################################################

use File::Basename;
use Cwd 'abs_path';
use strict;

my $history_location;

# Syntax:  fileContents(filename)
# Returns: String with contents of the file, or empty string if file
#          doens't exist.
sub fileContents {
    my ($filename) = @_;
    my $filecontents = "";
    if (-e $filename) {
        my $FD;
        open($FD, "< $filename") || die "Could not open $filename for reading, read block?";
        local $/;
        binmode $FD;
        $filecontents = <$FD>;
        close $FD;
    }
    return $filecontents;
}

sub fileContains {
    my ($filename, $text) = @_;
    # purposely not using perl grep here
    foreach my $line (split /\n/, fileContents("$filename")) {
        return 1 if ("$line" eq "$text");
    }
    return 0;
}

sub showUsage {
    my $prg = basename($0);
    print "Usage: $prg <path to Qt history>:\n";
}

while ( @ARGV ) {
    my $arg = shift @ARGV;
    if ($arg eq "-?" || $arg eq "-h" || $arg eq "-help" || $arg eq "?") {
        showUsage();
        exit 0;
    } elsif (!$history_location) {
        $history_location = $arg;
    } else {
        print "Unknown option: $arg\n\n";
        showUsage();
        exit 1;
    }
}

# Get current git-dir
my $git_dir = `git rev-parse --git-dir`;
chomp $git_dir;
if (!$git_dir) {
    print "Cannot find any Git dir!\n";
    exit 1;
}

# validate path for history repo
if (!$history_location || !-e $history_location) {
    print "You need to provide a path to the monolithic Qt repo!\n";
    exit 1;
}
my $history_git_dir = `cd $history_location && git rev-parse --git-dir`;
chomp $history_git_dir;
if (!$history_git_dir  || !-e "$history_location/$history_git_dir/objects") {
    print "Monolithic Qt repo path is not a valid Git repo!\n";
    exit 1;
}
$history_git_dir = abs_path("$history_location/$history_git_dir");
my $history_alternates_objects = "$history_git_dir/objects";

# check if we already point to this alternate object store
my $git_alternates_file = "$git_dir/objects/info/alternates";
my $found_alternate = fileContains($git_alternates_file, $history_alternates_objects);

# get first commit SHA1 of this repo which mentions branching from a commit
my $GIT_REVLIST;
my $git_pid = open($GIT_REVLIST, "git rev-list --reverse --grep='Branched from .*at commit' HEAD |")
    or die ("Failed to launch Git");
my @commits;
while (<$GIT_REVLIST>) {
    chomp;
    push(@commits, $_);
}
close($GIT_REVLIST);

my $found_any_grafts = 0;
mkdir("$git_dir/info");
my $graft_file = "$git_dir/info/grafts";
my @graft_lines;

foreach my $commit (@commits) {
    # find the graft point which the commit mentions
    my $commit_msg = `git show -s --format=%b $commit`;
    my $graft_to_commit = $commit_msg;
    $graft_to_commit =~ s/^.+Branched from .+at commit\n([a-f0-9]+)\n.*/$1/s;
    next if (!$graft_to_commit || $graft_to_commit eq $commit_msg);

    # Preserve any existing parents of the commit.
    my @existing_parents;
    my $GIT_CAT_FILE;
    open($GIT_CAT_FILE, "git cat-file commit $commit |") or die ("Failed to launch Git");
    while (<$GIT_CAT_FILE>) {
        if (/^parent ([0-9a-z]{40})/i) {
            push(@existing_parents, $1);
        }
    }
    close($GIT_CAT_FILE);

    # check that we don't already have this graft already setup
    my $graft_line = "$commit $graft_to_commit";
    $graft_line .= " " . join(" ", @existing_parents) if (@existing_parents);
    my $found_graft = fileContains($graft_file, $graft_line);
    if ($found_graft) {
        print "Graft for $commit already exists. Skipping...\n";
        $found_any_grafts = 1;
        next;
    }

    # verify that alternate object store contains the commit we want to graft to
    if (system("cd $history_location && git cat-file -e $graft_to_commit") != 0) {
        print "History repo ($history_location) does not contain commit $graft_to_commit!\n";
        print "Skipping this graft...\n";
        next;
    }

    print "Grafted $commit -> $graft_to_commit\n";
    push(@graft_lines, $graft_line);
    $found_any_grafts = 1;
}
if (!$found_any_grafts) {
    print "This repo does not refer to a graft point, so no grafts added!\n";
    exit 0;
}

# if our alternates file didn't contain the "history repo" path already
# add its path now
if (!$found_alternate) {
    my $ALTERNATES_FILE;
    open($ALTERNATES_FILE, ">> $git_alternates_file") || die "Could not open $git_alternates_file for writing, wrong permissions?";
    print $ALTERNATES_FILE "$history_alternates_objects\n";
    # Add alternates from alternates file in the history repo, in case it has additional alternates.
    my $HISTORY_ALTERNATES_FILE;
    if (open($HISTORY_ALTERNATES_FILE, "< $history_git_dir/objects/info/alternates")) {
        print("Reusing existing alternates in history repository\n");
        while (<$HISTORY_ALTERNATES_FILE>) {
            chomp;
            print $ALTERNATES_FILE $_ if (!fileContains($git_alternates_file, $_));
        }
        close($HISTORY_ALTERNATES_FILE);
    }
    close($ALTERNATES_FILE);
}

# Add graft lines from graft file in the history repo, in case it has additional grafts.
my $HISTORY_GRAFT_FILE;
if (open($HISTORY_GRAFT_FILE, "< $history_git_dir/info/grafts")) {
    print("Reusing existing grafts in history repository\n");
    while (<$HISTORY_GRAFT_FILE>) {
        chomp;
        push(@graft_lines, $_) if (!fileContains($graft_file, $_));
    }
    close($HISTORY_GRAFT_FILE);
}

# add graft
if (@graft_lines) {
    my $GRAFT_FILE;
    open($GRAFT_FILE, ">> $graft_file") || die "Could not open $graft_file for writing, wrong permissions?";
    print $GRAFT_FILE join("\n", @graft_lines) . "\n";
    close($GRAFT_FILE);
}