#! /usr/bin/env perl
# SPDX-License-Identifier: GPL-2.0
#
# Detect cycles in the header file dependency graph
# Vegard Nossum <vegardno@ifi.uio.no>
#

use strict;
use warnings;

use Getopt::Long;

my $opt_all;
my @opt_include;
my $opt_graph;

&Getopt::Long::Configure(qw(bundling pass_through));
&GetOptions(
        help    => \&help,
        version => \&version,

        all     => \$opt_all,
        "I=s"   => \@opt_include,
        graph   => \$opt_graph,
);

push @opt_include, 'include';
my %deps = ();
my %linenos = ();

my @headers = grep { strip($_) } @ARGV;

parse_all(@headers);

if($opt_graph) {
        graph();
} else {
        detect_cycles(@headers);
}


sub help {
        print "Usage: $0 [options] file...\n";
        print "\n";
        print "Options:\n";
        print "  --all\n";
        print "  --graph\n";
        print "\n";
        print "  -I includedir\n";
        print "\n";
        print "To make nice graphs, try:\n";
        print "  $0 --graph include/linux/kernel.h | dot -Tpng -o graph.png\n";
        exit;
}

sub version {
        print "headerdep version 2\n";
        exit;
}

# Get a file name that is relative to our include paths
sub strip {
        my $filename = shift;

        for my $i (@opt_include) {
                my $stripped = $filename;
                $stripped =~ s/^$i\///;

                return $stripped if $stripped ne $filename;
        }

        return $filename;
}

# Search for the file name in the list of include paths
sub search {
        my $filename = shift;
        return $filename if -f $filename;

        for my $i (@opt_include) {
                my $path = "$i/$filename";
                return $path if -f $path;
        }
        return;
}

sub parse_all {
        # Parse all the headers.
        my @queue = @_;
        while(@queue) {
                my $header = pop @queue;
                next if exists $deps{$header};

                $deps{$header} = [] unless exists $deps{$header};

                my $path = search($header);
                next unless $path;

                open(my $file, '<', $path) or die($!);
                chomp(my @lines = <$file>);
                close($file);

                for my $i (0 .. $#lines) {
                        my $line = $lines[$i];
                        if(my($dep) = ($line =~ m/^#\s*include\s*<(.*?)>/)) {
                                push @queue, $dep;
                                push @{$deps{$header}}, [$i + 1, $dep];
                        }
                }
        }
}

sub print_cycle {
        # $cycle[n] includes $cycle[n + 1];
        # $cycle[-1] will be the culprit
        my $cycle = shift;

        # Adjust the line numbers
        for my $i (0 .. $#$cycle - 1) {
                $cycle->[$i]->[0] = $cycle->[$i + 1]->[0];
        }
        $cycle->[-1]->[0] = 0;

        my $first = shift @$cycle;
        my $last = pop @$cycle;

        my $msg = "In file included";
        printf "%s from %s,\n", $msg, $last->[1] if defined $last;

        for my $header (reverse @$cycle) {
                printf "%s from %s:%d%s\n",
                        " " x length $msg,
                        $header->[1], $header->[0],
                        $header->[1] eq $last->[1] ? ' <-- here' : '';
        }

        printf "%s:%d: warning: recursive header inclusion\n",
                $first->[1], $first->[0];
}

# Find and print the smallest cycle starting in the specified node.
sub detect_cycles {
        my @queue = map { [[0, $_]] } @_;
        while(@queue) {
                my $top = pop @queue;
                my $name = $top->[-1]->[1];

                for my $dep (@{$deps{$name}}) {
                        my $chain = [@$top, [$dep->[0], $dep->[1]]];

                        # If the dep already exists in the chain, we have a
                        # cycle...
                        if(grep { $_->[1] eq $dep->[1] } @$top) {
                                print_cycle($chain);
                                next if $opt_all;
                                return;
                        }

                        push @queue, $chain;
                }
        }
}

sub mangle {
        $_ = shift;
        s/\//__/g;
        s/\./_/g;
        s/-/_/g;
        $_;
}

# Output dependency graph in GraphViz language.
sub graph {
        print "digraph {\n";

        print "\t/* vertices */\n";
        for my $header (keys %deps) {
                printf "\t%s [label=\"%s\"];\n",
                        mangle($header), $header;
        }

        print "\n";

        print "\t/* edges */\n";
        for my $header (keys %deps) {
                for my $dep (@{$deps{$header}}) {
                        printf "\t%s -> %s;\n",
                                mangle($header), mangle($dep->[1]);
                }
        }

        print "}\n";
}