package DateTime::TimeZone::Local::Unix;

use strict;
use warnings;
use namespace::autoclean;

our $VERSION = '2.21';

use Cwd 3;
use Try::Tiny;

use parent 'DateTime::TimeZone::Local';

sub Methods {
    return qw(
        FromEnv
        FromEtcTimezone
        FromEtcLocaltime
        FromEtcTIMEZONE
        FromEtcSysconfigClock
        FromEtcDefaultInit
    );
}

sub EnvVars { return 'TZ' }

## no critic (Variables::ProhibitPackageVars)
our $EtcDir = '/etc';
## use critic

sub _EtcFile {
    shift;
    return File::Spec->catfile( $EtcDir, @_ );
}

sub FromEtcLocaltime {
    my $class = shift;

    my $lt_file = $class->_EtcFile('localtime');
    return unless -r $lt_file && -s _;

    my $real_name;
    if ( -l $lt_file ) {

        # The _Readlink sub exists so the test suite can mock it.
        $real_name = $class->_Readlink($lt_file);
    }

    $real_name ||= $class->_FindMatchingZoneinfoFile($lt_file);

    if ( defined $real_name ) {
        my ( undef, $dirs, $file ) = File::Spec->splitpath($real_name);

        my @parts = grep { defined && length } File::Spec->splitdir($dirs),
            $file;

        foreach my $x ( reverse 0 .. $#parts ) {
            my $name = (
                $x < $#parts
                ? join '/', @parts[ $x .. $#parts ]
                : $parts[$x]
            );

            my $tz = try {
                ## no critic (Variables::RequireInitializationForLocalVars)
                local $SIG{__DIE__};
                DateTime::TimeZone->new( name => $name );
            };

            return $tz if $tz;
        }
    }
}

sub _Readlink {
    my $link = $_[1];

    # Using abs_path will resolve multiple levels of link indirection,
    # whereas readlink just follows the link to the next target.
    return Cwd::abs_path($link);
}

## no critic (Variables::ProhibitPackageVars)
our $ZoneinfoDir = '/usr/share/zoneinfo';
## use critic

# for systems where /etc/localtime is a copy of a zoneinfo file
sub _FindMatchingZoneinfoFile {
    shift;
    my $file_to_match = shift;

    # For some reason, under at least macOS 10.13 High Sierra,
    # /usr/share/zoneinfo is a link to a link to a directory. And no, I didn't
    # stutter. This is fine, and it passes the -d below. But File::Find does
    # not understand a link to be a directory, so rather than incur the
    # overhead of telling File::Find::find() to follow symbolic links, we just
    # resolve it here.
    my $zone_info_dir = $ZoneinfoDir;
    $zone_info_dir = readlink $zone_info_dir while -l $zone_info_dir;

    return unless -d $zone_info_dir;

    require File::Basename;
    require File::Compare;
    require File::Find;

    my $size = -s $file_to_match;

    my $real_name;
    try {
        ## no critic (Variables::RequireInitializationForLocalVars)
        local $SIG{__DIE__};
        local $_;

        File::Find::find(
            {
                wanted => sub {
                    if (
                           !defined $real_name
                        && -f $_
                        && !-l $_
                        && $size == -s _

                        # This fixes RT 24026 - apparently such a
                        # file exists on FreeBSD and it can cause a
                        # false positive
                        && File::Basename::basename($_) ne 'posixrules'
                        && File::Compare::compare( $_, $file_to_match ) == 0
                    ) {
                        $real_name = $_;

                        # File::Find has no mechanism for bailing in the
                        # middle of a find.
                        die { found => 1 };
                    }
                },
                no_chdir => 1,
            },
            $zone_info_dir,
        );
    }
    catch {
        die $_ unless ref $_ && $_->{found};
    };

    return $real_name;
}

sub FromEtcTimezone {
    my $class = shift;

    my $tz_file = $class->_EtcFile('timezone');
    return unless -f $tz_file && -r _;

    open my $fh, '<', $tz_file
        or die "Cannot read $tz_file: $!";
    my $name = do { local $/ = undef; <$fh> };
    close $fh or die $!;

    $name =~ s/^\s+|\s+$//g;

    return unless $class->_IsValidName($name);

    return try {
        ## no critic (Variables::RequireInitializationForLocalVars)
        local $SIG{__DIE__};
        DateTime::TimeZone->new( name => $name );
    };
}

sub FromEtcTIMEZONE {
    my $class = shift;

    my $tz_file = $class->_EtcFile('TIMEZONE');
    return unless -f $tz_file && -r _;

    ## no critic (InputOutput::RequireBriefOpen)
    open my $fh, '<', $tz_file
        or die "Cannot read $tz_file: $!";

    my $name;
    while ( defined( $name = <$fh> ) ) {
        if ( $name =~ /\A\s*TZ\s*=\s*(\S+)/ ) {
            $name = $1;
            last;
        }
    }

    close $fh or die $!;

    return unless $class->_IsValidName($name);

    return try {
        ## no critic (Variables::RequireInitializationForLocalVars)
        local $SIG{__DIE__};
        DateTime::TimeZone->new( name => $name );
    };
}

# RedHat uses this
sub FromEtcSysconfigClock {
    my $class = shift;

    my $clock_file = $class->_EtcFile('sysconfig/clock');
    return unless -r $clock_file && -f _;

    my $name = $class->_ReadEtcSysconfigClock($clock_file);

    return unless $class->_IsValidName($name);

    return try {
        ## no critic (Variables::RequireInitializationForLocalVars)
        local $SIG{__DIE__};
        DateTime::TimeZone->new( name => $name );
    };
}

# this is a separate function so that it can be overridden in the test suite
sub _ReadEtcSysconfigClock {
    shift;
    my $clock_file = shift;

    open my $fh, '<', $clock_file
        or die "Cannot read $clock_file: $!";

    ## no critic (Variables::RequireInitializationForLocalVars)
    local $_;
    while (<$fh>) {
        return $1 if /^(?:TIME)?ZONE="([^"]+)"/;
    }

    close $fh or die $!;
}

sub FromEtcDefaultInit {
    my $class = shift;

    my $init_file = $class->_EtcFile('default/init');
    return unless -r $init_file && -f _;

    my $name = $class->_ReadEtcDefaultInit($init_file);

    return unless $class->_IsValidName($name);

    return try {
        ## no critic (Variables::RequireInitializationForLocalVars)
        local $SIG{__DIE__};
        DateTime::TimeZone->new( name => $name );
    };
}

# this is a separate function so that it can be overridden in the test
# suite
sub _ReadEtcDefaultInit {
    shift;
    my $init_file = shift;

    open my $fh, '<', $init_file
        or die "Cannot read $init_file: $!";

    ## no critic (Variables::RequireInitializationForLocalVars)
    local $_;
    while (<$fh>) {
        return $1 if /^TZ=(.+)/;
    }

    close $fh or die $!;
}

1;

# ABSTRACT: Determine the local system's time zone on Unix

__END__

=pod

=encoding UTF-8

=head1 NAME

DateTime::TimeZone::Local::Unix - Determine the local system's time zone on Unix

=head1 VERSION

version 2.21

=head1 SYNOPSIS

  my $tz = DateTime::TimeZone->new( name => 'local' );

  my $tz = DateTime::TimeZone::Local->TimeZone();

=head1 DESCRIPTION

This module provides methods for determining the local time zone on a
Unix platform.

=head1 HOW THE TIME ZONE IS DETERMINED

This class tries the following methods of determining the local time
zone:

=over 4

=item * $ENV{TZ}

It checks C<< $ENV{TZ} >> for a valid time zone name.

=item * F</etc/localtime>

If this file is a symlink to an Olson database time zone file (usually
in F</usr/share/zoneinfo>) then it uses the target file's path name to
determine the time zone name. For example, if the path is
F</usr/share/zoneinfo/America/Chicago>, the time zone is
"America/Chicago".

Some systems just copy the relevant file to F</etc/localtime> instead
of making a symlink.  In this case, we look in F</usr/share/zoneinfo>
for a file that has the same size and content as F</etc/localtime> to
determine the local time zone.

=item * F</etc/timezone>

If this file exists, it is read and its contents are used as a time
zone name.

=item * F</etc/TIMEZONE>

If this file exists, it is opened and we look for a line starting like
"TZ = ...". If this is found, it should indicate a time zone name.

=item * F</etc/sysconfig/clock>

If this file exists, it is opened and we look for a line starting like
"TIMEZONE = ..." or "ZONE = ...". If this is found, it should indicate
a time zone name.

=item * F</etc/default/init>

If this file exists, it is opened and we look for a line starting like
"TZ=...". If this is found, it should indicate a time zone name.

=back

B<Note:> Some systems such as virtual machine boxes may lack any of these
files. You can confirm that this is case by running:

    $ ls -l /etc/localtime /etc/timezone /etc/TIMEZONE \
        /etc/sysconfig/clock /etc/default/init

If this is the case, then when checking for timezone handling you are
likely to get an exception:

    $ perl -wle 'use DateTime; DateTime->now( time_zone => "local" )'
    Cannot determine local time zone

In that case, you should consult your system F<man> pages for details on how
to address that problem. In one such case reported to us, a FreeBSD virtual
machine had been built without any of these files. The user was able to run
the FreeBSD F<tzsetup> utility. That installed F</etc/localtime>, after which
the above timezone diagnostic ran silently, I<i.e.>, without throwing an
exception.

=head1 SUPPORT

Bugs may be submitted at L<https://github.com/houseabsolute/DateTime-TimeZone/issues>.

I am also usually active on IRC as 'autarch' on C<irc://irc.perl.org>.

=head1 SOURCE

The source code repository for DateTime-TimeZone can be found at L<https://github.com/houseabsolute/DateTime-TimeZone>.

=head1 AUTHOR

Dave Rolsky <autarch@urth.org>

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2018 by Dave Rolsky.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

The full text of the license can be found in the
F<LICENSE> file included with this distribution.

=cut
