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}

sub new_id {
    unpack("H*", Crypt::URandom::urandom(8));
}

sub is_valid_name {
    $_[0] =~ $VALID_NAME_REGEXP;
}

# alias for backward compatibility
*trace = \&capture;

sub capture {
    my ($name, $code) = @_;
    if (!is_valid_name($name)) {
        my $msg = "invalid segment name: $name";
        $CROAK_INVALID_NAME ? croak($msg) : carp($msg);
    }
    my $wantarray = wantarray;

    my $enabled;
    my $sampled = $SAMPLED;
    if (defined $ENABLED) {
        $enabled = $ENABLED ? 1 : 0; # fix true or false (not undef)
    }
    elsif ($TRACE_ID) {
        $enabled = 0;                # called from parent capture
    }
    else {
        # root capture try sampling
        $sampled = $SAMPLER->() ? 1 : 0;
        $enabled = $sampled     ? 1 : 0;
    }
    local $ENABLED = $enabled;
    local $SAMPLED = $sampled;

    return $code->(AWS::XRay::Segment->new) if !$enabled;

    local $TRACE_ID = $TRACE_ID // new_trace_id();

    my $segment = AWS::XRay::Segment->new({ name => $name });
    unless (defined $segment->{type} && $segment->{type} eq "subsegment") {
        $_->apply_plugin($segment) for @PLUGINS;
    }

    local $SEGMENT_ID = $segment->{id};

    my @ret;
    eval {
        if ($wantarray) {
            @ret = $code->($segment);
        }
        elsif (defined $wantarray) {
            $ret[0] = $code->($segment);
        }
        else {
            $code->($segment);
        }
    };
    my $error = $@;
    if ($error) {
        $segment->{error} = Types::Serialiser::true;
        $segment->{cause} = {
            exceptions => [
                {
                    id      => new_id(),
                    message => "$error",
                    remote  => Types::Serialiser::true,
                },
            ],
        };
    }
    eval {
        $segment->close();
    };
    if ($@) {
        warn $@;
    }
    die $error if $error;
    return $wantarray ? @ret : $ret[0];
}

sub capture_from {
    my ($header,   $name,       $code)    = @_;
    my ($trace_id, $segment_id, $sampled) = parse_trace_header($header);

    local $AWS::XRay::SAMPLED = $sampled // $SAMPLER->();
    local $AWS::XRay::ENABLED = $AWS::XRay::SAMPLED;
    local ($AWS::XRay::TRACE_ID, $AWS::XRay::SEGMENT_ID) = ($trace_id, $segment_id);
    capture($name, $code);
}

sub parse_trace_header {
    my $header = shift or return;

    my ($trace_id, $segment_id, $sampled);
    if ($header =~ /Root=([0-9a-fA-F-]+)/) {
        $trace_id = $1;
    }
    if ($header =~ /Parent=([0-9a-fA-F]+)/) {
        $segment_id = $1;
    }
    if ($header =~ /Sampled=([^;]+)/) {
        $sampled = $1;
    }
    return ($trace_id, $segment_id, $sampled);
}

sub add_capture {
    my ($class, $package, @methods) = @_;
    no warnings 'redefine';
    no strict 'refs';
    for my $method (@methods) {
        my $orig = $package->can($method) or next;
        *{"${package}::${method}"} = sub {
            my @args = @_;
            capture(
                $package,
                sub {
                    my $segment = shift;
                    $segment->{metadata}->{method}  = $method;
                    $segment->{metadata}->{package} = $package;
                    $orig->(@args);
                },
            );
        };
    }
}

if ($ENV{LAMBDA_TASK_ROOT}) {
    # AWS::XRay is loaded in AWS Lambda worker.
    # notify the Lambda Runtime that initialization is complete.
    unless (mkdir '/tmp/.aws-xray') {
        # ignore the error if the directory is already exits or other process created it.
        my $err = $!;
        unless (-d '/tmp/.aws-xray') {
            warn "failed to make directory: $err";
        }
    }
    open my $fh, '>', '/tmp/.aws-xray/initialized' or warn "failed to create file: $!";
    close $fh;
    utime undef, undef, '/tmp/.aws-xray/initialized' or warn "failed to touch file: $!";

    # patch the capture
    no warnings 'redefine';
    no strict 'refs';
    my $org = \&capture;
    *capture = sub {
        my ($trace_id, $segment_id, $sampled) = parse_trace_header($ENV{_X_AMZN_TRACE_ID});
        local $AWS::XRay::SAMPLED = $sampled // $SAMPLER->();
        local $AWS::XRay::ENABLED = $AWS::XRay::SAMPLED;
        local ($AWS::XRay::TRACE_ID, $AWS::XRay::SEGMENT_ID) = ($trace_id, $segment_id);
        local *capture = $org;
        local *trace   = $org;
        capture(@_);
    };
    *trace = \&capture;
}

1;
__END__

=encoding utf-8

=head1 NAME

AWS::XRay - AWS X-Ray tracing library

=head1 SYNOPSIS

    use AWS::XRay qw/ capture /;

    capture "myApp", sub {
        capture "remote", sub {
            # do something ...
            capture "nested", sub {
                # ...
            };
        };
        capture "myHTTP", sub {
            my $segment = shift;
            # ...
            $segment->{http} = { # modify segment document
                request => {
                    method => "GET",
                    url    => "http://localhost/",
                },
                response => {
                    status => 200,
                },
            };
        };
    };

    my $header;
    capture "source", sub {
        my $segment = shift;