NAME
    Brickyard - Plugin system based on roles

SYNOPSIS
        use Brickyard;
        my $brickyard = Brickyard->new(base_package => 'My::App');
        my $root_config = MyApp::RootConfig->new;
        $brickyard->init_from_config('myapp.ini', $root_config);
        $_->some_method for $brickyard->plugins_with(-SomeRole);

DESCRIPTION
    This is a lightweight plugin system based on roles. It does not use
    Moose but relies on "Role::Basic" instead, and very few other modules.

    It takes its inspiration from Dist::Zilla, but has much less flexibility
    and therefore is also much less complex.

METHODS
  new
    Constructs a new object. Takes an optional hash of arguments to
    initialize the object.

  base_package
    Read-write accessor for the base package name that is used in
    "expand_package()". Defaults to "MyApp".

  parse_ini
    Takes a string that contains configuration in "INI" format and parses it
    into an array of configuration sections. It returns a reference to that
    array.

    Using an array, as opposed to a hash, ensures that the section order is
    preserved, so we know in which order to process plugins in Brickyard's
    "plugins_with()" method.

    Each array element corresponds to an "INI" section. Each section is
    itself a reference to an array with three elements:

    The first element is the section name. The second element is the package
    name of the plugin; it is obtained by expanding the section name using
    "expand_package()". The third element is a reference to a plugin
    configuration hash; it is the section's payload. If a section payload
    key occurs several times, it is turned into an array reference in the
    plugin configuration hash.

    The first section is the global section, denoted by the name "_". Any
    payload in the "INI" configuration that occurs before the first section
    ends up in this section.

    For example:

        ; A comment
        name = Foobar

        [@Default]

        [Some::Thing]
        foo = bar
        baz = 43
        baz = blah

    is parsed into this structure:

        [ '_',        'MyApp::Plugin::_',             { name => 'Foobar' } ],
        [ '@Default', 'MyApp::PluginBundle::Default', {} ],
        [   'Some::Thing',
            'MyApp::Plugin::Some::Thing',
            {   'baz' => [ '43', 'blah' ],
                'foo' => 'bar'
            }
        ]

    What if you want to pass more complex configuration like a hash of
    arrays? An "INI" file is basically just a key-value mapping. In that
    case you can use a special notation for the key where you use dots to
    separate the individual elements - array indices and hash keys. For
    example:

        foo.0.web.1  = bar
        foo.0.web.2  = baz
        foo.0.mailto = the-mailto
        foo.1.url    = the-url

    And this would be parsed into this structure:

        foo => [
            { web    => [ undef, 'bar', 'baz' ],
              mailto => 'the-mailto',
            },
            { url => 'the-url' }
        ]

  expand_package
    Takes an abbreviated package name and expands it into the real package
    name. "INI" section names are processed this way so you don't have to
    repeat common prefixes all the time.

    If "@" occurs at the start of the string, it is replaced by the base
    name plus <::PluginBundle::>.

    A "-" is replaced by the base name plus "::Role::".

    A "=" is replaced by the empty string, so the remainder is returned
    unaltered.

    If the package name still hasn't been altered by the expansions
    mentioned above, custom expansions are applied; see below.

    As a fallback, the base name plus "::Plugin::" is prepended.

    The base name is normally whatever "base_package()" returns, but if the
    string starts with "*", the asterisk is deleted and "Brickyard" is used
    for the base name.

    A combination of the default prefixes is not expanded, so "@=", for
    example, is treated as the fallback case, which is probably not what you
    intended.

    Here are some examples of package name expansion:

        @Service::Default     MyApp::PluginBundle::Service::Default
        *@Filter              Brickyard::PluginBundle::Filter
        *Filter               Brickyard::Plugin::Filter
        =Foo::Bar             Foo::Bar
        Some::Thing           MyApp::Plugin::Some::Thing
        -Thing::Frobnulizer   MyApp::Role::Thing::Frobnulizer

    You can also define custom expansions. There are two ways to do this.
    First you can pass a reference to an array of expansions to the
    "expand()" method, or you can define them using the "expand" key in the
    configuration's root section. Each expansion is a string that is
    evaluated for each package name. Custom expansions are useful if you
    have plugins in several namespaces, for example.

    Here is an example of defining a custom expansion directly on the
    Brickyard object:

        my $brickyard = Brickyard->new(
            base_package => 'My::App',
            expand       => [ 's/^%/MyOtherApp::Plugin::/' ],
        );

    Here is an example of defining it in the configuration's root section:

        expand = s/^%/MyOtherApp::Plugin::/

        [@Default]

        # this now refers to MyOtherApp::Plugin::Foo::Bar
        [%Foo::Bar]
        baz = 44

  init_from_config
    Takes a configuration file name specification or a reference to a string
    containing the "INI" string, a root object, and an optional callback.
    The file specification can be a simple file name or a colon-separated
    list of file names. Each of these files is parsed with "parse_ini()" and
    merged. The result is passed to "init_from_config_structure()", along
    with the root object and optional callback - see its documentation for
    what these things do.

    When two configurations are merged, the root sections are merged like a
    hash, but any plugin sections are appended in the order they are found.

    This mechanism exists so you can, for example, have sensitive
    information like passwords in a separate file. For example:

        $ cat myapp.ini
        key1   = foo
        key2.0 = bar0
        key2.1 = bar1
        [@Default]

        $ cat secret.ini
        username = admin
        password = mysecret
        [Foo::Bar]

    To process both configuration files, use:

        $brickyard->init_from_config(
            'myapp.ini:secret.ini', $root_config, $callback
        );

    This is the same as having the following all-in-one configuration file:

        key1     = foo
        key2.0   = bar0
        key2.1   = bar1
        username = admin
        password = mysecret

        [@Default]
        [Foo::Bar]

    We use colons to separate configuration file names so it's easy to get
    the specification from an environment variable.

    If the first argument is a scalar reference, it is assumed that it
    refers to the "INI" string. So you could pass the configuration
    directly, without having a separate configuration file, like this:

        my $config = <<EOINI;
        key1     = foo
        key2.0   = bar0
        key2.1   = bar1

        [@Default]
        [Foo::Bar]
        EOINI

        $brickyard->init_from_config(\$config, $root_config, $callback);

  init_from_config_structure
    Takes a configuration structure and a root object, and an optional
    callback. For each configuration section it creates a plugin object,
    initializes it with the plugin configuration hash and adds it to the
    brickyard's array of plugins.

    Any configuration keys that appear in the configuration's root section
    are set on the root object. So the root object can be anything that has
    set-accessors for all the configuration keys that can appear in the
    configuration's root section. One exception is the "expand" key, which
    is turned into a custom expansion; see above.

    The configuration needs to be a reference to a list of sections as
    returned by "init_from_config()", for example.

    If an object is created that consumes the Brickyard::Role::PluginBundle
    role, the bundle is processed recursively.

    If the callback is given, each value from a key-value pair is filtered
    through that callback. For example, you might want to support
    environment variable expansion like this:

        $brickyard->init_from_config(
            'myapp.ini',
            $root_config,
            sub {
                my $value = shift;
                $value =~ s/\$(\w+)/$ENV{$1} || "\$$1"/ge;
                $value;
            }
        );

  plugins
    Read-write accessor for the reference to an array of plugins.

  plugins_with
    Takes a role name and returns a list of all the plugins that consume
    this role. The result is cached, keyed by the role name.

  plugins_agree
    Takes a role name and a code reference and calls the code reference once
    for each plugin that consumes the role. It returns 1 if the code returns
    a true value for all plugins, 0 otherwise.

    An example will make this clearer:

        # Let the plugins decide
        sub value_is_valid {
            my ($self, $value) = @_;
            $self->brickyard->plugins_agree(-ValueChecker =>
                sub { $_->value_is_valid($value) }
        }

  reset_plugins
    Clears the array of plugins as well as the cache - see "plugins_with()".

  expand
    Holds custom package name expansions; see above.

INSTALLATION
    See perlmodinstall for information and options on installing Perl
    modules.

BUGS AND LIMITATIONS
    No bugs have been reported.

    Please report any bugs or feature requests through the web interface at
    <http://rt.cpan.org/Public/Dist/Display.html?Name=Brickyard>.

AVAILABILITY
    The latest version of this module is available from the Comprehensive
    Perl Archive Network (CPAN). Visit <http://www.perl.com/CPAN/> to find a
    CPAN site near you, or see <http://search.cpan.org/dist/Brickyard/>.

    The development version lives at <http://github.com/hanekomu/Brickyard>
    and may be cloned from <git://github.com/hanekomu/Brickyard.git>.
    Instead of sending patches, please fork this project using the standard
    git and github infrastructure.

AUTHOR
    Marcel Gruenauer <marcel@cpan.org>

COPYRIGHT AND LICENSE
    This software is copyright (c) 2010 by Marcel Gruenauer.

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

