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Comprehensive, flexible input validation and parsing with Perl, targeted at web applications

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README
NAME
    Brannigan - Comprehensive, flexible system for validating and parsing
    input, mainly targeted at web applications.

SYNOPSIS
            use Brannigan;

            my %scheme1 = ( name => 'scheme1', params => ... );
            my %scheme2 = ( name => 'scheme2', params => ... );
            my %scheme3 = ( name => 'scheme3', params => ... );

            # use the OO interface
            my $b = Brannigan->new(\%scheme1, \%scheme2);
            $b->add_scheme(\%scheme3);

            my $parsed = $b->process('scheme1', \%params);
            if ($parsed->{_rejects}) {
                    die $parsed->{_rejects};
            } else {
                    return $parsed;
            }

            # Or use the functional interface
            my $parsed = Brannigan::process(\%scheme1, \%params);
            if ($parsed->{_rejects}) {
                    die $parsed->{_rejects};
            } else {
                    return $parsed;
            }

    For a more comprehensive example, see "MANUAL" in this document or the
    Brannigan::Examples document.

DESCRIPTION
    Brannigan is an attempt to ease the pain of collecting, validating and
    parsing input parameters in web applications. It's designed to answer
    both of the main problems that web applications face:

    * Simple user input

      Brannigan can validate and parse simple, "flat", user input, possibly
      coming from web forms.

    * Complex data structures

      Brannigan can validate and parse complex data structures, possibly
      deserialized from JSON or XML data sent to web services and APIs.

    Brannigan's approach to data validation is as follows: define a
    structure of parameters and their needed validations, and let the module
    automatically examine input parameters against this structure. Brannigan
    provides you with common validation methods that are used everywhere,
    and also allows you to create custom validations easily. This structure
    also defines how, if at all, the input should be parsed. This is akin to
    schema-based validations such as XSD, but much more functional, and most
    of all flexible.

    Check the next section for an example of such a structure. I call this
    structure a validation/parsing scheme. Schemes can inherit all the
    properties of other schemes, which allows you to be much more flexible
    in certain situations. Imagine you have a blogging application. A base
    scheme might define all validations and parsing needed to create a new
    blog post from a user's input. When editing a post, however, some
    parameters that were required when creating the post might not be
    required now (so you can just use older values), and maybe new
    parameters are introduced. Inheritance helps you avoid repeating
    yourself. You can another scheme which gets all the properties of the
    base scheme, only changing whatever it is needs changing (and possibly
    adding specific properties that don't exist in the base scheme).

MANUAL
    In the following manual, we will look at the following example. It is
    based on Catalyst, but should be fairly understandable for non-Catalyst
    users. Do not be alarmed by the size of this, this is only because it
    displays basically every aspect of Brannigan.

    This example uses Catalyst, but should be pretty self explanatory. It's
    fairly complex, since it details pretty much all of the available
    Brannigan functionality, so don't be alarmed by the size of this thing.

            package MyApp::Controller::Post;

            use strict;
            use warnings;
            use Brannigan;

            # create a new Brannigan object with two validation/parsing schemes:
            my $b = Brannigan->new({
                    name => 'post',
                    ignore_missing => 1,
                    params => {
                            subject => {
                                    required => 1,
                                    length_between => [3, 40],
                            },
                            text => {
                                    required => 1,
                                    min_length => 10,
                                    validate => sub {
                                            my $value = shift;

                                            return undef unless $value;
                                        
                                            return $value =~ m/^lorem ipsum/ ? 1 : undef;
                                    }
                            },
                            day => {
                                    required => 0,
                                    integer => 1,
                                    value_between => [1, 31],
                            },
                            mon => {
                                    required => 0,
                                    integer => 1,
                                    value_between => [1, 12],
                            },
                            year => {
                                    required => 0,
                                    integer => 1,
                                    value_between => [1900, 2900],
                            },
                            section => {
                                    required => 1,
                                    integer => 1,
                                    value_between => [1, 3],
                                    parse => sub {
                                            my $val = shift;
                                        
                                            my $ret = $val == 1 ? 'reviews' :
                                                      $val == 2 ? 'receips' :
                                                      'general';
                                                  
                                            return { section => $ret };
                                    },
                            },
                            id => {
                                    required => 1,
                                    exact_length => 10,
                                    value_between => [1000000000, 2000000000],
                            },
                            '/^picture_(\d+)$/' => {
                                    length_between => [3, 100],
                                    validate => sub {
                                            my ($value, $num) = @_;

                                            ...
                                    },
                            },
                            picture_1 => {
                                    default => 'http://www.example.com/avatar.png',
                            },
                            array_of_ints => {
                                    array => 1,
                                    min_length => 3,
                                    values => {
                                            integer => 1,
                                    },
                            },
                            hash_of_langs => {
                                    hash => 1,
                                    keys => {
                                            _all => {
                                                    exact_length => 10,
                                            },
                                            en => {
                                                    required => 1,
                                            },
                                    },
                            },
                    },
                    groups => {
                            date => {
                                    params => [qw/year mon day/],
                                    parse => sub {
                                            my ($year, $mon, $day) = @_;
                                            return undef unless $year && $mon && $day;
                                            return { date => $year.'-'.$mon.'-'.$day };
                                    },
                            },
                            tags => {
                                    regex => '/^tags_(en|he|fr)$/',
                                    forbid_words => ['bad_word', 'very_bad_word'],
                                    parse => sub {
                                            return { tags => \@_ };
                                    },
                            },
                    },
            }, {
                    name => 'edit_post',
                    inherits_from => 'post',
                    params => {
                            subject => {
                                    required => 0, # subject is no longer required
                            },
                            id => {
                                    forbidden => 1,
                            },
                    },
            });

            # create the custom 'forbid_words' validation method
            $b->custom_validation('forbid_words', sub {
                    my $value = shift;

                    foreach (@_) {
                            return 0 if $value =~ m/$_/;
                    }

                    return 1;
            });

            # post a new blog post
            sub new_post : Local {
                    my ($self, $c) = @_;

                    # get input parameters hash-ref
                    my $params = $c->request->params;

                    # process the parameters
                    my $parsed_params = $b->process('post', $params);

                    if ($parsed_params->{_rejects}) {
                            die $c->list_errors($parsed_params);
                    } else {
                            $c->model('DB::BlogPost')->create($parsed_params);
                    }
            }

            # edit a blog post
            sub edit_post : Local {
                    my ($self, $c, $id) = @_;

                    my $params = $b->process('edit_posts', $c->req->params);

                    if ($params->{_rejects}) {
                            die $c->list_errors($params);
                    } else {
                            $c->model('DB::BlogPosts')->find($id)->update($params);
                    }
            }

  HOW BRANNIGAN WORKS
    In essence, Brannigan works in three stages (which all boil down to one
    single command):

    *   Input stage and preparation

        Brannigan receives a hash-ref of input parameters, or a hash-ref
        based data structure, and the name of a scheme to validate against.
        Brannigan then loads the scheme and prepares it (by merging it with
        inherited schemes) for later processing.

    *   Data validation

        Brannigan invokes all validation methods defined in the scheme on
        the input data, and generates a hash-ref of rejected parameters. For
        every parameter in this hash-ref, a list of failed validations is
        created in an array-ref.

    *   Data parsing

        Regardless of the previous stage, every parsing method defined in
        the scheme is applied on the relevant data. The data resulting from
        these parsing methods, along with the values of all input parameters
        for which no parsing methods were defined, is returned to the user
        in a hash-ref. This hash-ref also includes a _rejects key whose
        value is the rejects hash created in the previous stage.

        The reason I say this stage isn't dependant on the previous stage is
        simple. First of all, it's possible no parameters failed validation,
        but the truth is this stage doesn't care if a parameter failed
        validation. It will still parse it and return it to the user, and no
        errors are ever raised by Brannigan. It is the developer's (i.e.
        you) job to decide what to do in case rejects are present.

  HOW SCHEMES LOOK
    The validation/parsing scheme defines the structure of the data you're
    expecting to receive, along with information about the way it should be
    validated and parsed. Schemes are created by passing them to the
    Brannigan constructor. You can pass as many schemes as you like, and
    these schemes can inherit from one another. You can create the Brannigan
    object that gets these schemes wherever you want. Maybe in a controller
    of your web app that will directly use this object to validate and parse
    input it gets, or maybe in a special validation class that will hold all
    schemes. It doesn't matter where, as long as you make the object
    available for your application.

    A scheme is a hash-ref based data structure that has the following keys:

    *   name

        Defines the name of the scheme. Required.

    *   ignore_missing

        Boolean value indicating whether input parameters that are not
        referenced in the scheme should be added to the parsed output or
        not. Optional, defaults to false (i.e. parameters missing from the
        scheme will be added to the output as-is). You might find it is
        probably a good idea to turn this on, so any input parameters you're
        not expecting to receive from users are ignored.

    *   inherits_from

        Either a scalar naming a different scheme or an array-ref of scheme
        names. The new scheme will inherit all the properties of the
        scheme(s) defined by this key. If an array-ref is provided, the
        scheme will inherit their properties in the order they are defined.
        See the "CAVEATS" section for some "heads-up" about inheritance.

    *   params

        The params key is the most important part of the scheme, as it
        defines the expected input. This key takes a hash-ref containing the
        names of input parameters. Every such name (i.e. key) in itself is
        also a hash-ref. This hash-ref defines the necessary validation
        methods to assert for this parameter, and optionally a 'parse' and
        'default' method. The idea is this: use the name of the validation
        method as the key, and the appropriate values for this method as the
        value of this key. For example, if a certain parameter, let's say
        'subject', must be between 3 to 10 characters long, then your scheme
        will contain:

                subject => {
                        length_between => [3, 10]
                }

        The 'subject' parameter's value (from the user input), along with
        both of the values defined above (3 and 10) will be passed to the
        "length_between()" validation method. Now, suppose a certain subject
        sent to your app failed the "length_between()" validation; then the
        rejects hash-ref described earlier will have something like this:

                subject => ['length_between(3, 10)']

        Notice the values of the "length_between()" validation method were
        added to the string, so you can easily know why the parameter failed
        the validation.

        Custom validation methods: Aside for the built-in validation methods
        that come with Brannigan, a custom validation method can be defined
        for each parameter. This is done by adding a 'validate' key to the
        parameter, and an anonymous subroutine as the value. As with
        built-in methods, the parameter's value will be automatically sent
        to this method. So, for example, if the subject parameter from above
        must start with the words 'lorem ipsum', then we can define the
        subject parameter like so:

                subject => {
                        length_between => [3, 10],
                        validate => sub {
                                my $value = shift;

                                return $value =~ m/^lorem ipsum/ ? 1 : 0;
                        }
                }

        Custom validation methods, just like built-in ones, are expected to
        return a true value if the parameter passed the validation, or a
        false value otherwise. If a parameter failed a custom validation
        method, then 'validate' will be added to the list of failed
        validations for this parameter. So, in our 'subject' example, the
        rejects hash-ref will have something like this:

                subject => ['length_between(3, 10)', 'validate']

        Default values: For your convenience, Brannigan allows you to set
        default values for parameters that are not required (so, if you set
        a default value for a parameter, don't add the "required()"
        validation method to it). There are two ways to add a default value:
        either directly, or through an anonymous subroutine (just like the
        custom validation method). For example, maybe we'd like the
        'subject' parameter to have a default value of 'lorem ipsum dolor
        sit amet'. Then we can have the following definition:

                subject => {
                        length_between => [3, 10],
                        validate => sub {
                                my $value = shift;

                                return $value =~ m/^lorem ipsum/ ? 1 : 0;
                        },
                        default => 'lorem ipsum dolor sit amet'
                }

        Alternatively, you can give a parameter a generated default value by
        using an anonymous subroutine, like so:

                subject => {
                        length_between => [3, 10],
                        validate => sub {
                                my $value = shift;

                                return $value =~ m/^lorem ipsum/ ? 1 : 0;
                        },
                        default => sub {
                                return int(rand(100000000));
                        }
                }

        Notice that default values are added to missing parameters only at
        the parsing stage (i.e. stage 3 - after the validation stage), so
        validation methods do not apply to default values.

        Parse methods: It is more than possible that the way input
        parameters are passed to your application will not be exactly the
        way you'll eventually use them. That's where parsing methods can
        come in handy. Brannigan doesn't have any built-in parsing methods
        (obviously), so you must create these by yourself, just like custom
        validation methods. All you need to do is add a 'parse' key to the
        parameter's definition, with an anonymous subroutine. This
        subroutine also receives the value of the parameter automatically,
        and is expected to return a hash-ref of key-value pairs. You will
        probably find it that most of the time this hash-ref will only
        contain one key-value pair, and that the key will probably just be
        the name of the parameter. But note that when a parse method exists,
        Brannigan makes absolutely no assumptions of what else to do with
        that parameter, so you must tell it exactly how to return it. After
        all parameters were parsed by Brannigan, all these little hash-refs
        are merged into one hash-ref that is returned to the caller. If a
        parse method doesn't exist for a paramter, Brannigan will simply add
        it "as-is" to the resulting hash-ref. Returning to our subject
        example (which we defined must start with 'lorem ipsum'), let's say
        we want to substitute 'lorem ipsum' with 'effing awesome' before
        using this parameter. Then the subject definition will now look like
        this:

                subject => {
                        length_between => [3, 10],
                        validate => sub {
                                my $value = shift;

                                return $value =~ m/^lorem ipsum/ ? 1 : 0;
                        },
                        default => 'lorem ipsum dolor sit amet',
                        parse => sub {
                                my $value = shift;

                                $value =~ s/^lorem ipsum/effing awesome/;
                        
                                return { subject => $value };
                        }
                }

        If you're still not sure what happens when no parse method exists,
        then you can imagine Brannigan uses the following default parse
        method:

                param => {
                        parse => sub {
                                my $value = shift;

                                return { param => $value };
                        }
                }

        Regular expressions: As of version 0.3, parameter names can also be
        regular expressions in the form '/regex/'. Sometimes you cannot know
        the names of all parameters passed to your app. For example, you
        might have a dynamic web form which starts with a single field
        called 'url_1', but your app allows your visitors to dynamically add
        more fields, such as 'url_2', 'url_3', etc. Regular expressions are
        handy in such situations. Your parameter key can be '/^url_(\d+)$/',
        and all such fields will be matched. Regex params have a special
        feature: if your regex uses capturing, then captured values will be
        passed to the custom "validate" and "parse" methods (in their order)
        after the parameter's value. For example:

                '/^url_(\d+)$/' => {
                        validate => sub {
                                my ($value, $num) = @_;
                        
                                # $num has the value captured by (\d+) in the regex

                                return $value =~ m!^http://! ? 1 : undef;
                        },
                        parse => sub {
                                my ($value, $num) = @_;

                                return { urls => { $num => $value } };
                        },
                }

        Please note that a regex must be defined with a starting and
        trailing slash, in single quotes, otherwise it won't work. It is
        also important to note what happens when a parameter matches a regex
        rule (or perhaps rules), and also has a direct reference in the
        scheme. For example, let's say we have the following rules in our
        scheme:

                '/^sub(ject|headline)$/' => {
                        required => 1,
                        length_between => [3, 10],
                },
                subject => {
                        required => 0,
                }

        When validating and parsing the 'subject' parameter, Brannigan will
        automatically merge both of these references to the subject
        parameter, giving preference to the direct reference, so the actual
        structure on which the parameter will be validated is as follows:

                subject => {
                        required => 0,
                        length_between => [3, 10],
                }

        If your parameter matches more than one regex rule, they will all be
        merged, but there's no way (yet) to ensure in which order these
        regex rules will be merged.

        Complex data structures: As previously stated, Brannigan can also
        validate and parse a little more complex data structures. So, your
        parameter no longer has to be just a string or a number, but maybe a
        hash-ref or an array-ref. In the first case, you tell Brannigan the
        paramter is a hash-ref by adding a 'hash' key with a true value, and
        a 'keys' key with a hash-ref which is just like the 'params'
        hash-ref. For example, suppose you're receiving a 'name' parameter
        from the user as a hash-ref containing first and last names. That's
        how the 'name' parameter might be defined:

                name => {
                        hash => 1,
                        required => 1,
                        keys => {
                                first_name => {
                                        length_between => [3, 10],
                                },
                                last_name => {
                                        required => 1,
                                        min_length => 3,
                                },
                        }
                }

        What are we seeing here? We see that the 'name' parameter must be a
        hash-ref, that it's required, and that it has two keys: first_name,
        whose length must be between 3 to 10 if it's present, and last_name,
        which must be 3 characters or more, and must be present.

        An array parameter, on the other hand, is a little different.
        Similar to hashes, you define the parameter as an array-ref with the
        'array' key with a true value, and a 'values' key. This key has a
        hash-ref of validation and parse methods that will be applied to
        EVERY value inside this array. For example, suppose you're receiving
        a 'pictures' parameter from the user as an array-ref containing URLs
        to pictures on the web. That's how the 'pictures' parameter might be
        defined:

                pictures => {
                        array => 1,
                        length_between => [1, 5],
                        values => {
                                min_length => 3,
                                validate => sub {
                                        my $value = shift;

                                        return $value =~ m!^http://! ? 1 : 0;
                                },
                        },
                }

        What are we seeing this time? We see that the 'pictures' parameter
        must be an array, with no less than one item (i.e. value) and no
        more than five items (notice that we're using the same
        "length_between()" method from before, but in the context of an
        array, it doesn't validate against character count but item count).
        We also see that every value in the 'pictures' array must have a
        minimum length of three (this time it is characterwise), and must
        match 'http://' in its beginning.

        Since complex data structures are supported, you can define default
        values for parameters that aren't just strings or numbers (or
        methods), for example:

                complex_param => {
                        hash => 1,
                        keys => {
                                ...
                        },
                        default => { key1 => 'def1', key2 => 'def2' }
                }

        What Brannigan returns for such structures when they fail
        validations is a little different than before. Instead of an
        array-ref of failed validations, Brannigan will return a hash-ref.
        This hash-ref might contain a '_self' key with an array-ref of
        validations that failed specifically on the 'pictures' parameter
        (such as the 'required' validation for the 'name' parameter or the
        'length_between' validation for the 'pictures' parameter), and/or
        keys for each value in these structures that failed validation. If
        it's a hash, then the key will simply be the name of that key. If
        it's an array, it will be its index. For example, let's say the
        'first_name' key under the 'name' parameter failed the
        "length_between(3, 10)" validation method, and that the 'last_name'
        key was not present (and hence failed the "required()" validation).
        Also, let's say the 'pictures' parameter failed the
        "length_between(1, 5)" validation (for the sake of the argument,
        let's say it had 6 items instead of the maximum allowed 5), and that
        the 2nd item failed the min_length(3) validation, and the 6th item
        failed the custom validate method. Then our rejects hash-ref will
        have something like this:

                name => {
                        first_name => ['length_between(3, 10)'],
                        last_name => ['required(1)'],
                },
                pictures => {
                        _self => ['length_between(1, 5)'],
                        1 => ['min_length(3)'],
                        5 => ['validate'],
                }

        Notice the '_self' key under 'pictures' and that the numbering of
        the items of the 'pictures' array starts at zero (obviously).

        The beauty of Brannigan's data structure support is that it's
        recursive. So, it's not that a parameter can be a hash-ref and
        that's it. Every key in that hash-ref might be in itself a hash-ref,
        and every key in that hash-ref might be an array-ref, and every
        value in that array-ref might be a hash-ref... well, you get the
        idea. How might that look like? Well, just take a look at this:

                pictures => {
                        array => 1,
                        values => {
                                hash => 1,
                                keys => {
                                        filename => {
                                                min_length => 5,
                                        },
                                        source => {
                                                hash => 1,
                                                keys => {
                                                        website => {
                                                                validate => sub { ... },
                                                        },
                                                        license => {
                                                                one_of => [qw/GPL FDL CC/],
                                                        },
                                                },
                                        },
                                },
                        },
                }

        So, we have a pictures array that every value in it is a hash-ref
        with a filename key and a source key whose value is a hash-ref with
        a website key and a license key.

        Local validations: The _all "parameter" can be used in a scheme to
        define rules that apply to all of the parameters in a certain level.
        This can either be used directly in the 'params' key of the scheme,
        or in the 'keys' key of a hash parameter.

                _all => {
                        required => 1
                },
                subject => {
                        length_between => [3, 255]
                },
                text => {
                        min_length => 10
                }

        In the above example, both 'subject' and 'text' receive the
        "required()" validation methods.

    *   groups

        Groups are very useful to parse parameters that are somehow related
        together. This key takes a hash-ref containing the names of the
        groups (names are irrelevant, they're more for you). Every group
        will also take a hash-ref, with a rule defining which parameters are
        members of this group, and a parse method to use with these
        parameters (just like our custom parse method from the 'params'
        key). This parse method will automatically receive the values of all
        the parameters in the group, in the order they were defined.

        For example, suppose our app gets a user's birth date by using three
        web form fields: day, month and year. And suppose our app saves this
        date in a database in the format 'YYYY-MM-DD'. Then we can define a
        group, say 'date', that automatically does this. For example:

                date => {
                        params => [qw/year month day/],
                        parse => sub {
                                my ($year, $month, $day) = @_;

                                $month = '0'.$month if $month < 10;
                                $day = '0'.$day if $day < 10;

                                return { date => $year.'-'.$month.'-'.$day };
                        },
                }

        Alternative to the 'params' key, you can define a 'regex' key that
        takes a regex. All parameters whose name matches this regex will be
        parsed as a group. As oppose to using regexes in the 'params' key of
        the scheme, captured values in the regexes will not be passed to the
        parse method, only the values of the parameters will. Also, please
        note that there's no way to know in which order the values will be
        provided when using regexes for groups.

        For example, let's say our app receives one or more URLs (to
        whatever type of resource) in the input, in parameters named
        'url_1', 'url_2', 'url_3' and so on, and that there's no limit on
        the number of such parameters we can receive. Now, suppose we want
        to create an array of all of these URLs, possibly to push it to a
        database. Then we can create a 'urls' group such as this:

                urls => {
                        regex => '/^url_(\d+)$/',
                        parse => sub {
                                my @urls = @_;

                                return { urls => \@urls };
                        }
                }

  BUILT-IN VALIDATION METHODS
    As mentioned earlier, Brannigan comes with a set of built-in validation
    methods which are most common and useful everywhere. For a list of all
    validation methods provided by Brannigan, check Brannigan::Validations.

  CROSS-SCHEME CUSTOM VALIDATION METHODS
    Custom "validate" methods are nice, but when you want to use the same
    custom validation method in different places inside your scheme, or more
    likely in different schemes altogether, repeating the definition of each
    custom method in every place you want to use it is not very comfortable.
    Brannigan provides a simple mechanism to create custom, named validation
    methods that can be used across schemes as if they were internal
    methods.

    The process is simple: when creating your schemes, give the names of the
    custom validation methods and their relevant supplement values as with
    every built-in validation method. For example, suppose we want to create
    a custom validation method named 'forbid_words', that makes sure a
    certain text does not contain any words we don't like it to contain.
    Suppose this will be true for a parameter named 'text'. Then we define
    'text' like so:

            text => {
                    required => 1,
                    forbid_words => ['curse_word', 'bad_word', 'ugly_word'],
            }

    As you can see, we have provided the name of our custom method, and the
    words we want to forbid. Now we need to actually create this
    "forbid_words()" method. We do this after we've created our Brannigan
    object, by using the "custom_validation()" method, as in this example:

            $b->custom_validation('forbid_words', sub {
                    my ($value, @forbidden) = @_;

                    foreach (@forbidden) {
                            return 0 if $value =~ m/$_/;
                    }

                    return 1;
            });

    We give the "custom_validation()" method the name of our new method, and
    an anonymous subroutine, just like in "local" custom validation methods.

    And that's it. Now we can use the "forbid_words()" validation method
    across our schemes. If a paremeter failed our custom method, it will be
    added to the rejects like built-in methods. So, if 'text' failed our new
    method, our rejects hash-ref will contain:

            text => [ 'forbid_words(curse_word, bad_word, ugly_word)' ]

    As an added bonus, you can use this mechanism to override Brannigan's
    built-in validations. Just give the name of the validation method you
    wish to override, along with the new code for this method. Brannigan
    gives precedence to cross-scheme custom validations, so your method will
    be used instead of the internal one.

  NOTES ABOUT PARSE METHODS
    As stated earlier, your "parse()" methods are expected to return a
    hash-ref of key-value pairs. Brannigan collects all of these key-value
    pairs and merges them into one big hash-ref (along with all the
    non-parsed parameters).

    Brannigan actually allows you to have your "parse()" methods be
    two-leveled. This means that a value in a key-value pair in itself can
    be a hash-ref or an array-ref. This allows you to use the same key in
    different places, and Brannigan will automatically aggregate all of
    these occurrences, just like in the first level. So, for example,
    suppose your scheme has a regex rule that matches parameters like
    'tag_en' and 'tag_he'. Your parse method might return something like "{
    tags => { en => 'an english tag' } }" when it matches the 'tag_en'
    parameter, and something like "{ tags => { he => 'a hebrew tag' } }"
    when it matches the 'tag_he' parameter. The resulting hash-ref from the
    process method will thus include "{ tags => { en => 'an english tag', he
    => 'a hebrew tag' } }".

    Similarly, let's say your scheme has a regex rule that matches
    parameters like 'url_1', 'url_2', etc. Your parse method might return
    something like "{ urls => [$url_1] }" for 'url_1' and "{ urls =>
    [$url_2] }" for 'url_2'. The resulting hash-ref in this case will be "{
    urls => [$url_1, $url_2] }".

    Take note however that only two-levels are supported, so don't go crazy
    with this.

  SO HOW DO I PROCESS INPUT?
    OK, so we have created our scheme(s), we know how schemes look and work,
    but what now?

    Well, that's the easy part. All you need to do is call the "process()"
    method on the Brannigan object, passing it the name of the scheme to
    enforce and a hash-ref of the input parameters/data structure. This
    method will return a hash-ref back, with all the parameters after
    parsing. If any validations failed, this hash-ref will have a '_rejects'
    key, with the rejects hash-ref described earlier. Remember: Brannigan
    doesn't raise any errors. It's your job to decide what to do, and that's
    a good thing.

    Example schemes, input and output can be seen in Brannigan::Examples.

CONSTRUCTOR
  new( \%scheme | @schemes )
    Creates a new instance of Brannigan, with the provided scheme(s) (see
    "HOW SCHEMES LOOK" for more info on schemes).

OBJECT METHODS
  add_scheme( \%scheme | @schemes )
    Adds one or more schemes to the object. Every scheme hash-ref should
    have a "name" key with the name of the scheme. Existing schemes will be
    overridden. Returns the object itself for chainability.

  process( $scheme, \%params )
    Receives the name of a scheme and a hash-ref of input parameters (or a
    data structure), and validates and parses these paremeters according to
    the scheme (see "HOW SCHEMES LOOK" for detailed information about this
    process).

    Returns a hash-ref of parsed parameters according to the parsing scheme,
    possibly containing a list of failed validations for each parameter.

    Actual processing is done by Brannigan::Tree.

  process( \%scheme, \%params )
    Same as above, but takes a scheme hash-ref instead of a name hash-ref.
    That basically gives you a functional interface for Brannigan, so you
    don't have to go through the regular object oriented interface. The only
    downsides to this are that you cannot define custom validations using
    the "custom_validation()" method (defined below) and that your scheme
    must be standalone (it cannot inherit from other schemes). Note that
    when directly passing a scheme, you don't need to give the scheme a
    name.

  custom_validation( $name, $code )
    Receives the name of a custom validation method ($name), and a reference
    to an anonymous subroutine ($code), and creates a new validation method
    with that name and code, to be used across schemes in the Brannigan
    object as if they were internal methods. You can even use this to
    override internal validation methods, just give the name of the method
    you want to override and the new code.

CAVEATS
    Brannigan is still in an early stage. Currently, no checks are made to
    validate the schemes built, so if you incorrectly define your schemes,
    Brannigan will not croak and processing will probably fail. Also, there
    is no support yet for recursive inheritance or any crazy inheritance
    situation. While deep inheritance is supported, it hasn't been tested
    extensively. Also bugs are popping up as I go along, so keep in mind
    that you might encounter bugs (and please report any if that happens).

IDEAS FOR THE FUTURE
    The following list of ideas may or may not be implemented in future
    versions of Brannigan:

    *   Cross-scheme custom parsing methods

        Add an option to define custom parse methods in the Brannigan object
        that can be used in the schemes as if they were built-in methods
        (cross-scheme custom validations are already supported, next up is
        parse methods).

    *   Support for third-party validation methods

        Add support for loading validation methods defined in third-party
        modules (written like Brannigan::Validations) and using them in
        schemes as if they were built-in methods.

    *   Validate schemes by yourself

        Have Brannigan use itself to validate the schemes it receives from
        the developers (i.e. users of this module).

    *   Support loading schemes from JSON/XML

        Allow loading schemes from JSON/XML files or any other source. Does
        that make any sense?

    *   Something to aid rejects traversal

        Find something that would make traversal of the rejects list easier
        or whatever. Plus, printing the name of the validation method and
        its supplement values in the rejects list isn't always a good idea.
        For example, if we use the "one_of()" validation method with a big
        list of say 100 options, our rejects list will contain all these 100
        options, and that's not nice. So, think about something there.

SEE ALSO
    Brannigan::Validations, Brannigan::Tree, Brannigan::Examples.

AUTHOR
    Ido Perlmuter, "<ido at ido50 dot net>"

BUGS
    Please report any bugs or feature requests to "bug-brannigan at
    rt.cpan.org", or through the web interface at
    <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Brannigan>. I will be
    notified, and then you'll automatically be notified of progress on your
    bug as I make changes.

SUPPORT
    You can find documentation for this module with the perldoc command.

            perldoc Brannigan

    You can also look for information at:

    *   RT: CPAN's request tracker

        <http://rt.cpan.org/NoAuth/Bugs.html?Dist=Brannigan>

    *   AnnoCPAN: Annotated CPAN documentation

        <http://annocpan.org/dist/Brannigan>

    *   CPAN Ratings

        <http://cpanratings.perl.org/d/Brannigan>

    *   Search CPAN

        <http://search.cpan.org/dist/Brannigan/>

ACKNOWLEDGEMENTS
    Brannigan was inspired by Oogly (Al Newkirk) and the "Ketchup" jQuery
    validation plugin (<http://demos.usejquery.com/ketchup-plugin/>).

LICENSE AND COPYRIGHT
    Copyright 2010-2013 Ido Perlmuter.

    This program is free software; you can redistribute it and/or modify it
    under the terms of either: the GNU General Public License as published
    by the Free Software Foundation; or the Artistic License.

    See http://dev.perl.org/licenses/ for more information.

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