=head1 NAME

Jifty::Manual::Actions - 讓 Jifty 做事

=head1 DESCRIPTION

C<Jifty::Action> 抽象敘述了於編譯時期 (complie time) 宣告參數的想法
(L<"parameters"|Jifty::Manual::Glossary/parameter>).

在執行時期 (runtime)，動作 (Action) 會收集使用者輸入資料做為參數
(L<"arguments"|Jifty::Manual::Glossary/argument>),
並處理一些事情，最後回傳結果給使用者。

如果這些聽起來實在太一般，那是因為 -- 動作 (Action) 其實幾乎可以做 Jifty
裡的每一件事情。

C<Jifty::Action> 同時也會為你從參數產生 HTML -- 不需要自己手動寫 C<< <input> >> 標籤
或是手動處理由 GET 或 POST 傳回的參數，並且 Jifty 會自動幫你把不同的表單分派到相對應
的動作 (Action)。 C<Jifty::Action> 為你完成了所有該做的事情。

=head1 如何寫 Action 

Jifty 已經提供了一些預設的行為 (Action) 給你 -- 可參見
L<Jifty::Manual::ObjectModel> 以及在 L<Jifty::Action::Record> 會有動態產生的行為 (Action)
另外還有像是 L<Jifty::Action::Redirect>,
不過任何有用的程式都會需要定義他們自己需要的行為 (Action).
這就是講解你該如何寫你屬於你的行為 (Action).

每一個行為，都是 L<Jifty::Action> 的子類別，典型的像是 
I<AppName>::Action.

行為通常都會被存放在 I<AppName>::Action:: 的名稱空間中;
while that's just a convention, it will make your life easier if you follow it.

This, the simplest possible action, is:

    use warnings;
    use strict;

    package MyApp::Action::DoNothing;
    use base qw/MyApp::Action Jifty::Action/;

    1;

(Instead of copying-and-pasting that, or typing it in, though, you
could just run:

    jifty action --name DoNothing

in your application's directory, and Jifty would create a skeleton for
you. )

However, if you want to actually do something with your actions, you
need to define two things: their L<parameters|/parameters>, and a
L</take_action> method.

=head2 parameters

Every C<Jifty::Action> subclass should define a C<schema>, which contains
some C<param> declarations that describe what arguments it takes.
Supposing we were writing an action to post a blog article, we might start
out with parameters like thus:

    use Jifty::Param::Schema;
    use Jifty::Action schema {

    param 'title';
    param 'category';
    param 'body';

    };

However, we've only scratched the surface of the power the
C<param> API offers.  Parameters can have types, labels,
validators, canonicalizers, and even more. To start with, let's add
some types and labels:

    use Jifty::Param::Schema;
    use Jifty::Action schema {

    param title =>
        label is 'Title',
        max_length is 50,
        is mandatory;

    param category => 
        label is 'Category',
        max_length is 30;

    param body =>
        label is 'Entry',
        render as 'Textarea';

    };

Now, we can ask the action to render form fields, and it will know how
to display them. But, we can do even better. Let's improve the look of
that C<category> field, by making it a combobox (a combination
dropdown/text field), with some default values available:

    # ...
    param category => 
        label is 'Category',
        render as 'Combobox',
        available are qw( Personal Work Block );
    # ...

But a static list is lame. What we really want is a C<Category> model,
and to keep track of all the categories users have entered:

    # ...
    param categories => 
        label is 'Category',
        render as 'Select',
        available are defer {
            my $categories = MyBlog::Model::CategoryCollection->new;
            $categories->unlimit;
            [{
                display_from => 'name',
                value_from   => 'name',
                collection   => $categories,
            }];
        }
    ...

Now, Jifty will populate the combobox with the result of calling C<name>
on each element in C<$categories>. Alternatively, if you set
C<< value_from => 'id' >>, Jifty would automatically return the C<id> of
the category, for easy database reference. We don't do this with the
combobox, however, since a combobox displays the selected value in its
text field.

See L<Jifty::Action> and L<Jifty::Web::Form::Field> for more fields
you can set in the C<param> declaration, and see L<Jifty::Param::Schema>
for more about the syntax.

=head2 validation

C<Jifty::Action> can automatically validate arguments for you, as
appropriate. If an argument has C<valid_values>, then C<Jifty::Action>
will automatically verify if the given value matches one of
them. However, you can also write your own validators. Just write a
C<< sub validate_<parameter> >>, and it will be called as appropriate:

    use Regexp::Common 'profanity_us';

    sub validate_body {
       my $self = shift;
       my $body = shift;
       if ( $body =~ /$RE{profanity}/i) {
           return $self->validation_error(
               body => 'Would you speak like that in front of your mother? *cough*'
           );
       }
       return $self->validation_ok('body');
    }

You can also do validation in the model -- see
L<Jifty::Action::Record> 

=head2 canonicalization

If, instead of failing, you want to automatically modify
invalid content to be valid, you want a
L<canonicalizer|Jifty::Manual::Glossary/canonicalize>, not a
validator.

    use Regexp::Common 'profanity_us';

    sub canonicalize_body {
       my $self = shift;
       my $body = shift;
       $body =~ s/$RE{profanity}/**expletives**/gi;
       return $body;
    }

A L<canonicalizer|Jifty::Manual::Glossary/canonicalize> can also 
change other parts of the action.  This lets you update the display
dynamically in an L<AJAX|Jifty::Manual::Glossary/ajax>-enabled browser
based on what the user has entered.  For example, we can let a user
use magic syntax to provide tags for their blog post by surrounding the 
tags with square brackets.  You can also let the user know you're
doing something magical by using C<canonicalization_note> which 
will display a message to the user.

    use Jifty::Param::Schema;
    use Jifty::Action schema {
        param title =>
            label is 'Title',
            hints is "You can provide tags like this [tag1 tag2]",
            ajax canonicalizes;

        param tags =>
            label is 'Tags';
    };

    sub canonicalize_title {
        my $self = shift;
        my $value = shift;

        if ($value =~ s/\[(.*?)\]//) {
            # this clobbers, may want to merge
            $self->argument_value( tags => $1 );
            $self->canonicalization_note(
                title => 'Removed tags from your title'
            );
        }

        return $value;
    }


If you set C<ajax validates> or C<ajax canonicalizes>
for an argument, then Jifty will automatically validate or
canonicalize it in an L<AJAX|Jifty::Manual::Glossary/ajax>-enabled
browser when the user stops typing and puts the focus out of
the corresponding form field.

=head2 take_action

Once an action has arguments, it needs to do something with them. An
action does so in its C<take_action> sub, which will be called when an
action is submitted, and only if its arguments
L<validate|/validation>. 

Inside C<sub take_action>, subclasses can access their arguments via
C<< $self->argument_value('foo') >>. If you need to check whether you've
been passed an argument or not (as opposed to being passed a true
argument or not), use C<< $self->has_argument('foo') >>.

Once an action has done its task, it needs to inform the caller
whether or not it has succeeded, possibly with some status message. To
this end, every C<Jifty::Action> has a C<Jifty::Result> associated
with. C<Jifty::Result> carries both a failure/sucess code, and a
textual message describing the result of running the action.

Thus, if your action failed for some reason, you would, in
C<take_action>, write code like:

    $self->result->error('Could not write blog post');
    return;

If, however, the action completed successfully, you might write:

    $self->result->message('Posted to your blog');

Actions will default to successful with an empty message if you don't
do anything with the result object. Additionally, if you need to return more semantic
information than a simple message, you can set arbitrary content on
the result, using $self->result->content, e.g:

    $self->result->content( id => $new_post->id);

This information can be then used elsewhere to, for example,
automatically redirect you to a view page for that new blog post. The
view page template may have the following piece of code in it:

    <%args>
    $id => undef
    </%args>
    <%init>
    my $result = Jifty->web->response->result('post_blog');
    $id = $result->content('id') if $result and !defined $id;
    # load the record by $id and other stuff go here...
   </%init>

where C<'post_blog'> is the moniker for your post page action object.
In fact, that's exactly how actions "return" values to other components 
in your application.

Mutiple action "return values" are possible and arbitrary data structures
can be passed too:

    $self->result->content( keys   => $keys );
    $self->result->content( result => $collection);

It should also be mentioned that the response object is "per request". That is,
it usually can't live up to another user request. Therefore, when paging mechanism 
is applied to your view page, for example, you have to either pass some data 
to the link constructor or explicitly tell Jifty to preserve states for you.

See L</monikers>, the Jifty Pony site's source, and L<Jifty::Request::Mapper> for some 
more information.

=head1 USING ACTIONS

At their simplest, you can create and run actions yourself, e.g.:

    Jifty->web->new_action(
        class     => 'PostBlogEntry',
        arguments => {
            title    => 'A boring blog entry',
            category => 'Jifty',
            body     => 'This blog entry is lame.'
        }
    )->run;

Note that C<< Jifty->web->new_action >>, and all similar methods
(e.g. L<Jifty::Request::add_action|Jifty::Request/add_action>,
L<Jifty::Web::Form::add_action|Jifty::Web::Form/new_action>), will
automatically qualify the C<class> with either C<Jifty::Action::> or
C<I<AppName>::Action::> as necessary (I've told you putting actions in
I<AppName::Action::> would make your life easier!)

In practice, you'll rarely provide actions with arguments
yourself. Instead, you'll create an action with no or partial
arguments, often in the L<dispatcher|Jifty::Dispatcher>, or a Mason
component's C<< <%init%> >> block (See L</constructor arguments> for
details about passing arguments to actions on creation).

    my $create = Jifty->web->new_action(
        class   => 'PostBlogEntry',
        moniker => 'post_blog'
    );

Having created the action, you will, in one of your Mason components,
output a form where the user can fill in the action's arguments:

    <% Jifty->web->form->start %>
    <div class="post-metadata">
      <% $create->form_field('title') %>
      <% $create->form_field('category') %>
    </div>
      <% $create->form_field('body') %>
    <% Jifty->web->form->submit(label => "Post") %>
    %# or <% Jifty->web->link(label => "Post", submit => $create) %>
    %# or <% $action->button(label => "Post"); %>
    <% Jifty->web->form->end %>

C<form_field> will render the field, along with the C<label> as an
HTML C<< <input> >> tag that Jifty knows how to interpret to feed back
to your action as an argument when the form is submitted. If you need
to change the appearance of the field, Jifty outputs classes on the
fields, as well as providing some semantic C<< <div> >>s you can style
using CSS. (See L<Jifty::Manual::UsingCSSandJS> for some more details.)

See L<Jifty::Web::Form/submit>, L<Jifty::Web/link> and
L<Jifty::Action/button> for details on the different ways to generate
a submit button.

Additionally, instead of C<form_field>, you can use C<hidden> to
generate a C<hidden> input, which will not be viewable or editable in
a web browser. (Note that a knowledgeable user I<can> still submit a
form with a different value for that hidden input; If this concerns
you, make sure you have appropriate
L<ACLs|Jifty::Manual::AccessControl> in place. If it still worries
you, you probably want a L<continuation|Jifty::Continuation> here.)

=head2 monikers

You probably noticed the C<< moniker => 'post_blog' >>. Every action you
create in Jifty has an associated
L<moniker|Jifty::Manual::Glossary>. A C<moniker> is simply a unique
identifier for the action (unique per request, which in practice
typically means per HTML page). Since actions are constantly being
serialized (over HTTP, or Javascript AJAX calls, and so on), and
unpacked, we need a way refer to specific actions other than just
object identity, e.g. to extract its arguments or results in the
L<dispatcher|Jifty::Dispatcher> or a template. Monikers give us that. Given a
moniker, you can pull information about the associated action out of a
L<request|Jifty::Request> or L<response|Jifty::Response>.

If a moniker is unspecified, it will be autogenerated.

(XXX TODO Note about action registration here)

=head2 Argument Folding

If you write out more than one C<form_field> for a given argument in
the same form, and more than one is filled in, Jifty will C<fold> the
arguments into an array before filling them in to the action. This
provides a way to do, e.g. a C<BulkEdit> action that applies some set
of changes to many records at once.

(XXX TODO Note about C<constructor> parameters)

=head1 ACTIONS AS WEB SERVICES

Your actions are also automatically published as web services.
Clients can POST requsets, usually using the YAML or JSON request
format.  See C<bin/service> for a trivial generic webservice client.

(XXX TODO More about webservices)

=head1 SEE ALSO

L<Jifty::Action>, L<Jifty::Manual::Tutorial>

=cut
