# PODNAME: Config::Model::Cookbook::CreateModelFromDoc
# ABSTRACT: Create a configuration model from application documentation

=pod

=head1 Introduction

This page shows step by step how was created C<Popcon>'s model from
C<Popcon> documentation provided as comments in C<Popcon>'s sample
configuration file.

=head1 C<Popcon> configuration file

A quick looks in C</etc> directory shows that C<Popcon>'s configuration
is stored in C</etc/popularity-contest.conf</t>:

 # Config file for Debian's popularity-contest package.
 #
 # To change this file, use:
 #        dpkg-reconfigure popularity-contest
 #
 # You can also edit it by hand, if you so choose.
 #
 # See /usr/share/popularity-contest/default.conf for more info
 # on the options.
 
 MY_HOSTID="172921501FFFFFAAAA6897etc"
 PARTICIPATE="yes"
 USEHTTP="yes"
 DAY="5"

The important part is the mention of C<default.conf> which contains
all the required information to create C<Popcon>'s configuration model.

=head1 C<Popcon> documentation

Let's start from C<default.conf> file. Since this file is loaded
by C<popcon> I<before> loading C</etc/popularity-contest.conf</t>,
all values there can be used as application default values (aka
I<upstream_default>):

 # Default config file for Debian's popularity-contest package.
 #
 # Local overrides are in /etc/popularity-contest.conf
 
 # PARTICIPATE can be one of "yes" or "no".
 # If you don't want to participate in the contest, say "no"
 # and we won't send messages.
 #
 # If this option is missing, the default is "no".
 #
 PARTICIPATE="no"
 
 # MAILTO specifies the address to e-mail statistics to each week.
 #
 MAILTO="survey@popcon.debian.org"
 
 # MAILFROM is the forged sender email address you want to use in
 # email submitted to the popularity-contest.  If this is commented
 # out, no From: or Sender: lines will be added to the outgoing mail,
 # and it will be your MTA's job to add them.  This is usually what
 # you want.
 #
 # If your MTA is misconfigured or impossible to configure correctly,
 # and it always generates invalid From: and/or Sender: lines, you
 # can force different results by setting MAILFROM here.  This can
 # cause problems with spam bouncers, so most people should leave it
 # commented out.
 #
 #MAILFROM="root@example.org"
 
 # SUBMITURLS is a space separated list of where to submit
 # popularity-contest reports using http.
 SUBMITURLS="http://popcon.debian.org/cgi-bin/popcon.cgi"
 
 # USEHTTP enables http reporting.   Set this to 'yes' to enable it.
 USEHTTP="yes"
 
 # HTTP_PROXY allows one to specify an HTTP proxy server, the syntax is
 # HTTP_PROXY="http://proxy:port". This overrides the environment
 # variable http_proxy.
 
 # MY_HOSTID is a secret number that the popularity-contest receiver
 # uses to keep track of your submissions.  Whenever you send in a
 # new entry, it overwrites the last one that had the same HOSTID.
 #
 # This key was generated automatically so you should normally just
 # leave it alone.
 #
 #MY_HOSTID="_ID_"

This file contains everything we need:

=over

=item *

Parameter names

=item *

Documentation 

=item *

Default values

=back

Now, we will use our favorite editor to edit this file and add YAML
tags that can be understood by C<cme meta edit>

=head1 Creating the YAML skeleton

C<cme meta edit> is able to load a model described in
YAML. To do this the above file needs to be translated in YAML. That's
not as complicated as it may sound.

First, a YAML file must begin with B<--->. Then the class must be declared:

 ---
 class:
   PopCon:

Note that, like with Python language, the indentation is important to
define the structure of the file. Here, the C<PopCon> class is followed by
a ':' as it defines a new hierarchical level to describes the
configuration elements of this class:

     element:

Now we can deal with the configuration parameters. Let's detail the
C<PARTICIPATE> element. Here's the spec in from C<default.conf>:

 # PARTICIPATE can be one of "yes" or "no".
 # If you don't want to participate in the contest, say "no"
 # and we won't send messages.
 #
 # If this option is missing, the default is "no".
 #
 PARTICIPATE="no"

In the YAML file, the comments are moved in the C<description> field and
the value in the file is used as upstream default:

      PARTICIPATE:
        upstream_default: no
        description: >
         If you don't want to participate in the contest, 
         say "no" and we won't send messages.

Likewise for the remaining parameters:

      MAILTO:
        description: >
         specifies the address to e-mail statistics to each week.
        default: 'survey@popcon.debian.org'
      MAILFROM:
        description: >-
         MAILFROM is the forged sender email address you want to use
         in email submitted to the popularity-contest.  If this is
         commented out, no From: or Sender: lines will be added to the
         outgoing mail, and it will be your MTA's job to add them.  This
         is usually what you want. 
  
  
         If your MTA is misconfigured or
         impossible to configure correctly, and it always generates
         invalid From: and/or Sender: lines, you can force different
         results by setting MAILFROM here.  This can cause problems with
         spam bouncers, so most people should leave it commented out.

In the description above, the C<chimping> marker '-' after '>' is used to
keep paragraph formatting in the help.

      SUBMITURLS:
        description: >
         Space separated list of where to submit popularity-contest 
         reports using http.
        default: >
         http://popcon.debian.org/cgi-bin/popcon.cgi
        
      USEHTTP:
        description: >
         enables http reporting.   Set this to 'yes' to enable it.
        default: "yes"
        
      HTTP_PROXY:
        description: >
         allows one to specify an HTTP proxy server, the syntax is 
         "http://proxy:port". This overrides the environment variable 
         http_proxy.
        
      MY_HOSTID:
        description: >-
         secret number that the popularity-contest receiver uses to 
         keep track of your submissions.  Whenever you send in a new 
         entry, it overwrites the last one that had the same HOSTID.
  
         This key was generated automatically so you should normally 
         just leave it alone.

=head1 Loading the YAML skeleton

Now that the YAML file was created, you can turn it into a model and
load it in the model editor GUI with the following command:

 cme meta edit popcon -load-yaml popcon.yml -force

Note that the model is incomplete: some mandatory parameters are
missing from the YAML file so the I<-force> option must be used. These
missing parameters are also flagged with a red cross in the GUI.

=head1 Completing missing model parts

To complete the model, the easiest way is to run the wizard to
complete the missing values. In the GUI, you can use the menu
C<< File -> wizard >> to launch the wizard. 
Then click on the 'OK' button in
the new window.

The wizard will first stop on the parameter list (not because there's
an error, but because the parameter list is flagged as I<important>)

There, you can re-order the parameters by selecting one and clicking
on one of the blue arrows to move it up or down. Once you're
satisfied, click on I<Next>. 

The widget will now stop on the first missing information. Just select
the correct type ('leaf' here), click 'store' and 'Next'.

You can repeat these steps until the wizard exits.

=head1 Specifying read and write backend

Once the model is complete, it's time to specify how to read and write the file. In
C<Popcon> class specification:

=over

=item *

right-click on I<read_config>

=item *

click on I<push new node> to create a new read specification

=item *

right-click on the created item (shown at index "I<0>")

=back

You will get a window showing you the parameters to fill to specify
the read backend.

Now fill the blank on the right side. The backend to use is
C<ShellVar> since I<popularity-contest.conf> is made of shell
variables.

Since the write specification is identical, there's no need to specify
it. L<Config::Model> will do the right thing.

=head1 Testing the model

You can test the model by clicking on menu C<< Test -> Model >>. You
will be shown the C<Popcon> configuration editor GUI. The same that your
users will get.

If everything is fine, you can quit the model editor (menu File->quit)

=head1 The resulting model

The model you have just created is stored in C<lib/Config/Model/models/Popcon.pl>.

You can test directly this model with :

  cme edit -dev -try Popcon

=head1 Feedback welcome

Feel free to send comments and suggestion about this page to the author.

=head1 AUTHORS

Dominique Dumont <ddumont at cpan.org>
