# PODNAME: Alien::Build::Manual::PluginAuthor
# ABSTRACT: Alien::Build plugin author documentation
# VERSION

__END__

=pod

=encoding UTF-8

=head1 NAME

Alien::Build::Manual::PluginAuthor - Alien::Build plugin author documentation

=head1 VERSION

version 1.17_01

=head1 SYNOPSIS

your plugin:

 package Alien::Build::Plugin::Build::MyPlugin;
 
 use strict;
 use warnings;
 use Alien::Build::Plugin;
 
 has arg1 => 'default_for arg1';
 has arg2 => sub { [ 'default', 'for', 'arg2' ] };
 
 sub init
 {
   my($self, $meta) = @_;
   ...
 }
 
 1;

and then from L<alienfile>:

 use alienfile;
 plugin 'Build::MyPlugin' => (
   arg1 => 'override for arg1',
   arg2 => [ 'something', 'else' ],
 );

=head1 DESCRIPTION

This document explains how to write L<Alien::Build> plugins using the
L<Alien::Build::Plugin> base class.  Plugins use L<Alien::Build::Plugin>,
which sets the appropriate base class, and provides you with the C<has>
property builder.  C<has> takes two arguments, the name of the property
and the default value.  (As with L<Moose> and L<Moo>, you should use a
code reference to specify default values for non-string defaults).

The only method that you need to implement is C<init>.  From this method
you can add hooks to change the behavior of the L<alienfile> recipe.

 sub init
 {
   my($self, $meta) = @_;
   $meta->register_hook(
     probe => sub {
       my($build) = @_;
       if( ... )
       {
         return 'system';
       }
       else
       {
         return 'share';
       }
     },
   );
 }

Hooks get the L<Alien::Build> instance as their first argument, and depending
on the hook may get additional arguments.

You can also modify hooks using C<before_hook>, C<around_hook> and C<after_hook>:

 sub init
 {
   my($self, $meta) = @_;
   
   $meta->before_hook(
     build => sub {
       my($build) = @_;
       $build->log('this runs before the build');
     },
   );

   $meta->after_hook(
     build => sub {
       my($build) = @_;
       $build->log('this runs after the build');
     },
   );
   
   $meta->around_hook(
     build => sub {
       my $orig = shift;
       
       # around hooks are useful for setting environment variables
       local $ENV{CPPFLAGS} = '-I/foo/include';
       
       $orig->(@_);
     },
   );
 }

You can and should write tests for your plugin.  The best way to do
this is using L<Test::Alien::Build>, which allows you to write an
inline L<alienfile> in your test.

 use Test::V0;
 use Test::Alien::Build;
 
 my $build = alienfile_ok q{
   use alienfile;
   plugin 'Build::MyPlugin' => (
     arg1 => 'override for arg1',
     arg2 => [ 'something', 'else' ],
   );
   ...
 };
 
 # you can interrogate $build, it is an instance of L<Alien::Build>.
 
 my $alien = alien_build_ok;
 
 # you can interrogate $alien, it is an instance of L<Alien::Base>.

=head1 HOOKS

=head2 probe hook

 $meta->register_hook( probe => sub {
   my($build) = @_;
   return 'system' if ...; # system install
   return 'share';         # otherwise
 });
 
 $meta->register_hook( probe => [ $command ] );

This hook should return the string C<system> if the operating
system provides the library or tool.  It should return C<share>
otherwise.

You can also use a command that returns true when the tool
or library is available.  For example for use with C<pkg-config>:

 $meta->register_hook( probe =>
   [ '%{pkgconf} --exists libfoo' ] );

Or if you needed a minimum version:

 $meta->register_hook( probe =>
   [ '%{pkgconf} --atleast-version=1.00 libfoo' ] );

Note that this hook SHOULD NOT gather system properties, such as
cflags, libs, versions, etc, because the probe hook will be skipped
in the even the environment variable C<ALIEN_INSTALL_TYPE> is set.
The detection of these properties should instead be done by the
C<gather_system> hook, below.

=head2 gather_system hook

 $meta->register_hook( gather_system => sub {
   my($build) = @_;
   $build->runtime_prop->{cflags}  = ...;
   $build->runtime_prop->{libs}    = ...;
   $build->runtime_prop->{version} = ...;
 });

This hook is called for a system install to determine the properties
necessary for using the library or tool.  These properties should be
stored in the C<runtime_prop> hash as shown above.  Typical properties
that are needed for libraries are cflags and libs.  If at all possible
you should also try to determine the version of the library or tool.

=head2 download hook

 $meta->register_hook( download => sub {
   my($build) = @_;
   ...
 });

This hook is used to download from the internet the source.  Either as
an archive (like tar, zip, etc), or as a directory of files (git clone,
etc).  When the hook is called, the current working directory will be a
new empty directory, so you can save the download to the current
directory.  If you store a single file in the directory, L<Alien::Build>
will assume that it is an archive, which will be processed by the 
extract hook below.  If you store multiple files, L<Alien::Build> will
assume the current directory is the source root.  If no files are stored
at all, an exception with an appropriate diagnostic will be thrown.

B<Note>: If you register this hook, then the fetch, decode and prefer 
hooks will NOT be called.

=head2 fetch hook

 package Alien::Build::Plugin::MyPlugin;
 
 use strict;
 use warnings;
 use Alien::Build::Plugin;
 use Carp ();
 
 has '+url' => sub { Carp::croak "url is required property" };

 sub init
 {
   my($self, $meta) = @_;
   
   $meta->register_hook( fetch => sub {
     my($build, $url) = @_;
     ...
   }
 }
 
 1;

Used to fetch a resource.  The first time it will be called without an
argument, so the configuration used to find the resource should be
specified by the plugin's properties.  On subsequent calls the first
argument will be a URL.

Normally the first fetch will be to either a file or a directory listing.
If it is a file then the content should be returned as a hash reference
with the following keys:

 # content of file stored in Perl
 return {
   type     => 'file',
   filename => $filename,
   content  => $content,
   version  => $version,  # optional, if known
 };
 
 # content of file stored in the filesystem
 return {
   type     => 'file',
   filename => $filename,
   path     => $path,     # full file system path to file
   version  => $version,  # optional, if known
   tmp      => $tmp,      # optional
 };

C<$tmp> if set will indicate if the file is temporary or not, and can
be used by L<Alien::Build> to save a copy in some cases.  The default
is true, so L<Alien::Build> assumes the file or directory is temporary
if you don't tell it otherwise.

If the URL points to a directory listing you should return it as either
a hash reference containing a list of files:

 return {
   type => 'list',
   list => [
     # filename: each filename should be just the
     #   filename portion, no path or url.
     # url: each url should be the complete url
     #   needed to fetch the file.
     # version: OPTIONAL, may be provided by some fetch or prefer
     { filename => $filename1, url => $url1, version => $version1 },
     { filename => $filename2, url => $url2, version => $version2 },
   ]
 };

or if the listing is in HTML format as a hash reference containing the
HTML information:

 return {
   type => 'html',
   charset => $charset, # optional
   base    => $base,    # the base URL: used for computing relative URLs
   content => $content, # the HTML content
 };

or a directory listing (usually produced by ftp servers) as a hash
reference:

 return {
   type    => 'dir_listing',
   base    => $base,
   content => $content,
 };

=head2 decode hook

 sub init
 {
   my($self, $meta) = @_;
   
   $meta->register_hook( decode => sub {
     my($build, $res) = @_;
     ...
   }
 }

This hook takes a response hash reference from the C<fetch> hook above
with a type of C<html> or C<dir_listing> and converts it into a response
hash reference of type C<list>.  In short it takes an HTML or FTP file
listing response from a fetch hook and converts it into a list of filenames
and links that can be used by the prefer hook to choose the correct file to
download.  See C<fetch> for the specification of the input and response
hash references.

=head2 prefer hook

 sub init
 {
   my($self, $meta) = @_;
   
   $meta->register_hook( prefer => sub {
     my($build, $res) = @_;
     return {
       type => 'list',
       list => [sort @{ $res->{list} }],
     };
   }
 }

This hook sorts candidates from a listing generated from either the C<fetch>
or C<decode> hooks.  It should return a new list hash reference with the
candidates sorted from best to worst.  It may also remove candidates
that are totally unacceptable.

=head2 extract hook

 $meta->register_hook( extract => sub {
   my($build, $archive) = @_;
   ...
 });

=head2 patch hook

 $meta->register_hook( patch => sub {
   my($build) = @_;
   ...
 });

This hook is completely optional.  If registered, it will be triggered after
extraction and before build.  It allows you to apply any patches or make any
modifications to the source if they are necessary.

=head2 patch_ffi hook

 $meta->register_hook( patch_ffi => sub {
   my($build) = @_;
   ...
 });

This hook is exactly like the C<patch> hook, except it fires only on an
FFI build.

=head2 build hook

 $meta->register_hook( build => sub {
   my($build) = @_;
   ...
 });

This does the main build of the alienized project and installs it into
the staging area.  The current directory is the build root.  You need
to run whatever tools are necessary for the project, and install them
into C<%{.install.prefix}>.

=head2 build_ffi hook

 $meta->register_hook( build_ffi => sub {
   my($build) = @_;
   ...
 });

This is the same as C<build>, except it fires only on a FFI build.

=head2 gather_share hook

 $meta->register_hook( register_hook => sub {
   my($build) = @_;
   ... 
 });

This is the same as C<gather_system>, except it fires after a C<share>
install.

=head2 gather_ffi hook

 $meta->register_hook( register_ffi => sub {
   my($build) = @_;
   ... 
 });

This is the same as C<gatehr_share>, except it fires after a C<share> FFI
install.

=head2 override hook

 $meta->register_hook( override => asub {
   my($build) = @_;
 });

This allows you to alter the override logic.  It should return one of
C<share>, C<system>, C<defaul> or C<''>.  The default implementation is
just this:

 return $ENV{ALIEN_INSTALL_TYPE} || '';

=head1 AUTHOR

Author: Graham Ollis E<lt>plicease@cpan.orgE<gt>

Contributors:

Diab Jerius (DJERIUS)

Roy Storey

Ilya Pavlov

David Mertens (run4flat)

Mark Nunberg (mordy, mnunberg)

Christian Walde (Mithaldu)

Brian Wightman (MidLifeXis)

Zaki Mughal (zmughal)

mohawk (mohawk2, ETJ)

Vikas N Kumar (vikasnkumar)

Flavio Poletti (polettix)

Salvador Fandiño (salva)

Gianni Ceccarelli (dakkar)

Pavel Shaydo (zwon, trinitum)

Kang-min Liu (劉康民, gugod)

Nicholas Shipp (nshp)

Juan Julián Merelo Guervós (JJ)

Joel Berger (JBERGER)

Petr Pisar (ppisar)

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2017 by Graham Ollis.

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

=cut
