ikiwiki/doc/plugins/write.mdwn

ikiwiki [[plugins]] are written in perl. Each plugin is a perl module, in
the `IkiWiki::Plugin` namespace. The name of the plugin is typically in
lowercase, such as `IkiWiki::Plugin::inline`. Ikiwiki includes a
`IkiWiki::Plugin::skeleton` that can be fleshed out to make a useful
plugin. `IkiWiki::Plugin::pagecount` is another simple example.

# Note

One thing to keep in mind when writing a plugin is that ikiwiki is a wiki
*compiler*. So plugins influence pages when they are built, not when they
are loaded. A plugin that inserts the current time into a page, for
example, will insert the build time. Also, as a compiler, ikiwiki avoids
rebuilding pages unless they have changed, so a plugin that prints some
random or changing thing on a page will generate a static page that won't
change until ikiwiki rebuilds the page for some other reason, like the page
being edited.

# Registering plugins

Plugins should, when imported, call IkiWiki::hook to hook into ikiwiki's
processing. The function uses named parameters, and use varies depending on
the type of plugin being registered. Note that a plugin can call the
function more than once to register multiple hooks. All calls to
IkiWiki::hook should be passed a "type" parameter, which gives the type of
hook, a "id" paramter, which should be a unique string for this plugin, and
a "call" parameter, which is a reference to a function to call for the
hook.

# Writing a [[PreProcessorDirective]]

This is probably the most common use of a plugin.

        IkiWiki::hook(type => "preprocess", id => "foo", call => \&preprocess);

Replace "foo" with the command name that will be used inside brackers for
the preprocessor directive.

Each time the directive is processed, the referenced function (`preprocess`
in the example above) is called, and is passed named parameters. A "page"
parameter gives the name of the page that embedded the preprocessor
directive. All parameters included in the directive are included as named
parameters as well. Whatever the function returns goes onto the page in
place of the directive.

## Error handing

While a plugin can call ikiwiki's error routine for a fatal error, for
errors that aren't intended to halt the entire wiki build, including bad
parameters passed to a [[PreProcessorDirective]], etc, it's better to just
return the error message as the output of the plugin.

## Html issues

Note that if the [[htmlscrubber]] is enabled, html in
[[PreProcessorDirective]] output is sanitised, which may limit what your
plugin can do. Also, the rest of the page content is not in html format at
preprocessor time. Text output by a preprocessor directive will be passed
through markdown (or whatever engine is used to htmlize the page) along
with the rest of the page.

# Other types of hooks

Beyond PreProcessorDirectives, Other types of hooks that can be used by
plugins include:

## checkconfig

	IkiWiki::hook(type => "checkconfig", id => "foo", call => \&checkconfig);

This is useful if the plugin needs to check for, or modify ikiwiki's
configuration. It's called early in the ikiwiki startup process. The
function is passed no values. It's ok for the function to call
IkiWiki::error if something isn't configured right.

## filter

	IkiWiki::hook(type => "filter", id => "foo", call => \&filter);

Runs on the raw source of a page, before anything else touches it, and can
make arbitrary changes. The function is passed named parameters `page` and
`content` and should return the filtered content.

## htmlize

	IkiWiki::hook(type => "htmlize", id => "ext", call => \&filter);

Runs on the raw source of a page and turns it into html. The id parameter
specifies the filename extension that a file must have to be htmlized using
this plugin. This is how you can add support for new and exciting markup
languages to ikiwiki.

## pagetemplate

	IkiWiki::hook(type => "pagetemplate", id => "foo", call => \&pagetemplate);

Each time a page is rendered, a [[template|templates]] is filled out.
This hook allows modifying that template. The function is passed the name
of the page, and a `HTML::Template` object that is the template that will
be used to generate the page. It can manipulate that template, the most
common thing to do is probably to call $template->param() to add a new
custom parameter to the template.

## sanitize

	IkiWiki::hook(type => "sanitize", id => "foo", call => \&sanitize);

Use this to implement html sanitization or anything else that needs to
modify the content of a page after it has been fully converted to html.
The function is passed the page content and should return the sanitized
content.

## delete

	IkiWiki::hook(type => "delete", id => "foo", call => \&dele);

Each time a page or pages is removed from the wiki, the referenced function
is called, and passed the names of the source files that were removed.

## change

	IkiWiki::hook(type => "change", id => "foo", call => \&render);

Each time ikiwiki renders a change or addition (but not deletion) to the
wiki, the referenced function is called, and passed the names of the
source files that were rendered.

## cgi

	IkiWiki::hook(type => "cgi", id => "foo", call => \&cgi);

Use this to hook into ikiwiki's cgi script. Each registered cgi hook is
called in turn, and passed a CGI object. The hook should examine the
parameters, and if it will handle this CGI request, output a page and
terminate the program.

# Wiki configuration

A plugin can access the wiki's configuration via the `%IkiWiki::config`
hash. The best way to understand the contents of the hash is to look at
[[ikiwiki.setup]], which sets the hash content to configure the wiki.

# Wiki data

If your plugin needs to access data about other pages in the wiki. It can
use the following hashes, using a page name as the key:

* `%IkiWiki::links` lists the names of each page
  that a page links to, in an array reference.
* `%IkiWiki::pagemtime` contains the last modification time of each page
* `%IkiWiki::pagectime` contains the creation time of each page
* `%IkiWiki::renderedfiles` contains the name of the file rendered by a
  page
* `%IkiWiki::pagesources` contains the name of the source file for a page.
* `%IkiWiki::depends` contains a [[GlobList]] that is used to specify other
  pages that a page depends on. If one of its dependencies is updated, the
  page will also get rebuilt. 
  
  Many plugins will need to add dependencies to this hash; the best way to do
  it is by using the IkiWiki::add_depends function, which takes as its
  parameters the page name and a [[GlobList]] of dependencies to add.

# RCS plugins

ikiwiki's support for revision control systems also uses pluggable perl
modules. These are in the `IkiWiki::RCS` namespace, for example
`IkiWiki::RCS::svn`. 

Each RCS plugin must support all the IkiWiki::rcs\_* functions.
See IkiWiki::RCS::Stub for the full list of functions. It's ok if
rcs\_getctime does nothing except for throwing an error.

See [[about_RCS_backends]] for some more info.