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 [[HTMLSanitization]] 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 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.

### 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.

### render

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

Each time ikiwiki renders a change or addition (but not deletion) of a page to the wiki, the referenced function is called, and passed the name of the source file that was 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.

## Page templates

Plugins are mostly limited to changing the content of pages, to change the look and feel of the wiki it's generally better to use a stylesheet and [[templates]]. However, there are some hooks in the templates that plugins can use to add stuff to the wiki's UI:

### Adding content to the page header

Html that is added to $IkiWiki::config{headercontent} will show up in the
header of the page. One good thing to put here is a search form.

## 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.