Development:Module visibility and display

(This document is a draft proposal.)

Summary

We would like to create a generic API that allows the following:

Module display on front page can be customised, for example making it possible to create another module that behaves like Label (displaying arbitrary html rather than a link to activity view.php) - currently this is hardcoded hack for Label. This change should apply to other areas such as navigation block as well as course page.

Some modules can provide dynamic text, such as forum displaying unread messages. At present this is hardcoded so that only forum can do it.

Modules can be hidden completely, or greyed out, from the view of particular students according to either custom module behaviour, or (if not specified by module) default behaviour regarding a new capability moodle/course:viewactivity and the existing option for whether a non-available module is greyed out or hidden entirely.

This should take advantage of the existing modinfo cache in order that performance is not adversely affected.

API improvement

Following Petr's suggestions, we would also like to improve the API by switching the modinfo in-memory data structures to use defined classes instead of anonymous stdClass objects. This achieves the following:

Provides a location for documentation of these structures. (Currently they are undocumented.)

In future, allows functions to specify the required type (i.e. some functions require the information from modinfo, not just a row from the table; they will now be able to specify this). There is no plan to change function definitions immediately.

Where the type is defined, makes metadata available to IDEs, allowing code completion and automatic documentation viewing.

The following requirements should also be met:

100% backward compatibility for existing use of these structures by core and third-party modules (except within minor parts of the label code, which will be altered as part of this change).

100% backward compatibility for existing modinfo data (in database).

Removing existing hacks

Existing hacks regarding label in all areas of code (e.g. navigation, etc) will be changed from the logic 'is this a label?' to the logic 'does this activity have a url?' (and label will be changed to work with this)
Existing hacks regarding forum unread data will be removed and the forum unread code will be moved into the new API function. The code will be written in such a way as to have the same performance characteristics.

get_fast_modinfo change

The get_fast_modinfo function will be changed to return a new object of type course_modinfo, which will be compatible with the existing $modinfo return value.

While constructing this object, in addition to current behaviour, the system will:

support new values defined in _get_coursemodule_info

extend dynamic per-user calculation (that checks is something is visible to current user, ->uservisible) with additional checks

call the new module API (if provided) after calculating modinfo, to get dynamic information

course_modinfo

The new class course_modinfo will contain properties:

courseid, userid (ints)
sections (array of int => array of int)
cms (array of int => cm_info)
instances (array of string => array of int => cm_info)
groups - at present I can't tell what this is for as it seems to be empty for me even though there are groups on the course and I'm a member of one of them - hmmm - anyhow I will figure it out and implement it

These are identical to the values currently returned by modinfo, except for the use of cm_info class instead of bare stdClass for the information about modules.

There are three options for handling this class:

Make these properties public so that they can be accessed exactly as at present.

Make them private and use PHP magic __set and __get functions so that they can be read as normal but any attempt to write them would (while working) also cause a developer debug warning.

Make the properties public, but deprecate them, and create separate get methods (get_courseid, get_userid, etc) which are recommended for future use.

I initially favoured the second option but unfortunately, PHP being PHP, this doesn't quite work properly: specifically, you can't use the empty() function on such values. Since there might be places in the code that call empty(), maybe this isn't a good idea.

Consequently I tend to the third one; we should make better get methods such as get_cm($cmid) as well as just get_cms(), which may help make new code more readable.

Construction

The code that creates this information should largely be moved to this class (either in a constructor or in init methods etc) from its current location in get_fast_modinfo. get_fast_modinfo should remain responsible only for caching these objects.

cm_info class

The new class cm_info will contain existing properties:

id, instance, course, idnumber, visible, groupmode, groupingid, groupmembersonly, indent, completion, availablefrom, availableuntil, showavailability - data from course_modules row

extra, icon, iconcomponent, modname, name, sectionnum, conditionscompletion, conditionsgrade, modplural (wtf is this there when the singular name isn't and both should be available with get_string?!) - data from modinfo which was computed when generating the cache

availableinfo, available, uservisible - data relating to the current user which is computed dynamically when obtaining the modinfo object

This is the list of properties currently available in modinfo objects, so will be implemented as-is. The same question regarding use of __set, __get applies as above, but in this case it's perhaps more likely that people might call empty() on the existing properties; again, I propose retaining the above as public properties, but deprecated, and providing get_x methods for new use. Any new properties would be private and available only with get_ methods.

Some of the get methods might have a slightly different definition to the raw properties. For example get_icon should use the provided data to return a moodle_icon object, not a string.

The new methods are:

has_view() - true if the module should have a link to its view.php shown in navigation, be included in lists of 'did the user visit this module' stats, etc. (Basically this is the 'is not a label' method.)
get_url() - returns moodle_url to module view.php, or null if has_view is false (this reduces code duplication in various places)
get_content() - returns HTML content to be displayed on the course page where this module is placed; appears below the link, if present (this is how Label displays content on course page)
get_extra_classes() - returns additional CSS classes to be added to the A or DIV tag(s) for this item on main course page.
get_custom_data() - returns an optional mixed value containing custom data for this module, which needs to be available course-wide via the get_fast_modinfo function. If present, this data should be small in size.
get_after_link() - returns HTML code which displays after the link. This is normally not set by the system, but rather in _get_dynamic_coursemodule_info to display things like forum unread status.
get_after_edit_icons() - returns HTML code which displays after the standard icons (hide, edit, delete, etc) when editing. This is normally not set by the system, but rather in _get_dynamic_coursemodule_info in case the module has a specific feature that is needed on home page.

Modify _get_coursemodule_info

There will be a change to the existing module API function _get_coursemodule_info. This change will retain backward compatibility. I wrote documentation for the new function below; in that documentation, the # marker indicates a changed or new entry, other stuff is existing.

In get_fast_modinfo, the system can automatically turn the ->nolink option into a ->url which will either be a moodle_url or null (this avoids duplicate code working out the url mod/whatever/view.php?id=whatever in a zillion places). Possibly we could also allow ->url to be specified directly but this won't be supported everywhere, at least to start with.

PERFORMANCE CONCERNS: None. No changes would be made to existing modules except label, and that one doesn't add a database query. Anyway, this data is cached.

_get_coursemodule_info

This optional function returns additional information about an instance of your module, which can be accessed quickly when displaying the module.

You should return an object $info which may contain the following fields, all of which are optional:

->nolink #: set true if the module does not need a link.
->name: name of instance (text displayed in link on course page) - this will not be used if nolink is true.
->content #: HTML content to be displayed on the course page where this module is placed; appears below the link, if present (this is how Label displays content on course page)
->extraclasses #: Additional CSS classes to be added to the A or DIV tag(s) for this item on main course page.
->icon: specifies an icon to use for this instance instead of the normal module icon; you can either use the name of an icon which will be directly passed to the $OUTPUT->pix_icon function, or the special format mod/mymodule/iconname which will be passed to that function as two parameters iconname, mymodule.
->customdata #: A place to store a string or object containing custom data for this module, which needs to be available course-wide via the get_fast_modinfo function. If present, this data should be small in size.
->afterlink #: If specified, includes HTML code which displays after the link. This is normally not set by this function, but rather in _get_dynamic_coursemodule_info to display things like forum unread status.
->editicons #: If specified, includes HTML code which displays as part of the editing icons (hide, edit, delete, etc). This is normally not set by this function, but rather in _get_dynamic_coursemodule_info in case the module has a specific feature that is needed on home page.

->extra (deprecated in 2.1): puts content in a weird part of the A or DIV tag for the item; can be used to add attributes
->iconcomponent (deprecated in 2.1): doesn't appear to do anything?!

Extend dynamic calculation

Currently the modinfo code makes the following checks that apply dynamically per-request (and do not directly come from the cache) in order to create the ->uservisible member variable.

If ->groupmembersonly is set, checks if the user belongs to group or has accessallgroups.
If availability restrictions (date, grade, completion) are set, checks these.

My proposal is:

Make this part of the code (that 'specialises' a single mod value for the current user/request) into a separate function, just to simplify it.
Add a check for the moodle/course:viewactivity capability; if user doesn't have this capability, set ->uservisible to false. Also check the option about what to do with hidden activities; if this is set to the default 'grey it out', then set ->inactive to true.
- Note: The default value for moodle/course:viewactivity should be true for all roles, even guest. This maintains existing behaviour. Sites that don't want guests to view activities can change the main role definition for guest.
Change the 'restriction information' code so that it adds restriction information (this is things like 'Not available until 30 December 2010') into a ->restrictions member of modinfo
Call the _get_dynamic_coursemodule_info function (below) if the current module supplies one.

PERFORMANCE CONCERNS: Minimal. No new database queries are required.

New module API

A new module API function _get_dynamic_coursemodule_info will be defined. As parameters, this takes:

the contents of modinfo for this module (which will include data from get_coursemodule_info).
an optional userid (default 0 = current user).

When it returns, this returns a new version of modinfo that has been customised for the current user. This could include:

setting ->uservisible=false (to hide the activity entirely)
setting ->inactive to true (to grey it out) and maybe also adding text to the end of ->restrictions (to optionally display information about why the user can't access it, in case they wonder why it is greyed out)
setting ->afterlink = '16 unread' (to display dynamic data)
setting ->editicons (to add a custom editing icon for this module)

PERFORMANCE CONCERNS: None. Of standard modules, only the forum will implement this and it will use the same code as at present. Custom modules will need to be written carefully in a similar manner so that they also perform well (ie do any queries once for whole course and store in global cache, not once per module).

NOTE: Maybe this function also needs access to the rest of $modinfo? But it hasn't all been completely filled in because this function obviously hasn't run... still we could provide it if required...

Documentation