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====== General information ======

Plugins enhance the game with optional features.

They allow for special behaviours that can't be done through simple mapping, or require complex scripting actions - the only thing limiting is the imagination of the coder!

Current examples include:
  * message boards, on which players can leave messages
  * Imperial Post Office, that lets players exchange ingame mail
  * playing slot machines at casinos
  * [[:dev_todo:python_guilds|improved guild system]] - currently being tested



===== Existing plugins =====

Currently existing plugins are :
^ Name ^ Description ^ Status ^ Title for the event object ^
| [[cfanim]] | animate objects | experimental | Animator |
| [[cfpython]] | run Python scripts | working | Python |
| [[cflogger]] | logs events to a SQLITE database | experimental | SqliteLogger |
| [[cfnewspaper]] | newspaper generation | experimental | Newspaper |
| [[citylife]] | adds/removes NPCs in maps, to make towns lively | apparently stable | citylife |
| [[cfrhg]] | random house generator, adds random maps to unlinked exits in specified maps | apparently stable | cfrhg |
| <del>[[cf_darcap]]</del> | <del>Darcap specific plugin, handling various things</del> | <del>needs testing</del> replaced by quest/dialog mechanism |
| template | not a real plugin, but a skeleton to create new ones | up-to-date | |



====== Hooks ======

Plugin system works through //hooks//. A hook is merely an event taking place, to which plugins can respond. Default server behavior can sometimes be overridden totally.

The full list of events corresponds to the //event_xxx// archetypes, found in the [[http://crossfire.svn.sourceforge.net/viewvc/crossfire/arch/trunk/system/|/system folder of the archetypes]].

Events are either //global// or //object-specific//. Examples of global events include a player joining or exiting the game, a map being loaded. Examples of object-specific events include an item being applied, a player attacking a monster.

FIXME check parameters and such :)


===== Hooking to an object-specific event =====

Just add an //event_xxx// object into your object's inventory, and fill the ''title'' field with the plugin's title as defined in the table above. See the specific plugin documentation for optional arguments that need to be set to that object. Note that the ''slaying'' field must be set too whatever the plugin.

When an object-specific event is raised, affected object is sent to the plugin.

For some events, returning a non-zero value will prevent the default server processing to take place, allowing to override things. FIXME be more specific :)

The plugin registered function will get the following parameters. See specific events for the meaning of the field.
  * op: ''object*'' which is the current object containing the event.
  * activator: ''object*'', can be NULL.
  * third: ''object*'', can be NULL.
  * message: ''const char*'', can be NULL.
  * fix: ''int'' {FIXME} meaning?
  * event: ''object*'' representing the actual event object linking to plugin. Will be ''NULL'' for global events. Its fields mean:
    * ''subtype'': event code
    * ''title'': plugin name
    * ''slaying'': plugin specific value
  * talk: ''talk_info*'' (see dialog.h file) containing dialog information. Only meaningful and not NULL for an EVENT_SAY event.

Follows the full list of object-specific events.

==== Apply ====
Archetype: event_apply

This event is generated whenever the object is applied or unapplied.


==== Attacked ====
Archetype: event_attack

Bound to an object, it is triggered when the object is attacked (with a weapon or a spell). In this case, "op" is the object, "activator" is what hits the item, "third" is the weapon or spell used (can be equal to "activator"). Returning a non-zero value cancels the attack.

==== Attacks ====
Archetype: event_attacks

This event is used in two cases:
  * bound to a (hand) weapon, it is triggered each time the weapon is used by a player to attack something; this can typically be used to generate special effects when you hit a monster. In this case, "op" is the weapon, "activator" the player and "third" the item attacked. Returning a non-zero value cancels the attack
  * bound to an arrow, it is triggered when the arrow hits something. "op" is the arrow, "activator" what really hits (arrow can have stuff inside), "third" is the victim. Returning a non-zero value cancels the attack

==== Bought ====
Archetype: event_bought

This event is triggered when the associated object was paid by a player, but not yet marked as paid.

"op" is the item being bought, "activator" is the player buying.

Returning a non-zero value leaves the item as unpaid and prevents the player from buying still unpaid items.
==== Close ====
Archetype: event_close

Generated when a container is closed.

==== Death ====
Archetype: event_death

Generated when the object dies.

==== Destroy ====
Archetype: event_destroy

Used when the object is totally destroyed, either by a map reset or destruction by another item.

"op" is the object being destroyed.

The return value is ignored.
==== Drop ====
Archetype: event_drop

Generated when the object is dropped on the floor.
''WhoAmI'' is about to be dropped by ''WhoIsActivator''

Return 0 to allow the drop, any other value to prevent dropping.

==== Pickup ====
Archetype: event_pickup

''WhoAmI'' is about to be picked up by ''WhoIsActivator'' and put into ''WhoIsOther'' (will be WhoIsActivator if put into inventory, or container else). Event is called when all checks (weight, container, levitation, ...) are done, creature picking up can really pick up.

Return 0 to allow to pickup, non zero to prevent from picking up.

==== Say ====
Archetype: event_say

Generated when someone says something around the object.

==== Selling ====
Archetype: event_selling

Generated when ''op'' is being sold by ''activator''. Return 1 to prevent selling, 0 to allow.

==== Stop ====
Archetype: event_stop

Generated for a thrown object, when the object is stopped for some reason (wall, max distance, ...). Will not be called when hitting a living creature, but ''Attack'' is called.

Note that the object is inside a dummy container at this time. It can be removed.

==== Time ====
Archetype: event_time

Generated each time the object gets an opportunity to move.

Return non zero value to prevent the regular processing to occur.

==== Throw ====
Archetype: event_throw

Generated when the object is thrown. The object is still in the thrower's inventory, and can be removed to abort being thrown.



==== Trigger ====
Archetype: event_trigger

Used for various objects, like traps, teleporters or triggers. Generated when those objects are used (for example, when a player passes through a teleporter).

  * for a scroll/book/tome, generated when player writes into the item. ''op'' is the item, ''activator'' is the player, ''message'' is what player is trying to write. Return non zero to prevent writing. Event is generated before length is checked for overflow.
  * for a magical scroll, generated when player inscribes a spell in the item. ''op'' is the item, ''activator'' is the player, ''third'' is the spell being inscribed. Return non zero to prevent writing. Event is generated after all checks are done (player can really write the scroll, he didn't read it accidentally) but before sp/gr are decreased.
  * for teleporters (type 41), exits (type 66), directors (type 112), check inventory (type 64), swamps (type 138) called when something moves on the spot ; process can be aborted by returning a non zero value
  * for doors (type 23) and locked_door (type 20), called before a lockpicking is attempted ; no check (blocked or not, can be picked or not) was yet done, except that the item is a (locked) door ; process can be aborted by returning a non-zero value. ''op'' is the door, ''activator'' the player, and ''third'' the lockpicking skill

==== Timer ====
Archetype: event_timer

Generated when the timer connected triggered.


===== Hooking to global events =====

Those concern the game as a whole or can't be bound to a specific object. Those events may be "registered" by a plugin (it means that the plugin requests to get a message each time one of those events happens).

Plugin should use provided server callbacks to register itself. See the specific plugin documentation.

^ Event ^ Description ^ Parameters ^ Note ^
| Born | Generated when a new character is created. | ''object*'' pointing to player | |
| Clock | Generated at each game loop. | (none) | When no player is logged, the loop "stops", meaning that clock events are not generated anymore! |
| Crash | Generated when a server crash does occur. It is not a recursive event, so if a crash occur from *inside* the crash event handling, it is not called a second time, preventing infinite loops to occur. | (none) | This event is not implemented for now. |
| Gdeath | Generated whenever a player dies. | ''object*'' pointing to player, ''object*'' pointing to killer (can be NULL). | |
| Gkill | Generated whenever something/someone is killed. | ''object*'' pointing to dead object, ''object*'' pointing to killer. | |
| Kick | Generated when a player was kicked by a DM. | ''object*'' pointing to kicked player, ''const char*'' containing the parameter the DM used to kick | |
| Login | Generated whenever a player logs into the game. | ''player*'' pointing to player, ''const char*'' containing the hostname of the client. | |
| Logout | Generated whenever a player logs out of the game. | ''player*'' pointing to player, ''const char*'' containing the hostname of the client. | |
| Mapenter | Generated whenever someone enters a map. | ''object*'' pointing to the player, ''map*'' pointing to the map | |
| Mapleave | Generated whenever someone leaves a map. | ''object*'' pointing to the player, ''map*'' pointing to the map | |
| Mapload | Generated when a map is loaded in memory. | ''map*'' pointing to the map | |
| Mapreset | Generated each time a map is reset. | ''map*'' pointing to the map | |
| Mapunload | Generated when a map is being unloaded from memory. | ''map*'' pointing to the map | |
| Muzzle | Generated when a player was muzzled by a DM. | ''object*'' pointing to muzzled player, ''const char*'' containing the parameter the DM used to muzzle | |
| Remove | Generated when a player character is removed from the game ("quit" command). | ''object*'' pointing to the player | |
| Shout | Generated whenever someone shouts something. | ''object*'' pointing to talking player, ''const char*'' containing the message, ''int'' containing the priority | |
| Tell | Generated whenever someone tells something. | ''object*'' pointing to talking player, ''const char*'' containing the message, ''object*'' containing the recipient of the message | |

===== Registering a command =====

A plugin can register a custom game command. This command will work exactly like other commands from the player's point of view, accepting arguments and such.

A plugin can override an existing Crossfire command simply by declaring a command with the same name. Server command will be ignored.



====== Creating a plugin ======

===== Coding =====

Creating a plugin requires some knowledge of Crossfire's internals.

Plugins should use the ''common'' plugin helper library (located in ''[[http://crossfire.svn.sourceforge.net/viewvc/crossfire/server/trunk/plugins/common/|plugins/common]]'' directory), and use provided functions to manipulate Crossfire data. This library handles the actual communication with the server, and does some runtime checks on values.

**Warning:** a plugin can easily crash the server and/or corrupt files if care is not taken in data manipulation. Some checks are done through ''assert'', but there are times checks can't be done, thus it's the responsability of the plugin writer to take care of the plugin logic.

Some rules for plugin writing:
  * a plugin should never use ''free'' or equivalent on data the server allocated. Use provided free functions.
  * a plugin should never directly link to the Crossfire libraries (''common'', ''socket'', ...) and call functions. This may work on some platforms (Linux seems to handle that just fine), but will not work on others (example is Windows). Thus always use provided common plugin interface
  * a plugin should never change directly a value in a Crossfire object (player structure, ...), but use provided wrapping functions. Ideally, a plugin should not access directly that structure's memory to read values, either.

===== Client updating =====
FIXME expand/check: is an object removed automatically from player's inventory? is view updated? is fix_object() called?

===== Creating plugin skeleton =====

The simplest way is to look at the template plugin, available in [[http://crossfire.svn.sourceforge.net/viewvc/crossfire/server/trunk/plugins/template/|plugins/template directory of the server sources]]

In trunk, there now is a script, ''plugins/template/create_plugin.sh'', that will automate all steps below, excluding running ''configure && make && make install''. The syntax is: ''create_plugin.sh cftest "Test plugin"'' from the ''plugins/template'' directory.

In case you want to create a plugin manually, here are step by step instructions to create a basic plugin. Plugin name will be assumed to be ''cftest''. Paths are relative to server root.
  * create your plugin directory ''cftest'', in ''plugins''
  * copy ''plugins/template/plugin_template.c'' to ''plugins/template/cftest.c''
  * copy ''plugins/template/include/plugin_template.h'' to ''plugins/cftest/include/cftest.h''
  * modify ''plugins/cftest/cftest.c'' and ''plugins/cftest/include/cftest.h'' to correct the file names in the includes and such. You may also want to change the plugin's name
    * in particular, ''PLUGIN_NAME'' should be set to a unique identifier that will be your plugin's name for the ''slaying'' field of events.
  * copy ''plugins/template/Makefile.am'' to ''plugins/cftest/Makefile.am''
  * edit this file, to change all occurrences of ''plugin_template'' to ''cftest'' (that fixes paths and a few macros)
  * edit ''plugins/Makefile.am'', add ''cftest'' to the ''SUBDIRS'' line
  * edit ''configure.ac''
    * find the line ''AC_OUTPUT([Makefile''
    * somewhere in between other lines, add ''plugins/cftest/Makefile''

Whether you used the script or manually created a plugin, you need to do the following steps:
  * run ''autoconf && automake && configure && make && make install''
  * your plugin should be installed and ready to run

Now you need to write your actual plugin logic.

FIXME link to common plugin documentation (generated from doxygen hopefully)

FIXME specific Windows stuff / workspace/project issue


====== Plugin internals ======
This paragraph only concerns people wishing to write a plugin without using the ''common'' interface, or extending it. It is not intended for everyday use.

**Important note:** the API, and other parts, are valid for the ''trunk''. While it may still be correct for the ''branch'', one should ensure it works the same way. In particular, ''branch'' uses returned ''void*'' value to return values to plugin, whereas ''trunk'' uses an additional pointer parameter.


All functions available to plugins share the same prototype, ''f_plug_api'', defined in ''[[http://crossfire.svn.sourceforge.net/viewvc/crossfire/server/trunk/include/plugin.h?view=markup|include/plugin.h]]''.

===== Parameters sending =====
All parameters are sent through the use of variable argument lists, using the macros ''va_start'', ''va_arg'' and ''va_end''.

===== Data type =====
All functions accept as first parameter an ''int* type''. This parameter is used by server and plugin to exchange the type of a modified/returned value. Apart its presence for the variable argument list handling, it is used to check data coherence.

Data is exchanged as either a value or a pointer to a Crossfire structure. When the server needs to return a value to the plugin (for function wrapping, properties getting, ...), it expects the last argument to be a pointer to a variable of the returned value's type.

Data types available are defined in ''[[http://crossfire.svn.sourceforge.net/viewvc/crossfire/server/trunk/include/plugin.h?view=markup|include/plugin.h]]''.

Special case: when a ''CFAPI_STRING'' needs to be transferred, 2 parameters are expected, a pointer to the buffer and an integer to the buffer's size (which can't be always be determined automatically).

Note that signed/unsigned variables are transferred as signed, and should be cast appropriately when needed.

===== Basic data access =====
Access (get/set) to properties of the Crossfire objects, maps, structures is done through property wrappers.

Syntax for wrapper is eg ''cf_object_get_property(int* type, object* ob, int propcode, (property type)* value)''.

FIXME expand

===== Function wrapping =====
This wraps specific Crossfire functions. The calling convention is to send parameters in the same order as the wrapped function, and add as the last parameter a pointer to a variable of the same type as the return value which will receive the actual function return value. The hook return value will be a constant indicating whether the function was called or another error occurred (FIXME expand/check/make that true in the code ;p)

Let's take for example the wrapper for ''get_ob_key_value''.

The function prototype is:
<code>const char *get_ob_key_value(const object *op, const char *const key)</code>
(the return value is a [[dev:shared_strings|shared string]])

The ''[[http://crossfire.svn.sourceforge.net/viewvc/crossfire/server/trunk/server/plugins.c?view=markup|server-side]]'' hook is (note the NULL return value, since this is being worked on FIXME remove when fixed):
<code>
void* cfapi_object_get_key(int* type, ...)
{
    va_list args;
    const char* keyname;
    const char** value;
    object* op;

    va_start(args, type);
    op = va_arg(args, object*);
    keyname = va_arg(args, const char*);
    value = va_arg(args, const char**);
    va_end(args);

    *value = get_ob_key_value(op, keyname);
    *type = CFAPI_SSTRING;
    return NULL;
}
</code>

The plugin wrapper function, defined in ''[[http://crossfire.svn.sourceforge.net/viewvc/crossfire/server/trunk/plugins/common/plugin_common.c?view=markup|the common library]]'', is:

<code>
const char* cf_object_get_key(object* op, const char* keyname)
{
    int type;
    const char* value;
    cfapiObject_get_key(&type, op, keyname, &value);
    return value;
}
</code>

where ''cfapiObject_get_key'' is the matching hook.

===== Linked list handling =====
In some cases, objects are linked through the use of a ''next'' field, with a ''first_'' pointer somewhere (includes objects, friendly list, maps, archetypes). Since the ''next'' field will certainly be a property for the object, a convention for getting the ''first_'' item is to call this property getter with a NULL value for the object.

Thus, for the ''partylist'' linked list, the server-side functions looks like (parts edited out):
<code>
void* cfapi_party_get_property(int* type, ...)
{
[snipped]

    case CFAPI_PARTY_PROP_NEXT:
        rparty = va_arg(args, partylist**);
        *rparty = (party ? party->next : get_firstparty());
        *type = CFAPI_PPARTY;
        break;
</code>

The common library's function for first party is:
<code>
partylist* cf_party_get_first(void)
{
    int type;
    partylist* value;
    cfapiParty_get_property(&type, NULL, CFAPI_PARTY_PROP_NEXT, &value);
    assert(type == CFAPI_PPARTY);
    return value;
}
</code>

whereas access to the next party is done through:
<code>
partylist* cf_party_get_next(partylist* party)
{
    int type;
    partylist* value;
    cfapiParty_get_property(&type, party, CFAPI_PARTY_PROP_NEXT, &value);
    assert(type == CFAPI_PPARTY);
    return value;
}
</code>
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