/** \file event.h

  Functions for handling event triggers

  Because most of these functions can be called by signal
  handler, it is important to make it well defined when these
  functions produce output or perform memory allocations, since
  such functions may not be safely called by signal handlers.


*/
#ifndef FISH_EVENT_H
#define FISH_EVENT_H

#include <memory>

#include "common.h"

/**
   The signal number that is used to match any signal
*/
#define EVENT_ANY_SIGNAL -1

/**
   The process id that is used to match any process id
*/
#define EVENT_ANY_PID 0

/**
   Enumeration of event types
*/
enum
{
    EVENT_ANY, /**< Matches any event type (Not always any event, as the function name may limit the choice as well */
    EVENT_SIGNAL, /**< An event triggered by a signal */
    EVENT_VARIABLE, /**< An event triggered by a variable update */
    EVENT_EXIT, /**< An event triggered by a job or process exit */
    EVENT_JOB_ID, /**< An event triggered by a job exit */
    EVENT_GENERIC, /**< A generic event */
}
;

/**
   The structure which represents an event. The event_t struct has
   several event-related use-cases:

   - When used as a parameter to event_add, it represents a class of events, and function_name is the name of the function which will be called whenever an event matching the specified class occurs. This is also how events are stored internally.
   - When used as a parameter to event_get, event_remove and event_fire, it represents a class of events, and if the function_name field is non-zero, only events which call the specified function will be returned.
*/
struct event_t
{
public:

    /** Type of event */
    int type;

    /** The type-specific parameter. The int types are one of the following:

         signal: Signal number for signal-type events.Use EVENT_ANY_SIGNAL to match any signal
             pid: Process id for process-type events. Use EVENT_ANY_PID to match any pid.
             job_id: Job id for EVENT_JOB_ID type events
      */
    union
    {
        int signal;
        int job_id;
        pid_t pid;
    } param1;

    /** The string types are one of the following:

          variable: Variable name for variable-type events.
          param: The parameter describing this generic event.
    */
    wcstring str_param1;

    /**
       The name of the event handler function
    */
    wcstring function_name;

    /**
       The argument list. Only used when sending a new event using
       event_fire. In all other situations, the value of this variable
       is ignored.
    */
    wcstring_list_t arguments;

    event_t(int t);
    ~event_t();

    static event_t signal_event(int sig);
    static event_t variable_event(const wcstring &str);
    static event_t generic_event(const wcstring &str);
};

/**
   Add an event handler

   May not be called by a signal handler, since it may allocate new memory.
*/
void event_add_handler(const event_t &event);

/**
   Remove all events matching the specified criterion.

   May not be called by a signal handler, since it may free allocated memory.
*/
void event_remove(const event_t &event);

/**
   Return all events which match the specified event class

   This function is safe to call from a signal handler _ONLY_ if the
   out parameter is null.

   \param criterion Is the class of events to return. If the criterion has a non-null function_name, only events which trigger the specified function will return.
   \param out the list to add events to. May be 0, in which case no events will be added, but the result count will still be valid

   \return the number of found matches
*/
int event_get(const event_t &criterion, std::vector<event_t *> *out);

/**
    Returns whether an event listener is registered for the given signal.
    This is safe to call from a signal handler.
*/
bool event_is_signal_observed(int signal);

/**
   Fire the specified event. The function_name field of the event must
   be set to 0. If the event is of type EVENT_SIGNAL, no the event is
   queued, and will be dispatched the next time event_fire is
   called. If event is a null-pointer, all pending events are
   dispatched.

   This function is safe to call from a signal handler _ONLY_ if the
   event parameter is for a signal. Signal events not be fired, by the
   call to event_fire, instead they will be fired the next time
   event_fire is called with anull argument. This is needed to make
   sure that no code evaluation is ever performed by a signal handler.

   \param event the specific event whose handlers should fire. If
   null, then all delayed events will be fired.
*/
void event_fire(const event_t *event);

/** Like event_fire, but takes a signal directly. */
void event_fire_signal(int signal);

/**
   Initialize the event-handling library
*/
void event_init();

/**
   Destroy the event-handling library
*/
void event_destroy();

/**
   Free all memory used by the specified event
*/
void event_free(event_t *e);

/**
   Returns a string describing the specified event.
*/
wcstring event_get_desc(const event_t &e);

/**
   Fire a generic event with the specified name
*/
void event_fire_generic(const wchar_t *name, wcstring_list_t *args = NULL);

#endif