#ifndef UCORE_TIMERS_H_
#define UCORE_TIMERS_H_

#include <stddef.h>
#include <sys/queue.h>
#include <sys/time.h>
#include "rbtree.h"


struct UCTimer;
struct UCTimers;
struct UCoreClock;

//internal timer states
enum {
    //not running
    UC_TIMER_INACTIVE   = 0,
    //running
    UC_TIMER_ACTIVE     = 1,
    //running and pending to be fired in this run of uc_timers_run
    UC_TIMER_PENDING    = 2
};

/** Callback function which is called when the timer fires.
 * @param timers timer engine
 * @param the timer that fired
 */

typedef void (*uc_timer_cb)(struct UCTimers *timers, struct UCTimer *timer);

/** Timer struct. The internal members must not be messed with, and must
 * be zeroed out before using/adding a timer for the first time.
 *
 * The external members are user controllable, the calback member must be set
 * and the cookie members can be used to stuff away things that's handy to use
 * in the callback function
 */
struct UCTimer {
    //Internal members 
    RBNode rb_node; //the RBNode will hold a data pointer to the
                    //the UCTimer it's a member of. We might get rid of that member, and use CONTAINER_OF
                    //to find the UCTimer from a RBNode (Or just cast it, it's the 1. member..)

    //absolute time when the timer should be fired
    struct timeval timeout;
    size_t seq; //needed to keep timeout unique
                //as the rbtree can only handle unique values
    unsigned char state;
    TAILQ_ENTRY(UCTimer) ready_entry; //entry in ready_list in UCTimers

    //External members

    //callback function
    uc_timer_cb callback;

    //user data for the callback
    void *cookie_ptr;
    int cookie_int;
    int cookie_int2;
};


/** Timer engine. Must be initialized onnce.*/
struct UCTimers {
    RBTree timer_tree;
    struct UCoreClock *uclock;
    size_t seq; //used to generate unique timers
    TAILQ_HEAD(, UCTimer) ready_list; //pending timers to be fired while inside uc_timers_run
};

/** Initialize a timer engine for use.
 *  An UCTimers can be accessed in only one thread.
 *
 * @param t UCTimers struct to initialize
 */
void uc_timers_init(struct UCTimers *t);

/** Initialize a timer engine for use, with a user supplied clock.
 *
 * @param t UCTimers struct to initialize
 */
void uc_timers_init_ex(struct UCTimers *t, struct UCoreClock *uclock);

/** Add a (one-shot) timer to the timer engine.
 * User fills in the callback and any cookie members of the UCTimer. The callback
 * will be called when the timer expires, and the timer is removed from the engine
 * User is responsible for the lifetime and memory of the UCTimer, which must exist until
 * te timer is fired or removed.
 *
 * @param timers timer engine to add timer to.
 * @param timer timer to add
 * @param sec seconds from now until the timer filres
 * @param usec microseconds (after the @sec) until the timer fires.
 */
void uc_timer_add(struct UCTimers *timers, struct UCTimer *timer, int sec, int usec);

/** Remove a timer.
 * Note, the timer memory must have been zeroed out or the timer must have been added at least once
 * before uc_timer_remove can be called on a UCTimer.
 * uc_timer_remove does nothing if the timer has expired.
 *
 * @param timers timer engine to remove from
 * @param timer timer to remove
 */
void uc_timer_remove(struct UCTimers *timers, struct UCTimer *timer);

/** Get time of the first timer that will run.
 *
 * @param timers timer engine to query.
 * @param first output parameter filled in with the expiry time of the first timer.
 * @return 0 on success and @first is filled in. non-0 if there's no pending timers.
 */
int uc_timers_first(const struct UCTimers *timers, struct timeval *first);

/** Get the number of timers the engine is tracking.
 * (This function is O(n) )
 *
 * @param timers timer engine to query
 * @return the number of timers the engine keeps
 */
size_t uc_timer_count(const struct UCTimers *timers);

/** Check if a timer is running (i.e. hasn't expired and fired)
 *
 * @param timer timer to query
 * @return 0 if the timer has expired (or was never added) non-0 if it's running (active or pending)
 */
int uc_timer_running(const struct UCTimer *timer);

/** Run one iteration of the  timer engine, firing off any expired timers.
 * Typically this is called once in an event loop.
 *
 * @param timers timer engine to run
 * @param now The curent time. The engine will fire all timers whose expiry time is
 *            prior to this value.
 * @return the number of timers fired, or negative if an error occured(presently no errors
 *         are possible and the return value is always >= 0
 **/
int uc_timers_run(struct UCTimers *timers);

//uc_timers_destroy(struct UCTimers *timers) is currently missing..

#endif