#ifndef UCORE_WQUEUE_H_
#define UCORE_WQUEUE_H_

#include "mbuf.h"
#include "iomux.h"

enum UC_WQ_RESULT {
    /** INdicates the MBuf was fully processed and can be freed*/
    UC_WQ_DONE = 1,
    /** Indicates the MBuf was not fully processed, and will not be freed */
    UC_WQ_PARTIAL = 0,
    /** Indicats an error and further processing of the wqueue should not be done*/
    UC_WQ_ABORT = -1
};

/**
 * Callback that will be called when data can be written to the fd.
 * The return value from this function must be strictly followed.
 * Write events on an fd will be processed before read events.
 *
 * For one write event, the callback is called for all mbufs in the queue,
 * as long as UC_WQ_DONE is returned.
 *
 * If UC_WQ_PARTIAL is returned, queue processing is stopped, but any read
 * events will also be dispatched.
 * If UC_WQ_ABORT is done, no further processing is done, and the wqueue is not
 * acccessed any more, making it safe to destroy the wqueue before UC_WQ_ABORY is
 * returned.
 *
 * @param mux associated IOMux
 * @param the fd of the current wqueue
 * @return UC_WQ_DONE when the entire mbuf was written, and its memory can be released.
 *          UC_WQ_PARTIAL when partial data was written, the mbuf is not released,
 *          queue procesing is stopped, and the callback will be passed the same mbuf
 *          on the next write event, you need to provide a mean to know where to
 *          start processing the mbuf on the next event.
 *          UC_WQ_ABORT when all processing, both write and read events should be aborted
 *          for this event.
 * 
 */
typedef enum UC_WQ_RESULT (*wqueue_write_cb)(struct IOMux *mux, struct IOMuxFD *fd, struct MBuf *mbuf);

/**
 * Callback when read events are indicated.
 * The return value is currently unused. The wqueue is not accessed after
 * this callback returns, making it safe to destroy the wqueue before
 * the callback function returns.
 *
 * @param mux associated IOMux
 * @param the fd of the current wqueue
 */
typedef enum UC_WQ_RESULT (*wqueue_read_cb)(struct IOMux *mux, struct IOMuxFD *fd);

/** Represents a queue of data to write.
 */
struct UCWQueue {
    struct IOMuxFD fd;
    struct TailQ queue;
    struct IOMux *mux;
    wqueue_read_cb read_cb;
    wqueue_write_cb write_cb;

    unsigned int queue_len;
};

/** Initialize a wqueue. After this you need to 
 *  set the read_cb, write_cb. Set the fd.fd and fd.event
 *  and register the fd with the same IOMux as the mux parameter.
 *  Do not set the fd.callback.
 *
 *  Note that on some IOMux'es the read_cb may be called as 
 *  a result of read events, even if you havn't enabled
 *  MUX_EV_READ events.
 *
 *  The wqueue manages a queue of MBufs, and will enable write events 
 *  on the IOMux *  and call the write_cb when messages are enqueued.
 *
 *  @param wqueue wqueue to initialize
 *  @param mux the IOMux that you intend to register wqueue->fd on.
 */
void uc_wqueue_init(struct UCWQueue *wqueue, struct IOMux *mux);

/**
 * Frees all the enqueued mbufs.
 *
 * @return code from iomux_update_events, when write events need
 * to be unregisrted on the IOMux
 */
int uc_wqueue_clear(struct UCWQueue *wqueue);

/** 
 * Enqueues an mbuf onto the wqueue. The wqueue will take ownership
 * of the mbuf, and will be responsible for releasing its memory, 
 * mbuf->entry will be used by the wqueue.
 *
 * Write events will be enabled on the IOMux, and on write events
 * the write_cb is invoked for each message in the queue.
 *
 * @param wqueueu
 * @param mbuf mbuf to enqueue
 * @return code from iomux_update_events, when write events need
 * to be regisrted on the IOMux
 */
int uc_wqueue_enqueue(struct UCWQueue *wqueue, struct MBuf *mbuf);


/**
 *  Immediately write mbufs.
 *  This invokes the wqueue write callback immediately, just as if an
 *  write event from the IOMux had happened.
 *  
 *  As for a normal write event, the entire queue might not be 
 *  written, if the associated write callback detectes it cannot write
 *  more data.
 *
 *  @param wqueue
 *
 *  return 0 if no error occured, -1 if the write callback returned
 *  UC_WQ_ABORT
 */
int uc_wqueue_flush(struct UCWQueue *wqueue);

#endif