#ifndef UC_MBUF_H_
#define UC_MBUF_H_
#include <stdint.h>
#include <stddef.h>

#ifdef __GNUC__
#   define UC_INLINE inline __attribute__((always_inline))
#else
#   define UC_INLINE inline
#endif

enum UC_MBUF_FLAGS {
    UC_MBUF_FL_MALLOC        = 0x0001, //MBuf and MBuf->bufstart are seperatly malloc'd
    UC_MBUF_FL_MALLOC_BUF    = 0x0001, //MBuf is not malloc'd. MBuf->bufstart is malloc'd
    UC_MBUF_FL_MALLOC_INLINE = 0x0002, //MBuf is one big malloc. Can't be extended
    UC_MBUF_FL_STATIC        = 0x0004, //MBuf and MBuf->bustart is user controlled. Can't be extended
};

struct MBuf {
    /** prev/next pointer, user can use this for a linked list*/
    struct MBuf *prev;
    struct MBuf *next;
    /** Pointers the user can use to remember spots in
     * the data. (these must either be NULL pointers or point into
     * something in the buffer*/
    uint8_t *p1;
    uint8_t *p2;
    uint8_t *p3;
    uint8_t *p4;
    /**Arbitary pointer user can associate with the mbuf*/
    void *cookie;

    /*UC_MBUF_FLAGS. The upper 16 bits can be used by the application */
    uint32_t flags;
    /** Total no of bytes from bufstart*/
    uint32_t allocated;
    /** Start of the buffer*/
    uint8_t *bufstart;
    /** Start of the data in the buffer*/
    uint8_t *head;
    /** End of the buffer (one byte past the data) */
    uint8_t *tail;
    /** Internal data, if we allocate it inline */
    uint8_t inline_data[0];
};

/**
 * Concept: 
 * <--------- allocated ----------->
 *           <--- len  -->
 * +--------------------------------+
 * |Headroom| Data        |Tailroom |
 * +--------------------------------+
 * ^        ^             ^
 * |        |             |
 * |        |            tail
 * |       head
 * bufstart
 * 
 * Initially when empty, head == tail, and the length is 0. 
 * Data is added to the tail.
 *
 * If head == bufstart, there is no headroom
 * if tail points one past the allocated space, there is no 
 * tailroom (the buffer is full)
 *
 * Conventions:
 * push - prepend data to the buffer (in the head room part)
 *        (move head to the left)
 * pull - remove data from the beginning of the message.
 *        (move head to the right)
 * put  - Add data to the buffer.
 *        (move tail to the right)
 */

/** Allocate an mbuf with a length and headroom,
 * the buffer will have the flag UC_MBUF_FL_MALLOC
 * The total length of the buffer will be length+headroom
 *
 * @param len the initial length of the mbuf
 * @param the initial headroom of the mbuf
 * @return NULL if the allocation fails
 */
struct MBuf *uc_mbuf_new_hr(uint32_t len, uint32_t headroom);

/** As uc_mbuf_new_hr, but without any headroom*/
#define uc_mbuf_new(len) uc_mbuf_new_hr((len), 0)


/** Allocate an mbuf with a length and headroom,
 * the buffer will have the flag UC_MBUF_FL_MALLOC_INLINE
 * The total length of the buffer will be length+headroom
 *
 * @param len the initial length of the mbuf
 * @param the initial headroom of the mbuf
 * @return NULL if the allocation fails
 */
struct MBuf *uc_mbuf_new_inline_hr(uint32_t len, uint32_t headroom);

/** As uc_mbuf_new_inline_hr, but without any headroom*/
#define uc_mbuf_new_inline(len) uc_mbuf_new_inline_hr((len), 0)

/** @param mbuf the mbuf to free. (passing NULL is a no-op)*/
void uc_mbuf_free(struct MBuf *mbuf);

/** Create a new mbuf, with a copy of the data from the given
 * mbuf. The new mbuf will have the same headroom as the old one,
 * but no tailroom.
 *
 * @param mbuf mbuf to copy
 */
struct MBuf *uc_mbuf_copy_data(struct MBuf *mbuf);

/** Initialize an mbuf. This function is mostly used internally,
 * but can be used to e.g. create an mbuf based on a local array
 * (in which case UC_MBUF_FL_STATIC must be set), or other data 
 * whose memory is already allocated.
 *
 * The whole buffer must have len + headroom available data
 *
 * @param mbuf to initialise
 * @param buf start of the buffer
 * @param len length of the buffer (not including the headroom)
 * @param headroom the headroom in the buffer
 * @param flags The appropriate UC_MBUF_FLAGS
 */
void uc_mbuf_init(struct MBuf *mbuf, uint8_t *buf, uint32_t len, uint32_t headroom, uint32_t flags);

/** Zero out all the data in this mbuf, including the headroom
 *
 * @param mbuf mbuf to zero out
 */
void uc_mbuf_zero(struct MBuf *mbuf);

/**
 * @return the length of the data in this mbuf
 */
static UC_INLINE uint32_t uc_mbuf_len(struct MBuf *mbuf)
{
    return (uint32_t)(mbuf->tail - mbuf->head);
}

/**
 * @return the length of the tailroom in this mbuf
 */
static UC_INLINE uint32_t uc_mbuf_tailroom(struct MBuf *mbuf)
{
    return mbuf->allocated - (uint32_t)(mbuf->tail - mbuf->bufstart);
}

/**
 * @return the length of the headroom in this mbuf
 */
static UC_INLINE uint32_t uc_mbuf_headroom(struct MBuf *mbuf)
{
    return (uint32_t)(mbuf->head - mbuf->bufstart);
}


/** Append data data to this buffer
 * The returned pointer points at the end of the current 
 * data in the buffer, advancing the tail be size bytes . 
 * You need to insert the size bytes at in the returned pointer.
 *
 * @param size bytes to put in the buffer
 * @return NULL if the mbuf does not have room for the given size
 */
uint8_t *uc_mbuf_put(struct MBuf *mbuf, uint32_t size);

/** Prepend data to the buffer. The buffer needs to have enough
 * headroom to allow this.
 * The returned pointer points size bytes in front if the current
 * data in the buffer, retreating the head pointer by size butes
 * You need to insert the size bytes in the returned pointer.
 *
 * @oaram size bytes to prepend to the buffer
 * @return NULL if the mbuf does not have enough headroom
 */
uint8_t *uc_mbuf_push(struct MBuf *mbuf, uint32_t size);

/** Remove data from the buffer ("read" data from it) 
 * The returned pointer is the beginning of the data in the
 * buffer, advancing the head by size bytes.
 *
 * @param size number of bytes to pull
 * @return NULL if the buffer does not have at least size bytes
 **/
uint8_t *uc_mbuf_pull(struct MBuf *mbuf, uint32_t size);

/** Add more tailroom to an mbuf.
 * Can only be done with mbufs with either 
 * UC_MBUF_FL_MALLOC or UC_MBUF_FL_MALLOC_BUF.
 *
 * @param len additional tailroom to add to mbuf
 * @return 0 on success, otherwise failure
 *
 */
int uc_mbuf_extend_tailroom(struct MBuf *mbuf, uint32_t len);

/** Get a pointer to the data of the buffer
 * 
 * @return pointer to the start of the data (head)
 */
static UC_INLINE uint8_t *uc_mbuf_head(struct MBuf* mbuf)
{
    return mbuf->head;
}

#undef UC_INLINE

#endif