/**
 * @file  packet.c
 * @brief ENet packet management functions
 */
#include <string.h>
#define ENET_BUILDING_LIB 1
#include "enet/enet.h"

/** @defgroup Packet ENet packet functions
 *  @{
 */

/** Creates a packet that may be sent to a peer.
 *  @param data         initial contents of the packet's data; the packet's data will remain uninitialized if data is NULL.
 *  @param dataLength   size of the data allocated for this packet
 *  @param flags        flags for this packet as described for the ENetPacket structure.
 *  @returns the packet on success, NULL on failure
 */
ENetPacket * enet_packet_create(const void *data, size_t dataLength, enet_uint32 flags) {
    ENetPacket *packet = (ENetPacket *) enet_malloc(sizeof(ENetPacket));

    if (packet == NULL) {
        return NULL;
    }

    if (flags & ENET_PACKET_FLAG_NO_ALLOCATE) {
        packet->data = (enet_uint8 *) data;
    } else if (dataLength <= 0)   {
        packet->data = NULL;
    } else {
        packet->data = (enet_uint8 *) enet_malloc(dataLength);
        if (packet->data == NULL) {
            enet_free(packet);
            return NULL;
        }

        if (data != NULL) {
            memcpy(packet->data, data, dataLength);
        }
    }

    packet->referenceCount = 0;
    packet->flags        = flags;
    packet->dataLength   = dataLength;
    packet->freeCallback = NULL;
    packet->userData     = NULL;

    return packet;
}

ENetPacket * enet_packet_create_offset(const void *data, size_t dataLength, size_t dataOffset, enet_uint32 flags) {
    ENetPacket *packet = (ENetPacket *) enet_malloc(sizeof(ENetPacket));

    if (packet == NULL) {
        return NULL;
    }

    if (flags & ENET_PACKET_FLAG_NO_ALLOCATE) {
        packet->data = (enet_uint8 *) data;
    } else if ((dataLength + dataOffset) <= 0)   {
        packet->data = NULL;
    } else {
        packet->data = (enet_uint8 *) enet_malloc(dataLength + dataOffset);
        if (packet->data == NULL) {
            enet_free(packet);
            return NULL;
        }

        if (data != NULL) {
            memcpy(packet->data + dataOffset, data, dataLength);
        }
    }

    packet->referenceCount = 0;
    packet->flags        = flags;
    packet->dataLength   = dataLength + dataOffset;
    packet->freeCallback = NULL;
    packet->userData     = NULL;

    return packet;
}

/** Destroys the packet and deallocates its data.
 *  @param packet packet to be destroyed
 */
void enet_packet_destroy(ENetPacket *packet) {
    if (packet == NULL) {
        return;
    }

    if (packet->freeCallback != NULL) {
        (*packet->freeCallback)(packet);
    }
    if (!(packet->flags & ENET_PACKET_FLAG_NO_ALLOCATE) &&
      packet->data != NULL)
    {
        enet_free(packet->data);
    }
    enet_free(packet);
}

/** Attempts to resize the data in the packet to length specified in the
 *  dataLength parameter
 *  @param packet packet to resize
 *  @param dataLength new size for the packet data
 *  @returns 0 on success, < 0 on failure
 */
int enet_packet_resize(ENetPacket *packet, size_t dataLength) {
    enet_uint8 *newData;

    if (dataLength <= packet->dataLength || (packet->flags & ENET_PACKET_FLAG_NO_ALLOCATE)) {
        packet->dataLength = dataLength;

        return 0;
    }

    newData = (enet_uint8 *) enet_malloc(dataLength);
    if (newData == NULL) {
        return -1;
    }

    memcpy(newData, packet->data, packet->dataLength);
    enet_free(packet->data);

    packet->data       = newData;
    packet->dataLength = dataLength;

    return 0;
}

static int initializedCRC32 = 0;
static enet_uint32 crcTable [256];

static enet_uint32 reflect_crc(int val, int bits) {
    int result = 0, bit;

    for (bit = 0; bit < bits; bit++) {
        if (val & 1) { result |= 1 << (bits - 1 - bit); }
        val >>= 1;
    }

    return result;
}

static void initialize_crc32(void) {
    int byte;

    for (byte = 0; byte < 256; ++byte) {
        enet_uint32 crc = reflect_crc(byte, 8) << 24;
        int offset;

        for (offset = 0; offset < 8; ++offset) {
            if (crc & 0x80000000) {
                crc = (crc << 1) ^ 0x04c11db7;
            } else {
                crc <<= 1;
            }
        }

        crcTable [byte] = reflect_crc(crc, 32);
    }

    initializedCRC32 = 1;
}

enet_uint32 enet_crc32(const ENetBuffer *buffers, size_t bufferCount) {
    enet_uint32 crc = 0xFFFFFFFF;

    if (!initializedCRC32) { initialize_crc32(); }

    while (bufferCount-- > 0) {
        const enet_uint8 *data = (const enet_uint8 *) buffers->data,
          *dataEnd = &data [buffers->dataLength];

        while (data < dataEnd) {
            crc = (crc >> 8) ^ crcTable [(crc & 0xFF) ^ *data++];
        }

        ++buffers;
    }

    return ENET_HOST_TO_NET_32(~crc);
}

/** @} */