/* Routines for binary encoding of vote messages
 * Wire Format:
 *                                1  1  1  1  1  1
 *  0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 * |     Magic       |Flags|       ZERO            |
 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 * |                  Candidate ID                 |
 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 * |                                               |
 * |         Vote Count (only in response)         |
 * |                                               |
 * |                                               |
 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 *
 */

#include <string.h>
#include <stdbool.h>
#include <stdlib.h>
#include <stdint.h>
#include <netinet/in.h>
#include "Practical.h"
#include "VoteProtocol.h"

enum {
  REQUEST_SIZE = 4,
  RESPONSE_SIZE = 12,
  COUNT_SHIFT = 32,
  INQUIRE_FLAG = 0x0100,
  RESPONSE_FLAG = 0x0200,
  MAGIC = 0x5400,
  MAGIC_MASK = 0xfc00
};

typedef struct voteMsgBin voteMsgBin;

struct voteMsgBin {
  uint16_t header;
  uint16_t candidateID;
  uint32_t countHigh;
  uint32_t countLow;
};

size_t Encode(VoteInfo *v, uint8_t *outBuf, size_t bufSize) {
  if ((v->isResponse && bufSize < sizeof(voteMsgBin)) || bufSize < 2
      * sizeof(uint16_t))
    DieWithUserMessage("Output buffer too small", "");
  voteMsgBin *vm = (voteMsgBin *) outBuf;
  memset(outBuf, 0, sizeof(voteMsgBin)); // Be sure
  vm->header = MAGIC;
  if (v->isInquiry)
    vm->header |= INQUIRE_FLAG;
  if (v->isResponse)
    vm->header |= RESPONSE_FLAG;
  vm->header = htons(vm->header); // Byte order
  vm->candidateID = htons(v->candidate); // Know it will fit, by invariants
  if (v->isResponse) {
    vm->countHigh = htonl(v->count >> COUNT_SHIFT);
    vm->countLow = htonl((uint32_t) v->count);
    return RESPONSE_SIZE;
  } else {
    return REQUEST_SIZE;
  }
}

/* Extract message info from given buffer.
 * Leave input unchanged.
 */
bool Decode(uint8_t *inBuf, size_t mSize, VoteInfo *v) {

  voteMsgBin *vm = (voteMsgBin *) inBuf;

  // Attend to byte order; leave input unchanged
  uint16_t header = ntohs(vm->header);
  if ((mSize < REQUEST_SIZE) || ((header & MAGIC_MASK) != MAGIC))
    return false;
  /* message is big enough and includes correct magic number */
  v->isResponse = ((header & RESPONSE_FLAG) != 0);
  v->isInquiry = ((header & INQUIRE_FLAG) != 0);
  v->candidate = ntohs(vm->candidateID);
  if (v->isResponse && mSize >= RESPONSE_SIZE) {
    v->count = ((uint64_t) ntohl(vm->countHigh) << COUNT_SHIFT)
        | (uint64_t) ntohl(vm->countLow);
  }
  return true;
}