#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <netinet/in.h>
#include "Practical.h"

/* Read 2-byte length and place in big-endian order.
 * Then read the indicated number of bytes.
 * If the input buffer is too small for the data, truncate to fit and
 * return the negation of the *indicated* length.  Thus a negative return
 * other than -1 indicates that the message was truncated.
 * (Ambiguity is possible only if the caller passes an empty buffer.)
 * Input stream is always left empty.
 */
int GetNextMsg(FILE *in, uint8_t *buf, size_t bufSize) {
  uint16_t mSize = 0;
  uint16_t extra = 0;

  if (fread(&mSize, sizeof(uint16_t), 1, in) != 1)
    return -1;
  mSize = ntohs(mSize);
  if (mSize > bufSize) {
    extra = mSize - bufSize;
    mSize = bufSize; // Truncate
  }
  if (fread(buf, sizeof(uint8_t), mSize, in) != mSize) {
    fprintf(stderr, "Framing error: expected %d, read less\n", mSize);
    return -1;
  }
  if (extra > 0) { // Message was truncated
    uint8_t waste[BUFSIZE];
    fread(waste, sizeof(uint8_t), extra, in); // Try to flush the channel
    return -(mSize + extra); // Negation of indicated size
  } else
    return mSize;
}

/* Write the given message to the output stream, followed by
 * the delimiter.  Precondition: buf[] is at least msgSize.
 * Returns -1 on any error.
 */
int PutMsg(uint8_t buf[], size_t msgSize, FILE *out) {
  if (msgSize > UINT16_MAX)
    return -1;
  uint16_t payloadSize = htons(msgSize);
  if ((fwrite(&payloadSize, sizeof(uint16_t), 1, out) != 1) || (fwrite(buf,
      sizeof(uint8_t), msgSize, out) != msgSize))
    return -1;
  fflush(out);
  return msgSize;
}