#include <ring.h>
#include <stdlib.h>

/*
 * ring_new
 * build a new ring buffer object
 *
 * parameters:
 *   struct ring_t *buf - ring object (provided by user)
 *   size_t len - length to build the buffer
 *
 * returns the ring object (buf) or NULL if there is an error
 */

struct ring_t *ring_new(struct ring_t *buf, size_t len) {
  if(len < 3) {
    return NULL; 
  }

  buf->buflen = len + 1;
  buf->buffer = malloc(buf->buflen);

  if(buf->buffer == NULL) {
    return NULL;
  }

  buf->begin = buf->buffer;
  buf->end = buf->buffer + len;
  buf->writer = buf->buffer;
  buf->reader = buf->buffer;
  return buf;
}

/*
 * ring_write
 * write data into the buffer
 *
 * parameters:
 *   struct ring_t *buf - ring object (provided by user)
 *   char *str - string to write to the buffer
 *   size_t orig_len - length of the string to write
 *
 * returns the number of characters left to write
 */

size_t ring_write(struct ring_t *buf, char *str, size_t orig_len) {
  size_t len = orig_len;

  while(len > 0) {
    if(buf->writer == buf->end && buf->reader == buf->begin) {
      break;
    } else if(buf->writer == buf->end + 1) {
      buf->writer = buf->begin;
    }

    if(buf->writer == buf->reader - 1) {
      break;
    }

    *buf->writer = *str;
    --len, ++str, ++buf->writer;
  }

  return len;
}

/*
 * ring_read
 * read data from the buffer
 *
 * parameters:
 *   struct ring_t *buf - ring object (provided by user)
 *   size_t *len - length of the string to read (modified to the number of characters read)
 *
 * returns the number of characters left to read
 */

char *ring_read(struct ring_t *buf, size_t *len) {
  char *str = malloc(*len);
  size_t index = 0;

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

  while(index < *len && buf->reader != buf->writer) {
    str[index] = *buf->reader;
    ++index, ++buf->reader;

    if(buf->reader == buf->end + 1) {
      buf->reader = buf->begin;
    }
  }

  if(index == 0) {
    *len = 0;
    return NULL;
  } else {
    *len -= index;
    return str;
  }
}

/*
 * ring_readln
 * read a line of data from the buffer
 *
 * parameters:
 *   struct ring_t *buf - ring object (provided by user)
 *   size_t *len - length of the line read
 *
 * returns the retreived line
 */

char *ring_readln(struct ring_t *buf, size_t *len) {
  *len = 0;
  char *index = buf->reader;

  while(*index != '\n' && index != buf->writer) {
    ++index, ++(*len);

    if(index == buf->end + 1) {
      index = buf->begin;
    }
  }

  if(*index != '\n') {
    *len = 0;
    return NULL;
  } else {
    size_t length = *len + 1;
    char *str = ring_read(buf, &length);

    if(str != NULL) {
      str[*len] = '\0';
    }

    return str;
  }
}

/*
 * ring_del
 * delete a ring buffer object
 *
 * parameters:
 *   struct ring_t *buf - ring object (provided by user)
 *
 * returns nothing
 */

void ring_del(struct ring_t *buf) {
  buf->buflen = 0;
  buf->begin = NULL;
  buf->end = NULL;
  buf->writer = NULL;
  buf->reader = NULL;
  free(buf->buffer);
}