/*
 *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

// A ring buffer to hold arbitrary data. Provides no thread safety. Unless
// otherwise specified, functions return 0 on success and -1 on error.

#include "ring_buffer.h"

#include <stddef.h>  // size_t
#include <stdlib.h>
#include <string.h>

enum Wrap {
  SAME_WRAP,
  DIFF_WRAP
};

struct RingBuffer {
  size_t read_pos;
  size_t write_pos;
  size_t element_count;
  size_t element_size;
  enum Wrap rw_wrap;
  char* data;
};

// Get address of region(s) from which we can read data.
// If the region is contiguous, |data_ptr_bytes_2| will be zero.
// If non-contiguous, |data_ptr_bytes_2| will be the size in bytes of the second
// region. Returns room available to be read or |element_count|, whichever is
// smaller.
static size_t GetBufferReadRegions(RingBuffer* buf,
                                   size_t element_count,
                                   void** data_ptr_1,
                                   size_t* data_ptr_bytes_1,
                                   void** data_ptr_2,
                                   size_t* data_ptr_bytes_2) {

  const size_t readable_elements = WebRtc_available_read(buf);
  const size_t read_elements = (readable_elements < element_count ?
      readable_elements : element_count);
  const size_t margin = buf->element_count - buf->read_pos;

  // Check to see if read is not contiguous.
  if (read_elements > margin) {
    // Write data in two blocks that wrap the buffer.
    *data_ptr_1 = buf->data + buf->read_pos * buf->element_size;
    *data_ptr_bytes_1 = margin * buf->element_size;
    *data_ptr_2 = buf->data;
    *data_ptr_bytes_2 = (read_elements - margin) * buf->element_size;
  } else {
    *data_ptr_1 = buf->data + buf->read_pos * buf->element_size;
    *data_ptr_bytes_1 = read_elements * buf->element_size;
    *data_ptr_2 = NULL;
    *data_ptr_bytes_2 = 0;
  }

  return read_elements;
}

RingBuffer* WebRtc_CreateBuffer(size_t element_count, size_t element_size) {
  RingBuffer* self = NULL;
  if (element_count == 0 || element_size == 0) {
    return NULL;
  }

  self = malloc(sizeof(RingBuffer));
  if (!self) {
    return NULL;
  }

  self->data = malloc(element_count * element_size);
  if (!self->data) {
    free(self);
    self = NULL;
    return NULL;
  }

  self->element_count = element_count;
  self->element_size = element_size;

  return self;
}

int WebRtc_InitBuffer(RingBuffer* self) {
  if (!self) {
    return -1;
  }

  self->read_pos = 0;
  self->write_pos = 0;
  self->rw_wrap = SAME_WRAP;

  // Initialize buffer to zeros
  memset(self->data, 0, self->element_count * self->element_size);

  return 0;
}

void WebRtc_FreeBuffer(void* handle) {
  RingBuffer* self = (RingBuffer*)handle;
  if (!self) {
    return;
  }

  free(self->data);
  free(self);
}

size_t WebRtc_ReadBuffer(RingBuffer* self,
                         void** data_ptr,
                         void* data,
                         size_t element_count) {

  if (self == NULL) {
    return 0;
  }
  if (data == NULL) {
    return 0;
  }

  {
    void* buf_ptr_1 = NULL;
    void* buf_ptr_2 = NULL;
    size_t buf_ptr_bytes_1 = 0;
    size_t buf_ptr_bytes_2 = 0;
    const size_t read_count = GetBufferReadRegions(self,
                                                   element_count,
                                                   &buf_ptr_1,
                                                   &buf_ptr_bytes_1,
                                                   &buf_ptr_2,
                                                   &buf_ptr_bytes_2);

    if (buf_ptr_bytes_2 > 0) {
      // We have a wrap around when reading the buffer. Copy the buffer data to
      // |data| and point to it.
      memcpy(data, buf_ptr_1, buf_ptr_bytes_1);
      memcpy(((char*) data) + buf_ptr_bytes_1, buf_ptr_2, buf_ptr_bytes_2);
      buf_ptr_1 = data;
    } else if (!data_ptr) {
      // No wrap, but a memcpy was requested.
      memcpy(data, buf_ptr_1, buf_ptr_bytes_1);
    }
    if (data_ptr) {
      // |buf_ptr_1| == |data| in the case of a wrap.
      *data_ptr = buf_ptr_1;
    }

    // Update read position
    WebRtc_MoveReadPtr(self, (int) read_count);

    return read_count;
  }
}

size_t WebRtc_WriteBuffer(RingBuffer* self,
                          const void* data,
                          size_t element_count) {
  if (!self) {
    return 0;
  }
  if (!data) {
    return 0;
  }

  {
    const size_t free_elements = WebRtc_available_write(self);
    const size_t write_elements = (free_elements < element_count ? free_elements
        : element_count);
    size_t n = write_elements;
    const size_t margin = self->element_count - self->write_pos;

    if (write_elements > margin) {
      // Buffer wrap around when writing.
      memcpy(self->data + self->write_pos * self->element_size,
             data, margin * self->element_size);
      self->write_pos = 0;
      n -= margin;
      self->rw_wrap = DIFF_WRAP;
    }
    memcpy(self->data + self->write_pos * self->element_size,
           ((const char*) data) + ((write_elements - n) * self->element_size),
           n * self->element_size);
    self->write_pos += n;

    return write_elements;
  }
}

int WebRtc_MoveReadPtr(RingBuffer* self, int element_count) {
  if (!self) {
    return 0;
  }

  {
    // We need to be able to take care of negative changes, hence use "int"
    // instead of "size_t".
    const int free_elements = (int) WebRtc_available_write(self);
    const int readable_elements = (int) WebRtc_available_read(self);
    int read_pos = (int) self->read_pos;

    if (element_count > readable_elements) {
      element_count = readable_elements;
    }
    if (element_count < -free_elements) {
      element_count = -free_elements;
    }

    read_pos += element_count;
    if (read_pos > (int) self->element_count) {
      // Buffer wrap around. Restart read position and wrap indicator.
      read_pos -= (int) self->element_count;
      self->rw_wrap = SAME_WRAP;
    }
    if (read_pos < 0) {
      // Buffer wrap around. Restart read position and wrap indicator.
      read_pos += (int) self->element_count;
      self->rw_wrap = DIFF_WRAP;
    }

    self->read_pos = (size_t) read_pos;

    return element_count;
  }
}

size_t WebRtc_available_read(const RingBuffer* self) {
  if (!self) {
    return 0;
  }

  if (self->rw_wrap == SAME_WRAP) {
    return self->write_pos - self->read_pos;
  } else {
    return self->element_count - self->read_pos + self->write_pos;
  }
}

size_t WebRtc_available_write(const RingBuffer* self) {
  if (!self) {
    return 0;
  }

  return self->element_count - WebRtc_available_read(self);
}