/*
 * Copyright 2019 Google LLC. All Rights Reserved. This file and proprietary
 * source code may only be used and distributed under the Widevine Master
 * License Agreement.
 */

#include "odk_message.h"
#include "odk_message_priv.h"

#include <assert.h>
#include <stdio.h>
#include <string.h>

/*
 * C11 defines static_assert in assert.h. If it is available, force a compile
 * time error if the abstract ODK_Message struct size does not match its
 * implementation. If static_assert is not available, the runtime assert in
 * InitMessage will catch the mismatch at the time a message is initialized.
 */
#ifdef static_assert
static_assert(
    sizeof(ODK_Message) >= sizeof(ODK_Message_Impl),
    "sizeof(ODK_Message) is too small. You can increase "
    "SIZE_OF_ODK_MESSAGE_IMPL in odk_message.h to make it large enough.");
#endif

/*
 * Create a message structure that references a separate data buffer. An
 * initialized message is returned.  The caller is responsible for ensuring that
 * the buffer remains allocated for the lifetime of the message. |buffer| may be
 * NULL. Serialization into a message with a NULL buffer will cause the message
 * size to be incremented, but no data will be written into the message
 * buffer. This is useful for calculating the amount of space a message will
 * need, prior to doing the actual serialization. The buffer contents are
 * unchanged by this function.
 */
ODK_Message ODK_Message_Create(uint8_t* buffer, size_t capacity) {
  assert(sizeof(ODK_Message) >= sizeof(ODK_Message_Impl));
  ODK_Message message;
  ODK_Message_Impl* message_impl = (ODK_Message_Impl*)&message;
  message_impl->base = buffer;
  message_impl->capacity = capacity;
  message_impl->size = 0;
  message_impl->read_offset = 0;
  message_impl->status = MESSAGE_STATUS_OK;
  return message;
}

/*
 * Erase the contents of the message, set it to an empty state by setting the
 * message size and read offset to 0, effectively erasing the contents of the
 * message. The message data buffer pointer remains unchanged, i.e. the message
 * retains ownership of the buffer. The message buffer is zero-filled. The
 * message status is reset to MESSAGE_STATUS_OK.
 */
void ODK_Message_Clear(ODK_Message* message) {
  ODK_Message_Impl* message_impl = (ODK_Message_Impl*)message;
  assert(message_impl != NULL);
  message_impl->read_offset = 0;
  message_impl->size = 0;
  message_impl->status = MESSAGE_STATUS_OK;
  if (message_impl->base) {
    memset(message_impl->base, 0, message_impl->capacity);
  }
}

/*
 * Reset read pointer to the beginning of the message and clear status
 * so that parsing of the message will restart at the beginning of the
 * message. The message status is reset to MESSAGE_STATUS_OK.
 */
void ODK_Message_Reset(ODK_Message* message) {
  ODK_Message_Impl* message_impl = (ODK_Message_Impl*)message;
  assert(message_impl != NULL);
  message_impl->read_offset = 0;
  message_impl->status = MESSAGE_STATUS_OK;
}

/*
 * Return a pointer to the message data buffer, i.e. the message payload.
 * This is the buffer address that was passed into ODK_Message_Create.
 */
uint8_t* ODK_Message_GetBase(ODK_Message* message) {
  ODK_Message_Impl* message_impl = (ODK_Message_Impl*)message;
  assert(message_impl != NULL);
  return message_impl->base;
}

/*
 * Get the maximum number of bytes the message can hold.
 */
size_t ODK_Message_GetCapacity(ODK_Message* message) {
  ODK_Message_Impl* message_impl = (ODK_Message_Impl*)message;
  assert(message_impl != NULL);
  return message_impl->capacity;
}

/*
 * Get the number of bytes currently in the message
 */
size_t ODK_Message_GetSize(ODK_Message* message) {
  ODK_Message_Impl* message_impl = (ODK_Message_Impl*)message;
  assert(message_impl != NULL);
  return message_impl->size;
}

/*
 * Get the offset of where the next bytes will be read from the message data
 * buffer.
 */
size_t ODK_Message_GetOffset(ODK_Message* message) {
  ODK_Message_Impl* message_impl = (ODK_Message_Impl*)message;
  assert(message_impl != NULL);
  return message_impl->read_offset;
}

/*
 * Return the status of the message
 */
ODK_MessageStatus ODK_Message_GetStatus(ODK_Message* message) {
  ODK_Message_Impl* message_impl = (ODK_Message_Impl*)message;
  assert(message_impl != NULL);
  return message_impl->status;
}

/*
 * Set the message status to a specific value
 */
void ODK_Message_SetStatus(ODK_Message* message, ODK_MessageStatus status) {
  ODK_Message_Impl* message_impl = (ODK_Message_Impl*)message;
  assert(message_impl != NULL);
  /* preserve the first error */
  if (message_impl->status == MESSAGE_STATUS_OK) {
    message_impl->status = status;
  }
}

/*
 * Set the size of the message to a value. This may be needed after writing data
 * into the message data buffer.
 */
void ODK_Message_SetSize(ODK_Message* message, size_t size) {
  ODK_Message_Impl* message_impl = (ODK_Message_Impl*)message;
  assert(message_impl != NULL);
  assert(size <= message_impl->capacity);
  message_impl->size = size;
}

/*
 * Test if the integrity of a message. This means that the status must be
 * MESSAGE_STATUS_OK and that the base, read_offset, size and capacity of the
 * message are within the range of valid values. The message's base pointer
 * may be NULL if the buffer has not been assigned yet, that is not invalid.
 */
bool ODK_Message_IsValid(ODK_Message* message) {
  assert(message);
  ODK_Message_Impl* message_impl = (ODK_Message_Impl*)message;
  if (message_impl == NULL) {
    return false;
  }
  if (message_impl->status != MESSAGE_STATUS_OK) {
    return false;
  }
  if (message_impl->read_offset > message_impl->capacity ||
      message_impl->size > message_impl->capacity ||
      message_impl->read_offset > message_impl->size) {
    message_impl->status = MESSAGE_STATUS_OVERFLOW_ERROR;
    return false;
  }
  return true;
}