/*
 * Copyright (c) 2018 Vasile Vilvoiu <vasi.vilvoiu@gmail.com>
 *
 * libecbor is free software; you can redistribute it and/or modify
 * it under the terms of the MIT license. See LICENSE for details.
 */

#include "ecbor.h"
#include "ecbor_internal.h"

static ecbor_error_t
ecbor_initialize_decode_internal (ecbor_decode_context_t *context,
                                  const uint8_t *buffer,
                                  uint64_t buffer_size)
{
  if (!context) {
    return ECBOR_ERR_NULL_CONTEXT;
  }
  if (!buffer) {
    return ECBOR_ERR_NULL_INPUT_BUFFER;
  }

  context->in_position = buffer;
  context->bytes_left = buffer_size;
  
  return ECBOR_OK;
}

ecbor_error_t
ecbor_initialize_decode (ecbor_decode_context_t *context,
                         const uint8_t *buffer,
                         uint64_t buffer_size)
{
  ecbor_error_t rc =
    ecbor_initialize_decode_internal (context, buffer, buffer_size);

  if (rc != ECBOR_OK) {
    return rc;
  }

  context->mode = ECBOR_MODE_DECODE;
  context->nodes = NULL;
  context->node_capacity = 0;
  context->n_nodes = 0;
  
  return ECBOR_OK;
}

ecbor_error_t
ecbor_initialize_decode_streamed (ecbor_decode_context_t *context,
                                  const uint8_t *buffer,
                                  uint64_t buffer_size)
{
  ecbor_error_t rc =
    ecbor_initialize_decode_internal (context, buffer, buffer_size);

  if (rc != ECBOR_OK) {
    return rc;
  }
  
  context->mode = ECBOR_MODE_DECODE_STREAMED;
  context->nodes = NULL;
  context->node_capacity = 0;
  context->n_nodes = 0;
  
  return ECBOR_OK;
}

ecbor_error_t
ecbor_initialize_decode_tree (ecbor_decode_context_t *context,
                              const uint8_t *buffer,
                              uint64_t buffer_size,
                              ecbor_node_t *node_buffer,
                              uint64_t node_capacity)
{
  ecbor_error_t rc =
    ecbor_initialize_decode_internal (context, buffer, buffer_size);

  if (rc != ECBOR_OK) {
    return rc;
  }
  
  if (!node_buffer) {
    return ECBOR_ERR_NULL_NODE_BUFFER;
  }
  
  context->mode = ECBOR_MODE_DECODE_TREE;
  context->nodes = node_buffer;
  context->node_capacity = node_capacity;
  context->n_nodes = 0;
  
  return ECBOR_OK;
}

static inline ecbor_error_t
ecbor_decode_uint (ecbor_decode_context_t *context,
                   uint64_t *value,
                   uint64_t *size,
                   uint8_t additional)
{
  if (additional < 24) {
    /* value stored in additional information */
    (*value) = additional;
    (*size) = 1;
  } else {
    /* compute storage size */
    (*size) = (0x1 << (additional - ECBOR_ADDITIONAL_1BYTE));
    if (context->bytes_left < (*size)) {
      return ECBOR_ERR_INVALID_END_OF_BUFFER;
    }

    /* read actual value */
    switch (additional) {
      case ECBOR_ADDITIONAL_1BYTE:
        (*value) = *((uint8_t *) context->in_position);
        break;

      case ECBOR_ADDITIONAL_2BYTE:
        (*value) =
          ecbor_uint16_from_big_endian (*((uint16_t *) context->in_position));
        break;

      case ECBOR_ADDITIONAL_4BYTE:
        (*value) =
          ecbor_uint32_from_big_endian (*((uint32_t *) context->in_position));
        break;

      case ECBOR_ADDITIONAL_8BYTE:
        (*value) =
          ecbor_uint64_from_big_endian (*((uint64_t *) context->in_position));
        break;

      default:
        return ECBOR_ERR_INVALID_ADDITIONAL;
    }
    
    /* advance buffer */
    context->in_position += (*size);
    context->bytes_left -= (*size);
    
    /* meter the first byte */
    (*size) ++;
  }
  
  return ECBOR_OK;
}

static ecbor_error_t
ecbor_decode_next_internal (ecbor_decode_context_t *context,
                            ecbor_item_t *item,
                            int8_t is_chunk,
                            ecbor_major_type_t chunk_mtype)
{
  unsigned int additional;

  if (context->bytes_left == 0) {
    return ECBOR_END_OF_BUFFER;
  }
  if (context->mode != ECBOR_MODE_DECODE
      && context->mode != ECBOR_MODE_DECODE_STREAMED) {
    /* only allow known modes of operation; junk in <mode> will generate
       undefined behaviour */
    return ECBOR_ERR_WRONG_MODE;
  }
  
  /* clear item, just so we do not leave garbage on partial read */
  item->major_type = ECBOR_MT_UNDEFINED;
  item->size = 0;
  item->length = 0;
  item->is_indefinite = false;
  
  /* extract major type (most significant three bits) and additional info */
  item->major_type = (*context->in_position >> 5) & 0x07;
  additional = (*context->in_position & 0x1f);
  context->in_position ++; context->bytes_left --;
  
  /* check mandatory major type (in case we are reading string chunks);
     we do not want to continue parsing a malformed indefinite string and
     potentially explode the stack with subsequent calls */
  if (is_chunk && chunk_mtype != item->major_type) {
    if (item->major_type == ECBOR_MT_SPECIAL
        && additional == ECBOR_ADDITIONAL_INDEFINITE) {
      /* this is a valid stop code, pass it directly; note that this branch is
         only taken when inside an indefinite string */
      return ECBOR_END_OF_INDEFINITE;
    } else {
      /* this is not a stop code, and the item has the wrong major type */
      return ECBOR_ERR_INVALID_CHUNK_MAJOR_TYPE;
    }
  }
  
  /* handle type */
  switch (item->major_type) {

    /*
     * Integer types
     */
    case ECBOR_MT_UINT:
      return ecbor_decode_uint (context, &item->value.uinteger, &item->size,
                                additional);
    
    case ECBOR_MT_NINT:
      {
        /* read negative value as unsigned */
        ecbor_error_t rc = ecbor_decode_uint (context, &item->value.uinteger,
                                              &item->size, additional);
        if (rc != ECBOR_OK) {
          return rc;
        }

        /* parse as negative */
        item->value.integer = (-1) - item->value.uinteger;
      }
      break;

    /*
     * String types
     */
    case ECBOR_MT_BSTR:
    case ECBOR_MT_STR:
      /* keep buffer pointer from current pointer */
      item->value.string.str = context->in_position;
      item->value.string.n_chunks = 0;

      /* discriminate between definite and indefinite strings; we do not treat
       * indefinite strings as we do indefinite maps and arrays, in the sense
       * that we do not allow the user to manually walk each chunk
       */
      if (additional == ECBOR_ADDITIONAL_INDEFINITE) {
        ecbor_item_t chunk;
        ecbor_error_t rc;
        
        /* mark accordingly */
        item->is_indefinite = true;
        item->size = 1; /* already processed first byte */
        
        /* do not allow nested indefinite length strings */
        if (is_chunk) {
          return ECBOR_ERR_NESTET_INDEFINITE_STRING;
        }

        /* indefinite lenght string; read through all blocks to compute size */
        item->value.string.str = context->in_position;
        
        while (true) {
          /* read next chunk */
          rc = ecbor_decode_next_internal (context, &chunk, true,
                                           item->major_type);
          if (rc != ECBOR_OK) {
            if (rc == ECBOR_END_OF_INDEFINITE) {
              /* stop code found, break from loop */
              item->size += chunk.size; /* meter stop code as well */
              break;
            } else if (rc == ECBOR_END_OF_BUFFER) {
              /* treat a valid end of buffer as invalid since we did not yet
                 find the stop code */
              return ECBOR_ERR_INVALID_END_OF_BUFFER;
            } else if (rc != ECBOR_OK) {
              /* other error */
              return rc;
            }
          }

          /* add chunk size and length to item */
          item->size += chunk.size;
          item->length += chunk.length;
          item->value.string.n_chunks ++;
        }
      } else {
        /* read size of buffer */
        ecbor_error_t rc = ecbor_decode_uint (context, &item->length,
                                              &item->size, additional);
        if (rc != ECBOR_OK) {
          return rc;
        }

        /* advance */
        if (context->bytes_left < item->length) {
          return ECBOR_ERR_INVALID_END_OF_BUFFER;
        }
        context->in_position += item->length;
        context->bytes_left -= item->length;
        
        /* meter length of string to size of item */
        item->size += item->length;
      }
      break;

    /*
     * Arrays and maps
     */
    case ECBOR_MT_ARRAY:
    case ECBOR_MT_MAP:
      /* keep buffer pointer from current pointer */
      item->value.items = context->in_position;

      /* discriminate between definite and indefinite maps and arrays */
      if (additional == ECBOR_ADDITIONAL_INDEFINITE) {
        /* mark accordingly */
        item->is_indefinite = true;
        item->size = 1; /* already processed first byte */

        if (context->mode != ECBOR_MODE_DECODE_STREAMED) {
          /* we have an indefinite map or array and we're not in streamed mode;
             we have to walk children to compute size and advance to next item */
          ecbor_item_t child;
          ecbor_error_t rc;

          while (true) {
            /* read next chunk */
            rc = ecbor_decode_next_internal (context, &child, false,
                                             ECBOR_MT_UNDEFINED);
            if (rc != ECBOR_OK) {
              if (rc == ECBOR_END_OF_INDEFINITE) {
                /* stop code found, break from loop */
                item->size += child.size; /* meter stop code as well */
                break;
              } else if (rc == ECBOR_END_OF_BUFFER) {
                /* treat a valid end of buffer as invalid since we did not yet
                   find the stop code */
                return ECBOR_ERR_INVALID_END_OF_BUFFER;
              } else if (rc != ECBOR_OK) {
                /* other error */
                return rc;
              }
            }

            /* add chunk size to item size */
            item->size += child.size;
            item->length ++;
          }
          
          if ((item->major_type == ECBOR_MT_MAP) && (item->length % 2 != 0)) {
            /* incomplete key-value pair; we expect maps to have even number of
               items */
            return ECBOR_ERR_INVALID_KEY_VALUE_PAIR;
          }
        }
      } else {
        /* read size of map or array */
        ecbor_error_t rc = ecbor_decode_uint (context, &item->length,
                                              &item->size, additional);
        if (rc != ECBOR_OK) {
          return rc;
        }

        if (item->major_type == ECBOR_MT_MAP) {
          /* we keep the total number of items in length, yet the map has the
             number of key-value pairs encoded in the length */
          item->length *= 2;
        }

        if (context->mode != ECBOR_MODE_DECODE_STREAMED) {
          ecbor_item_t child;
          ecbor_error_t rc;
          uint64_t child_no;

          /* not in streamed mode; compute size so we can advance */
          for (child_no = 0; child_no < item->length; child_no ++) {
            /* read next child */
            rc = ecbor_decode_next_internal (context, &child, false,
                                             ECBOR_MT_UNDEFINED);
            if (rc != ECBOR_OK) {
              if (rc == ECBOR_END_OF_INDEFINITE) {
                /* stop code found, but none is expected */
                return ECBOR_ERR_INVALID_STOP_CODE;
              } else if (rc == ECBOR_END_OF_BUFFER) {
                /* treat a valid end of buffer as invalid since we did not yet
                   reach the end of the map or array */
                return ECBOR_ERR_INVALID_END_OF_BUFFER;
              } else if (rc != ECBOR_OK) {
                /* other error */
                return rc;
              }
            }

            /* add child size to item size */
            item->size += child.size;
          }
        }
      }
      break;

    case ECBOR_MT_TAG:
      {
        ecbor_error_t rc;

        /* decode tag */
        rc = ecbor_decode_uint (context, &item->value.tag.tag_value,
                                &item->size, additional);
        if (rc != ECBOR_OK) {
          return rc;
        }
        
        /* keep child pointer */
        item->value.tag.child = context->in_position;
        item->length = 1;
        
        if (context->mode != ECBOR_MODE_DECODE_STREAMED) {
          ecbor_item_t child;

          /* not in streamed mode; compute size so we can advance */
          rc = ecbor_decode_next_internal (context, &child, false,
                                           ECBOR_MT_UNDEFINED);
          if (rc != ECBOR_OK) {
            return rc;
          }

          /* add child size to item size */
          item->size += child.size;
        }
      }
      break;

    case ECBOR_MT_SPECIAL:
      if (additional == ECBOR_ADDITIONAL_INDEFINITE) {
        /* stop code */
        item->size = 1;
        return ECBOR_END_OF_INDEFINITE;
      } else {
        return ECBOR_ERR_CURRENTLY_NOT_SUPPORTED;
      }
      break;
    
    default:
      /* while this would theoretically be a case for invalid type, any 3 bit
         value should be a valid type, so this branch is an internal error and
         should never happen */
      return ECBOR_ERR_UNKNOWN;
  }
  
  return ECBOR_OK;
}

ecbor_error_t
ecbor_decode (ecbor_decode_context_t *context, ecbor_item_t *item)
{  
  if (!context) {
    return ECBOR_ERR_NULL_CONTEXT;
  }
  if (!item) {
    return ECBOR_ERR_NULL_ITEM;
  }

  if (context->mode != ECBOR_MODE_DECODE
      && context->mode != ECBOR_MODE_DECODE_STREAMED) {
    /* context is for wrong mode */
    return ECBOR_ERR_WRONG_MODE;
  }
  
  /* we just get the next item */
  return ecbor_decode_next_internal (context, item, false, ECBOR_MT_UNDEFINED);
}

extern ecbor_error_t
ecbor_decode_tree (ecbor_decode_context_t *context)
{
  ecbor_error_t rc = ECBOR_OK;
  ecbor_node_t *curr_node = NULL, *prev_node = NULL, *par_node = NULL;
  
  if (!context) {
    return ECBOR_ERR_NULL_CONTEXT;
  }
  
  /* initialization */
  context->n_nodes = 0;
  
  /* step into streamed mode; some of the semantic checks will be done here */
  context->mode = ECBOR_MODE_DECODE_STREAMED;

  /* consume until end of buffer or error */
  while (rc != ECBOR_OK) {

    /* allocate new node */
    if (context->n_nodes >= context->node_capacity) {
      rc = ECBOR_ERR_END_OF_NODE_BUFFER;
      goto end;
    }

    curr_node = &context->nodes[context->n_nodes];
    curr_node->next = NULL;
    curr_node->prev = NULL;
    curr_node->parent = NULL;
    curr_node->child = NULL;
    context->n_nodes ++;
    
    /* consume next item */
    rc = ecbor_decode_next_internal (context, &curr_node->item, false,
                                     ECBOR_MT_UNDEFINED);

    /* handle end of indefinite */
    if (rc == ECBOR_END_OF_INDEFINITE) {
      if ((!par_node)
          || (par_node->item.major_type != ECBOR_MT_MAP
              && par_node->item.major_type != ECBOR_MT_ARRAY)
          || (!par_node->item.is_indefinite)) {
        /* we are not in an indefinite map or array */
        rc = ECBOR_ERR_INVALID_STOP_CODE;
        goto end;
      }
      
      if (par_node && par_node->item.major_type == ECBOR_MT_MAP
          && prev_node && (prev_node->index % 2 == 0)) {
        /* map must have even number of children */
        rc = ECBOR_ERR_INVALID_KEY_VALUE_PAIR;
        goto end;
      }

      /* jump up one level */
      curr_node = par_node;
      par_node = curr_node->parent;
      prev_node = curr_node->prev;
      
      /* continue parsing */
      rc = ECBOR_OK;
      
      /* ignore this item, reuse it later */
      context->n_nodes --;
      continue;
    }
    
    /* check return code */
    if (rc == ECBOR_END_OF_BUFFER) {
      if (par_node) {
        /* we are not allowed to reach the end unless the item is top-level */
        rc = ECBOR_ERR_INVALID_END_OF_BUFFER;
        goto end;
      }
    } else if (rc != ECBOR_OK) {
      goto end;
    }
    
    /* link in tree */
    if (prev_node) {
      prev_node->next = curr_node;
      curr_node->prev = prev_node;
    }
    if (par_node) {
      curr_node->parent = par_node;
      if (!prev_node) {
        par_node->child = curr_node;
      }
    }
    
    /* handle new children */
    if (curr_node->item.major_type == ECBOR_MT_MAP
        || curr_node->item.major_type == ECBOR_MT_ARRAY
        || curr_node->item.major_type == ECBOR_MT_TAG) {
      /* jump a level down */
      par_node = curr_node;
      prev_node = NULL;
      continue;
    }
    
    /* handle end of definite maps and arrays, and tags */
    while (par_node
           && (par_node->item.major_type == ECBOR_MT_MAP
               || par_node->item.major_type == ECBOR_MT_ARRAY
               || par_node->item.major_type == ECBOR_MT_TAG)
           && !par_node->item.is_indefinite
           && par_node->item.length == (curr_node->index + 1)) {
      /* parent has filled all items, jump a level up */
      curr_node = par_node;
      par_node = curr_node->parent;
      prev_node = curr_node->prev;
    }
  }

end:
  /* return to tree mode and return error code */
  context->mode = ECBOR_MODE_DECODE_TREE;
  rc = (rc == ECBOR_END_OF_BUFFER ? ECBOR_OK : rc);
  if (rc != ECBOR_OK) {
    /* make sure we don't expose garbage to user */
    context->n_nodes = 0;
  }
  return rc;
}