/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at https://curl.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 * SPDX-License-Identifier: curl
 *
 ***************************************************************************/
/* <DESC>
 * Stream-parse a document using the streaming Expat parser.
 * </DESC>
 */
/* Written by David Strauss
 *
 * Expat => https://libexpat.github.io/
 *
 * gcc -Wall -I/usr/local/include xmlstream.c -lcurl -lexpat -o xmlstream
 *
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <expat.h>

#include <curl/curl.h>

struct MemoryStruct {
  char *memory;
  size_t size;
};

struct ParserStruct {
  int ok;
  size_t tags;
  size_t depth;
  struct MemoryStruct characters;
};

static void startElement(void *userData, const XML_Char *name,
                         const XML_Char **atts)
{
  struct ParserStruct *state = (struct ParserStruct *)userData;
  state->tags++;
  state->depth++;

  (void)name;
  (void)atts;

  /* Get a clean slate for reading in character data. */
  free(state->characters.memory);
  state->characters.memory = NULL;
  state->characters.size = 0;
}

static void characterDataHandler(void *userData, const XML_Char *s, int len)
{
  struct ParserStruct *state = (struct ParserStruct *)userData;
  struct MemoryStruct *mem = &state->characters;

  char *ptr = realloc(mem->memory, mem->size + (unsigned long)len + 1);
  if(!ptr) {
    /* Out of memory. */
    fprintf(stderr, "Not enough memory (realloc returned NULL).\n");
    state->ok = 0;
    return;
  }

  mem->memory = ptr;
  memcpy(&(mem->memory[mem->size]), s, len);
  mem->size += (unsigned long)len;
  mem->memory[mem->size] = 0;
}

static void endElement(void *userData, const XML_Char *name)
{
  struct ParserStruct *state = (struct ParserStruct *)userData;
  state->depth--;

  printf("%5lu   %10lu   %s\n", state->depth, state->characters.size, name);
}

static size_t write_cb(void *contents, size_t length, size_t nmemb,
                       void *userp)
{
  XML_Parser parser = (XML_Parser)userp;
  size_t real_size = length * nmemb;
  struct ParserStruct *state = (struct ParserStruct *)XML_GetUserData(parser);

  /* Only parse if we are not already in a failure state. */
  if(state->ok && XML_Parse(parser, contents, (int)real_size, 0) == 0) {
    enum XML_Error error_code = XML_GetErrorCode(parser);
    fprintf(stderr, "Parsing response buffer of length %lu failed"
            " with error code %d (%s).\n",
            real_size, error_code, XML_ErrorString(error_code));
    state->ok = 0;
  }

  return real_size;
}

int main(void)
{
  CURL *curl;

  CURLcode result = curl_global_init(CURL_GLOBAL_ALL);
  if(result != CURLE_OK)
    return (int)result;

  /* Initialize a libcurl handle. */
  curl = curl_easy_init();
  if(curl) {
    XML_Parser parser;
    struct ParserStruct state;

    /* Initialize the state structure for parsing. */
    memset(&state, 0, sizeof(state));
    state.ok = 1;

    /* Initialize a namespace-aware parser. */
    parser = XML_ParserCreateNS(NULL, '\0');
    XML_SetUserData(parser, &state);
    XML_SetElementHandler(parser, startElement, endElement);
    XML_SetCharacterDataHandler(parser, characterDataHandler);

    curl_easy_setopt(curl, CURLOPT_URL,
                     "https://www.w3schools.com/xml/simple.xml");
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_cb);
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)parser);

    printf("Depth   Characters   Closing Tag\n");

    /* Perform the request and any follow-up parsing. */
    result = curl_easy_perform(curl);
    if(result != CURLE_OK) {
      fprintf(stderr, "curl_easy_perform() failed: %s\n",
              curl_easy_strerror(result));
    }
    else if(state.ok) {
      /* Expat requiresult one final call to finalize parsing. */
      if(XML_Parse(parser, NULL, 0, 1) == 0) {
        enum XML_Error error_code = XML_GetErrorCode(parser);
        fprintf(stderr, "Finalizing parsing failed with error code %d (%s).\n",
                error_code, XML_ErrorString(error_code));
      }
      else {
        printf("                     --------------\n");
        printf("                     %lu tags total\n", state.tags);
      }
    }

    /* Clean up. */
    free(state.characters.memory);
    XML_ParserFree(parser);

    curl_easy_cleanup(curl);
  }

  curl_global_cleanup();

  return (int)result;
}
