/*
* compilation:
* gcc this_file.c -lcurl -ljansson
*/

#include <stdlib.h>
#include <string.h>
#include <jansson.h>
#include <curl/curl.h>

#define BUFFER_SIZE  (256 * 1024)  /* 256 KB */

struct write_result
{
    char *data;
    int pos;
};

static size_t write_response(void *ptr, size_t size, size_t nmemb, void *stream)
{
    struct write_result *result = (struct write_result *)stream;

    if(result->pos + size * nmemb >= BUFFER_SIZE - 1)
    {
        fprintf(stderr, "error: too small buffer\n");
        return 0;
    }

    memcpy(result->data + result->pos, ptr, size * nmemb);
    result->pos += size * nmemb;

    return size * nmemb;
}

static char *request(const char *url)
{
    CURL *curl = NULL;
    CURLcode status;
    struct curl_slist *headers = NULL;
    char *data = NULL;
    long code;

    curl_global_init(CURL_GLOBAL_ALL);
    curl = curl_easy_init();
    if(!curl)
        goto error;

    data = malloc(BUFFER_SIZE);
    if(!data)
        goto error;

    struct write_result write_result = {
        .data = data,
        .pos = 0
    };

    curl_easy_setopt(curl, CURLOPT_URL, url);

    headers = curl_slist_append(headers, "User-Agent: Jansson-Tutorial");
    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);

    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_response);
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &write_result);

    status = curl_easy_perform(curl);
    if(status != 0)
    {
        fprintf(stderr, "error: unable to request data from %s:\n", url);
        fprintf(stderr, "%s\n", curl_easy_strerror(status));
        goto error;
    }

    curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &code);
    if(code != 200)
    {
        fprintf(stderr, "error: server responded with code %ld\n", code);
        goto error;
    }

    curl_easy_cleanup(curl);
    curl_slist_free_all(headers);
    curl_global_cleanup();

    /* zero-terminate the result */
    data[write_result.pos] = '\0';

    return data;

error:
    if(data)
        free(data);
    if(curl)
        curl_easy_cleanup(curl);
    if(headers)
        curl_slist_free_all(headers);
    curl_global_cleanup();
    return NULL;
}

int main(int argc, char *argv[])
{
    size_t i, j;
    char *text;
    char *url = "https://api.hh.ru/industries";
    char *api_name = "industries";

    json_t *root;
    json_error_t error;

    text = request(url);
    if(!text)
        return 1;

    root = json_loads(text, 0, &error);
    free(text);

    if(!root)
    {
        fprintf(stderr, "error: on line %d: %s\n", error.line, error.text);
        return 1;
    }

    if(!json_is_array(root))
    {
        fprintf(stderr, "error: root is not an array\n");
        json_decref(root);
        return 1;
    }

    for(i = 0; i < json_array_size(root); i++)
    {
        json_t *item_0, *item_1, *name_0, *name_1;

        item_0 = json_array_get(root, i);
        if(!json_is_object(item_0))
        {
            fprintf(stderr, "error: list item %d is not an object\n", (int)(i + 1));
            json_decref(root);
            return 1;
        }

        name_0 = json_object_get(item_0, "name");
        if(!json_is_string(name_0))
        {
            fprintf(stderr, "error: list %d: name_0 is not a string\n", (int)(i + 1));
            return 1;
        }
        printf("%s\n", json_string_value(name_0));

        item_1 = json_object_get(item_0, api_name);
        if(!json_is_array(item_1))
        {
            fprintf(stderr, "error: list %d: item_1 is not an array\n", (int)(i + 1));
            json_decref(root);
            return 1;
        }
        for(j = 0; j < json_array_size(item_1); j++)
        {
            json_t *o = json_array_get(item_1, j);
            if(!json_is_object(o))
            {
                fprintf(stderr, "error: list %d: o is not a object\n", (int)(i + 1));
                return 1;
            }
            name_1 = json_object_get(o, "name");
            if(!json_is_string(name_1))
            {
                fprintf(stderr, "error: list %d: name_1 is not a string\n", (int)(i + 1));
                return 1;
            }
            printf("  %s\n", json_string_value(name_1));
        }

    }

    json_decref(root);
    return 0;
}