/*
 * Copyright (c) 2009-2016 Petri Lehtinen <petri@digip.org>
 *
 * Jansson is free software; you can redistribute it and/or modify
 * it under the terms of the MIT license. See LICENSE for details.
 */

#include <stdlib.h>
#include <string.h>

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

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

#define URL_FORMAT "https://api.github.com/repos/%s/%s/commits"
#define URL_SIZE   256

/* Return the offset of the first newline in text or the length of
   text if there's no newline */
static int newline_offset(const char *text) {
    const char *newline = strchr(text, '\n');
    if (!newline)
        return strlen(text);
    else
        return (int)(newline - text);
}

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);

    /* GitHub commits API v3 requires a User-Agent header */
    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;
    char *text;
    char url[URL_SIZE];

    json_t *root;
    json_error_t error;

    if (argc != 3) {
        fprintf(stderr, "usage: %s USER REPOSITORY\n\n", argv[0]);
        fprintf(stderr, "List commits at USER's REPOSITORY.\n\n");
        return 2;
    }

    snprintf(url, URL_SIZE, URL_FORMAT, argv[1], argv[2]);

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

    /*decode the JSON text we got as a response*/
    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 *data, *sha, *commit, *message;
        const char *message_text;

	/*get i'th element of the 'root' array*/
        data = json_array_get(root, i);

	/*Is 'data' a JSON object?*/
        if (!json_is_object(data)) {
            fprintf(stderr, "error: commit data %d is not an object\n", (int)(i + 1));
            json_decref(root);
            return 1;
        }

        sha = json_object_get(data, "sha");
        if (!json_is_string(sha)) {
            fprintf(stderr, "error: commit %d: sha is not a string\n", (int)(i + 1));
            return 1;
        }

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

        message = json_object_get(commit, "message");
        if (!json_is_string(message)) {
            fprintf(stderr, "error: commit %d: message is not a string\n", (int)(i + 1));
            json_decref(root);
            return 1;
        }

	/*extract C-style string from a JSON string*/
        message_text = json_string_value(message);
        printf("%.8s %.*s\n", json_string_value(sha), newline_offset(message_text),
               message_text);
    }

    /*decrease the reference count*/
    /*this way the recource is released*/
    json_decref(root);
    return 0;
}