#include <bson.h>
#include <mongoc.h>
#include <stdio.h>
#include <stdlib.h>

#ifdef _WIN32
#define sleep(_n) Sleep((_n) * 1000)
#endif


static void
print_bson (const bson_t *b)
{
   char *str;

   str = bson_as_json(b, NULL);
   fprintf(stdout, "%s\n", str);
   bson_free(str);
}


static mongoc_cursor_t *
query_collection (mongoc_collection_t *collection,
                  uint32_t        last_time)
{
   mongoc_cursor_t *cursor;
   bson_t query;
   bson_t gt;

   BSON_ASSERT(collection);

   bson_init(&query);
   bson_append_document_begin(&query, "ts", 2, &gt);
   bson_append_timestamp(&gt, "$gt", 3, last_time, 0);
   bson_append_document_end(&query, &gt);

   cursor = mongoc_collection_find(collection,
                                   (MONGOC_QUERY_TAILABLE_CURSOR |
                                    MONGOC_QUERY_AWAIT_DATA |
                                    MONGOC_QUERY_SLAVE_OK),
                                   0,
                                   0,
                                   0,
                                   &query,
                                   NULL,
                                   NULL);

   bson_destroy(&query);

   return cursor;
}


static void
tail_collection (mongoc_collection_t *collection)
{
   mongoc_cursor_t *cursor;
   uint32_t last_time;
   const bson_t *doc;
   bson_error_t error;
   bson_iter_t iter;

   BSON_ASSERT(collection);

   last_time = (uint32_t)time(NULL);

   while (true) {
      cursor = query_collection(collection, last_time);
      while (!mongoc_cursor_error(cursor, &error) &&
             mongoc_cursor_more(cursor)) {
         if (mongoc_cursor_next(cursor, &doc)) {
            if (bson_iter_init_find(&iter, doc, "ts") &&
                BSON_ITER_HOLDS_TIMESTAMP(&iter)) {
               bson_iter_timestamp(&iter, &last_time, NULL);
            }
            print_bson(doc);
         }
      }
      if (mongoc_cursor_error(cursor, &error)) {
         if ((error.domain == MONGOC_ERROR_QUERY) &&
             (error.code == MONGOC_ERROR_QUERY_NOT_TAILABLE)) {
            fprintf(stderr, "%s\n", error.message);
            exit(1);
         }
      }
      mongoc_cursor_destroy(cursor);
      sleep(1);
   }
}


int
main (int   argc,
      char *argv[])
{
   mongoc_collection_t *collection;
   mongoc_client_t *client;

   if (argc != 2) {
      fprintf(stderr, "usage: %s MONGO_URI\n", argv[0]);
      return EXIT_FAILURE;
   }

   mongoc_init();

   client = mongoc_client_new(argv[1]);
   if (!client) {
      fprintf(stderr, "Invalid URI: \"%s\"\n", argv[1]);
      return EXIT_FAILURE;
   }

   collection = mongoc_client_get_collection(client, "local", "oplog.rs");

   tail_collection(collection);

   mongoc_collection_destroy(collection);
   mongoc_client_destroy(client);

   return 0;
}
