/* Feel free to use this example code in any way
   you see fit (Public Domain) */

#include <sys/types.h>
#ifndef _WIN32
#include <sys/select.h>
#include <sys/socket.h>
#else
#include <winsock2.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <microhttpd.h>

#if defined(_MSC_VER) && _MSC_VER + 0 <= 1800
/* Substitution is OK while return value is not used */
#define snprintf _snprintf
#endif

#define PORT            8888
#define POSTBUFFERSIZE  512
#define MAXCLIENTS      2

enum ConnectionType
{
  GET = 0,
  POST = 1
};

static unsigned int nr_of_uploading_clients = 0;


/**
 * Information we keep per connection.
 */
struct connection_info_struct
{
  enum ConnectionType connectiontype;

  /**
   * Handle to the POST processing state.
   */
  struct MHD_PostProcessor *postprocessor;

  /**
   * File handle where we write uploaded data.
   */
  FILE *fp;

  /**
   * HTTP response body we will return, NULL if not yet known.
   */
  const char *answerstring;

  /**
   * HTTP status code we will return, 0 for undecided.
   */
  unsigned int answercode;
};


#define ASKPAGE \
  "<html><body>\n" \
  "Upload a file, please!<br>\n" \
  "There are %u clients uploading at the moment.<br>\n" \
  "<form action=\"/filepost\" method=\"post\" enctype=\"multipart/form-data\">\n" \
  "<input name=\"file\" type=\"file\">\n" \
  "<input type=\"submit\" value=\" Send \"></form>\n" \
  "</body></html>"
static const char *busypage =
  "<html><body>This server is busy, please try again later.</body></html>";
static const char *completepage =
  "<html><body>The upload has been completed.</body></html>";
static const char *errorpage =
  "<html><body>This doesn't seem to be right.</body></html>";
static const char *servererrorpage =
  "<html><body>Invalid request.</body></html>";
static const char *fileexistspage =
  "<html><body>This file already exists.</body></html>";
static const char *fileioerror =
  "<html><body>IO error writing to disk.</body></html>";
static const char *const postprocerror =
  "<html><head><title>Error</title></head><body>Error processing POST data</body></html>";


static enum MHD_Result
send_page (struct MHD_Connection *connection,
           const char *page,
           unsigned int status_code)
{
  enum MHD_Result ret;
  struct MHD_Response *response;

  response = MHD_create_response_from_buffer_static (strlen (page), page);
  if (! response)
    return MHD_NO;
  MHD_add_response_header (response,
                           MHD_HTTP_HEADER_CONTENT_TYPE,
                           "text/html");
  ret = MHD_queue_response (connection,
                            status_code,
                            response);
  MHD_destroy_response (response);

  return ret;
}


static enum MHD_Result
iterate_post (void *coninfo_cls,
              enum MHD_ValueKind kind,
              const char *key,
              const char *filename,
              const char *content_type,
              const char *transfer_encoding,
              const char *data,
              uint64_t off,
              size_t size)
{
  struct connection_info_struct *con_info = coninfo_cls;
  FILE *fp;
  (void) kind;               /* Unused. Silent compiler warning. */
  (void) content_type;       /* Unused. Silent compiler warning. */
  (void) transfer_encoding;  /* Unused. Silent compiler warning. */
  (void) off;                /* Unused. Silent compiler warning. */

  if (0 != strcmp (key, "file"))
  {
    con_info->answerstring = servererrorpage;
    con_info->answercode = MHD_HTTP_BAD_REQUEST;
    return MHD_YES;
  }

  if (! con_info->fp)
  {
    if (0 != con_info->answercode)   /* something went wrong */
      return MHD_YES;
    if (NULL != (fp = fopen (filename, "rb")))
    {
      fclose (fp);
      con_info->answerstring = fileexistspage;
      con_info->answercode = MHD_HTTP_FORBIDDEN;
      return MHD_YES;
    }
    /* NOTE: This is technically a race with the 'fopen()' above,
       but there is no easy fix, short of moving to open(O_EXCL)
       instead of using fopen(). For the example, we do not care. */
    con_info->fp = fopen (filename, "ab");
    if (! con_info->fp)
    {
      con_info->answerstring = fileioerror;
      con_info->answercode = MHD_HTTP_INTERNAL_SERVER_ERROR;
      return MHD_YES;
    }
  }

  if (size > 0)
  {
    if (! fwrite (data, sizeof (char), size, con_info->fp))
    {
      con_info->answerstring = fileioerror;
      con_info->answercode = MHD_HTTP_INTERNAL_SERVER_ERROR;
      return MHD_YES;
    }
  }

  return MHD_YES;
}


static void
request_completed (void *cls,
                   struct MHD_Connection *connection,
                   void **req_cls,
                   enum MHD_RequestTerminationCode toe)
{
  struct connection_info_struct *con_info = *req_cls;
  (void) cls;         /* Unused. Silent compiler warning. */
  (void) connection;  /* Unused. Silent compiler warning. */
  (void) toe;         /* Unused. Silent compiler warning. */

  if (NULL == con_info)
    return;

  if (con_info->connectiontype == POST)
  {
    if (NULL != con_info->postprocessor)
    {
      MHD_destroy_post_processor (con_info->postprocessor);
      nr_of_uploading_clients--;
    }

    if (con_info->fp)
      fclose (con_info->fp);
  }

  free (con_info);
  *req_cls = NULL;
}


static enum MHD_Result
answer_to_connection (void *cls,
                      struct MHD_Connection *connection,
                      const char *url,
                      const char *method,
                      const char *version,
                      const char *upload_data,
                      size_t *upload_data_size,
                      void **req_cls)
{
  (void) cls;               /* Unused. Silent compiler warning. */
  (void) url;               /* Unused. Silent compiler warning. */
  (void) version;           /* Unused. Silent compiler warning. */

  if (NULL == *req_cls)
  {
    /* First call, setup data structures */
    struct connection_info_struct *con_info;

    if (nr_of_uploading_clients >= MAXCLIENTS)
      return send_page (connection,
                        busypage,
                        MHD_HTTP_SERVICE_UNAVAILABLE);

    con_info = malloc (sizeof (struct connection_info_struct));
    if (NULL == con_info)
      return MHD_NO;
    con_info->answercode = 0;   /* none yet */
    con_info->fp = NULL;

    if (0 == strcmp (method, MHD_HTTP_METHOD_POST))
    {
      con_info->postprocessor =
        MHD_create_post_processor (connection,
                                   POSTBUFFERSIZE,
                                   &iterate_post,
                                   (void *) con_info);

      if (NULL == con_info->postprocessor)
      {
        free (con_info);
        return MHD_NO;
      }

      nr_of_uploading_clients++;

      con_info->connectiontype = POST;
    }
    else
    {
      con_info->connectiontype = GET;
    }

    *req_cls = (void *) con_info;

    return MHD_YES;
  }

  if (0 == strcmp (method, MHD_HTTP_METHOD_GET))
  {
    /* We just return the standard form for uploads on all GET requests */
    char buffer[1024];

    snprintf (buffer,
              sizeof (buffer),
              ASKPAGE,
              nr_of_uploading_clients);
    return send_page (connection,
                      buffer,
                      MHD_HTTP_OK);
  }

  if (0 == strcmp (method, MHD_HTTP_METHOD_POST))
  {
    struct connection_info_struct *con_info = *req_cls;

    if (0 != *upload_data_size)
    {
      /* Upload not yet done */
      if (0 != con_info->answercode)
      {
        /* we already know the answer, skip rest of upload */
        *upload_data_size = 0;
        return MHD_YES;
      }
      if (MHD_YES !=
          MHD_post_process (con_info->postprocessor,
                            upload_data,
                            *upload_data_size))
      {
        con_info->answerstring = postprocerror;
        con_info->answercode = MHD_HTTP_INTERNAL_SERVER_ERROR;
      }
      *upload_data_size = 0;

      return MHD_YES;
    }
    /* Upload finished */
    if (NULL != con_info->fp)
    {
      fclose (con_info->fp);
      con_info->fp = NULL;
    }
    if (0 == con_info->answercode)
    {
      /* No errors encountered, declare success */
      con_info->answerstring = completepage;
      con_info->answercode = MHD_HTTP_OK;
    }
    return send_page (connection,
                      con_info->answerstring,
                      con_info->answercode);
  }

  /* Note a GET or a POST, generate error */
  return send_page (connection,
                    errorpage,
                    MHD_HTTP_BAD_REQUEST);
}


int
main (void)
{
  struct MHD_Daemon *daemon;

  daemon = MHD_start_daemon (MHD_USE_INTERNAL_POLLING_THREAD,
                             PORT, NULL, NULL,
                             &answer_to_connection, NULL,
                             MHD_OPTION_NOTIFY_COMPLETED, &request_completed,
                             NULL,
                             MHD_OPTION_END);
  if (NULL == daemon)
  {
    fprintf (stderr,
             "Failed to start daemon.\n");
    return 1;
  }
  (void) getchar ();
  MHD_stop_daemon (daemon);
  return 0;
}