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

#include <errno.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>

#include <linux/limits.h>

#include <microhttpd.h>

#include "logger.h"
#include "templates.h"
#include "dirlisting.h"

#define DEFAULT_PORT 8888

struct ConnectionState {
  char cleanedURL[PATH_MAX];
  char localFileName[PATH_MAX];
  struct stat targetStat;
};

char *shareRoot;
struct MHD_Response *error403Response;
struct MHD_Response *error404Response;
struct MHD_Response *error500Response;

int running = 1;

void remove_trailing_slash(char *str) {
  size_t offset = strlen(str)-1;
  if((offset != 0) && (str[offset] == '/')) {
    str[offset] = '\0';
  }
}

void request_completed(void *cls,
                       struct MHD_Connection * connection,
                       void **ptr,
                       enum MHD_RequestTerminationCode toe) {
  struct ConnectionState *connstate = *ptr;

  // TODO: show IP+Port in log
  LOG(LVL_DEBUG, "Freeing state for request of %s", connstate->localFileName);

  free(connstate);
}

static int connection_handler(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 **ptr) {
  struct ConnectionState *connstate;

  struct MHD_Response *response;
  int ret;

  if (0 != strcmp(method, "GET")) {
    LOG(LVL_WARN, "Unexpected method: %s.", method);
    return MHD_NO;
  }

  if (*ptr == NULL) {
    // This is the first time this connection is seen.
    // Initialize the connection state
    connstate = malloc(sizeof(struct ConnectionState));
    *ptr = connstate;

    // set the local file name
    strncpy(connstate->localFileName, shareRoot, PATH_MAX);
    strncat(connstate->localFileName, url,
        PATH_MAX - strlen(connstate->localFileName));

    remove_trailing_slash(connstate->localFileName);

    strncpy(connstate->cleanedURL, url, PATH_MAX);
    remove_trailing_slash(connstate->cleanedURL);

    LOG(LVL_INFO, "New %s request for %s (local: %s)",
        method, url, connstate->localFileName);

    return MHD_YES;
  } else {
    connstate = *ptr;
  }

  if (0 != *upload_data_size) {
    return MHD_NO; // upload data in a GET!?
  }

  // check if url contains a "/.." sequence. If so, block the request as it is
  // trying to access the parent directory (and may be an attempt to leave the
  // shared space.
  if(NULL != strstr(url, "/..")) {
    LOG(LVL_WARN, "User is trying to access %s, which may be an attempt to leave the shared space.",
        url);

    return MHD_queue_response(connection, MHD_HTTP_FORBIDDEN, error403Response);
  }


  // check properties of the target file/dir
  if(stat(connstate->localFileName, &(connstate->targetStat)) == -1) {
    LOG(LVL_ERR, "Cannot stat %s: %s",
        connstate->localFileName, strerror(errno));

    return MHD_queue_response(connection, MHD_HTTP_NOT_FOUND, error404Response);
  }

  if(S_ISREG(connstate->targetStat.st_mode)) {
    LOG(LVL_DEBUG, "Serving %s as a regular file.", connstate->localFileName);

    // open a file descriptor to the file
    int fd = open(connstate->localFileName, O_RDONLY);

    if(fd == -1) {
      LOG(LVL_ERR, "Cannot open %s: %s",
          connstate->localFileName, strerror(errno));

      return MHD_queue_response(connection, MHD_HTTP_FORBIDDEN, error403Response);
    }

    // no error so far -> serve the file
    response = MHD_create_response_from_fd(
        connstate->targetStat.st_size,
        fd);

    ret = MHD_queue_response(connection, MHD_HTTP_OK, response);
    MHD_destroy_response(response);
    return ret;
  } else if(S_ISDIR(connstate->targetStat.st_mode)) {
    LOG(LVL_DEBUG, "Generating directory listing for %s.", connstate->localFileName);

    char *result = create_dirlisting(connstate->cleanedURL, connstate->localFileName);
    if(!result) {
      LOG(LVL_ERR, "Failed to generate dirlisting for %s.", connstate->localFileName);
      return MHD_queue_response(connection, MHD_HTTP_INTERNAL_SERVER_ERROR, error500Response);
    }

    response = MHD_create_response_from_buffer(
        strlen(result), result, MHD_RESPMEM_MUST_FREE);

    MHD_add_response_header(response, MHD_HTTP_HEADER_CONTENT_TYPE, "text/html");

    ret = MHD_queue_response(connection, MHD_HTTP_OK, response);
    MHD_destroy_response(response);
    return ret;
  } else {
    LOG(LVL_WARN,
        "%s is neither a directory nor a regular file. Don't allow the access.",
        connstate->localFileName);

    return MHD_queue_response(connection, MHD_HTTP_FORBIDDEN, error403Response);
  }

  // generate a 500 if request was not handled properly
  return MHD_queue_response(
    connection, MHD_HTTP_INTERNAL_SERVER_ERROR, error500Response);
}

int main(int argc, char ** argv) {
  struct MHD_Daemon *d;
  struct stat sBuf;

  int port;

  logger_init();

  if (argc < 2) {
    printf("%s <dir> [<port>]\n", argv[0]);
    return 1;
  }

  // check if shareRoot is an existing directory
  shareRoot = argv[1];
  if(stat(shareRoot, &sBuf) == -1) {
    LOG(LVL_FATAL, "Cannot stat %s: %s", shareRoot, strerror(errno));
    return EXIT_FAILURE;
  }

  if(!S_ISDIR(sBuf.st_mode)) {
    LOG(LVL_FATAL, "%s is not a directory!", shareRoot);
    return EXIT_FAILURE;
  }

  // remove trailing / from shareRoot
  remove_trailing_slash(shareRoot);

  LOG(LVL_INFO, "Shared directory is: %s", shareRoot);

  if(argc >= 3) {
    // a port was given on the command line, try to parse it
    if(sscanf(argv[2], "%i", &port) != 1) {
      LOG(LVL_FATAL, "%s is not a valid port number!", argv[2]);
      return EXIT_FAILURE;
    }

    if(port < 1 || port > 65535) {
      LOG(LVL_FATAL, "Port %i is out of range [1-65535]!", port);
      return EXIT_FAILURE;
    }

    LOG(LVL_INFO, "Using port: %i", port);
  } else {
    LOG(LVL_INFO, "Using default port: %i", DEFAULT_PORT);
    port = DEFAULT_PORT;
  }

  // create the static response for error pages
  error403Response = MHD_create_response_from_data(
      strlen(ERROR_403),
      (void*) ERROR_403,
      MHD_NO,
      MHD_NO);

  error404Response = MHD_create_response_from_data(
      strlen(ERROR_404),
      (void*) ERROR_404,
      MHD_NO,
      MHD_NO);

  error500Response = MHD_create_response_from_data(
      strlen(ERROR_500),
      (void*) ERROR_500,
      MHD_NO,
      MHD_NO);

  MHD_add_response_header(error403Response, MHD_HTTP_HEADER_CONTENT_TYPE, "text/html");
  MHD_add_response_header(error404Response, MHD_HTTP_HEADER_CONTENT_TYPE, "text/html");
  MHD_add_response_header(error500Response, MHD_HTTP_HEADER_CONTENT_TYPE, "text/html");

  d = MHD_start_daemon(MHD_USE_THREAD_PER_CONNECTION,
                       port,
                       NULL,
                       NULL,
                       &connection_handler,
                       NULL,
                       MHD_OPTION_NOTIFY_COMPLETED,
                       &request_completed, NULL,
                       MHD_OPTION_END);
  if (d == NULL) {
    LOG(LVL_FATAL, "Cannot start up libmicrohttpd.");
    return EXIT_FAILURE;
  }

  while(running) {
    getc(stdin);
  }

  LOG(LVL_INFO, "Shutting down...");

  MHD_stop_daemon(d);

  MHD_destroy_response(error403Response);
  MHD_destroy_response(error404Response);
  MHD_destroy_response(error500Response);

  logger_shutdown();
  return EXIT_SUCCESS;
}