#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 <signal.h>

#include <linux/limits.h>

#include <microhttpd.h>

#ifdef HAVE_MAGIC
#include <magic.h>
#endif

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

#define DEFAULT_PORT 8888

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

struct RequestRange {
  off_t start;
  off_t length;
};

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

#ifdef HAVE_MAGIC
magic_t magicCookie;
#endif

int running = 1;

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);
}

int parse_range(const char *range, off_t total_len, struct RequestRange *result) {
  char *numstr;
  char *dashptr;
  int dashpos;
  off_t num;

  LOG(LVL_DEBUG, "Requested Range is %s", range);

  if(range == NULL) {
    result->start = 0;
    result->length = total_len;
    return 0;
  }

  numstr = strchr(range, '=');
  if(numstr == NULL) {
    return -1;
  }

  numstr += 1;

  LOG(LVL_DUMP, "Numeric part of range: %s", numstr);

  dashptr = strchr(numstr, '-');
  if(dashptr == NULL) {
    // no '-' found
    return -1;
  }

  dashpos = dashptr - numstr;
  LOG(LVL_DUMP, "Dash found at position: %i", dashpos);

  if(dashpos == 0) {
    // example: bytes=-500
    // -> letzte 500 bytes ausgeben
    if(sscanf(dashptr+1, "%li", &num) != 1) {
      return -1;
    }

    // total = 1000, num = 100 -> start=500, length=500
    result->start = total_len - num - 1;
    result->length = num;
  } else {
    // examples: bytes=100-200; bytes=300-

    // parse the first number
    if(sscanf(numstr, "%li", &num) != 1) {
      return -1;
    }

    result->start = num;

    if(numstr[dashpos + 1] == '\0') {
      // everything from num to the end
      result->length = total_len - num;
      return 0;
    }

    // a complete range was given -> parse the second number
    if(sscanf(numstr+dashpos+1, "%li", &num) != 1) {
      return -1;
    }

    if(num < result->start) {
      return -1;
    }

    result->length = num - result->start + 1;
  }

  return 0;
}

int serv_regular_file(struct MHD_Connection *connection, struct ConnectionState *connstate) {
  struct MHD_Response *response;
  struct RequestRange range;
  const char *rangestr;
  char buf[256];
  int ret;

  LOG(LVL_DEBUG, "Serving %s as a regular file.", connstate->localFileName);

  rangestr = MHD_lookup_connection_value(connection, MHD_HEADER_KIND, "Range");

  if(0 != parse_range(rangestr, connstate->targetStat.st_size, &range)) {
    LOG(LVL_ERR, "Cannot parse range header.");
    return MHD_queue_response(connection, MHD_HTTP_INTERNAL_SERVER_ERROR, error500Response);
  }

  LOG(LVL_DUMP, "Requested range: start=%lu, length=%lu", range.start, range.length);

  // 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_at_offset(
      range.length,
      fd,
      range.start);

  // build content range header
  sprintf(buf, "bytes %li-%li/%li", range.start, range.start+range.length-1, connstate->targetStat.st_size);
  MHD_add_response_header(response, MHD_HTTP_HEADER_CONTENT_RANGE, buf);

  LOG(LVL_DUMP, "Content-Range: %s", buf);

#ifdef HAVE_MAGIC
  // if libmagic is available, determine the correct MIME type for the file
  const char *mimeType = magic_file(magicCookie, connstate->localFileName);
  LOG(LVL_DEBUG, "MIME type for %s: %s", connstate->localFileName, mimeType);
  MHD_add_response_header(response, MHD_HTTP_HEADER_CONTENT_TYPE, mimeType);
#endif

  ret = MHD_queue_response(connection, MHD_HTTP_OK, response);
  MHD_destroy_response(response);
  return ret;
}

int serv_directory(struct MHD_Connection *connection, struct ConnectionState *connstate) {
  struct MHD_Response *response;
  int ret;

  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;
}

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;

  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)) {
    return serv_regular_file(connection, connstate);
  } else if(S_ISDIR(connstate->targetStat.st_mode)) {
    return serv_directory(connection, connstate);
  } 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);
}

// signal handler for SIGTERM, SIGINT, etc.
// sets the flag for a clean shutdown
void sig_shutdown_handler(int sig) {
  LOG(LVL_DEBUG, "Handling signal: %i", sig);
  running = 0;
}

void init_signal_handlers(void) {
  struct sigaction sa;
  sa.sa_handler = sig_shutdown_handler;
  sigemptyset(&sa.sa_mask);
  sa.sa_flags = 0;
  sa.sa_restorer = NULL;

  if(sigaction(SIGTERM, &sa, NULL) == -1) {
    LOG(LVL_ERR, "sigaction [SIGTERM] failed: %s", strerror(errno));
  }

  if(sigaction(SIGINT, &sa, NULL) == -1) {
    LOG(LVL_ERR, "sigaction [SIGINT] failed: %s", strerror(errno));
  }

  sa.sa_handler = SIG_IGN;

  if(sigaction(SIGPIPE, &sa, NULL) == -1) {
    LOG(LVL_ERR, "sigaction [SIGPIPE] failed: %s", strerror(errno));
  }

}

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;
  }

#ifdef HAVE_MAGIC
  // initialize libmagic
  magicCookie = magic_open(MAGIC_SYMLINK | MAGIC_MIME_TYPE);
  if(!magicCookie) {
    LOG(LVL_ERR, "Cannot allocate magic cookie");
  } else {
    // load the default database
    if(magic_load(magicCookie, NULL) == -1) {
      LOG(LVL_ERR, "Cannot load default magic database: %s", magic_error(magicCookie));
      magic_close(magicCookie);
      magicCookie = 0;
    } else {
      LOG(LVL_INFO, "libmagic initialized successfully.");
    }
  }
#endif

  // setup the signal handlers
  init_signal_handlers();

  // 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) {
    sleep(60);
  }

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

  MHD_stop_daemon(d);

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

#ifdef HAVE_MAGIC
  magic_close(magicCookie);
#endif

  LOG(LVL_INFO, "Thanks for using fileshare.");
  logger_shutdown();
  return EXIT_SUCCESS;
}