/*
 * vim: sw=2 ts=2 expandtab
 *
 * "THE PIZZA-WARE LICENSE" (derived from "THE BEER-WARE LICENCE"):
 * Thomas Kolb <cfr34k@tkolb.de> wrote this file. As long as you retain this
 * notice you can do whatever you want with this stuff. If we meet some day,
 * and you think this stuff is worth it, you can buy me a pizza in return.
 * - Thomas Kolb
 */

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

#include <errno.h>

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

#include <arpa/inet.h>
#include <ifaddrs.h>
#include <netdb.h>
#include <sys/socket.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 "favicon.h"
#include "util.h"

#include "main.h"

#define DEFAULT_PORT 8888

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

#ifdef HAVE_MAGIC
magic_t magicCookie;
#endif

int running = 1;
int uploadEnabled = 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);

  // close the upload file if open
  if(connstate->upload_fd) {
    fclose(connstate->upload_fd);
  }

  if(connstate->postProcessor) {
    MHD_destroy_post_processor(connstate->postProcessor);
  }

  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, uploadEnabled);
  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;
}

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

  char *message, *title;
  unsigned int resultCode = MHD_HTTP_OK;

  switch(connstate->result) {
    case RC_OK:
      message = "Request was processed successfully.";
      title = "Success";
      resultCode = MHD_HTTP_OK;
      break;

    case RC_EXISTS:
      message = "The file you tried to upload already exists on the server.";
      title = "File already exists";
      resultCode = MHD_HTTP_INTERNAL_SERVER_ERROR;
      break;

    case RC_OPEN_FAILED:
      message = "Could not open the file on the server for writing.";
      title = "Open failed";
      resultCode = MHD_HTTP_INTERNAL_SERVER_ERROR;
      break;

    case RC_WRONG_TARGET:
      message = "You tried to put a new file into something which is not a directory.";
      title = "Target error";
      resultCode = MHD_HTTP_INTERNAL_SERVER_ERROR;
      break;

    case RC_WRITE_FAILED:
      message = "A write error occurred while storing uploaded data to the file.";
      title = "Write error";
      resultCode = MHD_HTTP_INTERNAL_SERVER_ERROR;
      break;
  }

  char *buffer = malloc(strlen(HEADER1 HEADER2 FOOTER) + 1024);

  sprintf(buffer,
      HEADER1
      "<title>%s</title>"
      HEADER2
      "<h1>%s</h1><p>%s</p>"
      "<p><a href=\".\">Back to the directory listing.</a></p>"
      FOOTER,
      title, title, message);

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

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

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


static int post_processor(void *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) {
  LOG(LVL_DUMP, "Entering POST handler (key=%s, filename=%s, contentType=%s, transferEncoding=%s, size=%u)",
      key, filename, content_type, transfer_encoding, size);

  struct ConnectionState *ci = (struct ConnectionState*)cls;

  if(kind == MHD_POSTDATA_KIND) {
    if(strcmp("data", key) == 0) {
      if(ci->upload_fd == NULL) {
        // file pointer not allocated yet

        // check if we are storing the new file into a directory
        if(!S_ISDIR(ci->targetStat.st_mode)) {
          LOG(LVL_WARN, "Cannot upload %s: Target path is not an existing directory.", filename);
          ci->result = RC_WRONG_TARGET;
          return MHD_NO;
        }

        // determine the path where to store the uploaded file
        strncpy(ci->uploadFilename, ci->localFileName, PATH_MAX);
        strcat(ci->uploadFilename, "/");
        strncat(ci->uploadFilename, filename, PATH_MAX-strlen(ci->uploadFilename));

        // check if the file already exists
        FILE *tmp = fopen(ci->uploadFilename, "rb");
        if(tmp) {
          LOG(LVL_WARN, "Cannot upload to %s: file exists.", ci->uploadFilename);
          ci->result = RC_EXISTS;
          fclose(tmp);
          return MHD_NO;
        }

        // file does not exist and can therefore be opened for writing
        ci->upload_fd = fopen(ci->uploadFilename, "wb");
        if(!ci->upload_fd) {
          LOG(LVL_WARN, "Cannot upload to %s: file cannot be created.", ci->uploadFilename);
          ci->result = RC_OPEN_FAILED;
          return MHD_NO;
        }

        if(0 == fwrite(data, size, 1, ci->upload_fd)) {
          LOG(LVL_WARN, "Cannot upload to %s: write operation failed.", ci->uploadFilename);
          ci->result = RC_WRITE_FAILED;
          return MHD_NO;
        }

        LOG(LVL_WARN, "Upload to %s started successfully.", ci->uploadFilename);
      } else {
        // file descriptor is already open
        if(0 == fwrite(data, size, 1, ci->upload_fd)) {
          LOG(LVL_WARN, "Cannot upload to %s: write operation failed.", ci->uploadFilename);
          ci->result = RC_WRITE_FAILED;
          return MHD_NO;
        }
      }
    }
    return MHD_YES;
  }

  return MHD_NO;
}

int key_value_iterator(void *cls,
                       enum MHD_ValueKind kind,
                       const char *key, const char *value) {
  struct ConnectionState *connstate = (struct ConnectionState*)cls;

  if(kind == MHD_GET_ARGUMENT_KIND) {
    if(strcmp(key, "upload") == 0) {
      connstate->uploadRequest = 1;
      return MHD_NO; // this is the only argument we search for
    }

    return MHD_YES;
  } else {
    return MHD_NO;
  }
}


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

    connstate->result = RC_OK;
    connstate->upload_fd = NULL;
    connstate->uploadRequest = 0;

    // 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, "%s %s (local: %s)",
        method, url, connstate->localFileName);

    if (0 == strcmp(method, "GET") || 0 == strcmp(method, "HEAD")) {
      // process GET arguments
      MHD_get_connection_values(connection, MHD_GET_ARGUMENT_KIND, key_value_iterator, connstate);

      connstate->postProcessor = NULL;
      connstate->requestType = GET;
    } else if(0 == strcmp(method, "POST")) {
      if(!uploadEnabled) {
        LOG(LVL_WARN,
            "Uploads are disabled, so POST requests are denied.",
            connstate->localFileName);
        return MHD_queue_response(connection, MHD_HTTP_FORBIDDEN, error403Response);
      } else {
        connstate->postProcessor = MHD_create_post_processor(connection, 1024*1024, post_processor, connstate);
        connstate->requestType = POST;
      }
    } else {
      LOG(LVL_WARN, "Unexpected method: %s.", method);
      return MHD_NO;
    }

    // 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);
    }

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

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

    // serv the favicon, if requested
    if(strcmp(url, "/favicon.png") == 0) {
      LOG(LVL_INFO, "Serving FavIcon request.");
      return MHD_queue_response(connection, MHD_HTTP_OK, faviconResponse);
    }

    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);
    }
  } else if(connstate->requestType == POST) {
    if (*upload_data_size != 0) {
      MHD_post_process (connstate->postProcessor, upload_data, *upload_data_size);
      *upload_data_size = 0;

      return MHD_YES;
    } else {
      return serv_result_page(connection, connstate);
    }
  }

  // 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));
  }
}

void print_urls(int port) {
  struct ifaddrs *ifaddr, *ifa;
  int family, s;
  char host[INET6_ADDRSTRLEN];

  if(getifaddrs(&ifaddr) == -1) {
    LOG(LVL_ERR, "getifaddrs failed: %s", strerror(errno));
    return;
  }

  for(ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
    if(ifa->ifa_addr == NULL) {
      continue;
    }

    family = ifa->ifa_addr->sa_family;

    if(family == AF_INET || family == AF_INET6) {
      s = getnameinfo(ifa->ifa_addr,
                      (family == AF_INET) ? sizeof(struct sockaddr_in)
                                          : sizeof(struct sockaddr_in6),
                      host,
                      INET6_ADDRSTRLEN,
                      NULL, 0,
                      NI_NUMERICHOST);

      if(s != 0) {
        LOG(LVL_ERR, "getnameinfo failed: %s", gai_strerror(s));
        continue;
      }

      if(family == AF_INET) {
        LOG(LVL_INFO, "%-8s: http://%s:%i", ifa->ifa_name, host, port);
      } else { // IPv6
        LOG(LVL_INFO, "%-8s: http://[%s]:%i", ifa->ifa_name, host, port);
      }
    }
  }

  freeifaddrs(ifaddr);
}

int parse_cmdline(int argc, char **argv, int *port, int *enableUpload, char **shareRoot) {
  int c;

  *enableUpload = 0;
  *port = DEFAULT_PORT;

  while ((c = getopt (argc, argv, "up:")) != -1) {
    switch (c) {
      case 'u':
        *enableUpload = 1;
        break;
      case 'p':
        // a port was given on the command line, try to parse it
        if(sscanf(optarg, "%i", port) != 1) {
          LOG(LVL_FATAL, "%s is not a valid port number!", optarg);
          return 1;
        }

        if(*port < 1 || *port > 65535) {
          LOG(LVL_FATAL, "Port %i is out of range [1-65535]!", *port);
          return 1;
        }
        break;
      case '?':
        if (optopt == 'p') {
          LOG(LVL_ERR, "Option -%c requires an argument.\n", optopt);
        } else if (isprint (optopt)) {
          LOG(LVL_ERR, "Unknown option `-%c'.\n", optopt);
        } else {
          LOG(LVL_ERR, "Unknown option character `\\x%x'.\n", optopt);
        }
        return 1;

      default:
        return 1;
    }
  }

  if(optind < argc) {
    // found non-option argument -> use as shared dir
    *shareRoot = argv[optind];
    return 0;
  }

  return 1;
}

int main(int argc, char ** argv) {
  struct MHD_Daemon *d, *d6;
  struct stat sBuf;

  int port;

  logger_init();

  LOG(LVL_INFO, "Welcome to fileshare " VERSION);

#ifndef DEBUG
  // don't show debug output in release build
  logger_set_verbosity(LVL_INFO);
#endif

  // parse command line arguments
  if(parse_cmdline(argc, argv, &port, &uploadEnabled, &shareRoot)) {
    LOG(LVL_ERR, "Failed to parse command line!");
    LOG(LVL_INFO, "Usage: %s [arguments] <dir>", argv[0]);
    LOG(LVL_INFO, "");
    LOG(LVL_INFO, "Arguments:");
    LOG(LVL_INFO, "");
    LOG(LVL_INFO, "\t-u       Enable Uploads");
    LOG(LVL_INFO, "\t-p port  Change the listening port.");
    LOG(LVL_INFO, "");
    return 1;
  }

  if(uploadEnabled) {
    LOG(LVL_WARN, "Uploads are enabled. Users can create new files anywhere in %s !", shareRoot);
  }

  // check if shareRoot is an existing directory
  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);
  LOG(LVL_INFO, "Using port: %i", 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");

  // static response for favicon
  faviconResponse = create_favicon_response();

  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_ERR, "Cannot start up libmicrohttpd listening on IPv4.");
  }

  d6 = MHD_start_daemon(MHD_USE_THREAD_PER_CONNECTION | MHD_USE_IPv6,
                        port,
                        NULL,
                        NULL,
                        &connection_handler,
                        NULL,
                        MHD_OPTION_NOTIFY_COMPLETED,
                        &request_completed, NULL,
                        MHD_OPTION_END);
  if (d6 == NULL) {
    LOG(LVL_ERR, "Cannot start up libmicrohttpd listening on IPv6.");
  }

  if(d == NULL && d6 == NULL) {
    LOG(LVL_FATAL, "Both IPv4 and IPv6 servers failed to start. Terminating.");
    return EXIT_FAILURE;
  }

  LOG(LVL_INFO, "Startup successful. Here are the IP addresses for this computer:");
  print_urls(port);

  while(running) {
    sleep(60);
  }

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

  MHD_stop_daemon(d);
  MHD_stop_daemon(d6);

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

#ifdef HAVE_MAGIC
  magic_close(magicCookie);
#endif

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