#include "api.h"

#include <string.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>
#include <SDL.h>
#include <SDL_thread.h>
#include <assert.h>

#if _WIN32
  // https://stackoverflow.com/questions/60645/overlapped-i-o-on-anonymous-pipe
  // https://docs.microsoft.com/en-us/windows/win32/procthread/creating-a-child-process-with-redirected-input-and-output
  #include <windows.h>
#else
  #include <errno.h>
  #include <unistd.h>
  #include <signal.h>
  #include <fcntl.h>
  #include <sys/types.h>
  #include <sys/wait.h>
#endif

#define READ_BUF_SIZE 2048
#define PROCESS_TERM_TRIES 3
#define PROCESS_TERM_DELAY 50
#define PROCESS_KILL_LIST_NAME "__process_kill_list__"

#if _WIN32

typedef DWORD process_error_t;
typedef HANDLE process_stream_t;
typedef HANDLE process_handle_t;
typedef wchar_t process_arglist_t[32767];
typedef wchar_t *process_env_t;

#define HANDLE_INVALID (INVALID_HANDLE_VALUE)
#define PROCESS_GET_HANDLE(P) ((P)->process_information.hProcess)

static volatile long PipeSerialNumber;

#else

typedef int process_error_t;
typedef int process_stream_t;
typedef pid_t process_handle_t;
typedef char **process_arglist_t;
typedef char **process_env_t;

#define HANDLE_INVALID (0)
#define PROCESS_GET_HANDLE(P) ((P)->pid)

#endif

#ifdef __GNUC__
#define UNUSED __attribute__((__unused__))
#else
#define UNUSED
#endif

typedef struct {
  bool running, detached;
  int returncode, deadline;
  long pid;
  #if _WIN32
    PROCESS_INFORMATION process_information;
    OVERLAPPED overlapped[2];
    bool reading[2];
    char buffer[2][READ_BUF_SIZE];
  #endif
  process_stream_t child_pipes[3][2];
} process_t;

typedef struct process_kill_s {
  int tries;
  uint32_t start_time;
  process_handle_t handle;
  struct process_kill_s *next;
} process_kill_t;

typedef struct {
  bool stop;
  SDL_mutex *mutex;
  SDL_cond *has_work, *work_done;
  SDL_Thread *worker_thread;
  process_kill_t *head;
  process_kill_t *tail;
} process_kill_list_t;

typedef enum {
  SIGNAL_KILL,
  SIGNAL_TERM,
  SIGNAL_INTERRUPT
} signal_e;

typedef enum {
  WAIT_NONE     = 0,
  WAIT_DEADLINE = -1,
  WAIT_INFINITE = -2
} wait_e;

typedef enum {
  STDIN_FD,
  STDOUT_FD,
  STDERR_FD,
  // Special values for redirection.
  REDIRECT_DEFAULT = -1,
  REDIRECT_DISCARD = -2,
  REDIRECT_PARENT = -3,
} filed_e;

static void close_fd(process_stream_t *handle) {
  if (*handle && *handle != HANDLE_INVALID) {
#ifdef _WIN32
    CloseHandle(*handle);
#else
    close(*handle);
#endif
    *handle = HANDLE_INVALID;
  }
}


static int kill_list_worker(void *ud);


static void kill_list_free(process_kill_list_t *list) {
  process_kill_t *node, *temp;
  SDL_WaitThread(list->worker_thread, NULL);
  SDL_DestroyMutex(list->mutex);
  SDL_DestroyCond(list->has_work);
  SDL_DestroyCond(list->work_done);
  node = list->head;
  while (node) {
    temp = node;
    node = node->next;
    free(temp);
  }
  memset(list, 0, sizeof(process_kill_list_t));
}


static bool kill_list_init(process_kill_list_t *list) {
  memset(list, 0, sizeof(process_kill_list_t));
  list->mutex = SDL_CreateMutex();
  list->has_work = SDL_CreateCond();
  list->work_done = SDL_CreateCond();
  list->head = list->tail = NULL;
  list->stop = false;
  if (!list->mutex || !list->has_work || !list->work_done) {
    kill_list_free(list);
    return false;
  }
  list->worker_thread = SDL_CreateThread(kill_list_worker, "process_kill", list);
  if (!list->worker_thread) {
    kill_list_free(list);
    return false;
  }
  return true;
}


static void kill_list_push(process_kill_list_t *list, process_kill_t *task) {
  if (!list) return;
  task->next = NULL;
  if (list->tail) {
    list->tail->next = task;
    list->tail = task;
  } else {
    list->head = list->tail = task;
  }
}


static void kill_list_pop(process_kill_list_t *list) {
  if (!list || !list->head) return;
  process_kill_t *head = list->head;
  list->head = list->head->next;
  if (!list->head) list->tail = NULL;
  head->next = NULL;
}


static void kill_list_wait_all(process_kill_list_t *list) {
  SDL_LockMutex(list->mutex);
  // wait until list is empty
  while (list->head)
    SDL_CondWait(list->work_done, list->mutex);
  // tell the worker to stop
  list->stop = true;
  SDL_CondSignal(list->has_work);
  SDL_UnlockMutex(list->mutex);
}


static void process_handle_close(process_handle_t *handle) {
#ifdef _WIN32
  if (*handle) {
    CloseHandle(*handle);
    *handle = NULL;
  }
#endif
  (void) 0;
}


static bool process_handle_is_running(process_handle_t handle, int *status) {
#ifdef _WIN32
  DWORD s;
  if (GetExitCodeProcess(handle, &s) && s != STILL_ACTIVE) {
    if (status != NULL)
      *status = s;
    return false;
  }
#else
  int s;
  if (waitpid(handle, &s, WNOHANG) != 0) {
    if (status != NULL)
      *status = WEXITSTATUS(s);
    return false;
  }
#endif
  return true;
}


static bool process_handle_signal(process_handle_t handle, signal_e sig) {
#if _WIN32
  switch(sig) {
    case SIGNAL_TERM: return GenerateConsoleCtrlEvent(CTRL_BREAK_EVENT, GetProcessId(handle));
    case SIGNAL_KILL: return TerminateProcess(handle, -1);
    case SIGNAL_INTERRUPT: return DebugBreakProcess(handle);
  }
#else
  switch (sig) {
    case SIGNAL_TERM: return kill(-handle, SIGTERM) == 0; break;
    case SIGNAL_KILL: return kill(-handle, SIGKILL) == 0; break;
    case SIGNAL_INTERRUPT: return kill(-handle, SIGINT) == 0; break;
  }
#endif
  return false;
}


static int kill_list_worker(void *ud) {
  process_kill_list_t *list = (process_kill_list_t *) ud;
  process_kill_t *current_task;
  uint32_t delay;

  while (true) {
    SDL_LockMutex(list->mutex);

    // wait until we have work to do
    while (!list->head && !list->stop)
      SDL_CondWait(list->has_work, list->mutex); // LOCK MUTEX

    if (list->stop) break;

    while ((current_task = list->head)) {
      if ((SDL_GetTicks() - current_task->start_time) < PROCESS_TERM_DELAY)
        break;
      kill_list_pop(list);
      if (process_handle_is_running(current_task->handle, NULL)) {
        if (current_task->tries < PROCESS_TERM_TRIES)
          process_handle_signal(current_task->handle, SIGNAL_TERM);
        else if (current_task->tries == PROCESS_TERM_TRIES)
          process_handle_signal(current_task->handle, SIGNAL_KILL);
        else
          goto free_task;

        // add the task back into the queue
        current_task->tries++;
        current_task->start_time = SDL_GetTicks();
        kill_list_push(list, current_task);
      } else {
        free_task:
        SDL_CondSignal(list->work_done);
        process_handle_close(&current_task->handle);
        free(current_task);
      }
    }
    delay = list->head ? (list->head->start_time + PROCESS_TERM_DELAY) - SDL_GetTicks() : 0;
    SDL_UnlockMutex(list->mutex);
    SDL_Delay(delay);
  }
  SDL_UnlockMutex(list->mutex);
  return 0;
}


static int push_error_string(lua_State *L, process_error_t err) {
#ifdef _WIN32
  char *msg = NULL;
  FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM
                | FORMAT_MESSAGE_ALLOCATE_BUFFER
                | FORMAT_MESSAGE_IGNORE_INSERTS,
                NULL,
                err,
                MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
                (char *) &msg,
                0,
                NULL);
  if (!msg)
    return 0;

  lua_pushstring(L, msg);
  LocalFree(msg);
#else
  lua_pushstring(L, strerror(err));
#endif
  return 1;
}

static void push_error(lua_State *L, const char *extra, process_error_t err) {
  const char *msg = "unknown error";
  extra = extra != NULL ? extra : "error";
  if (push_error_string(L, err))
    msg = lua_tostring(L, -1);
  lua_pushfstring(L, "%s: %s (%d)", extra, msg, err);
}

static bool poll_process(process_t* proc, int timeout) {
  uint32_t ticks;

  if (!proc->running)
    return false;

  if (timeout == WAIT_DEADLINE)
    timeout = proc->deadline;

  ticks = SDL_GetTicks();
  do {
    int status;
    if (!process_handle_is_running(PROCESS_GET_HANDLE(proc), &status)) {
      proc->running = false;
      proc->returncode = status;
      break;
    }
    if (timeout)
      SDL_Delay(timeout >= 5 ? 5 : 0);
  } while (timeout == WAIT_INFINITE || (int)SDL_GetTicks() - ticks < timeout);

  return proc->running;
}

static bool signal_process(process_t* proc, signal_e sig) {
  if (process_handle_signal(PROCESS_GET_HANDLE(proc), sig))
    poll_process(proc, WAIT_NONE);
  return true;
}


static UNUSED char *xstrdup(const char *str) {
  char *result = str ? malloc(strlen(str) + 1) : NULL;
  if (result) strcpy(result, str);
  return result;
}


static int process_arglist_init(process_arglist_t *list, size_t *list_len, size_t nargs) {
  *list_len = 0;
#ifdef _WIN32
  memset(*list, 0, sizeof(process_arglist_t));
#else
  *list = calloc(sizeof(char *), nargs + 1);
  if (!*list) return ENOMEM;
#endif
  return 0;
}


static int process_arglist_add(process_arglist_t *list, size_t *list_len, const char *arg, bool escape) {
  size_t len = *list_len;
#ifdef _WIN32
  int arg_len;
  wchar_t *cmdline = *list;
  wchar_t arg_w[32767];
  // this length includes the null terminator!
  if (!(arg_len = MultiByteToWideChar(CP_UTF8, 0, arg, -1, arg_w, 32767)))
    return GetLastError();
  if (arg_len + len > 32767)
    return ERROR_NOT_ENOUGH_MEMORY;

  if (!escape) {
    // replace the current null terminator with a space
    if (len > 0) cmdline[len-1] = ' ';
    memcpy(cmdline + len, arg_w, arg_len * sizeof(wchar_t));
    len += arg_len;
  } else {
    // if the string contains spaces, then we must quote it
    bool quote = wcspbrk(arg_w, L" \t\v\r\n");
    int backslash = 0, escaped_len = quote ? 2 : 0;
    for (int i = 0; i < arg_len; i++) {
      if (arg_w[i] == L'\\') {
        backslash++;
      } else if (arg_w[i] == L'"') {
        escaped_len += backslash + 1;
        backslash = 0;
      } else {
        backslash = 0;
      }
      escaped_len++;
    }
    // escape_len contains NUL terminator
    if (escaped_len + len > 32767)
      return ERROR_NOT_ENOUGH_MEMORY;
    // replace our previous NUL terminator with space
    if (len > 0) cmdline[len-1] = L' ';
    if (quote) cmdline[len++] = L'"';
    // we are not going to iterate over NUL terminator
    for (int i = 0;arg_w[i]; i++) {
      if (arg_w[i] == L'\\') {
        backslash++;
      } else if (arg_w[i] == L'"') {
        // add backslash + 1 backslashes
        for (int j = 0; j < backslash; j++)
          cmdline[len++] = L'\\';
        cmdline[len++] = L'\\';
        backslash = 0;
      } else {
        backslash = 0;
      }
      cmdline[len++] = arg_w[i];
    }
    if (quote) cmdline[len++] = L'"';
    cmdline[len++] = L'\0';
  }
#else
  char **cmd = *list;
  cmd[len] = xstrdup(arg);
  if (!cmd[len]) return ENOMEM;
  len++;
#endif
  *list_len = len;
  return 0;
}


static void process_arglist_free(process_arglist_t *list) {
#ifndef _WIN32
  char **cmd = *list;
  for (int i = 0; cmd[i]; i++)
    free(cmd[i]);
  free(cmd);
  *list = NULL;
#endif
}


static int process_env_init(process_env_t *env_list, size_t *env_len, size_t nenv) {
  *env_len = 0;
#ifdef _WIN32
  *env_list = NULL;
#else
  *env_list = calloc(sizeof(char *), nenv * 2);
  if (!*env_list) return ENOMEM;
#endif
  return 0;
}


#ifdef _WIN32
static int cmp_name(wchar_t *a, wchar_t *b) {
  wchar_t _A[32767], _B[32767], *A = _A, *B = _B, *a_eq, *b_eq;
  int na, nb, r;
  a_eq = wcschr(a, L'=');
  b_eq = wcschr(b, L'=');
  assert(a_eq);
  assert(b_eq);
  na = a_eq - a;
  nb = b_eq - b;
  r = LCMapStringW(LOCALE_INVARIANT, LCMAP_UPPERCASE, a, na, A, na);
  assert(r == na);
  A[na] = L'\0';
  r = LCMapStringW(LOCALE_INVARIANT, LCMAP_UPPERCASE, b, nb, B, nb);
  assert(r == nb);
  B[nb] = L'\0';

  for (;;) {
    wchar_t AA = *A++, BB = *B++;
    if (AA > BB)
      return 1;
    else if (AA < BB)
      return -1;
    else if (!AA && !BB)
      return 0;
  }
}


static int process_env_add_variable(process_env_t *env_list, size_t *env_list_len, wchar_t *var, size_t var_len) {
  wchar_t *list, *list_p;
  size_t block_var_len, list_len;
  list = list_p = *env_list;
  list_len = *env_list_len;
  if (list_len) {
    // check if it is already in the block
    while ((block_var_len = wcslen(list_p))) {
      if (cmp_name(list_p, var) == 0)
        return -1; // already installed
      list_p += block_var_len + 1;
    }
  }
  // allocate list + 1 characters for the block terminator
  list = realloc(list, (list_len + var_len + 1) * sizeof(wchar_t));
  if (!list) return ERROR_NOT_ENOUGH_MEMORY;
  // copy the env variable to the block
  memcpy(list + list_len, var, var_len * sizeof(wchar_t));
  // terminate the block again
  list[list_len + var_len] = L'\0';
  *env_list = list;
  *env_list_len = (list_len + var_len);
  return 0;
}


static int process_env_add_system(process_env_t *env_list, size_t *env_list_len) {
  int retval = 0;
  wchar_t *proc_env_block, *proc_env_block_p;
  int proc_env_len;

  proc_env_block = proc_env_block_p = GetEnvironmentStringsW();
  while ((proc_env_len = wcslen(proc_env_block_p))) {
    // try to add it to the list
    if ((retval = process_env_add_variable(env_list, env_list_len, proc_env_block_p, proc_env_len + 1)) > 0)
      goto cleanup;
    proc_env_block_p += proc_env_len + 1;
  }
  retval = 0;

cleanup:
  if (proc_env_block) FreeEnvironmentStringsW(proc_env_block);
  return retval;
}
#endif


static int process_env_add(process_env_t *env_list, size_t *env_len, const char *key, const char *value) {
#ifdef _WIN32
  wchar_t env_var[32767];
  int r, var_len = 0;
  if (!(r = MultiByteToWideChar(CP_UTF8, 0, key, -1, env_var, 32767)))
    return GetLastError();
  var_len += r;
  env_var[var_len-1] = L'=';
  if (!(r = MultiByteToWideChar(CP_UTF8, 0, value, -1, env_var + var_len, 32767 - var_len)))
    return GetLastError();
  var_len += r;
  return process_env_add_variable(env_list, env_len, env_var, var_len);
#else
  (*env_list)[*env_len] = xstrdup(key);
  if (!(*env_list)[*env_len])
    return ENOMEM;
  (*env_list)[*env_len + 1] = xstrdup(value);
  if (!(*env_list)[*env_len + 1])
    return ENOMEM;
  *env_len += 2;
#endif
  return 0;
}


static void process_env_free(process_env_t *list, size_t list_len) {
  if (!*list) return;
#ifdef _WIN32
  free(*list);
#else
  for (size_t i = 0; i < list_len; i++) free((*list)[i]);
  free(*list);
#endif
  *list = NULL;
}


static int process_start(lua_State* L) {
  int r, retval = 1;
  size_t env_len = 0, cmd_len = 0, arglist_len = 0, env_vars_len = 0;
  process_arglist_t arglist;
  process_env_t env_vars = NULL;
  const char *cwd = NULL;
  bool detach = false, escape = true;
  int deadline = 10, new_fds[3] = { STDIN_FD, STDOUT_FD, STDERR_FD };

  if (lua_isstring(L, 1)) {
    escape = false;
    // create a table that contains the string as the value
    lua_createtable(L, 1, 0);
    lua_pushvalue(L, 1);
    lua_rawseti(L, -2, 1);
    lua_replace(L, 1);
  }

  luaL_checktype(L, 1, LUA_TTABLE);
  #if LUA_VERSION_NUM > 501
    lua_len(L, 1);
  #else
    lua_pushinteger(L, (int)lua_objlen(L, 1));
  #endif
  cmd_len = luaL_checknumber(L, -1); lua_pop(L, 1);
  if (!cmd_len)
    return luaL_argerror(L, 1, "table cannot be empty");
  // check if each arguments is a string
  for (size_t i = 1; i <= cmd_len; ++i) {
    lua_rawgeti(L, 1, i);
    luaL_checkstring(L, -1);
    lua_pop(L, 1);
  }

  if (lua_istable(L, 2)) {
    lua_getfield(L, 2, "detach");  detach = lua_toboolean(L, -1);
    lua_getfield(L, 2, "timeout"); deadline = luaL_optnumber(L, -1, deadline);
    lua_getfield(L, 2, "cwd");     cwd = luaL_optstring(L, -1, NULL);
    lua_getfield(L, 2, "stdin");   new_fds[STDIN_FD] = luaL_optnumber(L, -1, STDIN_FD);
    lua_getfield(L, 2, "stdout");  new_fds[STDOUT_FD] = luaL_optnumber(L, -1, STDOUT_FD);
    lua_getfield(L, 2, "stderr");  new_fds[STDERR_FD] = luaL_optnumber(L, -1, STDERR_FD);
    for (int stream = STDIN_FD; stream <= STDERR_FD; ++stream) {
      if (new_fds[stream] > STDERR_FD || new_fds[stream] < REDIRECT_PARENT)
        return luaL_error(L, "error: redirect to handles, FILE* and paths are not supported");
    }
    lua_pop(L, 6); // pop all the values above

    luaL_getsubtable(L, 2, "env");
    // count environment variobles
    lua_pushnil(L);
    while (lua_next(L, -2) != 0) {
      luaL_checkstring(L, -2);
      luaL_checkstring(L, -1);
      lua_pop(L, 1);
      env_len++;
    }

    if (env_len) {
      if ((r = process_env_init(&env_vars, &env_vars_len, env_len)) != 0) {
        retval = -1;
        push_error(L, "cannot allocate environment list", r);
        goto cleanup;
      }

      lua_pushnil(L);
      while (lua_next(L, -2) != 0) {
        if ((r = process_env_add(&env_vars, &env_vars_len, lua_tostring(L, -2), lua_tostring(L, -1))) != 0) {
          retval = -1;
          push_error(L, "cannot copy environment variable", r);
          goto cleanup;
        }
        lua_pop(L, 1);
        env_len++;
      }
    }
  }

  // allocate and copy commands
  if ((r = process_arglist_init(&arglist, &arglist_len, cmd_len)) != 0) {
    retval = -1;
    push_error(L, "cannot create argument list", r);
    goto cleanup;
  }
  for (size_t i = 1; i <= cmd_len; i++) {
    lua_rawgeti(L, 1, i);
    if ((r = process_arglist_add(&arglist, &arglist_len, lua_tostring(L, -1), escape)) != 0) {
      retval = -1;
      push_error(L, "cannot add argument", r);
      goto cleanup;
    }
    lua_pop(L, 1);
  }

  process_t* self = lua_newuserdata(L, sizeof(process_t));
  memset(self, 0, sizeof(process_t));
  luaL_setmetatable(L, API_TYPE_PROCESS);
  self->deadline = deadline;
  self->detached = detach;
  #if _WIN32
    if (env_vars) {
      if ((r = process_env_add_system(&env_vars, &env_vars_len)) != 0) {
        retval = -1;
        push_error(L, "cannot add environment variable", r);
        goto cleanup;
      }
    }
    for (int i = 0; i < 3; ++i) {
      switch (new_fds[i]) {
        case REDIRECT_PARENT:
          switch (i) {
            case STDIN_FD: self->child_pipes[i][0] = GetStdHandle(STD_INPUT_HANDLE); break;
            case STDOUT_FD: self->child_pipes[i][1] = GetStdHandle(STD_OUTPUT_HANDLE); break;
            case STDERR_FD: self->child_pipes[i][1] = GetStdHandle(STD_ERROR_HANDLE); break;
          }
          self->child_pipes[i][i == STDIN_FD ? 1 : 0] = INVALID_HANDLE_VALUE;
        break;
        case REDIRECT_DISCARD:
          self->child_pipes[i][0] = INVALID_HANDLE_VALUE;
          self->child_pipes[i][1] = INVALID_HANDLE_VALUE;
        break;
        default: {
          if (new_fds[i] == i) {
            char pipeNameBuffer[MAX_PATH];
            sprintf(pipeNameBuffer, "\\\\.\\Pipe\\RemoteExeAnon.%08lx.%08lx", GetCurrentProcessId(), InterlockedIncrement(&PipeSerialNumber));
            self->child_pipes[i][0] = CreateNamedPipeA(pipeNameBuffer, PIPE_ACCESS_INBOUND | FILE_FLAG_OVERLAPPED,
              PIPE_TYPE_BYTE | PIPE_WAIT, 1, READ_BUF_SIZE, READ_BUF_SIZE, 0, NULL);
            if (self->child_pipes[i][0] == INVALID_HANDLE_VALUE) {
              push_error(L, "cannot create pipe", GetLastError());
              retval = -1;
              goto cleanup;
            }
            self->child_pipes[i][1] = CreateFileA(pipeNameBuffer, GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
            if (self->child_pipes[i][1] == INVALID_HANDLE_VALUE) {
              // prevent CloseHandle from messing up error codes
              DWORD err = GetLastError();
              CloseHandle(self->child_pipes[i][0]);
              push_error(L, "cannot open pipe", err);
              retval = -1;
              goto cleanup;
            }
            if (!SetHandleInformation(self->child_pipes[i][i == STDIN_FD ? 1 : 0], HANDLE_FLAG_INHERIT, 0) ||
                !SetHandleInformation(self->child_pipes[i][i == STDIN_FD ? 0 : 1], HANDLE_FLAG_INHERIT, 1)) {
                  push_error(L, "cannot set pipe permission", GetLastError());
                  retval = -1;
                  goto cleanup;
            }
          }
        } break;
      }
    }
    for (int i = 0; i < 3; ++i) {
      if (new_fds[i] != i) {
        self->child_pipes[i][0] = self->child_pipes[new_fds[i]][0];
        self->child_pipes[i][1] = self->child_pipes[new_fds[i]][1];
      }
    }
    STARTUPINFOW siStartInfo;
    memset(&self->process_information, 0, sizeof(self->process_information));
    memset(&siStartInfo, 0, sizeof(siStartInfo));
    siStartInfo.cb = sizeof(siStartInfo);
    siStartInfo.dwFlags |= STARTF_USESTDHANDLES;
    siStartInfo.hStdInput = self->child_pipes[STDIN_FD][0];
    siStartInfo.hStdOutput = self->child_pipes[STDOUT_FD][1];
    siStartInfo.hStdError = self->child_pipes[STDERR_FD][1];
    wchar_t cwd_w[MAX_PATH];
    if (cwd) // TODO: error handling
      MultiByteToWideChar(CP_UTF8, 0, cwd, -1, cwd_w, MAX_PATH);
    if (!CreateProcessW(NULL, arglist, NULL, NULL, true, (detach ? DETACHED_PROCESS : CREATE_NO_WINDOW) | CREATE_UNICODE_ENVIRONMENT, env_vars, cwd ? cwd_w : NULL, &siStartInfo, &self->process_information)) {
      push_error(L, NULL, GetLastError());
      retval = -1;
      goto cleanup;
    }
    self->pid = (long)self->process_information.dwProcessId;
    if (detach)
      CloseHandle(self->process_information.hProcess);
    CloseHandle(self->process_information.hThread);
  #else
    int control_pipe[2] = { 0 };
    for (int i = 0; i < 3; ++i) { // Make only the parents fd's non-blocking. Children should block.
      if (pipe(self->child_pipes[i]) || fcntl(self->child_pipes[i][i == STDIN_FD ? 1 : 0], F_SETFL, O_NONBLOCK) == -1) {
        push_error(L, "cannot create pipe", errno);
        retval = -1;
        goto cleanup;
      }
    }
    // create a pipe to get the exit code of exec()
    if (pipe(control_pipe) == -1) {
      lua_pushfstring(L, "Error creating control pipe: %s", strerror(errno));
      retval = -1;
      goto cleanup;
    }
    if (fcntl(control_pipe[1], F_SETFD, FD_CLOEXEC) == -1) {
      lua_pushfstring(L, "Error setting FD_CLOEXEC: %s", strerror(errno));
      retval = -1;
      goto cleanup;
    }

    self->pid = (long)fork();
    if (self->pid < 0) {
      push_error(L, "cannot create child process", errno);
      retval = -1;
      goto cleanup;
    } else if (!self->pid) {
      // child process
      if (!detach)
        setpgid(0,0);
      for (int stream = 0; stream < 3; ++stream) {
        if (new_fds[stream] == REDIRECT_DISCARD) { // Close the stream if we don't want it.
          close(self->child_pipes[stream][stream == STDIN_FD ? 0 : 1]);
          close(stream);
        } else if (new_fds[stream] != REDIRECT_PARENT) // Use the parent handles if we redirect to parent.
          dup2(self->child_pipes[new_fds[stream]][new_fds[stream] == STDIN_FD ? 0 : 1], stream);
        close(self->child_pipes[stream][stream == STDIN_FD ? 1 : 0]);
      }
      size_t set;
      for (set = 0; set < env_vars_len && setenv(env_vars[set], env_vars[set+1], 1) == 0; set += 2);
      if (set == env_vars_len && (!detach || setsid() != -1) && (!cwd || chdir(cwd) != -1))
        execvp(arglist[0], (char** const)arglist);
      write(control_pipe[1], &errno, sizeof(errno));
      _exit(-1);
    }
    // close our write side so we can read from child
    close(control_pipe[1]);
    control_pipe[1] = 0;

    // wait for child process to respond
    int sz, process_rc;
    while ((sz = read(control_pipe[0], &process_rc, sizeof(int))) == -1) {
      if (errno == EPIPE) break;
      if (errno != EINTR) {
        lua_pushfstring(L, "Error getting child process status: %s", strerror(errno));
        retval = -1;
        goto cleanup;
      }
    }

    if (sz) {
      // read something from pipe; exec failed
      int status;
      waitpid(self->pid, &status, 0);
      lua_pushfstring(L, "Error creating child process: %s", strerror(process_rc));
      retval = -1;
      goto cleanup;
    }

  #endif
  cleanup:
  #ifndef _WIN32
    if (control_pipe[0]) close(control_pipe[0]);
    if (control_pipe[1]) close(control_pipe[1]);
  #endif
  for (int stream = 0; stream < 3; ++stream) {
    process_stream_t* pipe = &self->child_pipes[stream][stream == STDIN_FD ? 0 : 1];
    if (*pipe) {
      close_fd(pipe);
    }
  }
  process_arglist_free(&arglist);
  process_env_free(&env_vars, env_vars_len);

  if (retval == -1)
    return lua_error(L);

  self->running = true;
  return retval;
}

static int g_read(lua_State* L, int stream, unsigned long read_size) {
  process_t* self = (process_t*) luaL_checkudata(L, 1, API_TYPE_PROCESS);
  long length = 0;
  if (stream != STDOUT_FD && stream != STDERR_FD)
    return luaL_error(L, "error: redirect to handles, FILE* and paths are not supported");
  #if _WIN32
    int writable_stream_idx = stream - 1;
    if (self->reading[writable_stream_idx] || !ReadFile(self->child_pipes[stream][0], self->buffer[writable_stream_idx], READ_BUF_SIZE, NULL, &self->overlapped[writable_stream_idx])) {
      if (self->reading[writable_stream_idx] || GetLastError() == ERROR_IO_PENDING) {
        self->reading[writable_stream_idx] = true;
        DWORD bytesTransferred = 0;
        if (GetOverlappedResult(self->child_pipes[stream][0], &self->overlapped[writable_stream_idx], &bytesTransferred, false)) {
          self->reading[writable_stream_idx] = false;
          length = bytesTransferred;
          memset(&self->overlapped[writable_stream_idx], 0, sizeof(self->overlapped[writable_stream_idx]));
        }
      } else {
        signal_process(self, SIGNAL_TERM);
        return 0;
      }
    } else {
      length = self->overlapped[writable_stream_idx].InternalHigh;
      memset(&self->overlapped[writable_stream_idx], 0, sizeof(self->overlapped[writable_stream_idx]));
    }
    lua_pushlstring(L, self->buffer[writable_stream_idx], length);
  #else
    luaL_Buffer b;
    luaL_buffinit(L, &b);
    uint8_t* buffer = (uint8_t*)luaL_prepbuffsize(&b, READ_BUF_SIZE);
    length = read(self->child_pipes[stream][0], buffer, read_size > READ_BUF_SIZE ? READ_BUF_SIZE : read_size);
    if (length == 0 && !poll_process(self, WAIT_NONE))
      return 0;
    else if (length < 0 && (errno == EAGAIN || errno == EWOULDBLOCK))
      length = 0;
    if (length < 0) {
      signal_process(self, SIGNAL_TERM);
      return 0;
    }
    luaL_addsize(&b, length);
    luaL_pushresult(&b);
  #endif
  return 1;
}

static int f_write(lua_State* L) {
  process_t* self = (process_t*) luaL_checkudata(L, 1, API_TYPE_PROCESS);
  size_t data_size = 0;
  const char* data = luaL_checklstring(L, 2, &data_size);
  long length;
  #if _WIN32
    DWORD dwWritten;
    if (!WriteFile(self->child_pipes[STDIN_FD][1], data, data_size, &dwWritten, NULL)) {
      push_error(L, NULL, GetLastError());
      signal_process(self, SIGNAL_TERM);
      return lua_error(L);
    }
    length = dwWritten;
  #else
    length = write(self->child_pipes[STDIN_FD][1], data, data_size);
    if (length < 0 && (errno == EAGAIN || errno == EWOULDBLOCK))
      length = 0;
    else if (length < 0) {
      push_error(L, "cannot write to child process", errno);
      signal_process(self, SIGNAL_TERM);
      return lua_error(L);
    }
  #endif
  lua_pushinteger(L, length);
  return 1;
}

static int f_close_stream(lua_State* L) {
  process_t* self = (process_t*) luaL_checkudata(L, 1, API_TYPE_PROCESS);
  int stream = luaL_checknumber(L, 2);
  close_fd(&self->child_pipes[stream][stream == STDIN_FD ? 1 : 0]);
  lua_pushboolean(L, 1);
  return 1;
}

// Generic stuff below here.
static int process_strerror(lua_State* L) {
  return push_error_string(L, luaL_checknumber(L, 1));
}

static int f_tostring(lua_State* L) {
  lua_pushliteral(L, API_TYPE_PROCESS);
  return 1;
}

static int f_pid(lua_State* L) {
  process_t* self = (process_t*) luaL_checkudata(L, 1, API_TYPE_PROCESS);
  lua_pushinteger(L, self->pid);
  return 1;
}

static int f_returncode(lua_State *L) {
  process_t* self = (process_t*) luaL_checkudata(L, 1, API_TYPE_PROCESS);
  if (self->running)
    return 0;
  lua_pushinteger(L, self->returncode);
  return 1;
}

static int f_read_stdout(lua_State* L) {
  return g_read(L, STDOUT_FD, luaL_optinteger(L, 2, READ_BUF_SIZE));
}

static int f_read_stderr(lua_State* L) {
  return g_read(L, STDERR_FD, luaL_optinteger(L, 2, READ_BUF_SIZE));
}

static int f_read(lua_State* L) {
  return g_read(L, luaL_checknumber(L, 2), luaL_optinteger(L, 3, READ_BUF_SIZE));
}

static int f_wait(lua_State* L) {
  process_t* self = (process_t*) luaL_checkudata(L, 1, API_TYPE_PROCESS);
  int timeout = luaL_optnumber(L, 2, 0);
  if (poll_process(self, timeout))
    return 0;
  lua_pushinteger(L, self->returncode);
  return 1;
}

static int self_signal(lua_State* L, signal_e sig) {
  process_t* self = (process_t*) luaL_checkudata(L, 1, API_TYPE_PROCESS);
  signal_process(self, sig);
  lua_pushboolean(L, 1);
  return 1;
}
static int f_terminate(lua_State* L) { return self_signal(L, SIGNAL_TERM); }
static int f_kill(lua_State* L) { return self_signal(L, SIGNAL_KILL); }
static int f_interrupt(lua_State* L) { return self_signal(L, SIGNAL_INTERRUPT); }

static int f_gc(lua_State* L) {
  process_kill_list_t *list = NULL;
  process_kill_t *p = NULL;
  process_t* self = (process_t*) luaL_checkudata(L, 1, API_TYPE_PROCESS);

  // get the kill_list for the lua_State
  if (lua_getfield(L, LUA_REGISTRYINDEX, PROCESS_KILL_LIST_NAME) == LUA_TUSERDATA)
    list = (process_kill_list_t *) lua_touserdata(L, -1);

  if (poll_process(self, 0) && !self->detached) {
    // attempt to kill the process if still running and not detached
    signal_process(self, SIGNAL_TERM);
    if (!list || !list->worker_thread || !(p = malloc(sizeof(process_kill_t)))) {
      // use synchronous waiting
      if (poll_process(self, PROCESS_TERM_DELAY)) {
        signal_process(self, SIGNAL_KILL);
        poll_process(self, PROCESS_TERM_DELAY);
      }
    } else {
      // put the handle into a queue for asynchronous waiting
      p->handle = PROCESS_GET_HANDLE(self);
      p->start_time = SDL_GetTicks();
      p->tries = 1;
      SDL_LockMutex(list->mutex);
      kill_list_push(list, p);
      SDL_CondSignal(list->has_work);
      SDL_UnlockMutex(list->mutex);
    }
  }
  close_fd(&self->child_pipes[STDIN_FD ][1]);
  close_fd(&self->child_pipes[STDOUT_FD][0]);
  close_fd(&self->child_pipes[STDERR_FD][0]);
  return 0;
}

static int f_running(lua_State* L) {
  process_t* self = (process_t*)luaL_checkudata(L, 1, API_TYPE_PROCESS);
  lua_pushboolean(L, poll_process(self, WAIT_NONE));
  return 1;
}

static int process_gc(lua_State *L) {
  process_kill_list_t *list = NULL;
  // get the kill_list for the lua_State
  if (lua_getfield(L, LUA_REGISTRYINDEX, PROCESS_KILL_LIST_NAME) == LUA_TUSERDATA) {
    list = (process_kill_list_t *) lua_touserdata(L, -1);
    kill_list_wait_all(list);
    kill_list_free(list);
  }
  return 0;
}

static const struct luaL_Reg process_metatable[] = {
  {"__gc", f_gc},
  {"__tostring", f_tostring},
  {"pid", f_pid},
  {"returncode", f_returncode},
  {"read", f_read},
  {"read_stdout", f_read_stdout},
  {"read_stderr", f_read_stderr},
  {"write", f_write},
  {"close_stream", f_close_stream},
  {"wait", f_wait},
  {"terminate", f_terminate},
  {"kill", f_kill},
  {"interrupt", f_interrupt},
  {"running", f_running},
  {NULL, NULL}
};

static const struct luaL_Reg lib[] = {
  { "start", process_start },
  { "strerror", process_strerror },
  { NULL, NULL }
};

int luaopen_process(lua_State *L) {
  process_kill_list_t *list = lua_newuserdata(L, sizeof(process_kill_list_t));
  if (kill_list_init(list))
    lua_setfield(L, LUA_REGISTRYINDEX, PROCESS_KILL_LIST_NAME);
  else
    lua_pop(L, 1); // discard the list

  // create the process metatable
  luaL_newmetatable(L, API_TYPE_PROCESS);
  luaL_setfuncs(L, process_metatable, 0);
  lua_pushvalue(L, -1);
  lua_setfield(L, -2, "__index");

  // create the process library
  luaL_newlib(L, lib);
  lua_newtable(L);
  lua_pushcfunction(L, process_gc);
  lua_setfield(L, -2, "__gc");
  lua_setmetatable(L, -2);

  API_CONSTANT_DEFINE(L, -1, "WAIT_INFINITE", WAIT_INFINITE);
  API_CONSTANT_DEFINE(L, -1, "WAIT_DEADLINE", WAIT_DEADLINE);

  API_CONSTANT_DEFINE(L, -1, "STREAM_STDIN", STDIN_FD);
  API_CONSTANT_DEFINE(L, -1, "STREAM_STDOUT", STDOUT_FD);
  API_CONSTANT_DEFINE(L, -1, "STREAM_STDERR", STDERR_FD);

  API_CONSTANT_DEFINE(L, -1, "REDIRECT_DEFAULT", REDIRECT_DEFAULT);
  API_CONSTANT_DEFINE(L, -1, "REDIRECT_STDOUT", STDOUT_FD);
  API_CONSTANT_DEFINE(L, -1, "REDIRECT_STDERR", STDERR_FD);
  API_CONSTANT_DEFINE(L, -1, "REDIRECT_PARENT", REDIRECT_PARENT); // Redirects to parent's STDOUT/STDERR
  API_CONSTANT_DEFINE(L, -1, "REDIRECT_DISCARD", REDIRECT_DISCARD); // Closes the filehandle, discarding it.

  return 1;
}