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

#include "buffer.h"
#include "case.h"
#include "env.h"
#include "error.h"
#include "exit.h"
#include "fd.h"
#include "getln.h"
#include "open.h"
#include "pathexec.h"
#include "sig.h"
#include "str.h"
#include "stralloc.h"
#include "uint_t.h"
#include "wait.h"

#include "control.h"
#include "fmtqfn.h"

#ifdef USE_CONFIG
  #include "fehsqm-config.h"
#else
  #include "auto_qmail.h"
#endif

#define WHO "qmail-dkverify"

/**
  @file  qmail-dkverify.c
  @brief stub routine for DKIM signature verification and indication in received message

  Steps:
  ------
  a) Store message with CRLF
  b) Get DKIM signature from message - if given:
  c)   Call qmail-dkim for verification
  d)   Include results as appended header
  e) Queue the message for processing
*/

char bufin[1024];                                        // RFC 5322: 998 chars - why?
buffer bi = BUFFER_INIT(read, 0, bufin, sizeof(bufin));  // read buffer
char bufout[1024];
buffer bo = BUFFER_INIT(write, 1, bufout, sizeof(bufout));  // output message

static void die(int e)
{
  _exit(e);
}

static void die_pipe(char *fn)
{
  unlink(fn);
  die(53);
}

static void die_write(char *fn)
{
  unlink(fn);
  die(53);
}

static void die_read()
{
  die(54);
}

static void out(char *s)
{
  if (buffer_puts(&bo, s) == -1) _exit(111);
}

static void zero()
{
  if (buffer_put(&bo, "\0", 1) == -1) _exit(111);
}

static void zerodie()
{
  zero();
  buffer_flush(&bo);
  _exit(111);
}

static void temp_nomem()
{
  out("ZOut of memory. (#4.3.0)\n");
  zerodie();
}

static void temp_chdir()
{
  out("ZUnable to switch to target directory. (#4.3.0)\n");
  zerodie();
}

static void temp_create()
{
  out("ZUnable to create DKIM stage file. (#4.3.0)\n");
  zerodie();
}

static void temp_unlink()
{
  out("ZUnable to unlink DKIM stage file. (#4.3.0)\n");
  zerodie();
}

static void temp_read()
{
  out("ZUnable to read message. (#4.3.0)\n");
  zerodie();
}

static void temp_socket()
{
  out("ZUnable to crate socket pair. (#4.3.0)\n");
  zerodie();
}

static void temp_control()
{
  out("ZUnable to read control files. (#4.3.0)\n");
  zerodie();
}

static stralloc me = {0};
static stralloc senddomain = {0};
static stralloc dkheader = {0};
static stralloc fndkin = {0};
static stralloc fndkout = {0};
static stralloc result = {0};

static void fnmake_dkim(unsigned long id)
{
  fndkin.len = fmtqfn(fndkin.s, "queue/dkim/", id, 1);
  id += id;
  fndkout.len = fmtqfn(fndkout.s, "queue/dkim/", id, 1);
}

static void dkim_stage()
{
  int r;
  int fd;
  char ch;
  struct stat st;

  if (!stralloc_ready(&fndkin, FMTQFN)) temp_nomem();
  if (!stralloc_ready(&fndkout, FMTQFN)) temp_nomem();

  fnmake_dkim(getpid());  // pre-staging
  fd = open_excl(fndkin.s);
  if (fd == -1) die_write(fndkin.s);

  buffer_init(&bi, read, 0, bufin, sizeof(bufin));
  buffer_init(&bo, write, fd, bufout, sizeof(bufout));

  for (int i = 0;;) {
    r = buffer_get(&bi, &ch, 1);
    if (r == 0) break;
    if (r == -1) temp_read();

    while (ch != '\n') {
      if (ch != '\r') buffer_put(&bo, &ch, 1);
      r = buffer_get(&bi, &ch, 1);
      if (r == -1) temp_read();
      i++;
    }
    buffer_put(&bo, "\r\n", 2);
  }

  if (buffer_flush(&bo) == -1) die(51);
  if (fstat(fd, &st) == -1) die_write(fndkin.s);
  if (fsync(fd) == -1) die_write(fndkin.s);
  if (close(fd) == -1) die_write(fndkin.s);
}

static int mess_dkim()
{
  stralloc line = {0};
  int match;
  int fd;
  int at = 0;
  int ket = 0;
  int end = 0;
  int len = 0;
  int r = 0;
  int i;

  fd = open_read(fndkin.s);
  if (fd == -1) die_read();
  buffer_init(&bi, read, fd, bufin, sizeof(bufin));

  if (!stralloc_copys(&senddomain, "")) temp_nomem();

  for (;;) {
    if (getln(&bi, &line, &match, '\n') == -1) temp_read();
    if (case_starts(line.s, "DKIM-Signature: ")) r = 1;
    if (r == 1) {
      if (case_starts(line.s, "From: ")) {  // fallback: From
        at = str_chr(line.s, '@');
        if (at < line.len) {
          end = str_chr(line.s, '\n');  // From: user@senddomain\n
          ket = str_chr(line.s, '>');   // From: User <user@senddomain>
          len = (ket < end) ? ket : end;
          len -= at - 1;
          if (len) {
            if (!stralloc_copyb(&senddomain, line.s + at + 1, len)) temp_nomem();
          } else if (!stralloc_copys(&senddomain, "uknown"))
            temp_nomem();
          r = 2;
        }
      }
      for (i = 0; i < line.len; ++i) {  // d=domain.tld
        if (*(line.s + i) == '=' && *(line.s + i - 1) == 'd') {
          ++i;  // gotcha
          while (*(line.s + i) != ';') {
            if (!stralloc_catb(&senddomain, line.s + i, 1)) temp_nomem();
            i++;
            r = 3;
          }
        }
      }
    }
    if (r >= 2 || !match) break;
  }
  if (senddomain.len < 2)
    if (!stralloc_copys(&senddomain, "unknown")) temp_nomem();
  if (!stralloc_0(&senddomain)) temp_nomem();

  return r;
}

static int dkim_verify()
{
  int child;
  int wstat;
  char *(args[6]);
  int r = -1;

  args[0] = "qmail-dkim";
  args[1] = "-V";
  args[2] = fndkin.s;
  args[3] = "none";
  args[4] = fndkout.s;
  args[5] = 0;

  if (!(child = fork())) {
    pathexec(args);
    if (errno) _exit(111);
    _exit(100);
  }

  wait_pid(&wstat, child);
  if (wait_crashed(wstat)) return 1;

  switch (r = wait_exitcode(wstat)) {
    case 10: return 1;
    default: return 0;
  }
}

static int dkim_result(const char *me)
{
  int max = 64;
  int fd;
  int j;
  char ch;
  int r = 0;

  if (!stralloc_copys(&result, "")) temp_nomem();

  if ((fd = open_read(fndkout.s)) == -1) return 0;  // nothing to read
  while ((r = read(fd, bufin, sizeof(bufin))) > 0)
    if (!stralloc_catb(&result, bufin, r)) temp_nomem();

  if (!stralloc_0(&result)) temp_nomem();

  if (result.len > 2) {
    if (case_starts(result.s, "pass")) r = 0;
    if (case_starts(result.s, "fail")) r = 35;
  } else if (!stralloc_copys(&result, "unknown")) {
    temp_nomem();
  }

  if (!stralloc_copys(&dkheader, "X-Authentication-Results: ")) temp_nomem();
  if (!stralloc_cats(&dkheader, senddomain.s)) temp_nomem();
  if (!stralloc_cats(&dkheader, "; dkim=")) temp_nomem();

  for (j = 0; j < result.len; j++) {
    ch = result.s[j];
    if (ch == '\r' || ch == '\n' || ch == '\0') continue;
    if (j <= max)
      if (!stralloc_catb(&dkheader, &ch, 1)) temp_nomem();
    if (ch == ' ' && (j > max)) {
      if (!stralloc_cats(&dkheader, "\n  ")) temp_nomem();
      max += max;
    }
  }

  if (!stralloc_cats(&dkheader, "; ")) temp_nomem();
  if (!stralloc_cats(&dkheader, me)) temp_nomem();
  if (!stralloc_0(&dkheader)) temp_nomem();

  return r;
}

static int qmail_queue()
{
  int fd;
  int r;
  int child;
  int wstat;
  int pi[2];
  char *(args[2]);
  char ch;

  if (pipe(pi) == -1) die_pipe(fndkin.s);

  args[0] = "qmail-queue";
  args[1] = 0;

  switch (child = vfork()) {
    case -1:
      close(pi[0]);
      close(pi[1]);
      die_write(fndkin.s);
    case 0:
      close(pi[1]);
      if (fd_move(0, pi[0]) == -1) die_pipe(fndkin.s);
      sig_pipedefault();
      pathexec(args);
      if (errno) _exit(111);
      _exit(100);
  }
  close(pi[0]);

  buffer_init(&bo, write, pi[1], bufout, sizeof(bufout));

  if (dkheader.len > 2) {  // write DKIM header
    if (buffer_put(&bo, dkheader.s, dkheader.len - 1) == -1) die_write(fndkout.s);
    if (buffer_put(&bo, "\n", 1) == -1) die_write(fndkout.s);
    if (buffer_flush(&bo) == -1) die_write(fndkout.s);
  }

  /* read/write message byte-by-byte; we need to remove the CR (inefficient) */

  if ((fd = open_read(fndkin.s)) == -1) die_read();
  while ((r = read(fd, &ch, 1)) > 0)
    if (ch != '\r')
      if (buffer_put(&bo, &ch, 1) == -1) die_write(fndkin.s);

  if (buffer_flush(&bo) == -1) die_write(fndkin.s);
  close(pi[1]);

  wait_pid(&wstat, child);
  if (wait_crashed(wstat)) return 1;

  switch (r = wait_exitcode(wstat)) {
    case 10: return 1;
    default: return 0;
  }

  return 0;
}

static void dkim_unlink()
{
  if (unlink(fndkin.s) == -1)
    if (errno != ENOENT) temp_unlink();
  if (unlink(fndkout.s) == -1)
    if (errno != ENOENT) temp_unlink();
}

int main()
{
  int r = 0;
  char *mode = 0;

  umask(033);
  if (chdir(auto_qmail) == -1) temp_chdir();
  if (control_init() == -1) temp_control();
  if (control_readline(&me, "control/me") == -1) temp_control();
  if (!stralloc_0(&me)) temp_nomem();

  dkim_stage();

  if (mess_dkim()) {
    dkim_verify();
    r = dkim_result(me.s);
  }

  /* we are done: call qmail-queue */

  mode = env_get("DKIM");
  if (!mode || *mode != '+') r = 0;

  qmail_queue();
  dkim_unlink();

  _exit(r);
}