/**
 * @file
 * Send/receive commands to/from an IMAP server
 *
 * @authors
 * Copyright (C) 1996-1998,2010,2012 Michael R. Elkins <me@mutt.org>
 * Copyright (C) 1996-1999 Brandon Long <blong@fiction.net>
 * Copyright (C) 1999-2009,2011 Brendan Cully <brendan@kublai.com>
 * Copyright (C) 2017-2023 Richard Russon <rich@flatcap.org>
 * Copyright (C) 2018 Mehdi Abaakouk <sileht@sileht.net>
 * Copyright (C) 2018-2023 Pietro Cerutti <gahr@gahr.ch>
 * Copyright (C) 2019 Fabian Groffen <grobian@gentoo.org>
 * Copyright (C) 2019 Federico Kircheis <federico.kircheis@gmail.com>
 * Copyright (C) 2019 Ian Zimmerman <itz@no-use.mooo.com>
 *
 * @copyright
 * This program is free software: you can redistribute it and/or modify it under
 * the terms of the GNU General Public License as published by the Free Software
 * Foundation, either version 2 of the License, or (at your option) any later
 * version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * @page imap_command Send/receive commands
 *
 * Send/receive commands to/from an IMAP server
 */

#include "config.h"
#include <ctype.h>
#include <errno.h>
#include <limits.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "private.h"
#include "mutt/lib.h"
#include "config/lib.h"
#include "email/lib.h"
#include "core/lib.h"
#include "conn/lib.h"
#include "adata.h"
#include "commands.h"
#include "edata.h"
#include "mdata.h"
#include "msn.h"
#include "mutt_logging.h"
#include "mx.h"

#define IMAP_CMD_BUFSIZE 512

/**
 * Capabilities - Server capabilities strings that we understand
 *
 * @note This must be kept in the same order as ImapCaps.
 */
static const char *const Capabilities[] = {
  "IMAP4",
  "IMAP4rev1",
  "STATUS",
  "ACL",
  "NAMESPACE",
  "AUTH=CRAM-MD5",
  "AUTH=GSSAPI",
  "AUTH=ANONYMOUS",
  "AUTH=OAUTHBEARER",
  "AUTH=XOAUTH2",
  "STARTTLS",
  "LOGINDISABLED",
  "IDLE",
  "SASL-IR",
  "ENABLE",
  "CONDSTORE",
  "QRESYNC",
  "LIST-EXTENDED",
  "COMPRESS=DEFLATE",
  "X-GM-EXT-1",
  "ID",
  NULL,
};

/**
 * cmd_queue_full - Is the IMAP command queue full?
 * @param adata Imap Account data
 * @retval true Queue is full
 */
static bool cmd_queue_full(struct ImapAccountData *adata)
{
  if (((adata->nextcmd + 1) % adata->cmdslots) == adata->lastcmd)
    return true;

  return false;
}

/**
 * cmd_new - Create and queue a new command control block
 * @param adata Imap Account data
 * @retval NULL The pipeline is full
 * @retval ptr New command
 */
static struct ImapCommand *cmd_new(struct ImapAccountData *adata)
{
  struct ImapCommand *cmd = NULL;

  if (cmd_queue_full(adata))
  {
    mutt_debug(LL_DEBUG3, "IMAP command queue full\n");
    return NULL;
  }

  cmd = adata->cmds + adata->nextcmd;
  adata->nextcmd = (adata->nextcmd + 1) % adata->cmdslots;

  snprintf(cmd->seq, sizeof(cmd->seq), "%c%04u", adata->seqid, adata->seqno++);
  if (adata->seqno > 9999)
    adata->seqno = 0;

  cmd->state = IMAP_RES_NEW;

  return cmd;
}

/**
 * cmd_queue - Add a IMAP command to the queue
 * @param adata Imap Account data
 * @param cmdstr Command string
 * @param flags  Server flags, see #ImapCmdFlags
 * @retval  0 Success
 * @retval <0 Failure, e.g. #IMAP_RES_BAD
 *
 * If the queue is full, attempts to drain it.
 */
static int cmd_queue(struct ImapAccountData *adata, const char *cmdstr, ImapCmdFlags flags)
{
  if (cmd_queue_full(adata))
  {
    mutt_debug(LL_DEBUG3, "Draining IMAP command pipeline\n");

    const int rc = imap_exec(adata, NULL, flags & IMAP_CMD_POLL);

    if (rc == IMAP_EXEC_ERROR)
      return IMAP_RES_BAD;
  }

  struct ImapCommand *cmd = cmd_new(adata);
  if (!cmd)
    return IMAP_RES_BAD;

  if (buf_add_printf(&adata->cmdbuf, "%s %s\r\n", cmd->seq, cmdstr) < 0)
    return IMAP_RES_BAD;

  return 0;
}

/**
 * cmd_handle_fatal - When ImapAccountData is in fatal state, do what we can
 * @param adata Imap Account data
 */
static void cmd_handle_fatal(struct ImapAccountData *adata)
{
  adata->status = IMAP_FATAL;

  if (!adata->mailbox)
    return;

  struct ImapMboxData *mdata = adata->mailbox->mdata;

  if ((adata->state >= IMAP_SELECTED) && (mdata->reopen & IMAP_REOPEN_ALLOW))
  {
    mx_fastclose_mailbox(adata->mailbox, true);
    mutt_error(_("Mailbox %s@%s closed"), adata->conn->account.user,
               adata->conn->account.host);
  }

  imap_close_connection(adata);
  if (!adata->recovering)
  {
    adata->recovering = true;
    if (imap_login(adata))
      mutt_clear_error();
    adata->recovering = false;
  }
}

/**
 * cmd_start - Start a new IMAP command
 * @param adata Imap Account data
 * @param cmdstr Command string
 * @param flags  Command flags, see #ImapCmdFlags
 * @retval  0 Success
 * @retval <0 Failure, e.g. #IMAP_RES_BAD
 */
static int cmd_start(struct ImapAccountData *adata, const char *cmdstr, ImapCmdFlags flags)
{
  int rc;

  if (adata->status == IMAP_FATAL)
  {
    cmd_handle_fatal(adata);
    return -1;
  }

  if (cmdstr && ((rc = cmd_queue(adata, cmdstr, flags)) < 0))
    return rc;

  if (flags & IMAP_CMD_QUEUE)
    return 0;

  if (buf_is_empty(&adata->cmdbuf))
    return IMAP_RES_BAD;

  rc = mutt_socket_send_d(adata->conn, adata->cmdbuf.data,
                          (flags & IMAP_CMD_PASS) ? IMAP_LOG_PASS : IMAP_LOG_CMD);
  buf_reset(&adata->cmdbuf);

  /* unidle when command queue is flushed */
  if (adata->state == IMAP_IDLE)
    adata->state = IMAP_SELECTED;

  return (rc < 0) ? IMAP_RES_BAD : 0;
}

/**
 * cmd_status - Parse response line for tagged OK/NO/BAD
 * @param s Status string from server
 * @retval  0 Success
 * @retval <0 Failure, e.g. #IMAP_RES_BAD
 */
static int cmd_status(const char *s)
{
  s = imap_next_word((char *) s);

  if (mutt_istr_startswith(s, "OK"))
    return IMAP_RES_OK;
  if (mutt_istr_startswith(s, "NO"))
    return IMAP_RES_NO;

  return IMAP_RES_BAD;
}

/**
 * cmd_parse_expunge - Parse expunge command
 * @param adata Imap Account data
 * @param s     String containing MSN of message to expunge
 *
 * cmd_parse_expunge: mark headers with new sequence ID and mark adata to be
 * reopened at our earliest convenience
 */
static void cmd_parse_expunge(struct ImapAccountData *adata, const char *s)
{
  unsigned int exp_msn;
  struct Email *e = NULL;

  mutt_debug(LL_DEBUG2, "Handling EXPUNGE\n");

  struct ImapMboxData *mdata = adata->mailbox->mdata;

  if (!mutt_str_atoui(s, &exp_msn) || (exp_msn < 1) ||
      (exp_msn > imap_msn_highest(&mdata->msn)))
  {
    return;
  }

  e = imap_msn_get(&mdata->msn, exp_msn - 1);
  if (e)
  {
    /* imap_expunge_mailbox() will rewrite e->index.
     * It needs to resort using EMAIL_SORT_UNSORTED anyway, so setting to INT_MAX
     * makes the code simpler and possibly more efficient. */
    e->index = INT_MAX;
    imap_edata_get(e)->msn = 0;
  }

  /* decrement seqno of those above. */
  const size_t max_msn = imap_msn_highest(&mdata->msn);
  for (unsigned int cur = exp_msn; cur < max_msn; cur++)
  {
    e = imap_msn_get(&mdata->msn, cur);
    if (e)
      imap_edata_get(e)->msn--;
    imap_msn_set(&mdata->msn, cur - 1, e);
  }
  imap_msn_shrink(&mdata->msn, 1);

  mdata->reopen |= IMAP_EXPUNGE_PENDING;
}

/**
 * cmd_parse_vanished - Parse vanished command
 * @param adata Imap Account data
 * @param s     String containing MSN of message to expunge
 *
 * Handle VANISHED (RFC7162), which is like expunge, but passes a seqset of UIDs.
 * An optional (EARLIER) argument specifies not to decrement subsequent MSNs.
 */
static void cmd_parse_vanished(struct ImapAccountData *adata, char *s)
{
  bool earlier = false;
  int rc;
  unsigned int uid = 0;

  struct ImapMboxData *mdata = adata->mailbox->mdata;

  mutt_debug(LL_DEBUG2, "Handling VANISHED\n");

  if (mutt_istr_startswith(s, "(EARLIER)"))
  {
    /* The RFC says we should not decrement msns with the VANISHED EARLIER tag.
     * My experimentation says that's crap. */
    earlier = true;
    s = imap_next_word(s);
  }

  char *end_of_seqset = s;
  while (*end_of_seqset)
  {
    if (!strchr("0123456789:,", *end_of_seqset))
      *end_of_seqset = '\0';
    else
      end_of_seqset++;
  }

  struct SeqsetIterator *iter = mutt_seqset_iterator_new(s);
  if (!iter)
  {
    mutt_debug(LL_DEBUG2, "VANISHED: empty seqset [%s]?\n", s);
    return;
  }

  while ((rc = mutt_seqset_iterator_next(iter, &uid)) == 0)
  {
    struct Email *e = mutt_hash_int_find(mdata->uid_hash, uid);
    if (!e)
      continue;

    unsigned int exp_msn = imap_edata_get(e)->msn;

    /* imap_expunge_mailbox() will rewrite e->index.
     * It needs to resort using EMAIL_SORT_UNSORTED anyway, so setting to INT_MAX
     * makes the code simpler and possibly more efficient. */
    e->index = INT_MAX;
    imap_edata_get(e)->msn = 0;

    if ((exp_msn < 1) || (exp_msn > imap_msn_highest(&mdata->msn)))
    {
      mutt_debug(LL_DEBUG1, "VANISHED: msn for UID %u is incorrect\n", uid);
      continue;
    }
    if (imap_msn_get(&mdata->msn, exp_msn - 1) != e)
    {
      mutt_debug(LL_DEBUG1, "VANISHED: msn_index for UID %u is incorrect\n", uid);
      continue;
    }

    imap_msn_remove(&mdata->msn, exp_msn - 1);

    if (!earlier)
    {
      /* decrement seqno of those above. */
      const size_t max_msn = imap_msn_highest(&mdata->msn);
      for (unsigned int cur = exp_msn; cur < max_msn; cur++)
      {
        e = imap_msn_get(&mdata->msn, cur);
        if (e)
          imap_edata_get(e)->msn--;
        imap_msn_set(&mdata->msn, cur - 1, e);
      }

      imap_msn_shrink(&mdata->msn, 1);
    }
  }

  if (rc < 0)
    mutt_debug(LL_DEBUG1, "VANISHED: illegal seqset %s\n", s);

  mdata->reopen |= IMAP_EXPUNGE_PENDING;

  mutt_seqset_iterator_free(&iter);
}

/**
 * cmd_parse_fetch - Load fetch response into ImapAccountData
 * @param adata Imap Account data
 * @param s     String containing MSN of message to fetch
 *
 * Currently only handles unanticipated FETCH responses, and only FLAGS data.
 * We get these if another client has changed flags for a mailbox we've
 * selected.  Of course, a lot of code here duplicates code in message.c.
 */
static void cmd_parse_fetch(struct ImapAccountData *adata, char *s)
{
  unsigned int msn, uid;
  struct Email *e = NULL;
  char *flags = NULL;
  int uid_checked = 0;
  bool server_changes = false;

  struct ImapMboxData *mdata = imap_mdata_get(adata->mailbox);

  mutt_debug(LL_DEBUG3, "Handling FETCH\n");

  if (!mutt_str_atoui(s, &msn))
  {
    mutt_debug(LL_DEBUG3, "Skipping FETCH response - illegal MSN\n");
    return;
  }

  if ((msn < 1) || (msn > imap_msn_highest(&mdata->msn)))
  {
    mutt_debug(LL_DEBUG3, "Skipping FETCH response - MSN %u out of range\n", msn);
    return;
  }

  e = imap_msn_get(&mdata->msn, msn - 1);
  if (!e || !e->active)
  {
    mutt_debug(LL_DEBUG3, "Skipping FETCH response - MSN %u not in msn_index\n", msn);
    return;
  }

  mutt_debug(LL_DEBUG2, "Message UID %u updated\n", imap_edata_get(e)->uid);
  /* skip FETCH */
  s = imap_next_word(s);
  s = imap_next_word(s);

  if (*s != '(')
  {
    mutt_debug(LL_DEBUG1, "Malformed FETCH response\n");
    return;
  }
  s++;

  while (*s)
  {
    SKIPWS(s);
    size_t plen = mutt_istr_startswith(s, "FLAGS");
    if (plen != 0)
    {
      flags = s;
      if (uid_checked)
        break;

      s += plen;
      SKIPWS(s);
      if (*s != '(')
      {
        mutt_debug(LL_DEBUG1, "bogus FLAGS response: %s\n", s);
        return;
      }
      s++;
      while (*s && (*s != ')'))
        s++;
      if (*s == ')')
      {
        s++;
      }
      else
      {
        mutt_debug(LL_DEBUG1, "Unterminated FLAGS response: %s\n", s);
        return;
      }
    }
    else if ((plen = mutt_istr_startswith(s, "UID")))
    {
      s += plen;
      SKIPWS(s);
      if (!mutt_str_atoui(s, &uid))
      {
        mutt_debug(LL_DEBUG1, "Illegal UID.  Skipping update\n");
        return;
      }
      if (uid != imap_edata_get(e)->uid)
      {
        mutt_debug(LL_DEBUG1, "UID vs MSN mismatch.  Skipping update\n");
        return;
      }
      uid_checked = 1;
      if (flags)
        break;
      s = imap_next_word(s);
    }
    else if ((plen = mutt_istr_startswith(s, "MODSEQ")))
    {
      s += plen;
      SKIPWS(s);
      if (*s != '(')
      {
        mutt_debug(LL_DEBUG1, "bogus MODSEQ response: %s\n", s);
        return;
      }
      s++;
      while (*s && (*s != ')'))
        s++;
      if (*s == ')')
      {
        s++;
      }
      else
      {
        mutt_debug(LL_DEBUG1, "Unterminated MODSEQ response: %s\n", s);
        return;
      }
    }
    else if (*s == ')')
    {
      break; /* end of request */
    }
    else if (*s)
    {
      mutt_debug(LL_DEBUG2, "Only handle FLAGS updates\n");
      break;
    }
  }

  if (flags)
  {
    imap_set_flags(adata->mailbox, e, flags, &server_changes);
    if (server_changes)
    {
      /* If server flags could conflict with NeoMutt's flags, reopen the mailbox. */
      if (e->changed)
        mdata->reopen |= IMAP_EXPUNGE_PENDING;
      else
        mdata->check_status |= IMAP_FLAGS_PENDING;
    }
  }
}

/**
 * cmd_parse_capability - Set capability bits according to CAPABILITY response
 * @param adata Imap Account data
 * @param s     Command string with capabilities
 */
static void cmd_parse_capability(struct ImapAccountData *adata, char *s)
{
  mutt_debug(LL_DEBUG3, "Handling CAPABILITY\n");

  s = imap_next_word(s);
  char *bracket = strchr(s, ']');
  if (bracket)
    *bracket = '\0';
  FREE(&adata->capstr);
  adata->capstr = mutt_str_dup(s);
  adata->capabilities = 0;

  while (*s)
  {
    for (size_t i = 0; Capabilities[i]; i++)
    {
      size_t len = mutt_istr_startswith(s, Capabilities[i]);
      if (len != 0 && ((s[len] == '\0') || isspace(s[len])))
      {
        adata->capabilities |= (1 << i);
        mutt_debug(LL_DEBUG3, " Found capability \"%s\": %zu\n", Capabilities[i], i);
        break;
      }
    }
    s = imap_next_word(s);
  }
}

/**
 * cmd_parse_list - Parse a server LIST command (list mailboxes)
 * @param adata Imap Account data
 * @param s     Command string with folder list
 */
static void cmd_parse_list(struct ImapAccountData *adata, char *s)
{
  struct ImapList *list = NULL;
  struct ImapList lb = { 0 };
  unsigned int litlen;

  if (adata->cmdresult)
    list = adata->cmdresult;
  else
    list = &lb;

  memset(list, 0, sizeof(struct ImapList));

  /* flags */
  s = imap_next_word(s);
  if (*s != '(')
  {
    mutt_debug(LL_DEBUG1, "Bad LIST response\n");
    return;
  }
  s++;
  while (*s)
  {
    if (mutt_istr_startswith(s, "\\NoSelect"))
      list->noselect = true;
    else if (mutt_istr_startswith(s, "\\NonExistent")) /* rfc5258 */
      list->noselect = true;
    else if (mutt_istr_startswith(s, "\\NoInferiors"))
      list->noinferiors = true;
    else if (mutt_istr_startswith(s, "\\HasNoChildren")) /* rfc5258*/
      list->noinferiors = true;

    s = imap_next_word(s);
    if (*(s - 2) == ')')
      break;
  }

  /* Delimiter */
  if (!mutt_istr_startswith(s, "NIL"))
  {
    char delimbuf[5] = { 0 }; // worst case: "\\"\0
    snprintf(delimbuf, sizeof(delimbuf), "%s", s);
    imap_unquote_string(delimbuf);
    list->delim = delimbuf[0];
  }

  /* Name */
  s = imap_next_word(s);
  /* Notes often responds with literals here. We need a real tokenizer. */
  if (imap_get_literal_count(s, &litlen) == 0)
  {
    if (imap_cmd_step(adata) != IMAP_RES_CONTINUE)
    {
      adata->status = IMAP_FATAL;
      return;
    }

    if (strlen(adata->buf) < litlen)
    {
      mutt_debug(LL_DEBUG1, "Error parsing LIST mailbox\n");
      return;
    }

    list->name = adata->buf;
    s = list->name + litlen;
    if (s[0] != '\0')
    {
      s[0] = '\0';
      s++;
      SKIPWS(s);
    }
  }
  else
  {
    list->name = s;
    /* Exclude rfc5258 RECURSIVEMATCH CHILDINFO suffix */
    s = imap_next_word(s);
    if (s[0] != '\0')
      s[-1] = '\0';
    imap_unmunge_mbox_name(adata->unicode, list->name);
  }

  if (list->name[0] == '\0')
  {
    adata->delim = list->delim;
    mutt_debug(LL_DEBUG3, "Root delimiter: %c\n", adata->delim);
  }
}

/**
 * cmd_parse_lsub - Parse a server LSUB (list subscribed mailboxes)
 * @param adata Imap Account data
 * @param s     Command string with folder list
 */
static void cmd_parse_lsub(struct ImapAccountData *adata, char *s)
{
  if (adata->cmdresult)
  {
    /* caller will handle response itself */
    cmd_parse_list(adata, s);
    return;
  }

  const bool c_imap_check_subscribed = cs_subset_bool(NeoMutt->sub, "imap_check_subscribed");
  if (!c_imap_check_subscribed)
    return;

  struct ImapList list = { 0 };

  adata->cmdresult = &list;
  cmd_parse_list(adata, s);
  adata->cmdresult = NULL;
  /* noselect is for a gmail quirk */
  if (!list.name || list.noselect)
    return;

  mutt_debug(LL_DEBUG3, "Subscribing to %s\n", list.name);

  struct Buffer *buf = buf_pool_get();
  struct Buffer *err = buf_pool_get();
  struct Url url = { 0 };

  account_to_url(&adata->conn->account, &url);
  url.path = list.name;

  const char *const c_imap_user = cs_subset_string(NeoMutt->sub, "imap_user");
  if (mutt_str_equal(url.user, c_imap_user))
    url.user = NULL;
  url_tobuffer(&url, buf, U_NO_FLAGS);

  if (!mailbox_add_simple(buf_string(buf), err))
    mutt_debug(LL_DEBUG1, "Error adding subscribed mailbox: %s\n", buf_string(err));

  buf_pool_release(&buf);
  buf_pool_release(&err);
}

/**
 * cmd_parse_myrights - Set rights bits according to MYRIGHTS response
 * @param adata Imap Account data
 * @param s     Command string with rights info
 */
static void cmd_parse_myrights(struct ImapAccountData *adata, const char *s)
{
  mutt_debug(LL_DEBUG2, "Handling MYRIGHTS\n");

  s = imap_next_word((char *) s);
  s = imap_next_word((char *) s);

  /* zero out current rights set */
  adata->mailbox->rights = 0;

  while (*s && !isspace((unsigned char) *s))
  {
    switch (*s)
    {
      case 'a':
        adata->mailbox->rights |= MUTT_ACL_ADMIN;
        break;
      case 'e':
        adata->mailbox->rights |= MUTT_ACL_EXPUNGE;
        break;
      case 'i':
        adata->mailbox->rights |= MUTT_ACL_INSERT;
        break;
      case 'k':
        adata->mailbox->rights |= MUTT_ACL_CREATE;
        break;
      case 'l':
        adata->mailbox->rights |= MUTT_ACL_LOOKUP;
        break;
      case 'p':
        adata->mailbox->rights |= MUTT_ACL_POST;
        break;
      case 'r':
        adata->mailbox->rights |= MUTT_ACL_READ;
        break;
      case 's':
        adata->mailbox->rights |= MUTT_ACL_SEEN;
        break;
      case 't':
        adata->mailbox->rights |= MUTT_ACL_DELETE;
        break;
      case 'w':
        adata->mailbox->rights |= MUTT_ACL_WRITE;
        break;
      case 'x':
        adata->mailbox->rights |= MUTT_ACL_DELMX;
        break;

      /* obsolete rights */
      case 'c':
        adata->mailbox->rights |= MUTT_ACL_CREATE | MUTT_ACL_DELMX;
        break;
      case 'd':
        adata->mailbox->rights |= MUTT_ACL_DELETE | MUTT_ACL_EXPUNGE;
        break;
      default:
        mutt_debug(LL_DEBUG1, "Unknown right: %c\n", *s);
    }
    s++;
  }
}

/**
 * find_mailbox - Find a Mailbox by its name
 * @param adata Imap Account data
 * @param name  Mailbox to find
 * @retval ptr Mailbox
 */
static struct Mailbox *find_mailbox(struct ImapAccountData *adata, const char *name)
{
  if (!adata || !adata->account || !name)
    return NULL;

  struct MailboxNode *np = NULL;
  STAILQ_FOREACH(np, &adata->account->mailboxes, entries)
  {
    struct ImapMboxData *mdata = imap_mdata_get(np->mailbox);
    if (mutt_str_equal(name, mdata->name))
      return np->mailbox;
  }

  return NULL;
}

/**
 * cmd_parse_status - Parse status from server
 * @param adata Imap Account data
 * @param s     Command string with status info
 *
 * first cut: just do mailbox update. Later we may wish to cache all mailbox
 * information, even that not desired by mailbox
 */
static void cmd_parse_status(struct ImapAccountData *adata, char *s)
{
  unsigned int litlen = 0;

  char *mailbox = imap_next_word(s);

  /* We need a real tokenizer. */
  if (imap_get_literal_count(mailbox, &litlen) == 0)
  {
    if (imap_cmd_step(adata) != IMAP_RES_CONTINUE)
    {
      adata->status = IMAP_FATAL;
      return;
    }

    if (strlen(adata->buf) < litlen)
    {
      mutt_debug(LL_DEBUG1, "Error parsing STATUS mailbox\n");
      return;
    }

    mailbox = adata->buf;
    s = mailbox + litlen;
    s[0] = '\0';
    s++;
    SKIPWS(s);
  }
  else
  {
    s = imap_next_word(mailbox);
    s[-1] = '\0';
    imap_unmunge_mbox_name(adata->unicode, mailbox);
  }

  struct Mailbox *m = find_mailbox(adata, mailbox);
  struct ImapMboxData *mdata = imap_mdata_get(m);
  if (!mdata)
  {
    mutt_debug(LL_DEBUG3, "Received status for an unexpected mailbox: %s\n", mailbox);
    return;
  }
  uint32_t olduv = mdata->uidvalidity;
  unsigned int oldun = mdata->uid_next;

  if (*s++ != '(')
  {
    mutt_debug(LL_DEBUG1, "Error parsing STATUS\n");
    return;
  }
  while ((s[0] != '\0') && (s[0] != ')'))
  {
    char *value = imap_next_word(s);

    errno = 0;
    const unsigned long ulcount = strtoul(value, &value, 10);
    const bool truncated = ((errno == ERANGE) && (ulcount == ULONG_MAX)) ||
                           ((unsigned int) ulcount != ulcount);
    const unsigned int count = (unsigned int) ulcount;

    // we accept truncating a larger value only for UIDVALIDITY, to accommodate
    // IMAP servers that use 64-bits for it. This seems to be what Thunderbird
    // is also doing, see #3830
    if (mutt_str_startswith(s, "UIDVALIDITY"))
    {
      if (truncated)
      {
        mutt_debug(LL_DEBUG1,
                   "UIDVALIDITY [%lu] exceeds 32 bits, "
                   "truncated to [%u]\n",
                   ulcount, count);
      }
      mdata->uidvalidity = count;
    }
    else
    {
      if (truncated)
      {
        mutt_debug(LL_DEBUG1, "Number in [%s] exceeds 32 bits\n", s);
        return;
      }
      else
      {
        if (mutt_str_startswith(s, "MESSAGES"))
          mdata->messages = count;
        else if (mutt_str_startswith(s, "RECENT"))
          mdata->recent = count;
        else if (mutt_str_startswith(s, "UIDNEXT"))
          mdata->uid_next = count;
        else if (mutt_str_startswith(s, "UNSEEN"))
          mdata->unseen = count;
      }
    }

    s = value;
    if ((s[0] != '\0') && (*s != ')'))
      s = imap_next_word(s);
  }
  mutt_debug(LL_DEBUG3, "%s (UIDVALIDITY: %u, UIDNEXT: %u) %d messages, %d recent, %d unseen\n",
             mdata->name, mdata->uidvalidity, mdata->uid_next, mdata->messages,
             mdata->recent, mdata->unseen);

  mutt_debug(LL_DEBUG3, "Running default STATUS handler\n");

  mutt_debug(LL_DEBUG3, "Found %s in mailbox list (OV: %u ON: %u U: %d)\n",
             mailbox, olduv, oldun, mdata->unseen);

  bool new_mail = false;
  const bool c_mail_check_recent = cs_subset_bool(NeoMutt->sub, "mail_check_recent");
  if (c_mail_check_recent)
  {
    if ((olduv != 0) && (olduv == mdata->uidvalidity))
    {
      if (oldun < mdata->uid_next)
        new_mail = (mdata->unseen > 0);
    }
    else if ((olduv == 0) && (oldun == 0))
    {
      /* first check per session, use recent. might need a flag for this. */
      new_mail = (mdata->recent > 0);
    }
    else
    {
      new_mail = (mdata->unseen > 0);
    }
  }
  else
  {
    new_mail = (mdata->unseen > 0);
  }

  m->has_new = new_mail;
  m->msg_count = mdata->messages;
  m->msg_unread = mdata->unseen;

  // force back to keep detecting new mail until the mailbox is opened
  if (m->has_new)
    mdata->uid_next = oldun;

  struct EventMailbox ev_m = { m };
  notify_send(m->notify, NT_MAILBOX, NT_MAILBOX_CHANGE, &ev_m);
}

/**
 * cmd_parse_enabled - Record what the server has enabled
 * @param adata Imap Account data
 * @param s     Command string containing acceptable encodings
 */
static void cmd_parse_enabled(struct ImapAccountData *adata, const char *s)
{
  mutt_debug(LL_DEBUG2, "Handling ENABLED\n");

  while ((s = imap_next_word((char *) s)) && (*s != '\0'))
  {
    if (mutt_istr_startswith(s, "UTF8=ACCEPT") || mutt_istr_startswith(s, "UTF8=ONLY"))
    {
      adata->unicode = true;
    }
    if (mutt_istr_startswith(s, "QRESYNC"))
      adata->qresync = true;
  }
}

/**
 * cmd_parse_exists - Parse EXISTS message from serer
 * @param adata  Imap Account data
 * @param pn     String containing the total number of messages for the selected mailbox
 */
static void cmd_parse_exists(struct ImapAccountData *adata, const char *pn)
{
  unsigned int count = 0;
  mutt_debug(LL_DEBUG2, "Handling EXISTS\n");

  if (!mutt_str_atoui(pn, &count))
  {
    mutt_debug(LL_DEBUG1, "Malformed EXISTS: '%s'\n", pn);
    return;
  }

  struct ImapMboxData *mdata = adata->mailbox->mdata;

  /* new mail arrived */
  if (count < imap_msn_highest(&mdata->msn))
  {
    /* Notes 6.0.3 has a tendency to report fewer messages exist than
     * it should. */
    mutt_debug(LL_DEBUG1, "Message count is out of sync\n");
  }
  else if (count == imap_msn_highest(&mdata->msn))
  {
    /* at least the InterChange server sends EXISTS messages freely,
     * even when there is no new mail */
    mutt_debug(LL_DEBUG3, "superfluous EXISTS message\n");
  }
  else
  {
    mutt_debug(LL_DEBUG2, "New mail in %s - %d messages total\n", mdata->name, count);
    mdata->reopen |= IMAP_NEWMAIL_PENDING;
    mdata->new_mail_count = count;
  }
}

/**
 * cmd_handle_untagged - Fallback parser for otherwise unhandled messages
 * @param adata Imap Account data
 * @retval  0 Success
 * @retval -1 Failure
 */
static int cmd_handle_untagged(struct ImapAccountData *adata)
{
  char *s = imap_next_word(adata->buf);
  char *pn = imap_next_word(s);

  const bool c_imap_server_noise = cs_subset_bool(NeoMutt->sub, "imap_server_noise");
  if ((adata->state >= IMAP_SELECTED) && isdigit((unsigned char) *s))
  {
    /* pn vs. s: need initial seqno */
    pn = s;
    s = imap_next_word(s);

    /* EXISTS, EXPUNGE, FETCH are always related to the SELECTED mailbox */
    if (mutt_istr_startswith(s, "EXISTS"))
      cmd_parse_exists(adata, pn);
    else if (mutt_istr_startswith(s, "EXPUNGE"))
      cmd_parse_expunge(adata, pn);
    else if (mutt_istr_startswith(s, "FETCH"))
      cmd_parse_fetch(adata, pn);
  }
  else if ((adata->state >= IMAP_SELECTED) && mutt_istr_startswith(s, "VANISHED"))
  {
    cmd_parse_vanished(adata, pn);
  }
  else if (mutt_istr_startswith(s, "CAPABILITY"))
  {
    cmd_parse_capability(adata, s);
  }
  else if (mutt_istr_startswith(s, "OK [CAPABILITY"))
  {
    cmd_parse_capability(adata, pn);
  }
  else if (mutt_istr_startswith(pn, "OK [CAPABILITY"))
  {
    cmd_parse_capability(adata, imap_next_word(pn));
  }
  else if (mutt_istr_startswith(s, "LIST"))
  {
    cmd_parse_list(adata, s);
  }
  else if (mutt_istr_startswith(s, "LSUB"))
  {
    cmd_parse_lsub(adata, s);
  }
  else if (mutt_istr_startswith(s, "MYRIGHTS"))
  {
    cmd_parse_myrights(adata, s);
  }
  else if (mutt_istr_startswith(s, "SEARCH"))
  {
    cmd_parse_search(adata, s);
  }
  else if (mutt_istr_startswith(s, "STATUS"))
  {
    cmd_parse_status(adata, s);
  }
  else if (mutt_istr_startswith(s, "ENABLED"))
  {
    cmd_parse_enabled(adata, s);
  }
  else if (mutt_istr_startswith(s, "BYE"))
  {
    mutt_debug(LL_DEBUG2, "Handling BYE\n");

    /* check if we're logging out */
    if (adata->status == IMAP_BYE)
      return 0;

    /* server shut down our connection */
    s += 3;
    SKIPWS(s);
    mutt_error("%s", s);
    cmd_handle_fatal(adata);

    return -1;
  }
  else if (c_imap_server_noise && mutt_istr_startswith(s, "NO"))
  {
    mutt_debug(LL_DEBUG2, "Handling untagged NO\n");

    /* Display the warning message from the server */
    mutt_error("%s", s + 2);
  }

  return 0;
}

/**
 * imap_cmd_start - Given an IMAP command, send it to the server
 * @param adata Imap Account data
 * @param cmdstr Command string to send
 * @retval  0 Success
 * @retval <0 Failure, e.g. #IMAP_RES_BAD
 *
 * If cmdstr is NULL, sends queued commands.
 */
int imap_cmd_start(struct ImapAccountData *adata, const char *cmdstr)
{
  return cmd_start(adata, cmdstr, IMAP_CMD_NO_FLAGS);
}

/**
 * imap_cmd_step - Reads server responses from an IMAP command
 * @param adata Imap Account data
 * @retval  0 Success
 * @retval <0 Failure, e.g. #IMAP_RES_BAD
 *
 * detects tagged completion response, handles untagged messages, can read
 * arbitrarily large strings (using malloc, so don't make it _too_ large!).
 */
int imap_cmd_step(struct ImapAccountData *adata)
{
  if (!adata)
    return -1;

  size_t len = 0;
  int c;
  int rc;
  int stillrunning = 0;
  struct ImapCommand *cmd = NULL;

  if (adata->status == IMAP_FATAL)
  {
    cmd_handle_fatal(adata);
    return IMAP_RES_BAD;
  }

  /* read into buffer, expanding buffer as necessary until we have a full
   * line */
  do
  {
    if (len == adata->blen)
    {
      MUTT_MEM_REALLOC(&adata->buf, adata->blen + IMAP_CMD_BUFSIZE, char);
      adata->blen = adata->blen + IMAP_CMD_BUFSIZE;
      mutt_debug(LL_DEBUG3, "grew buffer to %zu bytes\n", adata->blen);
    }

    /* back up over '\0' */
    if (len)
      len--;
    c = mutt_socket_readln_d(adata->buf + len, adata->blen - len, adata->conn, MUTT_SOCK_LOG_FULL);
    if (c <= 0)
    {
      mutt_debug(LL_DEBUG1, "Error reading server response\n");
      cmd_handle_fatal(adata);
      return IMAP_RES_BAD;
    }

    len += c;
  }
  /* if we've read all the way to the end of the buffer, we haven't read a
   * full line (mutt_socket_readln strips the \r, so we always have at least
   * one character free when we've read a full line) */
  while (len == adata->blen);

  /* don't let one large string make cmd->buf hog memory forever */
  if ((adata->blen > IMAP_CMD_BUFSIZE) && (len <= IMAP_CMD_BUFSIZE))
  {
    MUTT_MEM_REALLOC(&adata->buf, IMAP_CMD_BUFSIZE, char);
    adata->blen = IMAP_CMD_BUFSIZE;
    mutt_debug(LL_DEBUG3, "shrank buffer to %zu bytes\n", adata->blen);
  }

  adata->lastread = mutt_date_now();

  /* handle untagged messages. The caller still gets its shot afterwards. */
  if ((mutt_str_startswith(adata->buf, "* ") ||
       mutt_str_startswith(imap_next_word(adata->buf), "OK [")) &&
      cmd_handle_untagged(adata))
  {
    return IMAP_RES_BAD;
  }

  /* server demands a continuation response from us */
  if (adata->buf[0] == '+')
    return IMAP_RES_RESPOND;

  /* Look for tagged command completions.
   *
   * Some response handlers can end up recursively calling
   * imap_cmd_step() and end up handling all tagged command
   * completions.
   * (e.g. FETCH->set_flag->set_header_color->~h pattern match.)
   *
   * Other callers don't even create an adata->cmds entry.
   *
   * For both these cases, we default to returning OK */
  rc = IMAP_RES_OK;
  c = adata->lastcmd;
  do
  {
    cmd = &adata->cmds[c];
    if (cmd->state == IMAP_RES_NEW)
    {
      if (mutt_str_startswith(adata->buf, cmd->seq))
      {
        if (!stillrunning)
        {
          /* first command in queue has finished - move queue pointer up */
          adata->lastcmd = (adata->lastcmd + 1) % adata->cmdslots;
        }
        cmd->state = cmd_status(adata->buf);
        rc = cmd->state;
        if (cmd->state == IMAP_RES_NO || cmd->state == IMAP_RES_BAD)
        {
          mutt_message(_("IMAP command failed: %s"), adata->buf);
        }
      }
      else
      {
        stillrunning++;
      }
    }

    c = (c + 1) % adata->cmdslots;
  } while (c != adata->nextcmd);

  if (stillrunning)
  {
    rc = IMAP_RES_CONTINUE;
  }
  else
  {
    mutt_debug(LL_DEBUG3, "IMAP queue drained\n");
    imap_cmd_finish(adata);
  }

  return rc;
}

/**
 * imap_code - Was the command successful
 * @param s IMAP command status
 * @retval 1 Command result was OK
 * @retval 0 NO or BAD
 */
bool imap_code(const char *s)
{
  return cmd_status(s) == IMAP_RES_OK;
}

/**
 * imap_cmd_trailer - Extra information after tagged command response if any
 * @param adata Imap Account data
 * @retval ptr Extra command information (pointer into adata->buf)
 * @retval ""  Error (static string)
 */
const char *imap_cmd_trailer(struct ImapAccountData *adata)
{
  static const char *notrailer = "";
  const char *s = adata->buf;

  if (!s)
  {
    mutt_debug(LL_DEBUG2, "not a tagged response\n");
    return notrailer;
  }

  s = imap_next_word((char *) s);
  if (!s || (!mutt_istr_startswith(s, "OK") && !mutt_istr_startswith(s, "NO") &&
             !mutt_istr_startswith(s, "BAD")))
  {
    mutt_debug(LL_DEBUG2, "not a command completion: %s\n", adata->buf);
    return notrailer;
  }

  s = imap_next_word((char *) s);
  if (!s)
    return notrailer;

  return s;
}

/**
 * imap_exec - Execute a command and wait for the response from the server
 * @param adata Imap Account data
 * @param cmdstr Command to execute
 * @param flags  Flags, see #ImapCmdFlags
 * @retval #IMAP_EXEC_SUCCESS Command successful or queued
 * @retval #IMAP_EXEC_ERROR   Command returned an error
 * @retval #IMAP_EXEC_FATAL   Imap connection failure
 *
 * Also, handle untagged responses.
 */
int imap_exec(struct ImapAccountData *adata, const char *cmdstr, ImapCmdFlags flags)
{
  int rc;

  if (flags & IMAP_CMD_SINGLE)
  {
    // Process any existing commands
    if (adata->nextcmd != adata->lastcmd)
      imap_exec(adata, NULL, IMAP_CMD_POLL);
  }

  rc = cmd_start(adata, cmdstr, flags);
  if (rc < 0)
  {
    cmd_handle_fatal(adata);
    return IMAP_EXEC_FATAL;
  }

  if (flags & IMAP_CMD_QUEUE)
    return IMAP_EXEC_SUCCESS;

  const short c_imap_poll_timeout = cs_subset_number(NeoMutt->sub, "imap_poll_timeout");
  if ((flags & IMAP_CMD_POLL) && (c_imap_poll_timeout > 0) &&
      ((mutt_socket_poll(adata->conn, c_imap_poll_timeout)) == 0))
  {
    mutt_error(_("Connection to %s timed out"), adata->conn->account.host);
    cmd_handle_fatal(adata);
    return IMAP_EXEC_FATAL;
  }

  /* Allow interruptions, particularly useful if there are network problems. */
  mutt_sig_allow_interrupt(true);
  do
  {
    rc = imap_cmd_step(adata);
    // The queue is empty, so the single command has been processed
    if ((flags & IMAP_CMD_SINGLE) && (adata->nextcmd == adata->lastcmd))
      break;
  } while (rc == IMAP_RES_CONTINUE);
  mutt_sig_allow_interrupt(false);

  if (rc == IMAP_RES_NO)
    return IMAP_EXEC_ERROR;
  if (rc != IMAP_RES_OK)
  {
    if (adata->status != IMAP_FATAL)
      return IMAP_EXEC_ERROR;

    mutt_debug(LL_DEBUG1, "command failed: %s\n", adata->buf);
    return IMAP_EXEC_FATAL;
  }

  return IMAP_EXEC_SUCCESS;
}

/**
 * imap_cmd_finish - Attempt to perform cleanup
 * @param adata Imap Account data
 *
 * If a reopen is allowed, it attempts to perform cleanup (eg fetch new mail if
 * detected, do expunge). Called automatically by imap_cmd_step(), but may be
 * called at any time.
 *
 * mdata->check_status is set and will be used later by imap_check_mailbox().
 */
void imap_cmd_finish(struct ImapAccountData *adata)
{
  if (!adata)
    return;

  if (adata->status == IMAP_FATAL)
  {
    adata->closing = false;
    cmd_handle_fatal(adata);
    return;
  }

  if (!(adata->state >= IMAP_SELECTED) || (adata->mailbox && adata->closing))
  {
    adata->closing = false;
    return;
  }

  adata->closing = false;

  struct ImapMboxData *mdata = imap_mdata_get(adata->mailbox);

  if (mdata && mdata->reopen & IMAP_REOPEN_ALLOW)
  {
    // First remove expunged emails from the msn_index
    if (mdata->reopen & IMAP_EXPUNGE_PENDING)
    {
      mutt_debug(LL_DEBUG2, "Expunging mailbox\n");
      imap_expunge_mailbox(adata->mailbox, true);
      /* Detect whether we've gotten unexpected EXPUNGE messages */
      if (!(mdata->reopen & IMAP_EXPUNGE_EXPECTED))
        mdata->check_status |= IMAP_EXPUNGE_PENDING;
      mdata->reopen &= ~(IMAP_EXPUNGE_PENDING | IMAP_EXPUNGE_EXPECTED);
    }

    // Then add new emails to it
    if (mdata->reopen & IMAP_NEWMAIL_PENDING)
    {
      const size_t max_msn = imap_msn_highest(&mdata->msn);
      if (mdata->new_mail_count > max_msn)
      {
        if (!(mdata->reopen & IMAP_EXPUNGE_PENDING))
          mdata->check_status |= IMAP_NEWMAIL_PENDING;

        mutt_debug(LL_DEBUG2, "Fetching new mails from %zd to %u\n",
                   max_msn + 1, mdata->new_mail_count);
        imap_read_headers(adata->mailbox, max_msn + 1, mdata->new_mail_count, false);
      }
    }

    // And to finish inform about MUTT_REOPEN if needed
    if (mdata->reopen & IMAP_EXPUNGE_PENDING && !(mdata->reopen & IMAP_EXPUNGE_EXPECTED))
      mdata->check_status |= IMAP_EXPUNGE_PENDING;

    if (mdata->reopen & IMAP_EXPUNGE_PENDING)
      mdata->reopen &= ~(IMAP_EXPUNGE_PENDING | IMAP_EXPUNGE_EXPECTED);
  }

  adata->status = 0;
}

/**
 * imap_cmd_idle - Enter the IDLE state
 * @param adata Imap Account data
 * @retval  0 Success
 * @retval <0 Failure, e.g. #IMAP_RES_BAD
 */
int imap_cmd_idle(struct ImapAccountData *adata)
{
  int rc;

  if (cmd_start(adata, "IDLE", IMAP_CMD_POLL) < 0)
  {
    cmd_handle_fatal(adata);
    return -1;
  }

  const short c_imap_poll_timeout = cs_subset_number(NeoMutt->sub, "imap_poll_timeout");
  if ((c_imap_poll_timeout > 0) &&
      ((mutt_socket_poll(adata->conn, c_imap_poll_timeout)) == 0))
  {
    mutt_error(_("Connection to %s timed out"), adata->conn->account.host);
    cmd_handle_fatal(adata);
    return -1;
  }

  do
  {
    rc = imap_cmd_step(adata);
  } while (rc == IMAP_RES_CONTINUE);

  if (rc == IMAP_RES_RESPOND)
  {
    /* successfully entered IDLE state */
    adata->state = IMAP_IDLE;
    /* queue automatic exit when next command is issued */
    buf_addstr(&adata->cmdbuf, "DONE\r\n");
    rc = IMAP_RES_OK;
  }
  if (rc != IMAP_RES_OK)
  {
    mutt_debug(LL_DEBUG1, "error starting IDLE\n");
    return -1;
  }

  return 0;
}
