//! # Imap handling module
//!
//! uses [async-email/async-imap](https://github.com/async-email/async-imap)
//! to implement connect, fetch, delete functionality with standard IMAP servers.

use std::sync::atomic::{AtomicBool, Ordering};

use async_imap::{
    error::Result as ImapResult,
    types::{Capability, Fetch, Flag, Mailbox, Name, NameAttribute},
};
use async_std::sync::{Mutex, RwLock};
use async_std::task;

use crate::constants::*;
use crate::context::Context;
use crate::dc_receive_imf::dc_receive_imf;
use crate::events::Event;
use crate::imap_client::*;
use crate::job::{job_add, Action};
use crate::login_param::{CertificateChecks, LoginParam};
use crate::message::{self, update_server_uid};
use crate::oauth2::dc_get_oauth2_access_token;
use crate::param::Params;
use crate::stock::StockMessage;

mod idle;
pub mod select_folder;

const DC_IMAP_SEEN: usize = 0x0001;

type Result<T> = std::result::Result<T, Error>;

#[derive(Debug, Fail)]
pub enum Error {
    #[fail(display = "IMAP Connect without configured params")]
    ConnectWithoutConfigure,

    #[fail(display = "IMAP Connection Failed params: {}", _0)]
    ConnectionFailed(String),

    #[fail(display = "IMAP No Connection established")]
    NoConnection,

    #[fail(display = "IMAP Could not get OAUTH token")]
    OauthError,

    #[fail(display = "IMAP Could not login as {}", _0)]
    LoginFailed(String),

    #[fail(display = "IMAP Could not fetch")]
    FetchFailed(#[cause] async_imap::error::Error),

    #[fail(display = "IMAP operation attempted while it is torn down")]
    InTeardown,

    #[fail(display = "IMAP operation attempted while it is torn down")]
    SqlError(#[cause] crate::sql::Error),

    #[fail(display = "IMAP got error from elsewhere")]
    WrappedError(#[cause] crate::error::Error),

    #[fail(display = "IMAP select folder error")]
    SelectFolderError(#[cause] select_folder::Error),

    #[fail(display = "No mailbox selected, folder: {:?}", _0)]
    NoMailbox(String),

    #[fail(display = "IMAP other error: {:?}", _0)]
    Other(String),
}

impl From<crate::sql::Error> for Error {
    fn from(err: crate::sql::Error) -> Error {
        Error::SqlError(err)
    }
}

impl From<crate::error::Error> for Error {
    fn from(err: crate::error::Error) -> Error {
        Error::WrappedError(err)
    }
}

impl From<Error> for crate::error::Error {
    fn from(err: Error) -> crate::error::Error {
        crate::error::Error::Message(err.to_string())
    }
}

impl From<select_folder::Error> for Error {
    fn from(err: select_folder::Error) -> Error {
        Error::SelectFolderError(err)
    }
}

#[derive(Debug, Display, Clone, Copy, PartialEq, Eq)]
pub enum ImapActionResult {
    Failed,
    RetryLater,
    AlreadyDone,
    Success,
}

const PREFETCH_FLAGS: &str = "(UID ENVELOPE)";
const JUST_UID: &str = "(UID)";
const BODY_FLAGS: &str = "(FLAGS BODY.PEEK[])";
const SELECT_ALL: &str = "1:*";

#[derive(Debug, Default)]
pub struct Imap {
    config: RwLock<ImapConfig>,
    session: Mutex<Option<Session>>,
    connected: Mutex<bool>,
    interrupt: Mutex<Option<stop_token::StopSource>>,
    skip_next_idle_wait: AtomicBool,
    should_reconnect: AtomicBool,
}

#[derive(Debug)]
struct OAuth2 {
    user: String,
    access_token: String,
}

impl async_imap::Authenticator for OAuth2 {
    type Response = String;

    fn process(&self, _data: &[u8]) -> Self::Response {
        format!(
            "user={}\x01auth=Bearer {}\x01\x01",
            self.user, self.access_token
        )
    }
}

#[derive(Debug)]
enum FolderMeaning {
    Unknown,
    SentObjects,
    Other,
}

#[derive(Debug)]
struct ImapConfig {
    pub addr: String,
    pub imap_server: String,
    pub imap_port: u16,
    pub imap_user: String,
    pub imap_pw: String,
    pub certificate_checks: CertificateChecks,
    pub server_flags: usize,
    pub selected_folder: Option<String>,
    pub selected_mailbox: Option<Mailbox>,
    pub selected_folder_needs_expunge: bool,
    pub can_idle: bool,
    pub imap_delimiter: char,
}

impl Default for ImapConfig {
    fn default() -> Self {
        ImapConfig {
            addr: "".into(),
            imap_server: "".into(),
            imap_port: 0,
            imap_user: "".into(),
            imap_pw: "".into(),
            certificate_checks: Default::default(),
            server_flags: 0,
            selected_folder: None,
            selected_mailbox: None,
            selected_folder_needs_expunge: false,
            can_idle: false,
            imap_delimiter: '.',
        }
    }
}

impl Imap {
    pub fn new() -> Self {
        Default::default()
    }

    pub async fn is_connected(&self) -> bool {
        *self.connected.lock().await
    }

    pub fn should_reconnect(&self) -> bool {
        self.should_reconnect.load(Ordering::Relaxed)
    }

    pub fn trigger_reconnect(&self) {
        self.should_reconnect.store(true, Ordering::Relaxed)
    }

    async fn setup_handle_if_needed(&self, context: &Context) -> Result<()> {
        if self.config.read().await.imap_server.is_empty() {
            return Err(Error::InTeardown);
        }

        if self.should_reconnect() {
            self.unsetup_handle(context).await;
            self.should_reconnect.store(false, Ordering::Relaxed);
        } else if self.is_connected().await {
            return Ok(());
        }

        let server_flags = self.config.read().await.server_flags as i32;

        let connection_res: ImapResult<Client> =
            if (server_flags & (DC_LP_IMAP_SOCKET_STARTTLS | DC_LP_IMAP_SOCKET_PLAIN)) != 0 {
                let config = self.config.read().await;
                let imap_server: &str = config.imap_server.as_ref();
                let imap_port = config.imap_port;

                match Client::connect_insecure((imap_server, imap_port)).await {
                    Ok(client) => {
                        if (server_flags & DC_LP_IMAP_SOCKET_STARTTLS) != 0 {
                            client.secure(imap_server, config.certificate_checks).await
                        } else {
                            Ok(client)
                        }
                    }
                    Err(err) => Err(err),
                }
            } else {
                let config = self.config.read().await;
                let imap_server: &str = config.imap_server.as_ref();
                let imap_port = config.imap_port;

                Client::connect_secure(
                    (imap_server, imap_port),
                    imap_server,
                    config.certificate_checks,
                )
                .await
            };

        let login_res = match connection_res {
            Ok(client) => {
                let config = self.config.read().await;
                let imap_user: &str = config.imap_user.as_ref();
                let imap_pw: &str = config.imap_pw.as_ref();

                if (server_flags & DC_LP_AUTH_OAUTH2) != 0 {
                    let addr: &str = config.addr.as_ref();

                    if let Some(token) = dc_get_oauth2_access_token(context, addr, imap_pw, true) {
                        let auth = OAuth2 {
                            user: imap_user.into(),
                            access_token: token,
                        };
                        client.authenticate("XOAUTH2", &auth).await
                    } else {
                        return Err(Error::OauthError);
                    }
                } else {
                    client.login(imap_user, imap_pw).await
                }
            }
            Err(err) => {
                let message = {
                    let config = self.config.read().await;
                    let imap_server: &str = config.imap_server.as_ref();
                    let imap_port = config.imap_port;
                    context.stock_string_repl_str2(
                        StockMessage::ServerResponse,
                        format!("{}:{}", imap_server, imap_port),
                        err.to_string(),
                    )
                };
                // IMAP connection failures are reported to users
                emit_event!(context, Event::ErrorNetwork(message));
                return Err(Error::ConnectionFailed(err.to_string()));
            }
        };

        self.should_reconnect.store(false, Ordering::Relaxed);

        match login_res {
            Ok(session) => {
                *self.session.lock().await = Some(session);
                Ok(())
            }
            Err((err, _)) => {
                let imap_user = self.config.read().await.imap_user.to_owned();
                let message = context.stock_string_repl_str(StockMessage::CannotLogin, &imap_user);

                emit_event!(
                    context,
                    Event::ErrorNetwork(format!("{} ({})", message, err))
                );
                self.trigger_reconnect();
                Err(Error::LoginFailed(format!("cannot login as {}", imap_user)))
            }
        }
    }

    async fn unsetup_handle(&self, context: &Context) {
        info!(
            context,
            "IMAP unsetup_handle step 2 (acquiring session.lock)"
        );
        if let Some(mut session) = self.session.lock().await.take() {
            if let Err(err) = session.close().await {
                warn!(context, "failed to close connection: {:?}", err);
            }
        }
        *self.connected.lock().await = false;

        info!(context, "IMAP unsetup_handle step 3 (clearing config).");
        self.config.write().await.selected_folder = None;
        self.config.write().await.selected_mailbox = None;
        info!(context, "IMAP unsetup_handle step 4 (disconnected)");
    }

    async fn free_connect_params(&self) {
        let mut cfg = self.config.write().await;

        cfg.addr = "".into();
        cfg.imap_server = "".into();
        cfg.imap_user = "".into();
        cfg.imap_pw = "".into();
        cfg.imap_port = 0;

        cfg.can_idle = false;
    }

    /// Connects to imap account using already-configured parameters.
    pub fn connect_configured(&self, context: &Context) -> Result<()> {
        if async_std::task::block_on(self.is_connected()) && !self.should_reconnect() {
            return Ok(());
        }
        if !context.sql.get_raw_config_bool(context, "configured") {
            return Err(Error::ConnectWithoutConfigure);
        }

        let param = LoginParam::from_database(context, "configured_");
        // the trailing underscore is correct

        if task::block_on(self.connect(context, &param)) {
            self.ensure_configured_folders(context, true)
        } else {
            Err(Error::ConnectionFailed(format!("{}", param)))
        }
    }

    /// tries connecting to imap account using the specific login
    /// parameters
    pub async fn connect(&self, context: &Context, lp: &LoginParam) -> bool {
        if lp.mail_server.is_empty() || lp.mail_user.is_empty() || lp.mail_pw.is_empty() {
            return false;
        }

        {
            let addr = &lp.addr;
            let imap_server = &lp.mail_server;
            let imap_port = lp.mail_port as u16;
            let imap_user = &lp.mail_user;
            let imap_pw = &lp.mail_pw;
            let server_flags = lp.server_flags as usize;

            let mut config = self.config.write().await;
            config.addr = addr.to_string();
            config.imap_server = imap_server.to_string();
            config.imap_port = imap_port;
            config.imap_user = imap_user.to_string();
            config.imap_pw = imap_pw.to_string();
            config.certificate_checks = lp.imap_certificate_checks;
            config.server_flags = server_flags;
        }

        if let Err(err) = self.setup_handle_if_needed(context).await {
            warn!(context, "failed to setup imap handle: {}", err);
            self.free_connect_params().await;
            return false;
        }

        let teardown = match &mut *self.session.lock().await {
            Some(ref mut session) => match session.capabilities().await {
                Ok(caps) => {
                    if !context.sql.is_open() {
                        warn!(context, "IMAP-LOGIN as {} ok but ABORTING", lp.mail_user,);
                        true
                    } else {
                        let can_idle = caps.has_str("IDLE");
                        let caps_list = caps.iter().fold(String::new(), |s, c| {
                            if let Capability::Atom(x) = c {
                                s + &format!(" {}", x)
                            } else {
                                s + &format!(" {:?}", c)
                            }
                        });

                        self.config.write().await.can_idle = can_idle;
                        *self.connected.lock().await = true;
                        emit_event!(
                            context,
                            Event::ImapConnected(format!(
                                "IMAP-LOGIN as {}, capabilities: {}",
                                lp.mail_user, caps_list,
                            ))
                        );
                        false
                    }
                }
                Err(err) => {
                    info!(context, "CAPABILITY command error: {}", err);
                    true
                }
            },
            None => true,
        };

        if teardown {
            self.disconnect(context);

            false
        } else {
            true
        }
    }

    pub fn disconnect(&self, context: &Context) {
        task::block_on(async move {
            self.unsetup_handle(context).await;
            self.free_connect_params().await;
        });
    }

    pub async fn fetch(&self, context: &Context, watch_folder: &str) -> Result<()> {
        if !context.sql.is_open() {
            // probably shutdown
            return Err(Error::InTeardown);
        }
        self.setup_handle_if_needed(context).await?;

        while self.fetch_new_messages(context, &watch_folder).await? {
            // We fetch until no more new messages are there.
        }
        Ok(())
    }

    fn get_config_last_seen_uid<S: AsRef<str>>(&self, context: &Context, folder: S) -> (u32, u32) {
        let key = format!("imap.mailbox.{}", folder.as_ref());
        if let Some(entry) = context.sql.get_raw_config(context, &key) {
            // the entry has the format `imap.mailbox.<folder>=<uidvalidity>:<lastseenuid>`
            let mut parts = entry.split(':');
            (
                parts
                    .next()
                    .unwrap_or_default()
                    .parse()
                    .unwrap_or_else(|_| 0),
                parts
                    .next()
                    .unwrap_or_default()
                    .parse()
                    .unwrap_or_else(|_| 0),
            )
        } else {
            (0, 0)
        }
    }

    /// return Result with (uid_validity, last_seen_uid) tuple.
    pub(crate) fn select_with_uidvalidity(
        &self,
        context: &Context,
        folder: &str,
    ) -> Result<(u32, u32)> {
        task::block_on(async move {
            self.select_folder(context, Some(folder)).await?;

            // compare last seen UIDVALIDITY against the current one
            let (uid_validity, last_seen_uid) = self.get_config_last_seen_uid(context, &folder);

            let config = self.config.read().await;
            let mailbox = config
                .selected_mailbox
                .as_ref()
                .ok_or_else(|| Error::NoMailbox(folder.to_string()))?;

            let new_uid_validity = match mailbox.uid_validity {
                Some(v) => v,
                None => {
                    let s = format!("No UIDVALIDITY for folder {:?}", folder);
                    return Err(Error::Other(s));
                }
            };

            if new_uid_validity == uid_validity {
                return Ok((uid_validity, last_seen_uid));
            }

            if mailbox.exists == 0 {
                info!(context, "Folder \"{}\" is empty.", folder);

                // set lastseenuid=0 for empty folders.
                // id we do not do this here, we'll miss the first message
                // as we will get in here again and fetch from lastseenuid+1 then

                self.set_config_last_seen_uid(context, &folder, new_uid_validity, 0);
                return Ok((new_uid_validity, 0));
            }

            // uid_validity has changed or is being set the first time.
            // find the last seen uid within the new uid_validity scope.
            let new_last_seen_uid = match mailbox.uid_next {
                Some(uid_next) => {
                    uid_next - 1 // XXX could uid_next be 0?
                }
                None => {
                    warn!(
                        context,
                        "IMAP folder has no uid_next, fall back to fetching"
                    );
                    if let Some(ref mut session) = &mut *self.session.lock().await {
                        // note that we use fetch by sequence number
                        // and thus we only need to get exactly the
                        // last-index message.
                        let set = format!("{}", mailbox.exists);
                        match session.fetch(set, JUST_UID).await {
                            Ok(list) => list[0].uid.unwrap_or_default(),
                            Err(err) => {
                                return Err(Error::FetchFailed(err));
                            }
                        }
                    } else {
                        return Err(Error::NoConnection);
                    }
                }
            };

            self.set_config_last_seen_uid(context, &folder, new_uid_validity, new_last_seen_uid);
            info!(
                context,
                "uid/validity change: new {}/{} current {}/{}",
                new_last_seen_uid,
                new_uid_validity,
                uid_validity,
                last_seen_uid
            );
            Ok((new_uid_validity, new_last_seen_uid))
        })
    }

    async fn fetch_new_messages<S: AsRef<str>>(
        &self,
        context: &Context,
        folder: S,
    ) -> Result<bool> {
        let (uid_validity, last_seen_uid) =
            self.select_with_uidvalidity(context, folder.as_ref())?;

        let mut read_cnt = 0;

        let mut list = if let Some(ref mut session) = &mut *self.session.lock().await {
            // fetch messages with larger UID than the last one seen
            // (`UID FETCH lastseenuid+1:*)`, see RFC 4549
            let set = format!("{}:*", last_seen_uid + 1);
            match session.uid_fetch(set, PREFETCH_FLAGS).await {
                Ok(list) => list,
                Err(err) => {
                    return Err(Error::FetchFailed(err));
                }
            }
        } else {
            return Err(Error::NoConnection);
        };

        // prefetch info from all unfetched mails
        let mut new_last_seen_uid = last_seen_uid;
        let mut read_errors = 0;

        list.sort_unstable_by_key(|msg| msg.uid.unwrap_or_default());

        for msg in &list {
            let cur_uid = msg.uid.unwrap_or_default();
            if cur_uid <= last_seen_uid {
                // If the mailbox is not empty, results always include
                // at least one UID, even if last_seen_uid+1 is past
                // the last UID in the mailbox.  It happens because
                // uid+1:* is interpreted the same way as *:uid+1.
                // See https://tools.ietf.org/html/rfc3501#page-61 for
                // standard reference. Therefore, sometimes we receive
                // already seen messages and have to filter them out.
                info!(
                    context,
                    "fetch_new_messages: ignoring uid {}, last seen was {}", cur_uid, last_seen_uid
                );
                continue;
            }
            read_cnt += 1;

            let message_id = prefetch_get_message_id(msg).unwrap_or_default();

            if !precheck_imf(context, &message_id, folder.as_ref(), cur_uid) {
                // check passed, go fetch the rest
                if let Err(err) = self.fetch_single_msg(context, &folder, cur_uid).await {
                    info!(
                        context,
                        "Read error for message {} from \"{}\", trying over later: {}.",
                        message_id,
                        folder.as_ref(),
                        err
                    );
                    read_errors += 1;
                }
            } else {
                // we know the message-id already or don't want the message otherwise.
                info!(
                    context,
                    "Skipping message {} from \"{}\" by precheck.",
                    message_id,
                    folder.as_ref(),
                );
            }
            if read_errors == 0 {
                new_last_seen_uid = cur_uid;
            }
        }

        if new_last_seen_uid > last_seen_uid {
            self.set_config_last_seen_uid(context, &folder, uid_validity, new_last_seen_uid);
        }

        if read_errors > 0 {
            warn!(
                context,
                "{} mails read from \"{}\" with {} errors.",
                read_cnt,
                folder.as_ref(),
                read_errors
            );
        } else {
            info!(
                context,
                "{} mails read from \"{}\".",
                read_cnt,
                folder.as_ref()
            );
        }

        Ok(read_cnt > 0)
    }

    fn set_config_last_seen_uid<S: AsRef<str>>(
        &self,
        context: &Context,
        folder: S,
        uidvalidity: u32,
        lastseenuid: u32,
    ) {
        let key = format!("imap.mailbox.{}", folder.as_ref());
        let val = format!("{}:{}", uidvalidity, lastseenuid);

        context.sql.set_raw_config(context, &key, Some(&val)).ok();
    }

    /// Fetches a single message by server UID.
    ///
    /// If it succeeds, the message should be treated as received even
    /// if no database entries are created. If the function returns an
    /// error, the caller should try again later.
    async fn fetch_single_msg<S: AsRef<str>>(
        &self,
        context: &Context,
        folder: S,
        server_uid: u32,
    ) -> Result<()> {
        if !self.is_connected().await {
            return Err(Error::Other("Not connected".to_string()));
        }

        let set = format!("{}", server_uid);

        let msgs = if let Some(ref mut session) = &mut *self.session.lock().await {
            match session.uid_fetch(set, BODY_FLAGS).await {
                Ok(msgs) => msgs,
                Err(err) => {
                    // TODO maybe differentiate between IO and input/parsing problems
                    // so we don't reconnect if we have a (rare) input/output parsing problem?
                    self.trigger_reconnect();
                    warn!(
                        context,
                        "Error on fetching message #{} from folder \"{}\"; error={}.",
                        server_uid,
                        folder.as_ref(),
                        err
                    );
                    return Err(Error::FetchFailed(err));
                }
            }
        } else {
            // we could not get a valid imap session, this should be retried
            self.trigger_reconnect();
            return Err(Error::Other("Could not get IMAP session".to_string()));
        };

        if msgs.is_empty() {
            warn!(
                context,
                "Message #{} does not exist in folder \"{}\".",
                server_uid,
                folder.as_ref()
            );
        } else {
            let msg = &msgs[0];

            // XXX put flags into a set and pass them to dc_receive_imf
            let is_deleted = msg.flags().any(|flag| match flag {
                Flag::Deleted => true,
                _ => false,
            });
            let is_seen = msg.flags().any(|flag| match flag {
                Flag::Seen => true,
                _ => false,
            });

            let flags = if is_seen { DC_IMAP_SEEN } else { 0 };

            if !is_deleted && msg.body().is_some() {
                let body = msg.body().unwrap_or_default();
                if let Err(err) =
                    dc_receive_imf(context, &body, folder.as_ref(), server_uid, flags as u32)
                {
                    warn!(
                        context,
                        "dc_receive_imf failed for imap-message {}/{}: {:?}",
                        folder.as_ref(),
                        server_uid,
                        err
                    );
                }
            }
        }

        Ok(())
    }

    pub fn mv(
        &self,
        context: &Context,
        folder: &str,
        uid: u32,
        dest_folder: &str,
        dest_uid: &mut u32,
    ) -> ImapActionResult {
        task::block_on(async move {
            if folder == dest_folder {
                info!(
                    context,
                    "Skip moving message; message {}/{} is already in {}...",
                    folder,
                    uid,
                    dest_folder,
                );
                return ImapActionResult::AlreadyDone;
            }
            if let Some(imapresult) = self.prepare_imap_operation_on_msg(context, folder, uid) {
                return imapresult;
            }
            // we are connected, and the folder is selected

            // XXX Rust-Imap provides no target uid on mv, so just set it to 0
            *dest_uid = 0;

            let set = format!("{}", uid);
            let display_folder_id = format!("{}/{}", folder, uid);
            if let Some(ref mut session) = &mut *self.session.lock().await {
                match session.uid_mv(&set, &dest_folder).await {
                    Ok(_) => {
                        emit_event!(
                            context,
                            Event::ImapMessageMoved(format!(
                                "IMAP Message {} moved to {}",
                                display_folder_id, dest_folder
                            ))
                        );
                        return ImapActionResult::Success;
                    }
                    Err(err) => {
                        warn!(
                            context,
                            "Cannot move message, fallback to COPY/DELETE {}/{} to {}: {}",
                            folder,
                            uid,
                            dest_folder,
                            err
                        );
                    }
                }
            } else {
                unreachable!();
            };

            if let Some(ref mut session) = &mut *self.session.lock().await {
                match session.uid_copy(&set, &dest_folder).await {
                    Ok(_) => {
                        if !self.add_flag_finalized(context, uid, "\\Deleted").await {
                            warn!(context, "Cannot mark {} as \"Deleted\" after copy.", uid);
                            ImapActionResult::Failed
                        } else {
                            self.config.write().await.selected_folder_needs_expunge = true;
                            ImapActionResult::Success
                        }
                    }
                    Err(err) => {
                        warn!(context, "Could not copy message: {}", err);
                        ImapActionResult::Failed
                    }
                }
            } else {
                unreachable!();
            }
        })
    }

    async fn add_flag_finalized(&self, context: &Context, server_uid: u32, flag: &str) -> bool {
        // return true if we successfully set the flag or we otherwise
        // think add_flag should not be retried: Disconnection during setting
        // the flag, or other imap-errors, returns true as well.
        //
        // returning false means that the operation can be retried.
        if server_uid == 0 {
            return true; // might be moved but we don't want to have a stuck job
        }
        let s = server_uid.to_string();
        self.add_flag_finalized_with_set(context, &s, flag).await
    }

    async fn add_flag_finalized_with_set(
        &self,
        context: &Context,
        uid_set: &str,
        flag: &str,
    ) -> bool {
        if self.should_reconnect() {
            return false;
        }
        if let Some(ref mut session) = &mut *self.session.lock().await {
            let query = format!("+FLAGS ({})", flag);
            match session.uid_store(uid_set, &query).await {
                Ok(_) => {}
                Err(err) => {
                    warn!(
                        context,
                        "IMAP failed to store: ({}, {}) {:?}", uid_set, query, err
                    );
                }
            }
            true // we tried once, that's probably enough for setting flag
        } else {
            unreachable!();
        }
    }

    pub fn prepare_imap_operation_on_msg(
        &self,
        context: &Context,
        folder: &str,
        uid: u32,
    ) -> Option<ImapActionResult> {
        task::block_on(async move {
            if uid == 0 {
                return Some(ImapActionResult::Failed);
            }
            if !self.is_connected().await {
                // currently jobs are only performed on the INBOX thread
                // TODO: make INBOX/SENT/MVBOX perform the jobs on their
                // respective folders to avoid select_folder network traffic
                // and the involved error states
                if let Err(err) = self.connect_configured(context) {
                    warn!(context, "prepare_imap_op failed: {}", err);
                    return Some(ImapActionResult::RetryLater);
                }
            }
            match self.select_folder(context, Some(&folder)).await {
                Ok(()) => None,
                Err(select_folder::Error::ConnectionLost) => {
                    warn!(context, "Lost imap connection");
                    Some(ImapActionResult::RetryLater)
                }
                Err(select_folder::Error::NoSession) => {
                    warn!(context, "no imap session");
                    Some(ImapActionResult::Failed)
                }
                Err(select_folder::Error::BadFolderName(folder_name)) => {
                    warn!(context, "invalid folder name: {:?}", folder_name);
                    Some(ImapActionResult::Failed)
                }
                Err(err) => {
                    warn!(context, "failed to select folder: {:?}: {:?}", folder, err);
                    Some(ImapActionResult::RetryLater)
                }
            }
        })
    }

    pub fn set_seen(&self, context: &Context, folder: &str, uid: u32) -> ImapActionResult {
        task::block_on(async move {
            if let Some(imapresult) = self.prepare_imap_operation_on_msg(context, folder, uid) {
                return imapresult;
            }
            // we are connected, and the folder is selected
            info!(context, "Marking message {}/{} as seen...", folder, uid,);

            if self.add_flag_finalized(context, uid, "\\Seen").await {
                ImapActionResult::Success
            } else {
                warn!(
                    context,
                    "Cannot mark message {} in folder {} as seen, ignoring.", uid, folder
                );
                ImapActionResult::Failed
            }
        })
    }

    // only returns 0 on connection problems; we should try later again in this case *
    pub fn delete_msg(
        &self,
        context: &Context,
        message_id: &str,
        folder: &str,
        uid: &mut u32,
    ) -> ImapActionResult {
        task::block_on(async move {
            if let Some(imapresult) = self.prepare_imap_operation_on_msg(context, folder, *uid) {
                return imapresult;
            }
            // we are connected, and the folder is selected

            let set = format!("{}", uid);
            let display_imap_id = format!("{}/{}", folder, uid);

            // double-check that we are deleting the correct message-id
            // this comes at the expense of another imap query
            if let Some(ref mut session) = &mut *self.session.lock().await {
                match session.uid_fetch(set, PREFETCH_FLAGS).await {
                    Ok(msgs) => {
                        if msgs.is_empty() {
                            warn!(
                                context,
                                "Cannot delete on IMAP, {}: imap entry gone '{}'",
                                display_imap_id,
                                message_id,
                            );
                            return ImapActionResult::Failed;
                        }
                        let remote_message_id =
                            prefetch_get_message_id(msgs.first().unwrap()).unwrap_or_default();

                        if remote_message_id != message_id {
                            warn!(
                                context,
                                "Cannot delete on IMAP, {}: remote message-id '{}' != '{}'",
                                display_imap_id,
                                remote_message_id,
                                message_id,
                            );
                            *uid = 0;
                        }
                    }
                    Err(err) => {
                        warn!(
                            context,
                            "Cannot delete {} on IMAP: {}", display_imap_id, err
                        );
                        *uid = 0;
                    }
                }
            }

            // mark the message for deletion
            if !self.add_flag_finalized(context, *uid, "\\Deleted").await {
                warn!(
                    context,
                    "Cannot mark message {} as \"Deleted\".", display_imap_id
                );
                ImapActionResult::Failed
            } else {
                emit_event!(
                    context,
                    Event::ImapMessageDeleted(format!(
                        "IMAP Message {} marked as deleted [{}]",
                        display_imap_id, message_id
                    ))
                );
                self.config.write().await.selected_folder_needs_expunge = true;
                ImapActionResult::Success
            }
        })
    }

    pub fn ensure_configured_folders(&self, context: &Context, create_mvbox: bool) -> Result<()> {
        let folders_configured = context
            .sql
            .get_raw_config_int(context, "folders_configured");
        if folders_configured.unwrap_or_default() >= 3 {
            // the "3" here we increase if we have future updates to
            // to folder configuration
            return Ok(());
        }

        task::block_on(async move {
            if !self.is_connected().await {
                return Err(Error::NoConnection);
            }

            info!(context, "Configuring IMAP-folders.");

            if let Some(ref mut session) = &mut *self.session.lock().await {
                let folders = match self.list_folders(session, context).await {
                    Some(f) => f,
                    None => {
                        return Err(Error::Other("list_folders failed".to_string()));
                    }
                };

                let sentbox_folder =
                    folders
                        .iter()
                        .find(|folder| match get_folder_meaning(folder) {
                            FolderMeaning::SentObjects => true,
                            _ => false,
                        });
                info!(context, "sentbox folder is {:?}", sentbox_folder);

                let delimiter = self.config.read().await.imap_delimiter;
                let fallback_folder = format!("INBOX{}DeltaChat", delimiter);

                let mut mvbox_folder = folders
                    .iter()
                    .find(|folder| folder.name() == "DeltaChat" || folder.name() == fallback_folder)
                    .map(|n| n.name().to_string());

                if mvbox_folder.is_none() && create_mvbox {
                    info!(context, "Creating MVBOX-folder \"DeltaChat\"...",);

                    match session.create("DeltaChat").await {
                        Ok(_) => {
                            mvbox_folder = Some("DeltaChat".into());

                            info!(context, "MVBOX-folder created.",);
                        }
                        Err(err) => {
                            warn!(
                                context,
                                "Cannot create MVBOX-folder, trying to create INBOX subfolder. ({})",
                                err
                            );

                            match session.create(&fallback_folder).await {
                                Ok(_) => {
                                    mvbox_folder = Some(fallback_folder);
                                    info!(
                                        context,
                                        "MVBOX-folder created as INBOX subfolder. ({})", err
                                    );
                                }
                                Err(err) => {
                                    warn!(context, "Cannot create MVBOX-folder. ({})", err);
                                }
                            }
                        }
                    }
                    // SUBSCRIBE is needed to make the folder visible to the LSUB command
                    // that may be used by other MUAs to list folders.
                    // for the LIST command, the folder is always visible.
                    if let Some(ref mvbox) = mvbox_folder {
                        if let Err(err) = session.subscribe(mvbox).await {
                            warn!(context, "could not subscribe to {:?}: {:?}", mvbox, err);
                        }
                    }
                }
                context
                    .sql
                    .set_raw_config(context, "configured_inbox_folder", Some("INBOX"))?;
                if let Some(ref mvbox_folder) = mvbox_folder {
                    context.sql.set_raw_config(
                        context,
                        "configured_mvbox_folder",
                        Some(mvbox_folder),
                    )?;
                }
                if let Some(ref sentbox_folder) = sentbox_folder {
                    context.sql.set_raw_config(
                        context,
                        "configured_sentbox_folder",
                        Some(sentbox_folder.name()),
                    )?;
                }
                context
                    .sql
                    .set_raw_config_int(context, "folders_configured", 3)?;
            }
            info!(context, "FINISHED configuring IMAP-folders.");
            Ok(())
        })
    }

    async fn list_folders(&self, session: &mut Session, context: &Context) -> Option<Vec<Name>> {
        match session.list(Some(""), Some("*")).await {
            Ok(list) => {
                if list.is_empty() {
                    warn!(context, "Folder list is empty.",);
                }
                Some(list)
            }
            Err(err) => {
                eprintln!("list error: {:?}", err);
                warn!(context, "Cannot get folder list.",);

                None
            }
        }
    }

    pub fn empty_folder(&self, context: &Context, folder: &str) {
        task::block_on(async move {
            info!(context, "emptying folder {}", folder);

            // we want to report all error to the user
            // (no retry should be attempted)
            if folder.is_empty() {
                error!(context, "cannot perform empty, folder not set");
                return;
            }
            if let Err(err) = self.setup_handle_if_needed(context).await {
                error!(context, "could not setup imap connection: {:?}", err);
                return;
            }
            if let Err(err) = self.select_folder(context, Some(&folder)).await {
                error!(
                    context,
                    "Could not select {} for expunging: {:?}", folder, err
                );
                return;
            }

            if !self
                .add_flag_finalized_with_set(context, SELECT_ALL, "\\Deleted")
                .await
            {
                error!(context, "Cannot mark messages for deletion {}", folder);
                return;
            }

            // we now trigger expunge to actually delete messages
            self.config.write().await.selected_folder_needs_expunge = true;
            match self.select_folder::<String>(context, None).await {
                Ok(()) => {
                    emit_event!(context, Event::ImapFolderEmptied(folder.to_string()));
                }
                Err(err) => {
                    error!(context, "expunge failed {}: {:?}", folder, err);
                }
            }
        });
    }
}

/// Try to get the folder meaning by the name of the folder only used if the server does not support XLIST.
// TODO: lots languages missing - maybe there is a list somewhere on other MUAs?
// however, if we fail to find out the sent-folder,
// only watching this folder is not working. at least, this is no show stopper.
// CAVE: if possible, take care not to add a name here that is "sent" in one language
// but sth. different in others - a hard job.
fn get_folder_meaning_by_name(folder_name: &Name) -> FolderMeaning {
    let sent_names = vec!["sent", "sent objects", "gesendet"];
    let lower = folder_name.name().to_lowercase();

    if sent_names.into_iter().any(|s| s == lower) {
        FolderMeaning::SentObjects
    } else {
        FolderMeaning::Unknown
    }
}

fn get_folder_meaning(folder_name: &Name) -> FolderMeaning {
    if folder_name.attributes().is_empty() {
        return FolderMeaning::Unknown;
    }

    let mut res = FolderMeaning::Unknown;
    let special_names = vec!["\\Spam", "\\Trash", "\\Drafts", "\\Junk"];

    for attr in folder_name.attributes() {
        if let NameAttribute::Custom(ref label) = attr {
            if special_names.iter().any(|s| *s == label) {
                res = FolderMeaning::Other;
            } else if label == "\\Sent" {
                res = FolderMeaning::SentObjects
            }
        }
    }

    match res {
        FolderMeaning::Unknown => get_folder_meaning_by_name(folder_name),
        _ => res,
    }
}

fn precheck_imf(context: &Context, rfc724_mid: &str, server_folder: &str, server_uid: u32) -> bool {
    if let Ok((old_server_folder, old_server_uid, msg_id)) =
        message::rfc724_mid_exists(context, &rfc724_mid)
    {
        if old_server_folder.is_empty() && old_server_uid == 0 {
            info!(context, "[move] detected bbc-self {}", rfc724_mid,);
            context.do_heuristics_moves(server_folder.as_ref(), msg_id);
            job_add(
                context,
                Action::MarkseenMsgOnImap,
                msg_id.to_u32() as i32,
                Params::new(),
                0,
            );
        } else if old_server_folder != server_folder {
            info!(context, "[move] detected moved message {}", rfc724_mid,);
        }

        if old_server_folder != server_folder || old_server_uid != server_uid {
            update_server_uid(context, &rfc724_mid, server_folder, server_uid);
        }
        true
    } else {
        false
    }
}

fn parse_message_id(message_id: &[u8]) -> crate::error::Result<String> {
    let value = std::str::from_utf8(message_id)?;
    let addrs = mailparse::addrparse(value)
        .map_err(|err| format_err!("failed to parse message id {:?}", err))?;

    if let Some(info) = addrs.extract_single_info() {
        return Ok(info.addr);
    }

    bail!("could not parse message_id: {}", value);
}

fn prefetch_get_message_id(prefetch_msg: &Fetch) -> Result<String> {
    if prefetch_msg.envelope().is_none() {
        return Err(Error::Other(
            "prefetch: message has no envelope".to_string(),
        ));
    }

    if let Some(message_id) = prefetch_msg.envelope().unwrap().message_id {
        parse_message_id(&message_id).map_err(Into::into)
    } else {
        Err(Error::Other("prefetch: No message ID found".to_string()))
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_parse_message_id() {
        assert_eq!(
            parse_message_id(b"Mr.PRUe8HJBoaO.3whNvLCMFU0@testrun.org").unwrap(),
            "Mr.PRUe8HJBoaO.3whNvLCMFU0@testrun.org"
        );
        assert_eq!(
            parse_message_id(b"<Mr.PRUe8HJBoaO.3whNvLCMFU0@testrun.org>").unwrap(),
            "Mr.PRUe8HJBoaO.3whNvLCMFU0@testrun.org"
        );
    }
}