/*
 * meli - mailbox module.
 *
 * Copyright 2017 Manos Pitsidianakis
 *
 * This file is part of meli.
 *
 * meli 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 3 of the License, or
 * (at your option) any later version.
 *
 * meli 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 meli. If not, see <http://www.gnu.org/licenses/>.
 */

/*!
 * https://wiki2.dovecot.org/MailboxFormat/mbox
 */

use crate::async_workers::{Async, AsyncBuilder, AsyncStatus, WorkContext};
use crate::backends::*;
use crate::conf::AccountSettings;
use crate::email::parser::BytesExt;
use crate::email::*;
use crate::error::{MeliError, Result};
use crate::get_path_hash;
use crate::shellexpand::ShellExpandTrait;
use memmap::{Mmap, Protection};
use nom::bytes::complete::tag;
use nom::character::complete::digit1;
use nom::combinator::map_res;
use nom::{self, error::ErrorKind, IResult};

extern crate notify;
use self::notify::{watcher, DebouncedEvent, RecursiveMode, Watcher};
use std::collections::hash_map::{DefaultHasher, HashMap};
use std::fs::File;
use std::hash::Hasher;
use std::io::BufReader;
use std::io::Read;
use std::os::unix::io::AsRawFd;
use std::path::{Path, PathBuf};
use std::str::FromStr;
use std::sync::mpsc::channel;
use std::sync::{Arc, Mutex, RwLock};

type Offset = usize;
type Length = usize;

const F_OFD_SETLKW: libc::c_int = 38;

// Open file description locking
// # man fcntl
fn get_rw_lock_blocking(f: &File) {
    let fd: libc::c_int = f.as_raw_fd();
    let mut flock: libc::flock = libc::flock {
        l_type: libc::F_WRLCK as libc::c_short,
        l_whence: libc::SEEK_SET as libc::c_short,
        l_start: 0,
        l_len: 0, /* "Specifying 0 for l_len has the special meaning: lock all bytes starting at the location
                  specified by l_whence and l_start through to the end of file, no matter how large the file grows." */
        l_pid: 0, /* "By contrast with traditional record locks, the l_pid field of that structure must be set to zero when using the commands described below." */
    };
    let ptr: *mut libc::flock = &mut flock;
    let ret_val = unsafe { libc::fcntl(fd, F_OFD_SETLKW, ptr as *mut libc::c_void) };
    debug!(&ret_val);
    assert!(-1 != ret_val);
}

#[derive(Debug)]
struct MboxMailbox {
    hash: MailboxHash,
    name: String,
    path: PathBuf,
    fs_path: PathBuf,
    content: Vec<u8>,
    children: Vec<MailboxHash>,
    parent: Option<MailboxHash>,
    usage: Arc<RwLock<SpecialUsageMailbox>>,
    is_subscribed: bool,
    permissions: MailboxPermissions,
    pub total: Arc<Mutex<usize>>,
    pub unseen: Arc<Mutex<usize>>,
    index: Arc<Mutex<HashMap<EnvelopeHash, (Offset, Length)>>>,
}

impl BackendMailbox for MboxMailbox {
    fn hash(&self) -> MailboxHash {
        self.hash
    }

    fn name(&self) -> &str {
        self.name.as_str()
    }

    fn path(&self) -> &str {
        /* We know it's valid UTF-8 because we supplied it */
        self.path.to_str().unwrap()
    }

    fn change_name(&mut self, s: &str) {
        self.name = s.to_string();
    }

    fn clone(&self) -> Mailbox {
        Box::new(MboxMailbox {
            hash: self.hash,
            name: self.name.clone(),
            path: self.path.clone(),
            fs_path: self.fs_path.clone(),
            content: self.content.clone(),
            children: self.children.clone(),
            usage: self.usage.clone(),
            is_subscribed: self.is_subscribed,
            parent: self.parent,
            permissions: self.permissions,
            unseen: self.unseen.clone(),
            total: self.total.clone(),
            index: self.index.clone(),
        })
    }

    fn children(&self) -> &[MailboxHash] {
        &self.children
    }

    fn parent(&self) -> Option<MailboxHash> {
        self.parent
    }

    fn special_usage(&self) -> SpecialUsageMailbox {
        *self.usage.read().unwrap()
    }

    fn permissions(&self) -> MailboxPermissions {
        self.permissions
    }
    fn is_subscribed(&self) -> bool {
        self.is_subscribed
    }
    fn set_is_subscribed(&mut self, new_val: bool) -> Result<()> {
        self.is_subscribed = new_val;
        Ok(())
    }
    fn set_special_usage(&mut self, new_val: SpecialUsageMailbox) -> Result<()> {
        *self.usage.write()? = new_val;
        Ok(())
    }

    fn count(&self) -> Result<(usize, usize)> {
        Ok((*self.unseen.lock()?, *self.total.lock()?))
    }
}

/// `BackendOp` implementor for Mbox
#[derive(Debug, Default)]
pub struct MboxOp {
    hash: EnvelopeHash,
    path: PathBuf,
    offset: Offset,
    length: Length,
    slice: Option<Mmap>,
}

impl MboxOp {
    pub fn new(hash: EnvelopeHash, path: &Path, offset: Offset, length: Length) -> Self {
        MboxOp {
            hash,
            path: path.to_path_buf(),
            slice: None,
            offset,
            length,
        }
    }
}

impl BackendOp for MboxOp {
    fn as_bytes(&mut self) -> ResultFuture<Vec<u8>> {
        if self.slice.is_none() {
            self.slice = Some(Mmap::open_path(&self.path, Protection::Read)?);
        }
        /* Unwrap is safe since we use ? above. */
        let ret = Ok((unsafe {
            &self.slice.as_ref().unwrap().as_slice()[self.offset..self.offset + self.length]
        })
        .to_vec());
        Ok(Box::pin(async move { ret }))
    }

    fn fetch_flags(&self) -> ResultFuture<Flag> {
        let mut flags = Flag::empty();
        let file = std::fs::OpenOptions::new()
            .read(true)
            .write(true)
            .open(&self.path)?;
        get_rw_lock_blocking(&file);
        let mut buf_reader = BufReader::new(file);
        let mut contents = Vec::new();
        buf_reader.read_to_end(&mut contents)?;
        let (_, headers) = parser::headers::headers_raw(contents.as_slice())?;
        if let Some(start) = headers.find(b"Status:") {
            if let Some(end) = headers[start..].find(b"\n") {
                let start = start + b"Status:".len();
                let status = headers[start..start + end].trim();
                if status.contains(&b'F') {
                    flags.set(Flag::FLAGGED, true);
                }
                if status.contains(&b'A') {
                    flags.set(Flag::REPLIED, true);
                }
                if status.contains(&b'R') {
                    flags.set(Flag::SEEN, true);
                }
                if status.contains(&b'D') {
                    flags.set(Flag::TRASHED, true);
                }
                if status.contains(&b'T') {
                    flags.set(Flag::DRAFT, true);
                }
            }
        }
        if let Some(start) = headers.find(b"X-Status:") {
            let start = start + b"X-Status:".len();
            if let Some(end) = headers[start..].find(b"\n") {
                let status = headers[start..start + end].trim();
                if status.contains(&b'F') {
                    flags.set(Flag::FLAGGED, true);
                }
                if status.contains(&b'A') {
                    flags.set(Flag::REPLIED, true);
                }
                if status.contains(&b'R') {
                    flags.set(Flag::SEEN, true);
                }
                if status.contains(&b'D') {
                    flags.set(Flag::TRASHED, true);
                }
                if status.contains(&b'T') {
                    flags.set(Flag::DRAFT, true);
                }
            }
        }
        Ok(Box::pin(async move { Ok(flags) }))
    }

    fn set_flag(&mut self, _flag: Flag, _value: bool) -> ResultFuture<()> {
        Err(MeliError::new("Unimplemented."))
    }

    fn set_tag(&mut self, _tag: String, _value: bool) -> ResultFuture<()> {
        Err(MeliError::new("mbox doesn't support tags."))
    }
}

#[derive(Debug, Clone, Copy)]
pub enum MboxReader {
    MboxO,
    MboxRd,
    MboxCl,
    MboxCl2,
}

impl Default for MboxReader {
    fn default() -> Self {
        Self::MboxCl2
    }
}

macro_rules! find_From__line {
    ($input:expr) => {{
        //debug!("find_From__line invocation");
        let input = $input;
        let mut ptr = 0;
        let mut found = None;
        while ptr < input.len() {
            // Find next From_ candidate line.
            const TAG: &'static [u8] = b"\n\nFrom ";
            if let Some(end) = input[ptr..].find(TAG) {
                // This candidate is a valid From_ if it ends in a new line and the next line is
                // a header.
                if let Some(line_end) = input[ptr + end + TAG.len()..].find(b"\n") {
                    if crate::email::parser::headers::header(
                        &input[ptr + end + TAG.len() + line_end + 1..],
                    )
                    .is_ok()
                    {
                        found = Some(ptr + end);
                        break;
                    } else {
                        /* Ignore invalid From_ line. */
                        ptr += end + TAG.len() + line_end;
                    }
                } else {
                    /* Ignore invalid From_ line. */
                    ptr += end + TAG.len();
                }
            } else {
                found = Some(input.len());
                break;
            }
        }
        found
    }};
}

impl MboxReader {
    fn parse<'i>(&self, input: &'i [u8]) -> IResult<&'i [u8], Envelope> {
        let orig_input = input;
        let mut input = input;
        match self {
            Self::MboxO => {
                let next_offset: Option<(usize, usize)> = find_From__line!(input)
                    .and_then(|end| input.find(b"\n").and_then(|start| Some((start + 1, end))));

                if let Some((start, len)) = next_offset {
                    match Envelope::from_bytes(&input[start..len], None) {
                        Ok(mut env) => {
                            let mut flags = Flag::empty();
                            if env.other_headers().contains_key("Status") {
                                if env.other_headers()["Status"].contains('F') {
                                    flags.set(Flag::FLAGGED, true);
                                }
                                if env.other_headers()["Status"].contains('A') {
                                    flags.set(Flag::REPLIED, true);
                                }
                                if env.other_headers()["Status"].contains('R') {
                                    flags.set(Flag::SEEN, true);
                                }
                                if env.other_headers()["Status"].contains('D') {
                                    flags.set(Flag::TRASHED, true);
                                }
                            }
                            if env.other_headers().contains_key("X-Status") {
                                if env.other_headers()["X-Status"].contains('F') {
                                    flags.set(Flag::FLAGGED, true);
                                }
                                if env.other_headers()["X-Status"].contains('A') {
                                    flags.set(Flag::REPLIED, true);
                                }
                                if env.other_headers()["X-Status"].contains('R') {
                                    flags.set(Flag::SEEN, true);
                                }
                                if env.other_headers()["X-Status"].contains('D') {
                                    flags.set(Flag::TRASHED, true);
                                }
                                if env.other_headers()["X-Status"].contains('T') {
                                    flags.set(Flag::DRAFT, true);
                                }
                            }
                            env.set_flags(flags);
                            if len == input.len() {
                                Ok((&[], env))
                            } else {
                                input = &input[len + 2..];
                                Ok((input, env))
                            }
                        }
                        Err(err) => {
                            debug!("Could not parse mail {:?}", err);
                            Err(nom::Err::Error((input, ErrorKind::Tag)))
                        }
                    }
                } else {
                    let start: Offset = input.find(b"\n").map(|v| v + 1).unwrap_or(0);
                    match Envelope::from_bytes(&input[start..], None) {
                        Ok(mut env) => {
                            let mut flags = Flag::empty();
                            if env.other_headers().contains_key("Status") {
                                if env.other_headers()["Status"].contains("F") {
                                    flags.set(Flag::FLAGGED, true);
                                }
                                if env.other_headers()["Status"].contains("A") {
                                    flags.set(Flag::REPLIED, true);
                                }
                                if env.other_headers()["Status"].contains("R") {
                                    flags.set(Flag::SEEN, true);
                                }
                                if env.other_headers()["Status"].contains("D") {
                                    flags.set(Flag::TRASHED, true);
                                }
                            }
                            if env.other_headers().contains_key("X-Status") {
                                if env.other_headers()["X-Status"].contains("F") {
                                    flags.set(Flag::FLAGGED, true);
                                }
                                if env.other_headers()["X-Status"].contains("A") {
                                    flags.set(Flag::REPLIED, true);
                                }
                                if env.other_headers()["X-Status"].contains("R") {
                                    flags.set(Flag::SEEN, true);
                                }
                                if env.other_headers()["X-Status"].contains("D") {
                                    flags.set(Flag::TRASHED, true);
                                }
                                if env.other_headers()["X-Status"].contains("T") {
                                    flags.set(Flag::DRAFT, true);
                                }
                            }
                            env.set_flags(flags);
                            Ok((&[], env))
                        }
                        Err(err) => {
                            debug!("Could not parse mail at {:?}", err);
                            Err(nom::Err::Error((input, ErrorKind::Tag)))
                        }
                    }
                }
            }
            Self::MboxRd => {
                let next_offset: Option<(usize, usize)> = find_From__line!(input)
                    .and_then(|end| input.find(b"\n").and_then(|start| Some((start + 1, end))));

                if let Some((start, len)) = next_offset {
                    match Envelope::from_bytes(&input[start..len], None) {
                        Ok(mut env) => {
                            let mut flags = Flag::empty();
                            if env.other_headers().contains_key("Status") {
                                if env.other_headers()["Status"].contains('F') {
                                    flags.set(Flag::FLAGGED, true);
                                }
                                if env.other_headers()["Status"].contains('A') {
                                    flags.set(Flag::REPLIED, true);
                                }
                                if env.other_headers()["Status"].contains('R') {
                                    flags.set(Flag::SEEN, true);
                                }
                                if env.other_headers()["Status"].contains('D') {
                                    flags.set(Flag::TRASHED, true);
                                }
                            }
                            if env.other_headers().contains_key("X-Status") {
                                if env.other_headers()["X-Status"].contains('F') {
                                    flags.set(Flag::FLAGGED, true);
                                }
                                if env.other_headers()["X-Status"].contains('A') {
                                    flags.set(Flag::REPLIED, true);
                                }
                                if env.other_headers()["X-Status"].contains('R') {
                                    flags.set(Flag::SEEN, true);
                                }
                                if env.other_headers()["X-Status"].contains('D') {
                                    flags.set(Flag::TRASHED, true);
                                }
                                if env.other_headers()["X-Status"].contains('T') {
                                    flags.set(Flag::DRAFT, true);
                                }
                            }
                            env.set_flags(flags);
                            if len == input.len() {
                                Ok((&[], env))
                            } else {
                                input = &input[len + 2..];
                                Ok((input, env))
                            }
                        }
                        Err(err) => {
                            debug!("Could not parse mail {:?}", err);
                            Err(nom::Err::Error((input, ErrorKind::Tag)))
                        }
                    }
                } else {
                    let start: Offset = input.find(b"\n").map(|v| v + 1).unwrap_or(0);
                    match Envelope::from_bytes(&input[start..], None) {
                        Ok(mut env) => {
                            let mut flags = Flag::empty();
                            if env.other_headers().contains_key("Status") {
                                if env.other_headers()["Status"].contains('F') {
                                    flags.set(Flag::FLAGGED, true);
                                }
                                if env.other_headers()["Status"].contains('A') {
                                    flags.set(Flag::REPLIED, true);
                                }
                                if env.other_headers()["Status"].contains('R') {
                                    flags.set(Flag::SEEN, true);
                                }
                                if env.other_headers()["Status"].contains('D') {
                                    flags.set(Flag::TRASHED, true);
                                }
                            }
                            if env.other_headers().contains_key("X-Status") {
                                if env.other_headers()["X-Status"].contains('F') {
                                    flags.set(Flag::FLAGGED, true);
                                }
                                if env.other_headers()["X-Status"].contains('A') {
                                    flags.set(Flag::REPLIED, true);
                                }
                                if env.other_headers()["X-Status"].contains('R') {
                                    flags.set(Flag::SEEN, true);
                                }
                                if env.other_headers()["X-Status"].contains('D') {
                                    flags.set(Flag::TRASHED, true);
                                }
                                if env.other_headers()["X-Status"].contains('T') {
                                    flags.set(Flag::DRAFT, true);
                                }
                            }
                            env.set_flags(flags);
                            Ok((&[], env))
                        }
                        Err(err) => {
                            debug!("Could not parse mail {:?}", err);
                            Err(nom::Err::Error((input, ErrorKind::Tag)))
                        }
                    }
                }
            }
            Self::MboxCl | Self::MboxCl2 => {
                let start: Offset = input.find(b"\n").map(|v| v + 1).unwrap_or(0);
                input = &input[start..];
                let headers_end: usize = input.find(b"\n\n").unwrap_or(input.len());
                let content_length = if let Some(v) = input[..headers_end].find(b"Content-Length: ")
                {
                    v
                } else {
                    // Is not MboxCl{,2}
                    return Self::MboxRd.parse(orig_input);
                };
                let (_input, _) = if let Ok(s) = tag::<_, &[u8], (&[u8], nom::error::ErrorKind)>(
                    "Content-Length:",
                )(&input[content_length..])
                {
                    s
                } else {
                    return Self::MboxRd.parse(orig_input);
                };
                let (_input, bytes) = if let Ok(s) =
                    map_res::<&[u8], _, _, (&[u8], nom::error::ErrorKind), _, _, _>(
                        digit1,
                        |s: &[u8]| String::from_utf8_lossy(s).parse::<usize>(),
                    )(_input.ltrim())
                {
                    s
                } else {
                    return Self::MboxRd.parse(orig_input);
                };

                match Envelope::from_bytes(&input[..headers_end + bytes], None) {
                    Ok(mut env) => {
                        let mut flags = Flag::empty();
                        if env.other_headers().contains_key("Status") {
                            if env.other_headers()["Status"].contains("F") {
                                flags.set(Flag::FLAGGED, true);
                            }
                            if env.other_headers()["Status"].contains("A") {
                                flags.set(Flag::REPLIED, true);
                            }
                            if env.other_headers()["Status"].contains("R") {
                                flags.set(Flag::SEEN, true);
                            }
                            if env.other_headers()["Status"].contains("D") {
                                flags.set(Flag::TRASHED, true);
                            }
                        }
                        if env.other_headers().contains_key("X-Status") {
                            if env.other_headers()["X-Status"].contains("F") {
                                flags.set(Flag::FLAGGED, true);
                            }
                            if env.other_headers()["X-Status"].contains("A") {
                                flags.set(Flag::REPLIED, true);
                            }
                            if env.other_headers()["X-Status"].contains("R") {
                                flags.set(Flag::SEEN, true);
                            }
                            if env.other_headers()["X-Status"].contains("D") {
                                flags.set(Flag::TRASHED, true);
                            }
                            if env.other_headers()["X-Status"].contains("T") {
                                flags.set(Flag::DRAFT, true);
                            }
                        }
                        env.set_flags(flags);
                        if headers_end + 2 + bytes >= input.len() {
                            Ok((&[], env))
                        } else {
                            input = &input[headers_end + 3 + bytes..];
                            Ok((input, env))
                        }
                    }
                    Err(_err) => Self::MboxRd.parse(orig_input),
                }
            }
        }
    }
}

pub fn mbox_parse(
    index: Arc<Mutex<HashMap<EnvelopeHash, (Offset, Length)>>>,
    input: &[u8],
    file_offset: usize,
    reader: Option<MboxReader>,
) -> IResult<&[u8], Vec<Envelope>> {
    if input.is_empty() {
        return Err(nom::Err::Error((input, ErrorKind::Tag)));
    }
    let mut offset = 0;
    let mut index = index.lock().unwrap();
    let mut envelopes = Vec::with_capacity(32);

    let reader = reader.unwrap_or(MboxReader::MboxCl2);
    while !input[offset + file_offset..].is_empty() {
        let (next_input, env) = match reader.parse(&input[offset + file_offset..]) {
            Ok(v) => v,
            Err(e) => {
                // Try to recover from this error by finding a new candidate From_ line
                if let Some(next_offset) = find_From__line!(&input[offset + file_offset..]) {
                    offset += next_offset;
                    if offset != input.len() {
                        // If we are not at EOF, we will be at this point
                        //    "\n\nFrom ..."
                        //     ↑
                        // So, skip those two newlines.
                        offset += 2;
                    }
                } else {
                    return Err(e);
                }
                continue;
            }
        };
        let start: Offset = input[offset + file_offset..]
            .find(b"\n")
            .map(|v| v + 1)
            .unwrap_or(0);
        let len = input.len() - next_input.len() - offset - file_offset - start;
        index.insert(env.hash(), (offset + file_offset + start, len));
        offset += len + start;

        envelopes.push(env);
    }
    Ok((&[], envelopes))
}

/// Mbox backend
#[derive(Debug, Default)]
pub struct MboxType {
    account_name: String,
    path: PathBuf,
    mailbox_index: Arc<Mutex<HashMap<EnvelopeHash, MailboxHash>>>,
    mailboxes: Arc<Mutex<HashMap<MailboxHash, MboxMailbox>>>,
    prefer_mbox_type: Option<MboxReader>,
}

impl MailBackend for MboxType {
    fn is_online(&self) -> Result<()> {
        Ok(())
    }

    fn get(&mut self, mailbox: &Mailbox) -> Async<Result<Vec<Envelope>>> {
        let mut w = AsyncBuilder::new();
        let handle = {
            let tx = w.tx();
            let mailbox_hash = mailbox.hash();
            let mailbox_index = self.mailbox_index.clone();
            let mailboxes = self.mailboxes.clone();
            let mailbox_path = mailboxes.lock().unwrap()[&mailbox_hash].fs_path.clone();
            let prefer_mbox_type = self.prefer_mbox_type;
            let closure = move |_work_context| {
                let tx = tx.clone();
                let file = match std::fs::OpenOptions::new()
                    .read(true)
                    .write(true)
                    .open(&mailbox_path)
                {
                    Ok(f) => f,
                    Err(e) => {
                        tx.send(AsyncStatus::Payload(Err(MeliError::from(e))))
                            .unwrap();
                        return;
                    }
                };
                get_rw_lock_blocking(&file);
                let mut buf_reader = BufReader::new(file);
                let mut contents = Vec::new();
                if let Err(e) = buf_reader.read_to_end(&mut contents) {
                    tx.send(AsyncStatus::Payload(Err(MeliError::from(e))))
                        .unwrap();
                    return;
                };

                let mailboxes_lck = mailboxes.lock().unwrap();
                let mut mailbox_index_lck = mailbox_index.lock().unwrap();
                let index = mailboxes_lck[&mailbox_hash].index.clone();
                drop(mailboxes_lck);
                let payload = mbox_parse(index, contents.as_slice(), 0, prefer_mbox_type)
                    .map_err(MeliError::from)
                    .map(|(_, v)| {
                        for v in v.iter() {
                            mailbox_index_lck.insert(v.hash(), mailbox_hash);
                        }
                        v
                    });
                {
                    let mut mailbox_lock = mailboxes.lock().unwrap();
                    mailbox_lock
                        .entry(mailbox_hash)
                        .and_modify(|f| f.content = contents);
                }

                tx.send(AsyncStatus::Payload(payload)).unwrap();
                tx.send(AsyncStatus::Finished).unwrap();
            };
            Box::new(closure)
        };
        w.build(handle)
    }

    fn watch(
        &self,
        sender: RefreshEventConsumer,
        work_context: WorkContext,
    ) -> Result<std::thread::ThreadId> {
        let (tx, rx) = channel();
        let mut watcher = watcher(tx, std::time::Duration::from_secs(10))
            .map_err(|e| e.to_string())
            .map_err(MeliError::new)?;
        for f in self.mailboxes.lock().unwrap().values() {
            watcher
                .watch(&f.fs_path, RecursiveMode::Recursive)
                .map_err(|e| e.to_string())
                .map_err(MeliError::new)?;
            debug!("watching {:?}", f.fs_path.as_path());
        }
        let account_hash = {
            let mut hasher = DefaultHasher::new();
            hasher.write(self.account_name.as_bytes());
            hasher.finish()
        };
        let mailboxes = self.mailboxes.clone();
        let prefer_mbox_type = self.prefer_mbox_type;
        let handle = std::thread::Builder::new()
            .name(format!("watching {}", self.account_name,))
            .spawn(move || {
                // Move `watcher` in the closure's scope so that it doesn't get dropped.
                let _watcher = watcher;
                let _work_context = work_context;
                let mailboxes = mailboxes;
                loop {
                    match rx.recv() {
                        /*
                         * Event types:
                         *
                         * pub enum RefreshEventKind {
                         *     Update(EnvelopeHash, Envelope), // Old hash, new envelope
                         *     Create(Envelope),
                         *     Remove(EnvelopeHash),
                         *     Rescan,
                         * }
                         */
                        Ok(event) => match event {
                            /* Update */
                            DebouncedEvent::NoticeWrite(pathbuf)
                            | DebouncedEvent::Write(pathbuf) => {
                                let mailbox_hash = get_path_hash!(&pathbuf);
                                let file = match std::fs::OpenOptions::new()
                                    .read(true)
                                    .write(true)
                                    .open(&pathbuf)
                                {
                                    Ok(f) => f,
                                    Err(_) => {
                                        continue;
                                    }
                                };
                                get_rw_lock_blocking(&file);
                                let mut mailbox_lock = mailboxes.lock().unwrap();
                                let mut buf_reader = BufReader::new(file);
                                let mut contents = Vec::new();
                                if let Err(e) = buf_reader.read_to_end(&mut contents) {
                                    debug!(e);
                                    continue;
                                };
                                if contents
                                    .starts_with(mailbox_lock[&mailbox_hash].content.as_slice())
                                {
                                    if let Ok((_, envelopes)) = mbox_parse(
                                        mailbox_lock[&mailbox_hash].index.clone(),
                                        &contents[mailbox_lock[&mailbox_hash].content.len()..],
                                        mailbox_lock[&mailbox_hash].content.len(),
                                        prefer_mbox_type,
                                    ) {
                                        for env in envelopes {
                                            sender.send(RefreshEvent {
                                                account_hash,
                                                mailbox_hash,
                                                kind: RefreshEventKind::Create(Box::new(env)),
                                            });
                                        }
                                    }
                                } else {
                                    sender.send(RefreshEvent {
                                        account_hash,
                                        mailbox_hash,
                                        kind: RefreshEventKind::Rescan,
                                    });
                                }
                                mailbox_lock
                                    .entry(mailbox_hash)
                                    .and_modify(|f| f.content = contents);
                            }
                            /* Remove */
                            DebouncedEvent::NoticeRemove(pathbuf)
                            | DebouncedEvent::Remove(pathbuf) => {
                                if mailboxes
                                    .lock()
                                    .unwrap()
                                    .values()
                                    .any(|f| f.fs_path == pathbuf)
                                {
                                    let mailbox_hash = get_path_hash!(&pathbuf);
                                    sender.send(RefreshEvent {
                                        account_hash,
                                        mailbox_hash,
                                        kind: RefreshEventKind::Failure(MeliError::new(format!(
                                            "mbox mailbox {} was removed.",
                                            pathbuf.display()
                                        ))),
                                    });
                                    return;
                                }
                            }
                            DebouncedEvent::Rename(src, dest) => {
                                if mailboxes
                                    .lock()
                                    .unwrap()
                                    .values()
                                    .any(|f| &f.fs_path == &src)
                                {
                                    let mailbox_hash = get_path_hash!(&src);
                                    sender.send(RefreshEvent {
                                        account_hash,
                                        mailbox_hash,
                                        kind: RefreshEventKind::Failure(MeliError::new(format!(
                                            "mbox mailbox {} was renamed to {}.",
                                            src.display(),
                                            dest.display()
                                        ))),
                                    });
                                    return;
                                }
                            }
                            /* Trigger rescan of mailboxes */
                            DebouncedEvent::Rescan => {
                                for &mailbox_hash in mailboxes.lock().unwrap().keys() {
                                    sender.send(RefreshEvent {
                                        account_hash,
                                        mailbox_hash,
                                        kind: RefreshEventKind::Rescan,
                                    });
                                }
                                return;
                            }
                            _ => {}
                        },
                        Err(e) => debug!("watch error: {:?}", e),
                    }
                }
            })?;
        Ok(handle.thread().id())
    }
    fn mailboxes(&self) -> Result<HashMap<MailboxHash, Mailbox>> {
        Ok(self
            .mailboxes
            .lock()
            .unwrap()
            .iter()
            .map(|(h, f)| (*h, f.clone() as Mailbox))
            .collect())
    }

    fn operation(&self, env_hash: EnvelopeHash) -> Result<Box<dyn BackendOp>> {
        let mailbox_hash = self.mailbox_index.lock().unwrap()[&env_hash];
        let mailboxes_lck = self.mailboxes.lock().unwrap();
        let (offset, length) = {
            let index = mailboxes_lck[&mailbox_hash].index.lock().unwrap();
            index[&env_hash]
        };
        let mailbox_path = mailboxes_lck[&mailbox_hash].fs_path.clone();
        Ok(Box::new(MboxOp::new(
            env_hash,
            mailbox_path.as_path(),
            offset,
            length,
        )))
    }

    fn save(
        &self,
        _bytes: Vec<u8>,
        _mailbox_hash: MailboxHash,
        _flags: Option<Flag>,
    ) -> ResultFuture<()> {
        Err(MeliError::new("Unimplemented."))
    }

    fn as_any(&self) -> &dyn ::std::any::Any {
        self
    }
}

macro_rules! get_conf_val {
    ($s:ident[$var:literal]) => {
        $s.extra.get($var).ok_or_else(|| {
            MeliError::new(format!(
                "Configuration error ({}): mbox backend requires the field `{}` set",
                $s.name.as_str(),
                $var
            ))
        })
    };
    ($s:ident[$var:literal], $default:expr) => {
        $s.extra
            .get($var)
            .map(|v| {
                <_>::from_str(v).map_err(|e| {
                    MeliError::new(format!(
                        "Configuration error ({}): Invalid value for field `{}`: {}\n{}",
                        $s.name.as_str(),
                        $var,
                        v,
                        e
                    ))
                })
            })
            .unwrap_or_else(|| Ok($default))
    };
}

impl MboxType {
    pub fn new(
        s: &AccountSettings,
        _is_subscribed: Box<dyn Fn(&str) -> bool>,
    ) -> Result<Box<dyn MailBackend>> {
        let path = Path::new(s.root_mailbox.as_str()).expand();
        if !path.exists() {
            return Err(MeliError::new(format!(
                "\"root_mailbox\" {} for account {} is not a valid path.",
                s.root_mailbox.as_str(),
                s.name()
            )));
        }
        let prefer_mbox_type: String = get_conf_val!(s["prefer_mbox_type"], "auto".to_string())?;
        let ret = MboxType {
            account_name: s.name().to_string(),
            path,
            prefer_mbox_type: match prefer_mbox_type.as_str() {
                "auto" => None,
                "mboxo" => Some(MboxReader::MboxO),
                "mboxrd" => Some(MboxReader::MboxRd),
                "mboxcl" => Some(MboxReader::MboxCl),
                "mboxcl2" => Some(MboxReader::MboxCl2),
                _ => {
                    return Err(MeliError::new(format!(
                        "{} invalid `prefer_mbox_type` value: `{}`",
                        s.name(),
                        prefer_mbox_type,
                    )))
                }
            },
            ..Default::default()
        };
        let name: String = ret
            .path
            .file_name()
            .map(|f| f.to_string_lossy().into())
            .unwrap_or_default();
        let hash = get_path_hash!(&ret.path);

        let read_only = if let Ok(metadata) = std::fs::metadata(&ret.path) {
            metadata.permissions().readonly()
        } else {
            true
        };

        ret.mailboxes.lock().unwrap().insert(
            hash,
            MboxMailbox {
                hash,
                path: name.clone().into(),
                fs_path: ret.path.clone(),
                name,
                content: Vec::new(),
                children: Vec::new(),
                parent: None,
                usage: Arc::new(RwLock::new(SpecialUsageMailbox::Normal)),
                is_subscribed: true,
                permissions: MailboxPermissions {
                    create_messages: !read_only,
                    remove_messages: !read_only,
                    set_flags: !read_only,
                    create_child: !read_only,
                    rename_messages: !read_only,
                    delete_messages: !read_only,
                    delete_mailbox: !read_only,
                    change_permissions: false,
                },
                unseen: Arc::new(Mutex::new(0)),
                total: Arc::new(Mutex::new(0)),
                index: Default::default(),
            },
        );
        /* Look for other mailboxes */
        for (k, f) in s.mailboxes.iter() {
            if let Some(path_str) = f.extra.get("path") {
                let hash = get_path_hash!(path_str);
                let pathbuf: PathBuf = path_str.into();
                if !pathbuf.exists() || pathbuf.is_dir() {
                    return Err(MeliError::new(format!(
                        "mbox mailbox configuration entry \"{}\" path value {} is not a file.",
                        k, path_str
                    )));
                }
                let read_only = if let Ok(metadata) = std::fs::metadata(&pathbuf) {
                    metadata.permissions().readonly()
                } else {
                    true
                };

                ret.mailboxes.lock().unwrap().insert(
                    hash,
                    MboxMailbox {
                        hash,
                        name: k.to_string(),
                        fs_path: pathbuf,
                        path: k.into(),
                        content: Vec::new(),
                        children: Vec::new(),
                        parent: None,
                        usage: Arc::new(RwLock::new(f.usage.unwrap_or_default())),
                        is_subscribed: f.subscribe.is_true(),
                        permissions: MailboxPermissions {
                            create_messages: !read_only,
                            remove_messages: !read_only,
                            set_flags: !read_only,
                            create_child: !read_only,
                            rename_messages: !read_only,
                            delete_messages: !read_only,
                            delete_mailbox: !read_only,
                            change_permissions: false,
                        },
                        unseen: Arc::new(Mutex::new(0)),
                        total: Arc::new(Mutex::new(0)),
                        index: Default::default(),
                    },
                );
            } else {
                return Err(MeliError::new(format!(
                    "mbox mailbox configuration entry \"{}\" should have a \"path\" value set pointing to an mbox file.",
                    k
                )));
            }
        }
        Ok(Box::new(ret))
    }

    pub fn validate_config(s: &AccountSettings) -> Result<()> {
        let path = Path::new(s.root_mailbox.as_str()).expand();
        if !path.exists() {
            return Err(MeliError::new(format!(
                "\"root_mailbox\" {} for account {} is not a valid path.",
                s.root_mailbox.as_str(),
                s.name()
            )));
        }
        let prefer_mbox_type: Result<String> =
            get_conf_val!(s["prefer_mbox_type"], "auto".to_string());
        prefer_mbox_type?;
        Ok(())
    }
}