//! # vomit-sync
//!
//! `vomit-sync` provides full two-way synchronization between IMAP and
//! a local maildir. At the moment, it has to be called periodically to
//! keep the two synchronized.
//!
//! It uses the [log][1] crate for logging, so you can receive logs from it by
//! using any of the compatible logging libraries.
//!
//! [1]: https://crates.io/crates/log
//!
//! [vsync][2] is small CLI wrapper around `vomit-sync`.
//!
//! [2]: https://git.sr.ht/~bitfehler/vomit-sync/tree/master/item/cli/
//!
//! As the name implies, `vomit-sync` is part of the [vomit project][3].
//!
//! [3]: https://sr.ht/~bitfehler/vomit

use imap::extensions::list_status::ExtendedNames;
use imap::ClientBuilder;
use imap::Session;
use log::{debug, error, info, trace};
use maildir::Maildir;
use native_tls::TlsConnector;
use std::collections::BTreeSet;
use std::fs;
use std::io;
use std::iter::Iterator;
use std::path::PathBuf;
use std::thread;
use std::time::Instant;
use thiserror::Error;
use vomit::{Mailbox, VomitError};
use wildmatch::WildMatch;

mod flags;
mod mailboxes;
mod seqset;
mod state;
mod sync;

#[derive(Error, Debug)]
pub enum SyncError {
    #[error("IMAP error: {0}")]
    ProtocolError(#[from] imap::Error),
    #[error("invalid configuration: {0}")]
    ConfigError(&'static str),
    #[error("Refused to perform dangerous action - set 'force' option to override")]
    DangerousActionError(),
    #[error("failed to load state: {0}")]
    StateError(#[from] state::StateError),
    #[error("IPC error: {0}")]
    IPCError(#[from] spmc::SendError<mailboxes::SyncJob>),
    #[error("error accessing maildir: {0}")]
    IOError(#[from] io::Error),
    #[error("error managing maildir: {0}")]
    MaildirError(#[from] maildir::MaildirError),
    #[error("{0}")]
    MailboxesError(#[from] mailboxes::MailboxesError),
    #[error("error in maildir abstraction library: {0}")]
    VomitError(#[from] VomitError),
    #[error("{0}")]
    Error(&'static str),
    #[error("{0}")]
    E(String),
}

#[derive(Clone, Debug, PartialEq, Eq)]
pub enum SyncDirection {
    Pull,
    Push,
    TwoWay,
}

/// A set of options to control the synchronization process
#[derive(Clone, Debug)]
pub struct SyncOptions {
    /// The local maildir to sync to
    pub local: String,
    /// The IMAPS URL to sync from
    pub remote: String,
    /// The user for IMAP authentication
    pub user: String,
    /// The password for IMAP authentication
    pub password: String,
    /// The number of threads to use
    ///
    /// Each thread will use it's own IMAP session, so this must not be greater
    /// than the number of concurrent user sessions allowed by the IMAP server.
    pub threads: u8,
    /// Disable TLS certificate checks (e.g. for self-signed certs)
    pub unsafe_tls: bool,
    /// Only log with info level what actions (sync, create, delete) would be taken on
    /// which mailboxes (taking include/exclude into account), then exit.
    pub list_mailbox_actions: bool,
    /// A list of wildcard patterns to include only folders that match any of them.
    ///
    /// The wildcard pattern only supports `?` and `*` and must match the full mailbox name.
    pub include: Vec<String>,
    /// A list of wildcard patterns to exclude all folders that match any of them.
    ///
    /// The wildcard pattern only supports `?` and `*` and must match the full mailbox name.
    /// If used together with `include` and both match, `exclude` takes precedence.
    pub exclude: Vec<String>,
    /// Confirm execution of potentially dangerous actions (e.g. deleting mailboxes)
    pub force: bool,
}

macro_rules! measure {
    ( $m:expr, $x:expr ) => {{
        let start = Instant::now();
        let result = $x;
        let duration = start.elapsed();
        debug!("{} in {}ms", $m, duration.as_millis());
        result
    }};
}

const DATA_ITEMS_HMS: &str = "(HIGHESTMODSEQ)";

fn get_hierarchy_delimiter(names: &ExtendedNames) -> Result<String, SyncError> {
    let delims: BTreeSet<&str> = names
        .iter()
        .filter_map(|(name, _)| name.delimiter())
        .collect();
    if delims.len() != 1 {
        return Err(SyncError::E(format!(
            "Expected exactly on hierarchy delimiter, found {:?}",
            delims
        )));
    }
    Ok(String::from(delims.into_iter().next().unwrap()))
}

fn new_session(
    opts: &SyncOptions,
) -> Result<Session<impl std::io::Read + std::io::Write>, SyncError> {
    let (host, port) = match opts.remote.rsplit_once(':') {
        Some((host, port)) => (host, port),
        None => (opts.remote.as_str(), "993"),
    };

    let port = match port.parse() {
        Ok(p) => p,
        Err(e) => {
            error!("failed to parse remote port: {}", e);
            return Err(SyncError::ConfigError("invalid port"));
        }
    };

    debug!("Connecting to {}:{}", host, port);
    let client = if opts.unsafe_tls {
        ClientBuilder::new(host, port).connect(|domain, tcp| {
            let ssl_conn = TlsConnector::builder()
                .danger_accept_invalid_certs(true)
                .danger_accept_invalid_hostnames(true)
                .build()?;
            Ok(TlsConnector::connect(&ssl_conn, domain, tcp).unwrap())
        })?
    } else {
        ClientBuilder::new(host, port).native_tls()?
    };

    debug!("Logging in as {}", &opts.user);
    let mut session = client.login(&opts.user, &opts.password).map_err(|e| e.0)?;

    session.run_command_and_read_response("ENABLE QRESYNC")?;

    Ok(session)
}

fn check_server_capabilities_(opts: &SyncOptions) -> Result<(), SyncError> {
    let mut session = new_session(opts)?;
    let caps = session.capabilities()?;
    for cap in caps.iter() {
        trace!("Server capability: {:?}", cap);
    }
    session.logout()?;
    if !caps.has_str("QRESYNC") {
        return Err(SyncError::E(
            "Server does not support QRESYNC (RFC 7162)".to_string(),
        ));
    }
    if !caps.has_str("UIDPLUS") {
        return Err(SyncError::E(
            "Server does not support UIDPLUS (RFC 4315)".to_string(),
        ));
    }
    if !caps.has_str("LIST-STATUS") {
        return Err(SyncError::E(
            "Server does not support LIST-STATUS (RFC 5819)".to_string(),
        ));
    }
    Ok(())
}

/// List remote and local mailboxes with log level "info".
///
/// This is intended for human consumption. It can e.g. be presented to the
/// user as a verification that all mailboxes are found as expected.
pub fn list_mailboxes(opts: &SyncOptions) -> Result<(), SyncError> {
    let mut session = new_session(opts)?;
    let names = session.list_status(None, Some("*"), DATA_ITEMS_HMS)?;
    if names.is_empty() {
        return Err(SyncError::Error("No remote mailboxes found"));
    }

    let delimiter = get_hierarchy_delimiter(&names)?;
    let remote_mailboxes = mailboxes::load_remote(&names);
    let local_mailboxes = mailboxes::load_local(&opts.local, &delimiter)?;

    info!("Hierarchy delimiter: {}", delimiter);
    info!("Remote mailboxes:");
    for m in remote_mailboxes.keys() {
        info!("  {}", m);
    }
    info!("Local mailboxes:");
    for m in local_mailboxes.keys() {
        info!("  {}", m);
    }
    Ok(())
}

/// Check if the configured server supports the required IMAP capabilities
///
/// Currently, at least the QRESYNC capability is required ([RFC 7162][1]).
///
/// [1]: https://www.rfc-editor.org/rfc/rfc7162.html
pub fn check_server_capabilities(opts: &SyncOptions) -> Result<(), SyncError> {
    measure!(
        format!("Checked capabilities for {}", opts.remote),
        check_server_capabilities_(opts)
    )
}

fn sync_mailbox<T: io::Read + io::Write>(
    maildir_root: &str,
    sync_job: &mailboxes::SyncJob,
    direction: &SyncDirection,
    session: &mut Session<T>,
) -> Result<(), SyncError> {
    let mailbox = &sync_job.name;
    let dirname = Mailbox::virtual_to_dir(mailbox, &sync_job.delimiter);
    let mbpath: PathBuf = [maildir_root, &dirname].iter().collect();

    match sync_job.action {
        mailboxes::SyncAction::Sync => (),
        mailboxes::SyncAction::CreateLocal => {
            trace!("Creating local mailbox {}", mailbox);
            // Local dir creation will happen automatically
        }
        mailboxes::SyncAction::CreateRemote => {
            trace!("Creating remote mailbox {}", mailbox);
            session.create(mailbox)?
        }
        mailboxes::SyncAction::DeleteLocal => {
            trace!("Deleting local mailbox {}", mailbox);
            return fs::remove_dir_all(&mbpath).map_err(SyncError::IOError);
        }
        mailboxes::SyncAction::DeleteRemote => {
            trace!("Deleting remote mailbox {}", mailbox);
            return session.delete(mailbox).map_err(SyncError::ProtocolError);
        }
    };

    let maildir = Maildir::from(mbpath);
    maildir.create_dirs()?;

    let state = measure!(
        format!("Loaded state for {}", mailbox),
        state::SyncState::load(&maildir.path())?
    );

    let remote = session.select(mailbox)?;

    match direction {
        SyncDirection::Pull => sync::pull(session, sync_job, maildir, remote, state),
        SyncDirection::Push => sync::push(session, sync_job, maildir, remote, state),
        SyncDirection::TwoWay => sync::sync(session, sync_job, maildir, remote, state),
    }
    .map_err(|e| SyncError::E(format!("{}: {}", mailbox, e)))
}

fn worker_thread(
    i: u8,
    opts: &SyncOptions,
    direction: SyncDirection,
    rx: spmc::Receiver<mailboxes::SyncJob>,
) -> Result<(), SyncError> {
    let mut imap_session = new_session(opts)?;
    while let Ok(job) = rx.recv() {
        trace!("Syncing {} in worker thread {}", job.name, i);
        measure!(
            format!("Synced {}", job.name),
            sync_mailbox(&opts.local, &job, &direction, &mut imap_session)?
        );
    }
    imap_session.logout()?;
    Ok(())
}

fn sync_(opts: &SyncOptions, direction: SyncDirection) -> Result<(), SyncError> {
    info!("Syncing from {}", opts.remote);

    let mut root_state = state::RootState::load(&opts.local)?;

    let mut imap_session = new_session(opts)?;

    let names = imap_session.list_status(None, Some("*"), DATA_ITEMS_HMS)?;

    if names.is_empty() {
        return Err(SyncError::Error("No remote mailboxes found, giving up"));
    }

    let includes: Vec<WildMatch> = opts.include.iter().map(|p| WildMatch::new(p)).collect();
    let excludes: Vec<WildMatch> = opts.exclude.iter().map(|p| WildMatch::new(p)).collect();

    let delimiter = get_hierarchy_delimiter(&names)?;
    let remote_mailboxes_with_state = mailboxes::load_remote(&names);
    let remote_mailboxes: BTreeSet<&String> = remote_mailboxes_with_state.keys().collect();
    let local_mailboxes_with_state = measure!(
        format!("Loaded local mailboxes"),
        mailboxes::load_local(&opts.local, &delimiter)?
    );
    let local_mailboxes: BTreeSet<&String> = local_mailboxes_with_state.keys().collect();

    trace!("local: {:?}", local_mailboxes);
    trace!("remote: {:?}", remote_mailboxes);

    let only_local: BTreeSet<&String> = local_mailboxes
        .difference(&remote_mailboxes)
        .cloned()
        .collect();
    trace!("Only local: {:?}", only_local);
    let only_remote: BTreeSet<&String> = remote_mailboxes
        .difference(&local_mailboxes)
        .cloned()
        .collect();
    trace!("Only remote: {:?}", only_remote);
    let sync_jobs: Vec<mailboxes::SyncJob> = local_mailboxes
        .union(&remote_mailboxes)
        .cloned()
        .filter_map(|name| {
            // Apply user-provided include/exclude filter
            if !includes.is_empty() && !includes.iter().any(|e| e.matches(name)) {
                trace!("Skipping {} due to include filter", name);
                return None;
            }
            if excludes.iter().any(|e| e.matches(name)) {
                trace!("Skipping {} due to exclude filter", name);
                return None;
            }
            trace!("Processing mailbox {}", name);
            let delimiter = delimiter.clone();

            // We'll have to go through the tedious process of determining what to do
            // with mailboxes that are missing on one side.
            // trace!("Checking what to do with {}", name);
            let name = name.clone();
            if only_local.contains(&name) {
                match direction {
                    SyncDirection::Pull => {
                        // Delete locally, also from root state
                        mailboxes::sync_delete_local(name, delimiter, &mut root_state)
                    }
                    SyncDirection::Push => {
                        // Create remotely, add to root state
                        mailboxes::sync_create_remote(name, delimiter, &mut root_state)
                    }
                    SyncDirection::TwoWay => {
                        let dirname = Mailbox::virtual_to_dir(&name, &delimiter);
                        if root_state.subdirs.contains(&dirname) {
                            // Exists locally only because removed on server side
                            // Delete locally, also from root state
                            mailboxes::sync_delete_local(name, delimiter, &mut root_state)
                        } else {
                            // Exists locally only because created here
                            // Create remotely, add to root state
                            mailboxes::sync_create_remote(name, delimiter, &mut root_state)
                        }
                    }
                }
            } else if only_remote.contains(&name) {
                match direction {
                    SyncDirection::Pull => {
                        // Create locally (already happening), add to root state (after sync?)
                        mailboxes::sync_create_local(name, delimiter, &mut root_state)
                    }
                    SyncDirection::Push => {
                        // Delete remotely, also from root state
                        mailboxes::sync_delete_remote(name, delimiter, &mut root_state)
                    }
                    SyncDirection::TwoWay => {
                        let dirname = Mailbox::virtual_to_dir(&name, &delimiter);
                        if root_state.subdirs.contains(&dirname) {
                            // Exists remotely only because removed locally
                            // Delete remotely, also from root state
                            mailboxes::sync_delete_remote(name, delimiter, &mut root_state)
                        } else {
                            // Exists remotely only because created there
                            // Create locally (already happening), add to root state (after sync?)
                            mailboxes::sync_create_local(name, delimiter, &mut root_state)
                        }
                    }
                }
            } else {
                // Exists on both sides, just sync
                let state = local_mailboxes_with_state.get(&name).unwrap();
                let modseq = remote_mailboxes_with_state.get(&name).unwrap();
                if !state.has_local_changes() && state.last_seen.highest_mod_seq == *modseq {
                    trace!("Skipping {} because HIGHESTMODSEQ is in sync", name);
                    return None;
                }
                mailboxes::sync(name, delimiter)
            }
        })
        .collect();

    if opts.list_mailbox_actions {
        info!("The following actions would be performed:");
        for job in sync_jobs {
            info!("  {}: {:?}", job.name, job.action);
        }
        return Ok(());
    }

    let bail = sync_jobs
        .iter()
        .map(|job| match job.action {
            mailboxes::SyncAction::DeleteLocal => {
                error!("Refusing to delete local mailbox {}", job.name);
                true
            }
            mailboxes::SyncAction::DeleteRemote => {
                error!("Refusing to delete remote mailbox {}", job.name);
                true
            }
            _ => false,
        })
        .any(|b| b);
    if bail {
        return Err(SyncError::DangerousActionError());
    }

    root_state.save()?;
    drop(root_state);

    let thread_count = if sync_jobs.len() < opts.threads.into() {
        // Conversion must be safe here
        sync_jobs.len().try_into().unwrap()
    } else {
        opts.threads
    };

    let mut threads = Vec::new();
    let (mut tx, rx) = spmc::channel::<mailboxes::SyncJob>();

    info!(
        "Using {} threads to sync {} mailboxes",
        thread_count,
        sync_jobs.len()
    );
    for i in 1..thread_count {
        let rx = rx.clone();
        let opts = (*opts).clone();
        let dir = direction.clone();

        let t = thread::spawn(move || {
            if let Err(e) = worker_thread(i, &opts, dir, rx) {
                error!("Error in worker thread {}: {}", i, e);
            };
        });
        threads.push(t);
    }
    for job in sync_jobs {
        tx.send(job)?;
    }
    drop(tx);

    while let Ok(job) = rx.recv() {
        debug!("Syncing {} in main thread ({:?})", job.name, job.action);
        measure!(
            format!("Synced {}", job.name),
            sync_mailbox(&opts.local, &job, &direction, &mut imap_session)?
        );
    }

    _ = imap_session.logout();

    for t in threads {
        t.join().unwrap();
    }

    info!("Sync successful");
    Ok(())
}

/// Apply all changes from IMAP to the local maildir
///
/// This overwrites any changes that may have happened on the local side.
pub fn pull(opts: &SyncOptions) -> Result<(), SyncError> {
    measure!(
        format!("Pulled from {}", opts.remote),
        sync_(opts, SyncDirection::Pull)
    )
}

/// Apply all changes in local maildir to IMAP
///
/// This overwrites any changes that may have happened on the IMAP side.
pub fn push(opts: &SyncOptions) -> Result<(), SyncError> {
    measure!(
        format!("Pushed to {}", opts.remote),
        sync_(opts, SyncDirection::Push)
    )
}

/// Synchronize local and remote changes between IMAP and local maildir
///
/// This includes fetching new mail, deleting expunged mails, updating tags, etc.
pub fn sync(opts: &SyncOptions) -> Result<(), SyncError> {
    measure!(
        format!("Synced with {}", opts.remote),
        sync_(opts, SyncDirection::TwoWay)
    )
}