use std::collections::BTreeMap;
use std::collections::BTreeSet;
use std::sync::Arc;
use std::sync::Mutex;

use sequoia_openpgp as openpgp;
use openpgp::Cert;
use openpgp::Fingerprint;
use openpgp::KeyHandle;
use openpgp::KeyID;
use openpgp::Result;
use openpgp::policy::NullPolicy;

use sequoia_net as net;
use net::reqwest;

use crate::email_to_userid;
use crate::LazyCert;
use crate::Store;
use crate::store::StatusListener;
use crate::store::StatusUpdate;
use crate::store::StoreError;
use crate::store::UserIDQueryParams;

use super::TRACE;

const NP: &NullPolicy = unsafe { &NullPolicy::new() };

// Reliable keyservers.
/// keys.openpgp.org.
pub const KEYS_OPENPGP_ORG_URL: &str = "hkps://keys.openpgp.org";
/// A reliable SKS keyserver.
pub const SKS_URL: &str = "hkps://keyserver.ubuntu.com";
/// mailvelope's keyserver.
pub const MAILVELOPE_URL: &str = "hkps://keys.mailvelope.com";
/// proton's keyserver.
pub const PROTON_URL: &str = "hkps://api.protonmail.ch";

/// A keyserver backend.
pub struct KeyServer<'a> {
    inner: Mutex<KeyServerInner<'a>>,
}
assert_send_and_sync!(KeyServer<'_>);

struct KeyServerInner<'a> {
    keyserver: net::KeyServer,

    id: String,
    tx: usize,
    listeners: Vec<Box<dyn StatusListener + Send + Sync>>,

    // A cache.  We only cache certificates; we don't cache User ID
    // searches.

    // Primary keys and subkeys.
    hits_fpr: BTreeMap<Fingerprint, Arc<LazyCert<'a>>>,
    hits_keyid: BTreeMap<KeyID, Fingerprint>,
    // What we failed to look up.
    misses_fpr: BTreeSet<Fingerprint>,
    misses_keyid: BTreeSet<KeyID>,
}

impl KeyServer<'_> {
    /// Returns a new key server instance.
    pub fn new(url: &str) -> Result<Self> {
        Ok(Self {
            inner: Mutex::new(KeyServerInner {
                keyserver: net::KeyServer::new(url)?,
                id: if url.len() <= 10 {
                    // Only prefix "key server" if the URL is short.
                    format!("key server {}", url)
                } else {
                    url.to_string()
                },
                tx: 0,
                listeners: Vec::new(),
                hits_fpr: Default::default(),
                hits_keyid: Default::default(),
                misses_fpr: Default::default(),
                misses_keyid: Default::default(),
            }),
        })
    }

    /// Returns a key server instance that uses `keys.openpgp.org`.
    pub fn keys_openpgp_org() -> Result<Self> {
        Self::new(KEYS_OPENPGP_ORG_URL)
    }

    /// Returns a key server instance that uses a reliable SKS
    /// keyserver.
    pub fn sks() -> Result<Self> {
        Self::new(SKS_URL)
    }

    /// Returns a key server instance that uses mailvelope's
    /// keyserver.
    pub fn mailvelope() -> Result<Self> {
        Self::new(MAILVELOPE_URL)
    }

    /// Returns a key server instance that uses proton's keyserver.
    pub fn proton() -> Result<Self> {
        Self::new(PROTON_URL)
    }

    /// Sends status updates to the listener.
    pub fn add_listener(&mut self, listener: Box<dyn StatusListener + Send + Sync>) {
        self.inner.lock().unwrap().listeners.push(listener);
    }
}

impl<'a> KeyServerInner<'a> {
    // Looks for a certificate in the cache.
    fn check_cache(&self, kh: &KeyHandle)
        -> Option<Result<Vec<Arc<LazyCert<'a>>>>>
    {
        let kh_;
        let kh = if let KeyHandle::KeyID(keyid) = kh {
            if let Some(fpr) = self.hits_keyid.get(keyid) {
                kh_ = KeyHandle::Fingerprint(fpr.clone());
                &kh_
            } else if self.misses_keyid.contains(keyid) {
                return Some(Err(StoreError::NotFound(
                    KeyHandle::from(kh.clone())).into()));
            } else {
                kh
            }
        } else {
            kh
        };
        if let KeyHandle::Fingerprint(fpr) = kh {
            if let Some(cert) = self.hits_fpr.get(fpr) {
                return Some(Ok(vec![ cert.clone() ]));
            }
            if self.misses_fpr.contains(fpr) {
                return Some(Err(StoreError::NotFound(
                    KeyHandle::from(kh.clone())).into()));
            }
        }

        None
    }

    // Adds the cert to the in-memory cache.
    fn cache(&mut self, cert: &Arc<LazyCert<'a>>) {
        for k in cert.keys() {
            self.hits_fpr.insert(k.fingerprint(), cert.clone());
            self.hits_keyid.insert(k.keyid(), k.fingerprint());
        }
    }

    /// Deletes the key with the given fingerprint from the cache.
    fn delete_from_cache(&mut self, cert: &LazyCert<'_>) {
        for key in cert.keys() {
            let fp = key.fingerprint();
            self.hits_fpr.remove(&fp);

            let keyid = KeyID::from(fp);
            // XXX: Technically, a key ID could map to multiple
            // fingerprints, so we may be removing the wrong entry here.
            // But, by using a BTreeMap<KeyID, Fingerprint> we do accept
            // this kind of loss in the first place, as later cache
            // insertions will overwrite any existing mappings.
            self.hits_keyid.remove(&keyid);
        }
    }
}

impl<'a> KeyServer<'a> {
    /// Deletes the key with the given fingerprint from the cache.
    pub(crate) fn delete_from_cache<I>(&self, certs: I)
        where I: Iterator<Item=Arc<LazyCert<'a>>>,
    {
        let mut inner = self.inner.lock().unwrap();
        for cert in certs {
            inner.delete_from_cache(&cert);
        }
    }
}

/// Sends a status update.
macro_rules! update {
    ( $self:expr, $update:ident, $($args:expr),* ) => {{
        if ! $self.listeners.is_empty() {
            let update = StatusUpdate::$update(
                $self.tx, &$self.id, $($args),*);

            for sub in $self.listeners.iter() {
                sub.update(&update);
            }
        }
    }}
}

impl<'a> Store<'a> for KeyServer<'a> {
    fn lookup_by_cert(&self, kh: &KeyHandle) -> Result<Vec<Arc<LazyCert<'a>>>> {
        let mut certs = self.lookup_by_cert_or_subkey(kh)?;

        // The match may be on a subkey.  Only return the certificates
        // whose primary key aliases kh.
        certs.retain(|cert| {
            kh.aliases(KeyHandle::from(cert.fingerprint()))
        });

        if certs.is_empty() {
            Err(StoreError::NotFound(KeyHandle::from(kh.clone())).into())
        } else {
            Ok(certs)
        }
    }

    fn lookup_by_cert_or_subkey(&self, kh: &KeyHandle) -> Result<Vec<Arc<LazyCert<'a>>>> {
        tracer!(TRACE, "KeyServer::lookup_by_cert_or_subkey");

        // Check the cache.
        t!("Looking up {} on keyserver...", kh);
        let mut inner = self.inner.lock().unwrap();
        if ! inner.listeners.is_empty() {
            inner.tx += 1;
            update!(inner, LookupStarted, kh, None);
        };

        if let Some(r) = inner.check_cache(kh) {
            t!("Found in in-memory cache");
            match r.as_ref() {
                Ok(certs) => {
                    update!(inner, LookupFinished, kh,
                            &certs[..], Some("Found in in-memory cache"));
                }
                Err(err) => {
                    update!(inner, LookupFailed, kh, Some(&err));
                }
            }
            return r;
        }

        // It's not in the cache, look it up on the key server.
        let rt = tokio::runtime::Runtime::new().unwrap();

        // The keyserver interface currently only returns a single
        // result.
        let r = rt.block_on(async {
            inner.keyserver.get(kh.clone()).await
        });

        match r {
            Ok(certs) => {
                let certs: Vec<_> =
                    certs.into_iter()
                    .filter_map(Result::ok)
                    .map(|c| Arc::new(LazyCert::from(c))).collect();

                for cert in &certs {
                    t!("keyserver returned {}", cert.fingerprint());

                    // Add the result to the cache.
                    inner.cache(cert);
                }

                // Make sure the key server gave us the right
                // certificate.
                let requested: Vec<_> =
                    certs.iter().filter(
                        |cert| cert.keys().any(|k| k.key_handle().aliases(kh)))
                    .cloned()
                    .collect();

                if ! requested.is_empty() {
                    update!(inner, LookupFinished, kh, &requested[..], None);
                    Ok(requested)
                } else {
                    let err = KeyServerError::UnexpectedResults(
                        kh.clone(),
                        certs.iter().map(|c| c.fingerprint()).collect())
                        .into();
                    t!("{}", err);
                    update!(inner, LookupFailed, kh, Some(&err));
                    Err(StoreError::NotFound(
                        KeyHandle::from(kh.clone())).into())
                }
            }
            Err(err) => {
                t!("keyserver returned an error: {}", err);

                if let Some(net::Error::NotFound)
                    = err.downcast_ref::<net::Error>()
                {
                    update!(inner, LookupFailed, kh, None);
                    Err(StoreError::NotFound(
                        KeyHandle::from(kh.clone())).into())
                } else {
                    update!(inner, LookupFailed, kh, Some(&err));
                    Err(err)
                }
            }
        }
    }

    fn select_userid(&self, query: &UserIDQueryParams, pattern: &str)
        -> Result<Vec<Arc<LazyCert<'a>>>>
    {
        tracer!(TRACE, "KeyServer::select_userid");

        t!("{}", pattern);
        t!("Looking {:?} up on the keyserver... ", pattern);
        let mut inner = self.inner.lock().unwrap();
        if ! inner.listeners.is_empty() {
            inner.tx += 1;
            update!(inner, SearchStarted, pattern, None);
        }

        let email_;
        let email = if query.email && query.anchor_start && query.anchor_end {
            match email_to_userid(pattern) {
                Ok(email) => {
                    email_ = email.value().to_vec();
                    Some(String::from_utf8_lossy(&email_))
                },
                Err(err) => {
                    t!("{:?}: invalid email address: {}", pattern, err);
                    None
                }
            }
        } else {
            None
        };

        let rt = tokio::runtime::Runtime::new().unwrap();
        let (ks, wkd) = rt.block_on(async {
            // Query the keyserver.
            let ks = inner.keyserver.search(pattern);

            // And the WKD (if it appears to be an email address).
            let wkd = async {
                if let Some(email) = email.as_ref() {
                    net::wkd::get(&reqwest::Client::new(), email).await
                } else {
                    // If it is not an email, it's not an error.
                    Ok(Vec::new())
                }
            };

            tokio::join!(ks, wkd)
        });

        let mut certs: Vec<Result<Cert>> = Vec::new();
        match ks {
            Ok(c) => {
                t!("Key server returned {} results", c.len());
                if ! inner.listeners.is_empty() {
                    let msg = format!("Key server returned {} results", c.len());
                    update!(inner, SearchStatus, pattern, &msg);
                }
                certs.extend(c);
            },
            Err(err) => t!("Key server response: {}", err),
        }
        match wkd {
            Ok(c) => {
                t!("WKD server returned {} results", c.len());
                if ! inner.listeners.is_empty() {
                    let msg = format!("WKD server returned {} results",
                                      c.len());
                    update!(inner, SearchStatus, pattern, &msg);
                }
                certs.extend(c);
            },
            Err(err) => t!("WKD server response: {}", err),
        }

        // Sort, merge, and cache.
        let mut certs = certs.into_iter().flatten().collect::<Vec<Cert>>();
        certs.sort_by_key(|c| c.fingerprint());
        certs.dedup_by(|a, b| {
            if a.fingerprint() != b.fingerprint() {
                return false;
            }

            // b is kept.  So merge into b.
            match b.clone().merge_public(a.clone()) {
                Ok(combined) => *b = combined,
                Err(err) => {
                    t!("Merging copies of {}: {}",
                       a.keyid(), err);
                }
            }

            true
        });

        let mut certs: Vec<_> =
            certs.into_iter().map(|c| Arc::new(LazyCert::from(c))).collect();

        // Add the results to the cache.
        certs.iter().for_each(|cert| inner.cache(cert));

        // Only keep the certificates that actually satisfy the
        // constraints.
        certs.retain(|cert| {
            let cert = cert.to_cert()
                .expect("LazyCert should already be canonicalized");
            query.check_cert(cert, pattern)
        });

        if certs.is_empty() {
            update!(inner, SearchFailed, pattern, None);
            Err(StoreError::NoMatches(pattern.to_string()).into())
        } else {
            if TRACE || ! inner.listeners.is_empty() {
                let msg = format!(
                    "Got {} results:\n  {}",
                    certs.len(),
                    certs.iter()
                        .map(|cert: &Arc<LazyCert>| {
                            format!(
                                "{} ({})",
                                cert.keyid().to_hex(),
                                cert.with_policy(NP, None)
                                    .and_then(|vc| vc.primary_userid())
                                    .map(|ua| {
                                        String::from_utf8_lossy(ua.userid().value())
                                            .into_owned()
                                    })
                                    .unwrap_or_else(|_| {
                                        cert.userids().next()
                                            .map(|userid| {
                                                String::from_utf8_lossy(userid.value())
                                                    .into_owned()
                                            })
                                            .unwrap_or("<unknown>".into())
                                    }))
                        })
                        .collect::<Vec<_>>()
                        .join("\n  "));
                t!("{}", msg);
                update!(inner, SearchFinished, pattern, &certs[..], Some(&msg));
            }
            Ok(certs)
        }
    }

    fn fingerprints<'b>(&'b self) -> Box<dyn Iterator<Item=Fingerprint> + 'b> {
        // Return the entries in our cache.
        Box::new(self
                 .inner.lock().unwrap()
                 .hits_fpr
                 .keys()
                 .cloned()
                 .collect::<Vec<_>>()
                 .into_iter())
    }
}

/// [`KeyServer`] specific error codes.
#[non_exhaustive]
#[derive(thiserror::Error, Debug)]
pub enum KeyServerError {
    /// Keyserver returned the wrong certs.
    #[error("Keyserver returned the wrong certs: {1:?} (wanted: {0})")]
    UnexpectedResults(KeyHandle, Vec<Fingerprint>),
}
