// Copyright 2018 Mozilla
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
// this file except in compliance with the License. You may obtain a copy of the
// License at http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software distributed
// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
// CONDITIONS OF ANY KIND, either express or implied. See the License for the
// specific language governing permissions and limitations under the License.

use std;
use std::collections::HashMap;

use futures::{future, Future, Stream};
use hyper;
// TODO: enable TLS support; hurdle is cross-compiling openssl for Android.
// See https://github.com/mozilla/mentat/issues/569
// use hyper_tls;
use hyper::{Method, Request, StatusCode, Error as HyperError};
use hyper::header::{ContentType};
use rusqlite;
// TODO: https://github.com/mozilla/mentat/issues/570
// use serde_cbor;
use serde_json;
use tokio_core::reactor::Core;
use uuid::Uuid;

use mentat_core::Entid;
use metadata::SyncMetadataClient;
use metadata::HeadTrackable;
use schema::ensure_current_version;

use errors::{
    TolstoyError,
    Result,
};

use tx_processor::{
    Processor,
    TxReceiver,
    TxPart,
};

use tx_mapper::TxMapper;

// TODO it would be nice to be able to pass
// in a logger into Syncer::flow; would allow for a "debug mode"
// and getting useful logs out of clients.
// See https://github.com/mozilla/mentat/issues/571
// Below is some debug Android-friendly logging:

// use std::os::raw::c_char;
// use std::os::raw::c_int;
// use std::ffi::CString;
// pub const ANDROID_LOG_DEBUG: i32 = 3;
// extern { pub fn __android_log_write(prio: c_int, tag: *const c_char, text: *const c_char) -> c_int; }

pub fn d(message: &str) {
    println!("d: {}", message);
    // let message = CString::new(message).unwrap();
    // let message = message.as_ptr();
    // let tag = CString::new("RustyToodle").unwrap();
    // let tag = tag.as_ptr();
    // unsafe { __android_log_write(ANDROID_LOG_DEBUG, tag, message) };
}

pub struct Syncer {}

// TODO this is sub-optimal, we don't need to walk the table
// to query the last thing in it w/ an index on tx!!
// but it's the hammer at hand!
// See https://github.com/mozilla/mentat/issues/572
struct InquiringTxReceiver {
    pub last_tx: Option<Entid>,
    pub is_done: bool,
}

impl InquiringTxReceiver {
    fn new() -> InquiringTxReceiver {
        InquiringTxReceiver {
            last_tx: None,
            is_done: false,
        }
    }
}

impl TxReceiver for InquiringTxReceiver {
    fn tx<T>(&mut self, tx_id: Entid, _datoms: &mut T) -> Result<()>
    where T: Iterator<Item=TxPart> {
        self.last_tx = Some(tx_id);
        Ok(())
    }

    fn done(&mut self) -> Result<()> {
        self.is_done = true;
        Ok(())
    }
}

struct UploadingTxReceiver<'c> {
    pub tx_temp_uuids: HashMap<Entid, Uuid>,
    pub is_done: bool,
    remote_client: &'c RemoteClient,
    remote_head: &'c Uuid,
    rolling_temp_head: Option<Uuid>,
}

impl<'c> UploadingTxReceiver<'c> {
    fn new(client: &'c RemoteClient, remote_head: &'c Uuid) -> UploadingTxReceiver<'c> {
        UploadingTxReceiver {
            tx_temp_uuids: HashMap::new(),
            remote_client: client,
            remote_head: remote_head,
            rolling_temp_head: None,
            is_done: false
        }
    }
}

impl<'c> TxReceiver for UploadingTxReceiver<'c> {
    fn tx<T>(&mut self, tx_id: Entid, datoms: &mut T) -> Result<()>
    where T: Iterator<Item=TxPart> {
        // Yes, we generate a new UUID for a given Tx, even if we might
        // already have one mapped locally. Pre-existing local mapping will
        // be replaced if this sync succeeds entirely.
        // If we're seeing this tx again, it implies that previous attempt
        // to sync didn't update our local head. Something went wrong last time,
        // and it's unwise to try to re-use these remote tx mappings.
        // We just leave garbage txs to be GC'd on the server.
        let tx_uuid = Uuid::new_v4();
        self.tx_temp_uuids.insert(tx_id, tx_uuid);
        let mut tx_chunks = vec![];

        // TODO separate bits of network work should be combined into single 'future'

        // Upload all chunks.
        for datom in datoms {
            let datom_uuid = Uuid::new_v4();
            tx_chunks.push(datom_uuid);
            d(&format!("putting chunk: {:?}, {:?}", &datom_uuid, &datom));
            // TODO switch over to CBOR once we're past debugging stuff.
            // See https://github.com/mozilla/mentat/issues/570
            // let cbor_val = serde_cbor::to_value(&datom)?;
            // self.remote_client.put_chunk(&datom_uuid, &serde_cbor::ser::to_vec_sd(&cbor_val)?)?;
            self.remote_client.put_chunk(&datom_uuid, &serde_json::to_string(&datom)?)?;
        }

        // Upload tx.
        // NB: At this point, we may choose to update remote & local heads.
        // Depending on how much we're uploading, and how unreliable our connection
        // is, this might be a good thing to do to ensure we make at least some progress.
        // Comes at a cost of possibly increasing racing against other clients.
        match self.rolling_temp_head {
            Some(parent) => {
                d(&format!("putting transaction: {:?}, {:?}, {:?}", &tx_uuid, &parent, &tx_chunks));
                self.remote_client.put_transaction(&tx_uuid, &parent, &tx_chunks)?;
                
            },
            None => {
                d(&format!("putting transaction: {:?}, {:?}, {:?}", &tx_uuid, &self.remote_head, &tx_chunks));
                self.remote_client.put_transaction(&tx_uuid, self.remote_head, &tx_chunks)?;
            }
        }

        d(&format!("updating rolling head: {:?}", tx_uuid));
        self.rolling_temp_head = Some(tx_uuid.clone());

        Ok(())
    }

    fn done(&mut self) -> Result<()> {
        self.is_done = true;
        Ok(())
    }
}

impl Syncer {
    fn upload_ours(db_tx: &mut rusqlite::Transaction, from_tx: Option<Entid>, remote_client: &RemoteClient, remote_head: &Uuid) -> Result<()> {
        let mut uploader = UploadingTxReceiver::new(remote_client, remote_head);
        Processor::process(db_tx, from_tx, &mut uploader)?;
        if !uploader.is_done {
            bail!(TolstoyError::TxProcessorUnfinished);
        }
        // Last tx uuid uploaded by the tx receiver.
        // It's going to be our new head.
        if let Some(last_tx_uploaded) = uploader.rolling_temp_head {
            // Upload remote head.
            remote_client.put_head(&last_tx_uploaded)?;

            // On succes:
            // - persist local mappings from the receiver
            // - update our local "remote head".
            TxMapper::set_bulk(db_tx, &uploader.tx_temp_uuids)?;
            SyncMetadataClient::set_remote_head(db_tx, &last_tx_uploaded)?;
        }

        Ok(())
    }

    pub fn flow(sqlite: &mut rusqlite::Connection, server_uri: &String, user_uuid: &Uuid) -> Result<()> {
        d(&format!("sync flowing"));

        ensure_current_version(sqlite)?;
        
        // TODO configure this sync with some auth data
        let remote_client = RemoteClient::new(server_uri.clone(), user_uuid.clone());
        let mut db_tx = sqlite.transaction()?;

        let remote_head = remote_client.get_head()?;
        d(&format!("remote head {:?}", remote_head));

        let locally_known_remote_head = SyncMetadataClient::remote_head(&db_tx)?;
        d(&format!("local head {:?}", locally_known_remote_head));

        // Local head: latest transaction that we have in the store,
        // but with one caveat: its tx might will not be mapped if it's
        // never been synced successfully.
        // In other words: if latest tx isn't mapped, then HEAD moved
        // since last sync and server needs to be updated.
        let mut inquiring_tx_receiver = InquiringTxReceiver::new();
        // TODO don't just start from the beginning... but then again, we should do this
        // without walking the table at all, and use the tx index.
        Processor::process(&db_tx, None, &mut inquiring_tx_receiver)?;
        if !inquiring_tx_receiver.is_done {
            bail!(TolstoyError::TxProcessorUnfinished);
        }
        let have_local_changes = match inquiring_tx_receiver.last_tx {
            Some(tx) => {
                match TxMapper::get(&db_tx, tx)? {
                    Some(_) => false,
                    None => true
                }
            },
            None => false
        };

        // Check if the server is empty - populate it.
        if remote_head == Uuid::nil() {
            d(&format!("empty server!"));
            Syncer::upload_ours(&mut db_tx, None, &remote_client, &remote_head)?;
        
        // Check if the server is the same as us, and if our HEAD moved.
        } else if locally_known_remote_head == remote_head {
            d(&format!("server unchanged since last sync."));
            
            if !have_local_changes {
                d(&format!("local HEAD did not move. Nothing to do!"));
                return Ok(());
            }

            d(&format!("local HEAD moved."));
            // TODO it's possible that we've successfully advanced remote head previously,
            // but failed to advance our own local head. If that's the case, and we can recognize it,
            // our sync becomes just bumping our local head. AFAICT below would currently fail.
            if let Some(upload_from_tx) = TxMapper::get_tx_for_uuid(&db_tx, &locally_known_remote_head)? {
                d(&format!("Fast-forwarding the server."));
                Syncer::upload_ours(&mut db_tx, Some(upload_from_tx), &remote_client, &remote_head)?;
            } else {
                d(&format!("Unable to fast-forward the server; missing local tx mapping"));
                bail!(TolstoyError::TxIncorrectlyMapped(0));
            }
            
        // We diverged from the server.
        // We'll need to rebase/merge ourselves on top of it.
        } else {
            d(&format!("server changed since last sync."));

            bail!(TolstoyError::NotYetImplemented(
                format!("Can't yet sync against changed server. Local head {:?}, remote head {:?}", locally_known_remote_head, remote_head)
            ));
        }

        // Commit everything, if there's anything to commit!
        // Any new tx->uuid mappings and the new HEAD. We're synced!
        db_tx.commit()?;

        Ok(())
    }
}

#[derive(Serialize,Deserialize)]
struct SerializedHead {
    head: Uuid
}

#[derive(Serialize)]
struct SerializedTransaction<'a> {
    parent: &'a Uuid,
    chunks: &'a Vec<Uuid>
}

struct RemoteClient {
    base_uri: String,
    user_uuid: Uuid
}


impl RemoteClient {
    fn new(base_uri: String, user_uuid: Uuid) -> Self {
        RemoteClient {
            base_uri: base_uri,
            user_uuid: user_uuid
        }
    }

    fn bound_base_uri(&self) -> String {
        // TODO escaping
        format!("{}/{}", self.base_uri, self.user_uuid)
    }

    fn get_uuid(&self, uri: String) -> Result<Uuid> {
        let mut core = Core::new()?;
        // TODO enable TLS, see https://github.com/mozilla/mentat/issues/569
        // let client = hyper::Client::configure()
        //     .connector(hyper_tls::HttpsConnector::new(4, &core.handle()).unwrap())
        //     .build(&core.handle());
        let client = hyper::Client::new(&core.handle());

        d(&format!("client"));

        let uri = uri.parse()?;

        d(&format!("parsed uri {:?}", uri));
        
        let work = client.get(uri).and_then(|res| {
            println!("Response: {}", res.status());

            res.body().concat2().and_then(move |body| {
                let head_json: SerializedHead = serde_json::from_slice(&body).map_err(|e| {
                    std::io::Error::new(std::io::ErrorKind::Other, e)
                })?;
                Ok(head_json)
            })
        });

        d(&format!("running..."));

        let head_json = core.run(work)?;
        d(&format!("got head: {:?}", &head_json.head));
        Ok(head_json.head)
    }

    fn put<T>(&self, uri: String, payload: T, expected: StatusCode) -> Result<()>
    where hyper::Body: std::convert::From<T>, {
        let mut core = Core::new()?;
        // TODO enable TLS, see https://github.com/mozilla/mentat/issues/569
        // let client = hyper::Client::configure()
        //     .connector(hyper_tls::HttpsConnector::new(4, &core.handle()).unwrap())
        //     .build(&core.handle());
        let client = hyper::Client::new(&core.handle());

        let uri = uri.parse()?;

        d(&format!("PUT {:?}", uri));

        let mut req = Request::new(Method::Put, uri);
        req.headers_mut().set(ContentType::json());
        req.set_body(payload);

        let put = client.request(req).and_then(|res| {
            let status_code = res.status();

            if status_code != expected {
                d(&format!("bad put response: {:?}", status_code));
                future::err(HyperError::Status)
            } else {
                future::ok(())
            }
        });

        core.run(put)?;
        Ok(())
    }

    fn put_transaction(&self, transaction_uuid: &Uuid, parent_uuid: &Uuid, chunks: &Vec<Uuid>) -> Result<()> {
        // {"parent": uuid, "chunks": [chunk1, chunk2...]}
        let transaction = SerializedTransaction {
            parent: parent_uuid,
            chunks: chunks
        };

        let uri = format!("{}/transactions/{}", self.bound_base_uri(), transaction_uuid);
        let json = serde_json::to_string(&transaction)?;
        d(&format!("serialized transaction: {:?}", json));
        self.put(uri, json, StatusCode::Created)
    }

    fn get_head(&self) -> Result<Uuid> {
        let uri = format!("{}/head", self.bound_base_uri());
        self.get_uuid(uri)
    }

    fn put_head(&self, uuid: &Uuid) -> Result<()> {
        // {"head": uuid}
        let head = SerializedHead {
            head: uuid.clone()
        };

        let uri = format!("{}/head", self.bound_base_uri());
        let json = serde_json::to_string(&head)?;
        d(&format!("serialized head: {:?}", json));
        self.put(uri, json, StatusCode::NoContent)
    }

    fn put_chunk(&self, chunk_uuid: &Uuid, payload: &String) -> Result<()> {
        let uri = format!("{}/chunks/{}", self.bound_base_uri(), chunk_uuid);
        d(&format!("serialized chunk: {:?}", payload));
        // TODO don't want to clone every datom!
        self.put(uri, payload.clone(), StatusCode::Created)
    }
}

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

    #[test]
    fn test_remote_client_bound_uri() {
        let user_uuid = Uuid::from_str(&"316ea470-ce35-4adf-9c61-e0de6e289c59").expect("uuid");
        let server_uri = String::from("https://example.com/api/0.1");
        let remote_client = RemoteClient::new(server_uri, user_uuid);
        assert_eq!("https://example.com/api/0.1/316ea470-ce35-4adf-9c61-e0de6e289c59", remote_client.bound_base_uri());
    }
}