use async_std::{
    channel::{unbounded, Receiver, Sender},
    path::PathBuf,
    task::spawn,
};
use std::{collections::HashMap, error::Error, fmt};

const ENTRY: &str = "EntryPoint";

#[derive(Debug)]
enum ErrorCode {
    // General
    Undefined(String),
    // Cache
    EntryNotFound(String),
    InvalidCommitData,
    // Store
    DatabaseAlreadyExists(String),
}

impl fmt::Display for ErrorCode {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            ErrorCode::Undefined(msg) => write!(f, "{}", msg),
            ErrorCode::EntryNotFound(id) => write!(f, "entry '{}' was not found", id),
            ErrorCode::InvalidCommitData => write!(f, "commit data was not a database store"),
            ErrorCode::DatabaseAlreadyExists(name) => {
                write!(f, "database '{}' already exists", name)
            }
        }
    }
}

mod errorcodes {
    use super::*;

    const ITEMS: [&str; 2] = ["one", "two"];

    #[test]
    fn undefined_display() {
        for item in ITEMS {
            let err = ErrorCode::Undefined(item.to_string());
            assert_eq!(err.to_string(), item);
        }
    }

    #[test]
    fn bad_entry() {
        for item in ITEMS {
            let err = ErrorCode::EntryNotFound(item.to_string());
            assert_eq!(err.to_string(), format!("entry '{}' was not found", item));
        }
    }

    #[test]
    fn invalid_commit_data() {
        let err = ErrorCode::InvalidCommitData;
        assert_eq!(err.to_string(), "commit data was not a database store");
    }

    #[test]
    fn database_already_exists() {
        for item in ITEMS {
            let err = ErrorCode::DatabaseAlreadyExists(item.to_string());
            assert_eq!(
                err.to_string(),
                format!("database '{}' already exists", item)
            );
        }
    }
}

#[derive(Debug)]
pub struct MTTError {
    code: ErrorCode,
}

impl MTTError {
    fn new<S>(msg: S) -> Self
    where
        S: Into<String>,
    {
        let text = msg.into();
        Self {
            code: ErrorCode::Undefined(text),
        }
    }

    fn from_code(code: ErrorCode) -> Self {
        Self { code: code }
    }
}

impl Error for MTTError {}

impl fmt::Display for MTTError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.code)
    }
}

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

    #[test]
    fn create_with_str() {
        let msgs = ["one", "two"];
        for msg in msgs {
            let err = MTTError::new(msg);
            assert_eq!(err.to_string(), msg);
        }
    }

    #[test]
    fn create_with_string() {
        let msg = "three";
        let err = MTTError::new(msg.to_string());
        assert_eq!(err.to_string(), msg);
    }

    #[test]
    fn create_from_code() {
        let code = ErrorCode::Undefined("oops".to_string());
        let err = MTTError::from_code(code);
        match err.code {
            ErrorCode::Undefined(_) => (),
            _ => assert!(false, "{:?} is not undefined", err.code),
        }
    }

    #[test]
    fn create_missing_entry() {
        let code = ErrorCode::EntryNotFound("an_id".to_string());
        let err = MTTError::from_code(code);
        match err.code {
            ErrorCode::EntryNotFound(_) => (),
            _ => assert!(false, "{:?} is not undefined", err.code),
        }
    }
}

#[derive(Clone, Debug)]
struct Storage<D> {
    id: Option<String>,
    data: Option<D>,
    // delete: bool,
}

impl Storage<D> {
    fn from_id<S>(id: S) -> Self
    where
        S: Into<String>,
    {
        Self {
            id: Some(id.into()),
            data: None,
        }
    }

    fn from_datatype(dt: DataType) -> Self {
        Self {
            id: None,
            data: Some(dt),
        }
    }
}

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

    #[test]
    fn from_id_with_str() {
        let ids = ["first", "second"];
        for id in ids {
            let output = Storage::from_id(id);
            assert_eq!(output.id, Some(id.to_string()));
            assert!(
                output.data.is_none(),
                "The storage data should have been Non."
            );
        }
    }

    #[test]
    fn from_id_with_string() {
        let id = "my_id".to_string();
        let output = Storage::from_id(id.clone());
        assert_eq!(output.id, Some(id));
    }

    #[test]
    fn from_store() {
        let output = Storage::from_datatype(DataType::new("store"));
        assert!(output.id.is_none(), "id should be None.");
        assert!(output.data.is_some(), "There should be data");
        let result = output.data.unwrap();
        match result {
            DataType::DBMap(_) => (),
            _ => assert!(false, "{:?} should have been DataType::DBMap.", result),
        }
    }

    #[test]
    fn from_database() {
        let output = Storage::from_datatype(DataType::new("database"));
        let result = output.data.unwrap();
        match result {
            DataType::TableMap(_) => (),
            _ => assert!(false, "{:?} should have been DataType::TableMap.", result),
        }
    }
}

#[derive(Clone, Debug)]
struct Store {
    data: HashMap<String, Storage<Database>>,
}

impl Store {
    fn new() -> Self {
        Self {
            data: HashMap::new(),
        }
    }

    fn add_new<S>(&mut self, name: S) -> Result<(), MTTError>
    where
        S: Into<String>,
    {
        let dbname = name.into();
        match self.get(&dbname) {
            Some(_) => Err(MTTError::from_code(ErrorCode::DatabaseAlreadyExists(
                dbname,
            ))),
            None => {
                self.data
                    .insert(dbname, Storage::from_datatype(DataType::new("database")));
                Ok(())
            }
        }
    }

    fn get(&self, name: &str) -> Option<&Storage<Database>> {
        self.data.get(name)
    }
}

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

    #[test]
    fn get_no_database() -> Result<(), MTTError> {
        let store = Store::new();
        match store.get("missing_name") {
            Some(_) => Err(MTTError::new("should have returned None")),
            None => Ok(()),
        }
    }

    #[test]
    fn add_database_str() {
        let mut store = Store::new();
        let names = ["first", "second"];
        for name in names {
            store.add_new(name).unwrap();
            let output = store.get(name).unwrap();
            assert!(output.data.is_some(), "There should be a data type.");
            match output.data.clone().unwrap() {
                DataType::TableMap(_) => (),
                _ => assert!(
                    false,
                    "{:?} should have been DataType::TableMap.",
                    output.data
                ),
            }
            assert!(output.id.is_none(), "Should not have an id.");
        }
    }

    #[test]
    fn add_database_string() {
        let mut store = Store::new();
        let name = "third".to_string();
        store.add_new(name.clone()).unwrap();
        let output = store.get(&name).unwrap();
        match output.data.clone().unwrap() {
            DataType::TableMap(_) => (),
            _ => assert!(
                false,
                "{:?} should have been DataType::TableMap.",
                output.data
            ),
        }
    }

    #[test]
    fn no_duplicate_database_names() -> Result<(), MTTError> {
        let mut store = Store::new();
        let name = "duplicate";
        store.add_new(name).unwrap();
        match store.add_new(name) {
            Ok(_) => Err(MTTError::new("should have been an error")),
            Err(err) => match err.code {
                ErrorCode::DatabaseAlreadyExists(dbname) => {
                    assert_eq!(dbname, name);
                    Ok(())
                }
                _ => Err(MTTError::new(format!(
                    "{:?} should have been DatabaseAlreadyExists.",
                    err.code
                ))),
            },
        }
    }
}

#[derive(Clone, Debug)]
struct Database;

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

    #[test]
    fn create() {
        Database::new();
    }
}

impl Database {
    fn new() -> Self {
        Self {}
    }
}

#[derive(Clone, Debug)]
enum DataType {
    DBMap(Store),
    TableMap(Database),
}

impl DataType {
    fn new(dtype: &str) -> DataType {
        match dtype {
            "store" => Self::DBMap(Store::new()),
            "database" => Self::TableMap(Database::new()),
            _ => unreachable!(),
        }
    }
}

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

    #[test]
    fn create_store() {
        let dtype = DataType::new("store");
        match dtype {
            DataType::DBMap(_) => (),
            _ => assert!(false, "{:?} is not incorrect data type", dtype),
        }
    }

    #[test]
    fn create_database() {
        let dtype = DataType::new("database");
        match dtype {
            DataType::TableMap(_) => (),
            _ => assert!(false, "{:?} is not incorrect data type", dtype),
        }
    }
}

#[derive(Debug)]
enum FromCache {
    Ok,
    Data(HashMap<String, DataType>),
    Error(MTTError),
}

struct CacheQuery {
    ids: Vec<String>,
    reply: Sender<FromCache>,
}

struct CacheCommit {
    reply: Sender<FromCache>,
    data: DataType,
}

impl CacheCommit {
    fn new(data: DataType, channel: Sender<FromCache>) -> Result<Self, MTTError> {
        match data {
            DataType::DBMap(_) => (),
            _ => return Err(MTTError::from_code(ErrorCode::InvalidCommitData)),
        }
        Ok(Self {
            data: data,
            reply: channel,
        })
    }
}

mod commits {
    use super::*;

    #[test]
    fn create() -> Result<(), MTTError> {
        let (s, _) = unbounded();
        match CacheCommit::new(DataType::new("store"), s) {
            Ok(output) => match output.data {
                DataType::DBMap(_) => Ok(()),
                _ => Err(MTTError::new(format!(
                    "{:?} should have been DBMap",
                    output.data
                ))),
            },
            Err(err) => Err(err),
        }
    }

    #[test]
    fn bad_data_type() -> Result<(), MTTError> {
        let (s, _) = unbounded();
        match CacheCommit::new(DataType::new("database"), s) {
            Ok(_) => Err(MTTError::new("CacheCommit::new did not return error")),
            Err(err) => match err.code {
                ErrorCode::InvalidCommitData => Ok(()),
                _ => Err(MTTError::new(format!(
                    "{:?} is not the correct error",
                    err.code
                ))),
            },
        }
    }
}

enum ToCache {
    Query(CacheQuery),
    Commit(CacheCommit),
}

#[derive(Clone)]
pub struct MoreThanText {
    session: Vec<String>,
    cache: Sender<Vec<String>>,
}

impl MoreThanText {
    async fn new(cache: Sender<Vec<String>>) -> Result<Self, MTTError> {
        Ok(Self {
            session: [ENTRY.to_string()].to_vec(),
            cache: cache,
        })
    }
}

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

    #[async_std::test]
    async fn create() {
        let (s, _) = unbounded();
        let mtt = MoreThanText::new(s).await.unwrap();
        assert_eq!(mtt.session, [ENTRY]);
    }
}

struct Cache;

impl Cache {
    async fn new<P>(_dir: P) -> Result<Self, MTTError>
    where
        P: Into<PathBuf>,
    {
        Ok(Self {})
    }

    async fn query(&self, qry: &Vec<String>) -> Result<HashMap<String, DataType>, MTTError> {
        let mut output = HashMap::new();
        for id in qry {
            if id == ENTRY {
                output.insert(ENTRY.to_string(), DataType::new("store"));
            } else {
                return Err(MTTError::from_code(ErrorCode::EntryNotFound(
                    id.to_string(),
                )));
            }
        }
        Ok(output)
    }

    async fn commit(&self) -> Result<(), MTTError> {
        Ok(())
    }

    async fn start(&self, listener: Receiver<ToCache>) {
        loop {
            match listener.recv().await.unwrap() {
                ToCache::Query(qry) => match self.query(&qry.ids).await {
                    Ok(data) => qry.reply.send(FromCache::Data(data)).await.unwrap(),
                    Err(error) => qry.reply.send(FromCache::Error(error)).await.unwrap(),
                },
                ToCache::Commit(commit) => match self.commit().await {
                    Ok(_) => commit.reply.send(FromCache::Ok).await.unwrap(),
                    Err(error) => commit.reply.send(FromCache::Error(error)).await.unwrap(),
                },
            }
        }
    }
}

#[cfg(test)]
mod caches {
    use super::*;
    use tempfile::tempdir;

    async fn start_cache<P>(dir: P) -> Sender<ToCache>
    where
        P: Into<PathBuf>,
    {
        let (s, r) = unbounded();
        let datadir = dir.into();
        spawn(async move {
            let cache = Cache::new(datadir).await.unwrap();
            cache.start(r).await;
        });
        s
    }

    async fn send_request(data: Vec<&str>, channel: Sender<ToCache>) -> FromCache {
        let mut ids = Vec::new();
        for id in data.iter() {
            ids.push(id.to_string());
        }
        let (s, r) = unbounded();
        let msg = ToCache::Query(CacheQuery { ids: ids, reply: s });
        channel.send(msg).await.unwrap();
        r.recv().await.unwrap()
    }

    #[async_std::test]
    async fn create() {
        let dir = tempdir().unwrap();
        let s_cache = start_cache(dir.path()).await;
        let result = send_request(vec![ENTRY], s_cache).await;
        match result {
            FromCache::Data(data) => match data.get(ENTRY) {
                Some(output) => match output {
                    DataType::DBMap(_) => (),
                    _ => assert!(false, "{:?} is not a database store.", output),
                },
                None => assert!(false, "Should contain entry point."),
            },
            _ => assert!(false, "{:?} should have been a store.", result),
        }
    }

    #[async_std::test]
    async fn bad_entry() {
        let dir = tempdir().unwrap();
        let s_cache = start_cache(dir.path()).await;
        let result = send_request(vec!["bad_id"], s_cache).await;
        match result {
            FromCache::Error(_) => (),
            _ => assert!(false, "{:?} should have been an error.", result),
        }
    }

    #[async_std::test]
    async fn empty_commit() {
        let dir = tempdir().unwrap();
        let s_cache = start_cache(dir.path()).await;
        let (s, r) = unbounded();
        let msg = ToCache::Commit(CacheCommit::new(DataType::new("store"), s).unwrap());
        s_cache.send(msg).await.unwrap();
        let result = r.recv().await.unwrap();
        match result {
            FromCache::Ok => (),
            _ => assert!(false, "{:?} should have been an Ok.", result),
        }
    }

    #[async_std::test]
    async fn get_store() {
        let dir = tempdir().unwrap();
        let cache = Cache::new(dir.path()).await.unwrap();
        let output = cache.query(&[ENTRY.to_string()].to_vec()).await.unwrap();
        let result = output.get(ENTRY).unwrap();
        match result {
            DataType::DBMap(_) => (),
            _ => assert!(false, "{:?} should have been an Ok.", result),
        }
    }

    #[async_std::test]
    async fn bad_get() {
        let dir = tempdir().unwrap();
        let cache = Cache::new(dir.path()).await.unwrap();
        let bad_id = "really_bad_id";
        match cache.query(&[bad_id.to_string()].to_vec()).await {
            Ok(_) => assert!(false, "Should have produced an error."),
            Err(err) => match err.code {
                ErrorCode::EntryNotFound(id) => assert_eq!(id, bad_id),
                _ => assert!(false, "{:?} should have been EntryNotFound.", err.code),
            },
        }
    }
}

pub async fn start_db<P>(_dir: P) -> Result<MoreThanText, MTTError>
where
    P: Into<PathBuf>,
{
    let (s, r) = unbounded();
    spawn(async move {
        loop {
            r.recv().await.unwrap();
        }
    });
    Ok(MoreThanText::new(s).await.unwrap())
}

#[cfg(test)]
mod db_start_up {
    use super::*;
    use tempfile::tempdir;

    #[async_std::test]
    async fn initial_session() {
        let dir = tempdir().unwrap();
        let mtt = start_db(dir.path()).await.unwrap();
        assert_eq!(mtt.session, [ENTRY]);
    }
}