pub mod error;

use async_std::{
    fs::{create_dir, read, write},
    path::Path,
    sync::{Arc, Mutex},
};
use error::DBError;
use rand::{distributions::Alphanumeric, thread_rng, Rng};
use std::{
    collections::HashMap,
    fmt, str,
    time::{Duration, Instant},
};

const DATA: &str = "data";

#[derive(Clone)]
enum CacheType {
    Raw(String),
}

impl CacheType {
    fn entry_type(&self) -> String {
        match self {
            CacheType::Raw(_) => "Raw".to_string(),
        }
    }

    fn to_bytes(&self) -> Vec<u8> {
        let mut output = self.entry_type().into_bytes();
        output.push(0);
        match self {
            CacheType::Raw(s) => output.append(&mut s.as_bytes().to_vec()),
        }
        return output;
    }

    fn from_bytes(data: Vec<u8>) -> CacheType {
        let mut data_iter = data.iter();
        let mut holder: u8 = *data_iter.next().unwrap();
        while holder != 0 {
            holder = *data_iter.next().unwrap();
        }
        let mut output: Vec<u8> = Vec::new();
        for letter in data_iter {
            output.push(letter.clone());
        }
        CacheType::Raw(str::from_utf8(&output).unwrap().to_string())
    }
}

impl fmt::Display for CacheType {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            CacheType::Raw(s) => write!(f, "{}", s),
        }
    }
}

#[derive(Clone)]
struct CacheEntry {
    data: CacheType,
    last_used: Instant,
}

impl CacheEntry {
    fn new(data: CacheType) -> Self {
        Self {
            data: data,
            last_used: Instant::now(),
        }
    }

    fn elapsed(&self) -> Duration {
        self.last_used.elapsed()
    }

    fn touch(&mut self) {
        self.last_used = Instant::now();
    }

    fn update(&mut self, data: CacheType) {
        self.data = data;
        self.touch();
    }
}

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

#[derive(Clone)]
pub struct MoreThanText {
    cache: Arc<Mutex<HashMap<String, CacheEntry>>>,
    dir: String,
}

impl MoreThanText {
    pub async fn new(dir: &str) -> Result<Self, DBError> {
        let data_dir = Path::new(dir).join(DATA);
        if !data_dir.is_dir().await {
            match create_dir(&data_dir).await {
                Ok(_) => (),
                Err(err) => {
                    let mut error = DBError::new("failed to create data directory");
                    error.add_source(err);
                    return Err(error);
                }
            }
        }
        Ok(Self {
            cache: Arc::new(Mutex::new(HashMap::new())),
            dir: data_dir.to_str().unwrap().to_string(),
        })
    }

    fn filename(&self, id: &str) -> String {
        let filename = Path::new(&self.dir).join(&id);
        filename.into_os_string().into_string().unwrap()
    }

    async fn add_entry(&self, entry: CacheType) -> Result<String, DBError> {
        let mut id: String = "".to_string();
        let mut dup = true;
        while dup {
            id = thread_rng().sample_iter(&Alphanumeric).take(32).collect();
            dup = Path::new(&self.dir).join(&id).as_path().exists().await;
        }
        match write(Path::new(&self.filename(&id)), entry.to_bytes()).await {
            Ok(_) => (),
            Err(err) => {
                let mut error = DBError::new("data write");
                error.add_source(err);
                return Err(error);
            }
        };
        let mut cache = self.cache.lock().await;
        let data = CacheEntry::new(entry);
        cache.insert(id.clone(), data);
        Ok(id)
    }

    async fn get_entry(&self, id: &str) -> Result<CacheEntry, DBError> {
        let mut cache = self.cache.lock().await;
        match cache.get_mut(id) {
            Some(entry) => {
                entry.touch();
                Ok(entry.clone())
            }
            None => match read(Path::new(&self.filename(id))).await {
                Ok(content) => {
                    let data = CacheEntry::new(CacheType::from_bytes(content));
                    cache.insert(id.to_string(), data.clone());
                    Ok(data)
                }
                Err(_) => Err(DBError::new("cache entry not found")),
            },
        }
    }

    async fn update_entry(&self, id: &str, entry: CacheType) -> Result<(), DBError> {
        match self.get_entry(id).await {
            Ok(_) => (),
            Err(err) => return Err(err),
        }
        match write(Path::new(&self.filename(id)), entry.to_bytes()).await {
            Ok(_) => (),
            Err(err) => {
                let mut error = DBError::new("data write");
                error.add_source(err);
                return Err(error);
            }
        }
        let mut cache = self.cache.lock().await;
        let data = CacheEntry::new(entry);
        cache.insert(id.to_string(), data);
        Ok(())
    }
}

#[cfg(test)]
mod setup {
    use super::*;
    use async_std::fs::remove_dir_all;
    use tempfile::{tempdir, TempDir};

    pub struct MTT {
        pub db: MoreThanText,
        pub dir: TempDir,
    }

    impl MTT {
        pub async fn new() -> Self {
            let dir = tempdir().unwrap();
            let db = MoreThanText::new(dir.path().to_str().unwrap())
                .await
                .unwrap();
            Self { db: db, dir: dir }
        }

        pub async fn create_io_error(&self) {
            remove_dir_all(self.dir.path().join(DATA)).await.unwrap();
        }
    }
}

#[cfg(test)]
mod init {
    use super::*;
    use std::error::Error;
    use tempfile::tempdir;

    #[async_std::test]
    async fn create_data_dir() {
        let dir = tempdir().unwrap();
        MoreThanText::new(dir.path().to_str().unwrap())
            .await
            .unwrap();
        let data_dir = dir.path().join(DATA);
        assert!(data_dir.is_dir(), "Did not create the data directory.");
        dir.close().unwrap();
    }

    #[async_std::test]
    async fn existing_data_dir() {
        let dir = tempdir().unwrap();
        let data_dir = dir.path().join(DATA);
        create_dir(data_dir).await.unwrap();
        MoreThanText::new(dir.path().to_str().unwrap())
            .await
            .unwrap();
        dir.close().unwrap();
    }

    #[async_std::test]
    async fn bad_data_dir() {
        let msg = "could not create directory";
        match MoreThanText::new("kljsdgfhslkfrh").await {
            Ok(_) => assert!(false, "This test should fail to create a data directory"),
            Err(err) => {
                assert_eq!(err.to_string(), "failed to create data directory");
                assert!(err.source().is_some(), "Must include the source error.");
                let err_msg = err.source().unwrap().to_string();
                assert!(err_msg.contains(msg), "'{}' not in '{}'", msg, err_msg);
            }
        };
    }
}

#[cfg(test)]
mod cache {
    use super::*;
    use async_std::fs::read;
    use setup::MTT;
    use std::error::Error;

    #[async_std::test]
    async fn entry_ids_are_random() {
        let mtt = MTT::new().await;
        let data1 = CacheType::Raw("one".to_string());
        let data2 = CacheType::Raw("two".to_string());
        let id1 = mtt.db.add_entry(data1).await.unwrap();
        let id2 = mtt.db.add_entry(data2).await.unwrap();
        assert_ne!(id1, id2, "Ids should be unique.")
    }

    #[async_std::test]
    async fn store_cache() {
        let mtt = MTT::new().await;
        let data = "something";
        let expected = CacheType::Raw(data.to_string());
        let id = mtt.db.add_entry(expected.clone()).await.unwrap();
        let output = mtt.db.get_entry(&id).await.unwrap();
        assert_eq!(output.to_string(), data);
        let dfile = mtt.dir.path().join(DATA).join(&id);
        assert!(dfile.is_file(), "Cache file should exist.");
        let content = read(dfile).await.unwrap();
        assert_eq!(content, expected.to_bytes());
    }

    #[async_std::test]
    async fn get_entry_uodates_time() {
        let mtt = MTT::new().await;
        let id = "something";
        let holder = CacheEntry {
            data: CacheType::Raw("old".to_string()),
            last_used: Instant::now() - Duration::from_secs(200),
        };
        let mut cache = mtt.db.cache.lock().await;
        cache.insert(id.to_string(), holder);
        drop(cache);
        mtt.db.get_entry(&id).await.unwrap();
        let cache = mtt.db.cache.lock().await;
        let entry = cache.get(id).unwrap();
        let held = entry.elapsed();
        assert!(
            Duration::from_secs(1) > held,
            "Duration was {:?}, should have been close to 0s.",
            held
        );
    }

    #[async_std::test]
    async fn retrieve_from_disk() {
        let mtt = MTT::new().await;
        let id = "someid";
        let data = CacheType::Raw("stored".to_string());
        write(mtt.dir.path().join(DATA).join(id), data.to_bytes())
            .await
            .unwrap();
        let output = mtt.db.get_entry(id).await.unwrap();
        assert_eq!(output.to_string(), data.to_string());
        let cache = mtt.db.cache.lock().await;
        let stored = cache.get(id);
        assert!(stored.is_some(), "Did not store entry in the cache.");
    }

    #[async_std::test]
    async fn store_bad_file() {
        let mtt = MTT::new().await;
        let msg = "could not write to file";
        mtt.create_io_error().await;
        match mtt.db.add_entry(CacheType::Raw("fail".to_string())).await {
            Ok(_) => assert!(false, "This test should fail."),
            Err(err) => {
                assert_eq!(err.to_string(), "data write");
                assert!(err.source().is_some(), "Must include the source error.");
                let err_msg = err.source().unwrap().to_string();
                assert!(err_msg.contains(msg), "'{}' not in '{}'", msg, err_msg);
            }
        }
    }

    #[async_std::test]
    async fn retrieve_bad_id() {
        let mtt = MTT::new().await;
        match mtt.db.get_entry(&"Not Valid").await {
            Ok(_) => assert!(false, "Should have raised an error."),
            Err(err) => assert_eq!(err.to_string(), "cache entry not found"),
        }
    }

    #[async_std::test]
    async fn update_cache_entry() {
        let mtt = MTT::new().await;
        let id = "updateable";
        let holder = CacheEntry {
            data: CacheType::Raw("elder".to_string()),
            last_used: Instant::now() - Duration::from_secs(500),
        };
        let mut cache = mtt.db.cache.lock().await;
        cache.insert(id.to_string(), holder);
        drop(cache);
        let expected = "different";
        let expect = CacheType::Raw(expected.to_string());
        mtt.db.update_entry(id, expect.clone()).await.unwrap();
        let output = mtt.db.get_entry(id).await.unwrap();
        assert_eq!(output.to_string(), expected);
        let cache = mtt.db.cache.lock().await;
        let entry = cache.get(id).unwrap();
        let held = entry.elapsed();
        assert!(
            Duration::from_secs(1) > held,
            "Duration was {:?}, should have been close to 0s.",
            held
        );
        drop(cache);
        let content = read(mtt.dir.path().join(DATA).join(id)).await.unwrap();
        assert_eq!(content, expect.to_bytes());
    }

    #[async_std::test]
    async fn update_bad_id() {
        let mtt = MTT::new().await;
        match mtt
            .db
            .update_entry("wilma", CacheType::Raw("wrong".to_string()))
            .await
        {
            Ok(_) => assert!(false, "Bad id should raise an error."),
            Err(err) => assert_eq!(err.to_string(), "cache entry not found"),
        }
    }

    #[async_std::test]
    async fn update_bad_file() {
        let mtt = MTT::new().await;
        let msg = "could not write to file";
        let id = mtt
            .db
            .add_entry(CacheType::Raw("fleeting".to_string()))
            .await
            .unwrap();
        mtt.create_io_error().await;
        match mtt
            .db
            .update_entry(&id, CacheType::Raw("failure".to_string()))
            .await
        {
            Ok(_) => assert!(false, "This should produce a write failure."),
            Err(err) => {
                assert_eq!(err.to_string(), "data write");
                assert!(err.source().is_some(), "Must include the source error.");
                let err_msg = err.source().unwrap().to_string();
                assert!(err_msg.contains(msg), "'{}' not in '{}'", msg, err_msg);
            }
        }
    }
}

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

    #[test]
    fn raw_get_type() {
        let holder = CacheType::Raw("nothing important".to_string());
        assert_eq!(holder.entry_type(), "Raw");
    }

    #[test]
    fn raw_get_bytes() {
        let data = "addams";
        let holder = CacheType::Raw(data.to_string());
        let mut expected = holder.entry_type().into_bytes();
        expected.push(0);
        expected.append(&mut data.as_bytes().to_vec());
        let output = holder.to_bytes();
        assert_eq!(output, expected);
    }

    #[test]
    fn raw_from_bytes() {
        let holder = CacheType::Raw("stored item".to_string());
        let data = holder.to_bytes();
        let output = CacheType::from_bytes(data);
        assert_eq!(output.to_string(), holder.to_string());
    }
}

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

    #[test]
    fn init() {
        let text = "new entry";
        let holder = CacheEntry::new(CacheType::Raw(text.to_string()));
        assert_eq!(holder.to_string(), text);
        let held = holder.elapsed();
        assert!(
            Duration::from_secs(1) > held,
            "Duration was {:?}, should have been close to 0s.",
            held
        );
    }

    #[test]
    fn older() {
        let secs = 800;
        let holder = CacheEntry {
            data: CacheType::Raw("older".to_string()),
            last_used: Instant::now() - Duration::from_secs(secs),
        };
        let held = holder.elapsed() - Duration::from_secs(secs);
        assert!(
            Duration::from_secs(1) > held,
            "{:?} should be close to {}s",
            holder.elapsed(),
            secs
        );
    }

    #[test]
    fn accessed() {
        let mut holder = CacheEntry {
            data: CacheType::Raw("older".to_string()),
            last_used: Instant::now() - Duration::from_secs(700),
        };
        holder.touch();
        let held = holder.elapsed();
        assert!(
            Duration::from_secs(1) > held,
            "Duration was {:?}, should have been close to 0s.",
            held
        );
    }

    #[test]
    fn updated() {
        let text = "new data";
        let mut holder = CacheEntry {
            data: CacheType::Raw("old data".to_string()),
            last_used: Instant::now() - Duration::from_secs(900),
        };
        holder.update(CacheType::Raw(text.to_string()));
        assert_eq!(holder.to_string(), text);
        let held = holder.elapsed();
        assert!(
            Duration::from_secs(1) > held,
            "Duration was {:?}, should have been close to 0s.",
            held
        );
    }
}