/*
 * This file is part of espanso.
 *
 * Copyright (C) 2019-2021 Federico Terzi
 *
 * espanso is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * espanso is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with espanso.  If not, see <https://www.gnu.org/licenses/>.
 */

use anyhow::Result;
use serde_json::Value;
use std::{
  collections::HashMap,
  path::{Path, PathBuf},
  sync::{Arc, Mutex},
};
use thiserror::Error;

use super::KVS;

const DEFAULT_KVS_DIR_NAME: &str = "kvs";

#[derive(Clone)]
pub struct PersistentJsonKVS {
  kvs_dir: PathBuf,
  store: Arc<Mutex<HashMap<String, Value>>>,
}

impl PersistentJsonKVS {
  pub fn new(base_dir: &Path) -> Result<Self> {
    let kvs_dir = base_dir.join(DEFAULT_KVS_DIR_NAME);
    if !kvs_dir.is_dir() {
      std::fs::create_dir_all(&kvs_dir)?;
    }

    Ok(Self {
      kvs_dir,
      store: Arc::new(Mutex::new(HashMap::new())),
    })
  }
}

impl KVS for PersistentJsonKVS {
  fn get<T: serde::de::DeserializeOwned>(&self, key: &str) -> Result<Option<T>> {
    if !is_valid_key_name(key) {
      return Err(PersistentJsonKVSError::InvalidKey(key.to_string()).into());
    }

    let mut lock = self.store.lock().expect("unable to obtain KVS read lock");

    if let Some(cached_value) = lock.get(key) {
      let converted_value = serde_json::from_value(cached_value.clone())?;
      return Ok(Some(converted_value));
    }

    // Not found in the cache, read from the file
    let target_file = self.kvs_dir.join(key);
    if target_file.is_file() {
      let content = std::fs::read_to_string(&target_file)?;
      let deserialized_value: Value = serde_json::from_str(&content)?;
      let converted_value = serde_json::from_value(deserialized_value.clone())?;

      lock.insert(key.to_string(), deserialized_value);

      return Ok(Some(converted_value));
    }

    Ok(None)
  }

  fn set<T: serde::Serialize>(&self, key: &str, value: T) -> Result<()> {
    if !is_valid_key_name(key) {
      return Err(PersistentJsonKVSError::InvalidKey(key.to_string()).into());
    }

    let mut lock = self.store.lock().expect("unable to obtain KVS write lock");

    let serialized_value = serde_json::to_value(value)?;
    let serialized_string = serde_json::to_string(&serialized_value)?;

    lock.insert(key.to_string(), serialized_value);

    let target_file = self.kvs_dir.join(key);
    std::fs::write(target_file, serialized_string)?;

    Ok(())
  }

  fn delete(&self, key: &str) -> Result<()> {
    if !is_valid_key_name(key) {
      return Err(PersistentJsonKVSError::InvalidKey(key.to_string()).into());
    }

    let mut lock = self.store.lock().expect("unable to obtain KVS delete lock");

    lock.remove(key);

    let target_file = self.kvs_dir.join(key);
    if target_file.is_file() {
      std::fs::remove_file(target_file)?;
    }

    Ok(())
  }
}

fn is_valid_key_name(key: &str) -> bool {
  if key.is_empty() || key.len() > 200 {
    return false;
  }

  if !key.chars().all(|c| c.is_ascii_alphanumeric() || c == '_') {
    return false;
  }

  true
}

#[derive(Error, Debug)]
pub enum PersistentJsonKVSError {
  #[error("The provided key `{0}` is is invalid. Keys must only be composed of ascii letters, numbers and underscores.")]
  InvalidKey(String),
}

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

  #[test]
  fn test_valid_key_names() {
    assert!(is_valid_key_name("key"));
    assert!(is_valid_key_name("key_name"));
    assert!(is_valid_key_name("Another_long_key_name_2"));
  }

  #[test]
  fn test_invalid_key_names() {
    assert!(!is_valid_key_name(""));
    assert!(!is_valid_key_name("with space"));
    assert!(!is_valid_key_name("with/special"));
    assert!(!is_valid_key_name("with\\special"));
  }
}