/*-
 * cdns-rs - a simple sync/async DNS query library
 * Copyright (C) 2020  Aleksandr Morozov
 * 
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 *  file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

/// This file contains configuration caches.

use std::path::Path;
use std::sync::Arc;
use std::time::SystemTime;

use tokio::fs;

use tokio::sync::Mutex;


use crate::cfg_host_parser::HostConfig;
use crate::cfg_resolv_parser::ResolveConfig;
use crate::{async_write_error, internal_error, internal_error_map, error::*};

use super::cfg_parsers::*;

lazy_static!{
    pub static ref CACHE: CachesController = CachesController::new();
}


pub trait CacheOperations
{
    fn is_reload_allowed(&self) -> bool;
}

#[derive(Clone, Debug)]
struct CacheTime<'cache>
{
    path: &'cache Path,
    last_modif: SystemTime,
}

impl<'cache> CacheTime<'cache>
{
    async 
    fn new(path: &'cache Path) -> CDnsResult<CacheTime<'cache>>
    {
        return Ok(CacheTime { path: path, last_modif: Self::get_last_modified(path).await? });
    }

    fn fake(path: &'cache Path) -> Self
    {
        return Self { path: path, last_modif: SystemTime::now() };
    }

    async 
    fn get_last_modified(path: &'cache Path) -> CDnsResult<SystemTime>
    {
        let metadata = fs::metadata(path).await.map_err(|e| 
            internal_error_map!(CDnsErrorType::InternalError, "fs::metadata::modified() not supported on this platform: '{}'", e)
        )?;

        let last_modif = 
            metadata.modified().map_err(|e| 
                internal_error_map!(CDnsErrorType::InternalError, "fs::metadata::modified() not supported on this platform: '{}'", e)
            )?;

        return Ok(last_modif);
    }

    async 
    fn check_modified(&mut self) -> CDnsResult<bool>
    {
        // in case if get_last_modified() will return Err, return what was cached prevously
        let last_modif = 
            match Self::get_last_modified(self.path).await
            {
                Ok(t) => t,
                Err(e) => internal_error!(CDnsErrorType::InternalError, "{}", e),
            };

        return Ok(self.last_modif != last_modif);
    }
}

#[derive(Clone, Debug)]
pub struct CacheInstance<T: Default + ConfigParser<T> + CacheOperations>//, P: ConfigParser<T>>
{
    last_modif: CacheTime<'static>,
    cache: Arc<T>,
   // f: PhantomData<P>,
}

impl<T: Default + ConfigParser<T> + CacheOperations> Default for CacheInstance<T>
{
    fn default() -> Self 
    {
        return 
            Self 
            {
                last_modif: CacheTime::fake(T::get_file_path()), 
                cache: Arc::new(T::default()),
              //  f: PhantomData,
            };
    }
}

impl<T: Default + ConfigParser<T> + CacheOperations> CacheInstance<T>
{
    async  
    fn new() -> CDnsResult<Self>
    {
        return Ok(
            Self 
            {
                last_modif: CacheTime::new(T::get_file_path()).await?, 
                cache: Arc::new(T::parse_config().await?),
                //f: PhantomData,
            }
        );
    }

    async 
    fn read_config() -> CDnsResult<Arc<T>>
    {
        return Ok(Arc::new(T::parse_config().await?));
    }

    async 
    fn check_modified(&mut self) -> CDnsResult<()>
    {
        // in case if get_last_modified() will return Err, save what was cached prevously
        if self.cache.is_reload_allowed() == false
        {
            // just return OK
            return Ok(());
        }

        if self.last_modif.check_modified().await? == true
        {
            // reload
            self.cache = Self::read_config().await?;
        }
        
        return Ok(());
    }

    fn clone_cache(&self) -> Arc<T>
    {
        return self.cache.clone();
    }
}

pub struct CachesController
{
    resolv_cache: Mutex<CacheInstance<ResolveConfig>>,
    host_cache: Mutex<CacheInstance<HostConfig>>
}

unsafe impl Sync for CachesController{}
unsafe impl Send for CachesController{}

impl CachesController
{
    /// Just creates insrance, but does not read anything from disk. 
    fn new() -> Self
    {
        /*let resolve_cache_res = CacheInstance::<ResolveConfig>::new().await;

        let host_cache_res = CacheInstance::<HostConfig>::new().await;

        let resolve_cache = 
            match resolve_cache_res
            {
                Ok(r) => r,
                Err(e) =>
                {
                    write_error!("{}", e);

                    CacheInstance::default()
                }
            };
        
        let host_cache = 
            match host_cache_res
            {
                Ok(r) => r,
                Err(e) =>
                {
                    write_error!("{}", e);

                    CacheInstance::default()
                }
            };
    */

        return 
            CachesController
            { 
                resolv_cache: Mutex::new(CacheInstance::default()),//resolve_cache),
                host_cache: Mutex::new(CacheInstance::default()),//host_cache),
            };
    }

    pub async 
    fn is_resolve_cached(&self) -> bool
    {
        return !self.resolv_cache.lock().await.cache.is_default();
    }

    pub async 
    fn is_host_cached(&self) -> bool
    {
        return !self.host_cache.lock().await.cache.is_default();
    }

    async 
    fn try_cache_resolve(&self) -> CDnsResult<Arc<ResolveConfig>>
    {
        let mut mutx_resolv = self.resolv_cache.lock().await;
        mutx_resolv.check_modified().await?;

        return Ok(mutx_resolv.clone_cache());
    }

    pub async 
    fn clone_resolve_list(&self) -> CDnsResult<Arc<ResolveConfig>>
    {
        // clone from cache and/or reload cache
        match self.try_cache_resolve().await
        {
            Ok(r) => return Ok(r),
            Err(e) => 
            {
                async_write_error!("{}", e);

                // try to read directly, this ignores all reload restrictions
                return CacheInstance::<ResolveConfig>::read_config().await;
            }
        }
    }

    async 
    fn try_cache_host(&self) -> CDnsResult<Arc<HostConfig>>
    {
        let mut mutx_host = self.host_cache.lock().await;
        mutx_host.check_modified().await?;

        return Ok(mutx_host.clone_cache());
    }

    pub async 
    fn clone_host_list(&self) -> CDnsResult<Arc<HostConfig>>
    {
        match self.try_cache_host().await
        {
            Ok(r) => return Ok(r),
            Err(e) =>
            {
                async_write_error!("{}", e);

                // try to read directly, this ignores all reload restrictions
                return CacheInstance::<HostConfig>::read_config().await;
            }
        }
    }
}


#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
async fn test_init()
{
    let res = CACHE.clone_resolve_list().await;
    assert_eq!(res.is_ok(), true, "{}", res.err().unwrap());

    let res = res.unwrap();

    println!("{:?}", res);

    let res = CACHE.clone_host_list().await;
    assert_eq!(res.is_ok(), true, "{}", res.err().unwrap());

    let res = res.unwrap();

    println!("{:?}", res);
}