/// Internal namespace.
pub( crate ) mod private
{
  use crate::*;
  use crate::abs::*;
  use once_cell::sync::Lazy;
  use std::sync::Mutex;
  use dashmap::DashMap;
  use std::sync::Arc;

  /// Registry of contexts.
  #[ derive( Debug ) ]
  pub struct Registry< Context >
  where
    Context : ContextInterface,
  {
    contexts : DashMap< Id, Context >,
    contexts_with_name : DashMap< String, Id >,
    current_context_name : Option< String >,
  }

  impl< Context > Registry< Context >
  where
    Context : ContextInterface,
  {

    /// Static constructor.
    pub const fn new() -> Lazy< Arc< Mutex< Registry< Context > > > >
    {
      Lazy::new( ||
      {
        let contexts = DashMap::new();
        let contexts_with_name = DashMap::new();
        let current_context_name = None;
        Arc::new( Mutex::new( Registry::< Context >
        {
          contexts,
          contexts_with_name,
          current_context_name,
        }))
      })
    }

    // /// Get current context or crate a new one if it does not exist.
    // pub fn current( _registry : &mut Lazy< Arc< Mutex< Registry< Context > > > > ) -> Context::Changer
    // {
    //   // unsafe
    //   // {
    //     let registry = _registry.lock().unwrap();
    //     let current_name : Option< String > = registry.current_context_name.clone();
    //     /* xxx : redo */
    //     if current_name.is_none()
    //     {
    //       drop( registry );
    //       Self::obtain( _registry )
    //     }
    //     else
    //     {
    //       let id = *registry.contexts_with_name.get( &current_name.unwrap() ).unwrap().value();
    //       // registry.contexts.get_mut( &id ).unwrap().value_mut();
    //       registry.contexts.get_mut( &id ).unwrap().value_mut().changer()
    //     }
    //   // }
    // }

    /// Construct a new context.
    pub fn current( _registry : &mut Lazy< Arc< Mutex< Registry< Context > > > >  ) -> Context::Changer
    {
      // unsafe
      // {
        let registry = _registry.lock().unwrap();
        let mut current_name : Option< String > = registry.current_context_name.clone();
        if current_name.is_none()
        {
          current_name = Some( "default".into() )
        }
        let current_name = current_name.unwrap();
        if registry.contexts_with_name.contains_key( &current_name )
        {
          let id = *registry.contexts_with_name.get( &current_name ).unwrap().value();
          registry.contexts.get_mut( &id ).unwrap().value_mut().changer()
        }
        else
        {
          let context : Context = make!();
          let id = context.id();
          registry.contexts_with_name.insert( current_name.clone(), context.id() );
          registry.contexts.insert( id, context );
          registry.contexts.get_mut( &id ).unwrap().value_mut().changer()
        }
      // }
    }

  }

  // static mut REGISTRY : Lazy< Arc< Mutex< Registry > > > = Lazy::new( ||
  // {
  //   let contexts = DashMap::new();
  //   let contexts_with_name = DashMap::new();
  //   let current_context_name = None;
  //   Arc::new( Mutex::new( Registry
  //   {
  //     contexts,
  //     contexts_with_name,
  //     current_context_name,
  //   }))
  // });
//
//   /// Get current context or crate a new one if it does not exist.
//   pub fn current< Context : ContextInterface >() -> ContextChanger
//   {
//     unsafe
//     {
//       let registry = REGISTRY.lock().unwrap();
//       let current_name : Option< String > = registry.current_context_name.clone();
//       /* xxx : redo */
//       if current_name.is_none()
//       {
//         drop( registry );
//         obtain::< Context >()
//       }
//       else
//       {
//         let id = *registry.contexts_with_name.get( &current_name.unwrap() ).unwrap().value();
//         registry.contexts.get( &id ).unwrap().value().changer()
//       }
//     }
//   }
//
//   /// Construct a new context.
//   pub fn obtain< Context : ContextInterface >() -> ContextChanger
//   {
//     unsafe
//     {
//       let registry = REGISTRY.lock().unwrap();
//       let mut current_name : Option< String > = registry.current_context_name.clone();
//       if current_name.is_none()
//       {
//         current_name = Some( "default".into() )
//       }
//       let current_name = current_name.unwrap();
//       if registry.contexts_with_name.contains_key( &current_name )
//       {
//         let id = *registry.contexts_with_name.get( &current_name ).unwrap().value();
//         registry.contexts.get( &id ).unwrap().value().changer()
//       }
//       else
//       {
//         let context : Context = make!();
//         let id = context.id();
//         registry.contexts_with_name.insert( current_name.clone(), context.id() );
//         registry.contexts.insert( id, context );
//         registry.contexts.get( &id ).unwrap().value().changer()
//       }
//     }
//   }

}

/// Protected namespace of the module.
pub mod protected
{
  pub use super::
  {
    orphan::*,
    // private::current,
    // private::obtain,
    // private:: Registry,
  };
}

pub use protected::*;

/// Parented namespace of the module.
pub mod orphan
{
  pub use super::
  {
    exposed::*,
    private:: Registry,
  };
}

/// Exposed namespace of the module.
pub mod exposed
{
  pub use super::
  {
    prelude::*,
    // private::current as context,
  };
}

pub use exposed::*;

/// Prelude to use essentials: `use my_module::prelude::*`.
pub mod prelude
{
  pub use super::private::
  {
  };
}