// file      : odb/cache-traits.hxx
// copyright : Copyright (c) 2009-2012 Code Synthesis Tools CC
// license   : GNU GPL v2; see accompanying LICENSE file

#ifndef ODB_CACHE_TRAITS_HXX
#define ODB_CACHE_TRAITS_HXX

#include <odb/pre.hxx>

#include <odb/traits.hxx>
#include <odb/forward.hxx>
#include <odb/session.hxx>
#include <odb/pointer-traits.hxx>

namespace odb
{
  // pointer_cache_type
  //
  // Used to convert an object pointer to the canonical form (non-const),
  // suitable for insertion into the cache.
  //
  template <typename P,
            typename E = typename pointer_traits<P>::element_type,
            typename O = typename object_traits<E>::object_type,
            pointer_kind pk = pointer_traits<P>::kind>
  struct pointer_cache_type
  {
    typedef typename object_traits<O>::pointer_type pointer_type;

    static pointer_type
    convert (const P& p)
    {
      return pointer_traits<P>::const_pointer_cast (p);
    }
  };

  template <typename P, typename T, pointer_kind pk>
  struct pointer_cache_type<P, T, T, pk>
  {
    // If element_type and object_type are the same, then it is already
    // the canonical pointer.
    //
    static const P&
    convert (const P& p) {return p;}
  };

  template <typename P, typename E, typename O>
  struct pointer_cache_type<P, E, O, pk_unique>
  {
    // If the pointer is unique, then casting it can transfer ownership.
    // So return null pointer, which will be ignored down the chain.
    //
    typedef typename object_traits<O>::pointer_type pointer_type;

    static pointer_type
    convert (const P&) {return pointer_type ();}
  };

  template <typename P, typename T>
  struct pointer_cache_type<P, T, T, pk_unique>
  {
    typedef typename object_traits<T>::pointer_type pointer_type;

    static pointer_type
    convert (const P&) {return pointer_type ();}
  };

  // reference_cache_type
  //
  // Used to convert an object reference to the canonical form (non-const),
  // suitable for insertion into the cache.
  //
  template <typename T,
            typename O = typename object_traits<T>::object_type>
  struct reference_cache_type
  {
    static O&
    convert (T& r)
    {
      return const_cast<O&> (r);
    }
  };

  template <typename T>
  struct reference_cache_type<T, T>
  {
    // If the types are the same, then it is already the canonical form.
    //
    static T&
    convert (T& r) {return r;}
  };

  // pointer_cache_traits
  //
  // Caching traits for objects passed by pointer. P should be the canonical
  // pointer (non-const).
  //
  template <typename P>
  struct no_id_pointer_cache_traits
  {
    typedef P pointer_type;
    struct position_type {};

    static position_type
    insert (odb::database&, const pointer_type&)
    {
      return position_type ();
    }
  };

  template <typename P>
  struct no_op_pointer_cache_traits
  {
    typedef P pointer_type;
    typedef typename pointer_traits<pointer_type>::element_type object_type;
    typedef typename object_traits<object_type>::id_type id_type;
    struct position_type {};

    struct insert_guard
    {
      insert_guard () {}
      insert_guard (const position_type&) {}

      position_type
      position () const {return position_type ();}

      void
      release () {}

      void
      reset (const position_type&) {}
    };

    static position_type
    insert (odb::database&, const id_type&, const pointer_type&)
    {
      return position_type ();
    }

    static position_type
    insert (odb::database&, const pointer_type&) {return position_type ();}

    static pointer_type
    find (odb::database&, const id_type&) {return pointer_type ();}

    static void
    erase (odb::database&, const id_type&) {}

    static void
    erase (const position_type&) {}
  };

  template <typename P, pointer_kind pk>
  struct pointer_cache_traits_impl
  {
    typedef P pointer_type;
    typedef odb::pointer_traits<pointer_type> pointer_traits;
    typedef typename pointer_traits::element_type object_type;
    typedef typename object_traits<object_type>::id_type id_type;
    typedef session::object_position<object_type> position_type;

    struct insert_guard
    {
      insert_guard () {}
      insert_guard (const position_type& pos): pos_ (pos) {}
      ~insert_guard () {erase (pos_);}

      position_type
      position () const {return pos_;}

      void
      release () {pos_.map_ = 0;}

      // Note: doesn't call erase() on the old position (assumes not set).
      //
      void
      reset (const position_type& pos) {pos_ = pos;}

    private:
      position_type pos_;
    };

    // We need the insert() overload with explicit id to handle self-
    // references. In such cases the object is not yet loaded and the
    // id member does not contain the correct id.
    //
    // Qualify the database type to resolve a phony ambiguity in VC 10.
    //
    static position_type
    insert (odb::database& db, const id_type& id, const pointer_type& p)
    {
      if (session::has_current ())
        return session::current ().insert<object_type> (db, id, p);
      else
        return position_type ();
    }

    static position_type
    insert (odb::database& db, const pointer_type& p)
    {
      const id_type& id (
        object_traits<object_type>::id (
          pointer_traits::get_ref (p)));

      return insert (db, id, p);
    }

    static pointer_type
    find (odb::database& db, const id_type& id)
    {
      if (session::has_current ())
        return session::current ().find<object_type> (db, id);
      else
        return pointer_type ();
    }

    static void
    erase (odb::database& db, const id_type& id)
    {
      if (session::has_current ())
        session::current ().erase<object_type> (db, id);
    }

    static void
    erase (const position_type& p)
    {
      if (p.map_ != 0)
        session::current ().erase<object_type> (p);
    }
  };

  // Unique pointers don't work with the object cache.
  //
  template <typename P>
  struct pointer_cache_traits_impl<P, pk_unique>:
    no_op_pointer_cache_traits<P> {};

  template <typename P>
  struct pointer_cache_traits:
    pointer_cache_traits_impl<P, pointer_traits<P>::kind> {};

  // reference_cache_traits
  //
  // Caching traits for objects passed by reference. T should be the
  // canonical object type (non-const). Only if the object pointer
  // kind is raw do we add the object to the session.
  //
  template <typename T>
  struct no_id_reference_cache_traits
  {
    typedef T object_type;
    struct position_type {};

    static position_type
    insert (odb::database&, object_type&)
    {
      return position_type ();
    }
  };

  template <typename T>
  struct no_op_reference_cache_traits
  {
    typedef T object_type;
    typedef typename object_traits<object_type>::id_type id_type;
    struct position_type {};

    struct insert_guard
    {
      insert_guard () {}
      insert_guard (const position_type&) {}

      position_type
      position () const {return position_type ();}

      void
      release () {}

      void
      reset () {}
    };

    static position_type
    insert (odb::database&, const id_type&, object_type&)
    {
      return position_type ();
    }

    static position_type
    insert (odb::database&, object_type&)
    {
      return position_type ();
    }
  };

  template <typename T, pointer_kind pk>
  struct reference_cache_traits_impl: no_op_reference_cache_traits<T> {};

  template <typename T>
  struct reference_cache_traits_impl<T, pk_raw>
  {
    typedef T object_type;
    typedef typename object_traits<object_type>::pointer_type pointer_type;
    typedef typename object_traits<object_type>::id_type id_type;

    typedef pointer_cache_traits<pointer_type> pointer_traits;
    typedef typename pointer_traits::position_type position_type;
    typedef typename pointer_traits::insert_guard insert_guard;

    static position_type
    insert (odb::database& db, const id_type& id, object_type& obj)
    {
      pointer_type p (&obj);
      return pointer_traits::insert (db, id, p);
    }

    static position_type
    insert (odb::database& db, object_type& obj)
    {
      pointer_type p (&obj);
      return pointer_traits::insert (db, p);
    }
  };

  template <typename T>
  struct reference_cache_traits:
    reference_cache_traits_impl<
    T, pointer_traits<typename object_traits<T>::pointer_type>::kind> {};
}

#include <odb/post.hxx>

#endif // ODB_CACHE_TRAITS_HXX