/*
  Copyright 2019 Larry Gritz and the other authors and contributors.
  All Rights Reserved.

  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions are
  met:
  * Redistributions of source code must retain the above copyright
    notice, this list of conditions and the following disclaimer.
  * Redistributions in binary form must reproduce the above copyright
    notice, this list of conditions and the following disclaimer in the
    documentation and/or other materials provided with the distribution.
  * Neither the name of the software's owners nor the names of its
    contributors may be used to endorse or promote products derived from
    this software without specific prior written permission.
  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

  (This is the Modified BSD License)
*/


#pragma once

#include <memory>
#include <vector>

#include <OpenImageIO/export.h>
#include <OpenImageIO/string_view.h>
#include <OpenImageIO/typedesc.h>
#include <OpenImageIO/ustring.h>


OIIO_NAMESPACE_BEGIN


namespace pvt {

// Helper template to detect if a type is one if the string types that
// OIIO tends to use.
// clang-format off
template<typename T> struct is_string : std::false_type {};
template<> struct is_string<ustring> : std::true_type {};
template<> struct is_string<string_view> : std::true_type {};
template<> struct is_string<std::string> : std::true_type {};
// clang-format on

}  // namespace pvt



// AttrDelegate should not be used directly in user code!
//
// This is a helper template that allows the notation
//    Class object;
//    object["name"] = value;
// to work as a shorthand for
//    object.attribute ("name", TypeDesc_of_value, &value);
// and for
//    value = object["name"].get<type>();
// to work as a shorthand for extracting the named attribute via
// object.getattribute() and assigning it to the result.
//
// Basically, the class in question needs to posess these three methods,
// working in the usual idiomatic way for OIIO:
//
//      void attribute (string_view name, TypeDesc type, void* data);
//      bool getattribute (string_view name, TypeDesc type, void *data);
//      TypeDesc getattributetype (string_view name);
//
// Then the array access notation can be added with the following members
// of the class C:
//
//     AttrDelegate<const C> operator[](string_view name) const
//     {
//         return { this, name };
//     }
//     AttrDelegate<C> operator[](string_view name) {
//         return { this, name };
//     }
//
// This allows the following convenient notation:
//
// 1. Adding attributes, type implied by the C++ type of what's assigned:
//        C obj;
//        obj["foo"] = 42;       // adds integer
//        obj["bar"] = 39.8f;    // adds float
//        obj["baz"] = "hello";  // adds string
// 2. Retrieving attributes:
//         int i = obj["foo"].get<int>();
//         float f = obj["bar"].get<float>();
//         std::string s = obj["baz"].get<std::string>();
//    If the object does not posess an attribute of that name (and/or of
//    that type), it will instead return the default value for that type.
//    A specific default value override may be provided as an argument to
//    the get() method:
//         float aspect = obj["aspectratio"].get<float>(1.0f);
//

template<class C> class AttrDelegate {
public:
    AttrDelegate(C* obj, string_view name)
        : m_obj(obj)
        , m_name(name)
        , m_readonly(std::is_const<C>::value)
    {
    }

    // Assignment to a delegate should copy the value into an attribute,
    // calling attribute(name,typedesc,&data). Except for strings, which are
    // handled separately.
    template<typename T,
             typename std::enable_if<!pvt::is_string<T>::value, int>::type = 0>
    inline const T& operator=(const T& val)
    {
        if (!m_readonly)
            const_cast<C*>(m_obj)->attribute(m_name, TypeDescFromC<T>::value(),
                                             &val);
        return val;
    }

    // String types are a special case because we don't directly copy their
    // data, instead call the attribute(name,string_view) variant.
    template<typename T,
             typename std::enable_if<pvt::is_string<T>::value, int>::type = 1>
    inline const T& operator=(const T& val)
    {
        if (!m_readonly)
            const_cast<C*>(m_obj)->attribute(m_name, string_view(val));
        return val;
    }
    // char arrays are special
    inline const char* operator=(const char* val)
    {
        if (!m_readonly)
            const_cast<C*>(m_obj)->attribute(m_name, string_view(val));
        return val;
    }


    // `Delegate->type()` returns the TypeDesc describing the data, or
    // TypeUnknown if no such attribute exists.
    TypeDesc type() const { return m_obj->getattributetype(m_name); }

    // `Delegate->get<T>(defaultval=T())` retrieves the data as type T,
    // or the defaultval if no such named data exists or is not the
    // designated type.
    template<typename T,
             typename std::enable_if<!pvt::is_string<T>::value, int>::type = 0>
    inline T get(const T& defaultval = T()) const
    {
        T result;
        if (!m_obj->getattribute(m_name, TypeDescFromC<T>::value(), &result))
            result = defaultval;
        return result;
    }

    // Using enable_if, make a slightly different version of get<> for
    // strings, which need to do some ustring magic because we can't
    // directly store in a std::string or string_view.
    template<typename T,
             typename std::enable_if<pvt::is_string<T>::value, int>::type = 1>
    inline T get(const T& defaultval = T()) const
    {
        ustring s;
        return m_obj->getattribute(m_name, TypeString, &s) ? T(s.string())
                                                           : defaultval;
    }

    // `Delegate->as_string(defaultval="")` returns the data, no matter its
    // type, as a string. Returns the defaultval if no such data exists at
    // all.
    inline std::string as_string(const std::string& defaultval = std::string())
    {
        std::string s;
        TypeDesc t = m_obj->getattributetype(m_name);
        if (t == TypeString) {  // Attrib is a string? Return it.
            s = get<std::string>();
        } else if (t != TypeUnknown) {  // Non-string attrib? Convert.
            const int localsize = 64;   // Small types copy to stack, avoid new
            char localbuffer[localsize];
            char* buffer = localbuffer;
            std::unique_ptr<char[]> allocbuffer;
            if (t.size() > localsize) {
                allocbuffer.reset(new char[t.size()]);
                buffer = allocbuffer.get();
            }
            if (m_obj->getattribute(m_name, t, buffer))
                s = tostring(t, buffer);
            else
                s = defaultval;
        } else {  // No attrib? Return default.
            s = defaultval;
        }
        return s;
    }

    // Allow direct assignment to string, equivalent to calling as_string().
    inline operator std::string() { return as_string(); }

protected:
    C* m_obj;
    string_view m_name;
    bool m_readonly = false;
};


OIIO_NAMESPACE_END