/++
Implementation templates for new Godot-D native scripts
+/
module godot.api.script;

import std.meta, std.traits;
import std.experimental.allocator, std.experimental.allocator.mallocator;
import core.stdc.stdlib : malloc, free;

import godot.abi, godot;
import godot.api.udas;
import godot.api.traits, godot.api.wrap;
import godot.api.reference;

/++
Base class for D native scripts. Native script instances will be attached to a
Godot (C++) object of Base class.
+/
class GodotScript(Base) if (isGodotBaseClass!Base) {
    Base owner;
    alias owner this;

    pragma(inline, true)
    inout(To) as(To)() inout if (isGodotBaseClass!To) {
        static assert(extends!(Base, To), typeof(this).stringof ~ " does not extend " ~ To.stringof);
        return cast(inout(To))(owner.getGDExtensionObject);
    }

    pragma(inline, true)
    inout(To) as(To, this From)() inout if (extendsGodotBaseClass!To) {
        static assert(extends!(From, To) || extends!(To, From), From.stringof ~
                " is not polymorphic to " ~ To.stringof);
        return opCast!To(); // use D dynamic cast
    }

    ///
    pragma(inline, true)
    bool opEquals(T, this This)(in T other) const 
            if (extends!(T, This) || extends!(This, T)) {
        static if (extendsGodotBaseClass!T)
            return this is other;
        else {
            const void* a = owner._godot_object.ptr, b = other._godot_object.ptr;
            return a is b;
        }
    }
    ///
    pragma(inline, true)
    int opCmp(T)(in T other) const if (isGodotClass!T) {
        const void* a = owner._godot_object.ptr, b = other.getGodotObject._godot_object.ptr;
        return a is b ? 0 : a < b ? -1 : 1;
    }

    //@disable new(size_t s);

    /// HACK to work around evil bug in which cast(void*) invokes `alias this`
    /// https://issues.dlang.org/show_bug.cgi?id=6777
    void* opCast(T : void*)() {
        import std.traits;

        alias This = typeof(this);
        static assert(!is(Unqual!This == Unqual!Base));
        union U {
            void* ptr;
            This c;
        }

        U u;
        u.c = this;
        return u.ptr;
    }

    const(void*) opCast(T : const(void*))() const {
        import std.traits;

        alias This = typeof(this);
        static assert(!is(Unqual!This == Unqual!Base));
        union U {
            const(void*) ptr;
            const(This) c;
        }

        U u;
        u.c = this;
        return u.ptr;
    }
}

package(godot) void initialize(T)(T t) if (extendsGodotBaseClass!T) {
    import godot.node;

    template isOnInit(string memberName) {
        static if (__traits(getProtection, __traits(getMember, T, memberName)) == "public")
            enum bool isOnInit = hasUDA!(__traits(getMember, T, memberName), OnInit);
        else
            enum bool isOnInit = false;
    }

    foreach (n; Filter!(isOnInit, FieldNameTuple!T)) {
        alias M = typeof(mixin("t." ~ n));
        static assert(getUDAs!(mixin("t." ~ n), OnInit).length == 1, "Multiple OnInits on "
                ~ T.stringof ~ "." ~ n);

        enum OnInit raii = is(getUDAs!(mixin("t." ~ n), OnInit)[0]) ?
            OnInit.makeDefault!(M, T)() : getUDAs!(mixin("t." ~ n), OnInit)[0];

        static if (raii.autoCreate) {
            mixin("t." ~ n) = memnew!M();
            static if (raii.autoAddChild && OnInit.canAddChild!(M, T)) {
                t.owner.addChild(mixin("t." ~ n).getGodotObject);
            }
        }
    }

    // call _init
    foreach (mf; godotMethods!T) {
        enum string funcName = godotName!mf;
        alias Args = Parameters!mf;
        static if (funcName == "_init" && Args.length == 0)
            t._init();
    }
}

package(godot) void finalize(T)(T t) if (extendsGodotBaseClass!T) {
}

/++
Generic null check for all Godot classes. Limitations in D prevent using `is null`
on Godot base classes because they're really struct wrappers.
+/
@nogc nothrow pragma(inline, true)
bool isNull(T)(in T t) if (isGodotClass!T) {
    static if (extendsGodotBaseClass!T)
        return t is null;
    else
        return t._godot_object.ptr is null;
}

/++
Allocate a new T and attach it to a new Godot object.
+/
RefOrT!T memnew(T)() if (extendsGodotBaseClass!T) {
    import godot.refcounted;

    // NOTE: Keep in sync with register.d register(T) template
    static if (hasUDA!(T, Rename))
        enum string name = godotName!T;
    else 
        enum string name = __traits(identifier, T);

    //GodotClass!T o = GodotClass!T._new();
    auto snName = StringName(name);
    auto obj = _godot_api.classdb_construct_object(cast(GDExtensionStringNamePtr) snName);
    assert(obj !is null);

    T o = cast(T) _godot_api.object_get_instance_binding(obj, _GODOT_library, &_instanceCallbacks);
    //static if(extends!(T, RefCounted))
    //{
    //	bool success = o.initRef();
    //	assert(success, "Failed to init refcount");
    //}
    // Set script and let Object create the script instance
    //o.setScript(NativeScriptTemplate!T);
    // Skip typecheck in release; should always be T
    //assert(o.as!T);
    //T t = cast(T)_godot_nativescript_api.godot_nativescript_get_userdata(o._godot_object);
    //T t = cast(T) &o._godot_object;
    return refOrT(o);
}

RefOrT!T memnew(T)() if (isGodotBaseClass!T) {
    import godot.refcounted;

    /// FIXME: block those that aren't marked instanciable in API JSON (actually a generator bug)
    T t = T._new();
    static if (extends!(T, RefCounted)) {
        bool success = t.initRef();
        assert(success, "Failed to init refcount");
    }
    return refOrT(t); /// TODO: remove _new and use only this function?
}

void memdelete(T)(T t) if (isGodotClass!T) {
    _godot_api.object_destroy(t.getGDExtensionObject.ptr);
}

package(godot) extern (C) __gshared GDExtensionInstanceBindingCallbacks _instanceCallbacks = {
    &___binding_create_callback,
    &___binding_free_callback,
    &___binding_reference_callback
};

extern (C) static void* ___binding_create_callback(void* p_token, void* p_instance) {
    return null;
}

extern (C) static void ___binding_free_callback(void* p_token, void* p_instance, void* p_binding) {
}

extern (C) static GDExtensionBool ___binding_reference_callback(void* p_token, void* p_instance, GDExtensionBool p_reference) {
    return cast(GDExtensionBool) true;
}

extern (C) package(godot) void* createFunc(T)(void* data) //nothrow @nogc
{
    import std.conv;

    static assert(is(T == class));
    static assert(__traits(compiles, new T()), "script class " ~ T.stringof ~ " must have default constructor");
    static import godot;

    import std.exception;
    import godot.api.register : _GODOT_library;

    // NOTE: Keep in sync with register.d register(T) template
    static if (hasUDA!(T, Rename))
        enum string name = godotName!T;
    else 
        enum string name = __traits(identifier, T);

    T t = cast(T) _godot_api.mem_alloc(__traits(classInstanceSize, T));

    emplace(t);
    // class must have default ctor to be properly initialized
    // t.__ctor();

    //static if(extendsGodotBaseClass!T)
    {
        StringName classname = name;
        StringName snInternalName = (GodotClass!T)._GODOT_internal_name;
        if (!t.owner._godot_object.ptr)
            t.owner._godot_object.ptr = _godot_api.classdb_construct_object(cast(GDExtensionStringNamePtr) snInternalName);
        _godot_api.object_set_instance(cast(void*) t.owner._godot_object.ptr, cast(GDExtensionStringNamePtr) classname, cast(
                void*) t);
    }
    //else
    //	t.owner._godot_object.ptr = cast(void*) t;
    godot.initialize(t);

    _godot_api.object_set_instance_binding(cast(void*) t.owner._godot_object.ptr, _GODOT_library, cast(
            void*) t, &_instanceCallbacks);

    return cast(void*) t.owner._godot_object.ptr;
}

extern (C) package(godot) void destroyFunc(T)(void* userData, void* instance) //nothrow @nogc
{
    static import godot;

    T t = cast(T) instance;
    godot.finalize(t);
    _godot_api.mem_free(cast(void*) t);
    //Mallocator.instance.dispose(t);
}