#pragma once

#include <mbgl/gl/types.hpp>
#include <mbgl/gl/segment.hpp>
#include <mbgl/util/ignore.hpp>
#include <mbgl/util/indexed_tuple.hpp>
#include <mbgl/util/variant.hpp>

#include <cstddef>
#include <vector>
#include <set>
#include <functional>

namespace mbgl {
namespace gl {

class DisabledAttribute {
public:
    void bind(Context&, AttributeLocation, std::size_t vertexOffset) const;

    friend bool operator==(const DisabledAttribute&,
                           const DisabledAttribute&) {
        return true;
    }
};

template <class T, std::size_t N>
class AttributeBinding {
public:
    AttributeBinding(BufferID vertexBuffer_,
                     std::size_t vertexSize_,
                     std::size_t attributeOffset_,
                     std::size_t attributeSize_ = N)
        : vertexBuffer(vertexBuffer_),
          vertexSize(vertexSize_),
          attributeOffset(attributeOffset_),
          attributeSize(attributeSize_)
        {}

    void bind(Context&, AttributeLocation, std::size_t vertexOffset) const;

    friend bool operator==(const AttributeBinding& lhs,
                           const AttributeBinding& rhs) {
        return lhs.vertexBuffer == rhs.vertexBuffer
            && lhs.vertexSize == rhs.vertexSize
            && lhs.attributeOffset == rhs.attributeOffset
            && lhs.attributeSize == rhs.attributeSize;
    }

private:
    BufferID vertexBuffer;
    std::size_t vertexSize;
    std::size_t attributeOffset;
    std::size_t attributeSize;
};

/*
    gl::Attribute<T,N> manages the binding of a vertex buffer to a GL program attribute.
      - T is the underlying primitive type (exposed as Attribute<T,N>::ValueType)
      - N is the number of components in the attribute declared in the shader (exposed as Attribute<T,N>::Dimensions)
*/
template <class T, std::size_t N>
class Attribute {
public:
    using ValueType = T;
    static constexpr size_t Dimensions = N;
    using Value = std::array<T, N>;

    using Location = AttributeLocation;

    using Binding = variant<
        DisabledAttribute,
        AttributeBinding<T, N>>;

    /*
        Create a binding for this attribute.  The `attributeSize` parameter may be used to
        override the number of components available in the buffer for each vertex.  Thus,
        a buffer with only one float for each vertex can be bound to a `vec2` attribute
    */
    template <class Vertex, class DrawMode>
    static Binding binding(const VertexBuffer<Vertex, DrawMode>& buffer,
                           std::size_t attributeIndex,
                           std::size_t attributeSize = N) {
        static_assert(std::is_standard_layout<Vertex>::value, "vertex type must use standard layout");
        return AttributeBinding<T, N> {
            buffer.buffer,
            sizeof(Vertex),
            Vertex::attributeOffsets[attributeIndex],
            attributeSize
        };
    }

    static void bind(Context& context,
                     const Location& location,
                     Binding& oldBinding,
                     const Binding& newBinding,
                     std::size_t vertexOffset) {
        if (oldBinding == newBinding) {
            return;
        }

        Binding::visit(newBinding, [&] (const auto& binding) {
            binding.bind(context, location, vertexOffset);
        });

        oldBinding = newBinding;
    }
};

#define MBGL_DEFINE_ATTRIBUTE(type_, n_, name_)        \
    struct name_ {                                     \
        static auto name() { return #name_; }          \
        using Type = ::mbgl::gl::Attribute<type_, n_>; \
    }

namespace detail {

// Attribute binding requires member offsets. The only standard way to
// obtain an offset is the offsetof macro. The offsetof macro has defined
// behavior only for standard layout types. That rules out std::tuple and
// any other solution that relies on chained inheritance. Manually implemented
// variadic specialization looks like the only solution. Fortunately, we
// only use a maximum of five attributes.

template <class... As>
class Vertex;

template <>
class Vertex<> {
public:
    using VertexType = Vertex<>;
};

template <class A1>
class Vertex<A1> {
public:
    typename A1::Value a1;

    using VertexType = Vertex<A1>;
    static const std::size_t attributeOffsets[1];
};

template <class A1, class A2>
class Vertex<A1, A2> {
public:
    typename A1::Value a1;
    typename A2::Value a2;

    using VertexType = Vertex<A1, A2>;
    static const std::size_t attributeOffsets[2];
};

template <class A1, class A2, class A3>
class Vertex<A1, A2, A3> {
public:
    typename A1::Value a1;
    typename A2::Value a2;
    typename A3::Value a3;

    using VertexType = Vertex<A1, A2, A3>;
    static const std::size_t attributeOffsets[3];
};

template <class A1, class A2, class A3, class A4>
class Vertex<A1, A2, A3, A4> {
public:
    typename A1::Value a1;
    typename A2::Value a2;
    typename A3::Value a3;
    typename A4::Value a4;

    using VertexType = Vertex<A1, A2, A3, A4>;
    static const std::size_t attributeOffsets[4];
};

template <class A1, class A2, class A3, class A4, class A5>
class Vertex<A1, A2, A3, A4, A5> {
public:
    typename A1::Value a1;
    typename A2::Value a2;
    typename A3::Value a3;
    typename A4::Value a4;
    typename A5::Value a5;

    using VertexType = Vertex<A1, A2, A3, A4, A5>;
    static const std::size_t attributeOffsets[5];
};

template <class A1>
const std::size_t Vertex<A1>::attributeOffsets[1] = {
    offsetof(VertexType, a1)
};

template <class A1, class A2>
const std::size_t Vertex<A1, A2>::attributeOffsets[2] = {
    offsetof(VertexType, a1),
    offsetof(VertexType, a2)
};

template <class A1, class A2, class A3>
const std::size_t Vertex<A1, A2, A3>::attributeOffsets[3] = {
    offsetof(VertexType, a1),
    offsetof(VertexType, a2),
    offsetof(VertexType, a3)
};

template <class A1, class A2, class A3, class A4>
const std::size_t Vertex<A1, A2, A3, A4>::attributeOffsets[4] = {
    offsetof(VertexType, a1),
    offsetof(VertexType, a2),
    offsetof(VertexType, a3),
    offsetof(VertexType, a4)
};

template <class A1, class A2, class A3, class A4, class A5>
const std::size_t Vertex<A1, A2, A3, A4, A5>::attributeOffsets[5] = {
    offsetof(VertexType, a1),
    offsetof(VertexType, a2),
    offsetof(VertexType, a3),
    offsetof(VertexType, a4),
    offsetof(VertexType, a5)
};

} // namespace detail

AttributeLocation bindAttributeLocation(ProgramID, AttributeLocation, const char * name);
std::set<std::string> getActiveAttributes(ProgramID);

template <class... As>
class Attributes {
public:
    using Types = TypeList<As...>;
    using Locations = IndexedTuple<
        TypeList<As...>,
        TypeList<typename As::Type::Location...>>;
    using Bindings = IndexedTuple<
        TypeList<As...>,
        TypeList<typename As::Type::Binding...>>;
    using NamedLocations = std::vector<std::pair<const std::string, AttributeLocation>>;

    using Vertex = detail::Vertex<typename As::Type...>;

    template <class A>
    static constexpr std::size_t Index = TypeIndex<A, As...>::value;

    static Locations bindLocations(const ProgramID& id) {
        std::set<std::string> activeAttributes = getActiveAttributes(id);

        AttributeLocation location = -1;
        auto bindAndIncrement = [&](const char* name) {
            location++;
            return bindAttributeLocation(id, location, name);
        };
        return Locations{ (activeAttributes.count(As::name()) ? bindAndIncrement(As::name())
                                                              : -1)... };
    }

    template <class Program>
    static Locations loadNamedLocations(const Program& program) {
        return Locations{ program.attributeLocation(As::name())... };
    }

    static NamedLocations getNamedLocations(const Locations& locations) {
        return NamedLocations{ { As::name(), locations.template get<As>() }... };
    }

    template <class DrawMode>
    static Bindings bindings(const VertexBuffer<Vertex, DrawMode>& buffer) {
        return Bindings { As::Type::binding(buffer, Index<As>)... };
    }

    static void bind(Context& context,
                     const Locations& locations,
                     Bindings& oldBindings,
                     const Bindings& newBindings,
                     std::size_t vertexOffset) {
        util::ignore({ (As::Type::bind(context,
                                       locations.template get<As>(),
                                       oldBindings.template get<As>(),
                                       newBindings.template get<As>(),
                                       vertexOffset), 0)... });
    }
};

namespace detail {

template <class...>
struct ConcatenateAttributes;

template <class... As, class... Bs>
struct ConcatenateAttributes<TypeList<As...>, TypeList<Bs...>> {
    using Type = Attributes<As..., Bs...>;
};

} // namespace detail

template <class A, class B>
using ConcatenateAttributes = typename detail::ConcatenateAttributes<
    typename A::Types,
    typename B::Types>::Type;

} // namespace gl
} // namespace mbgl