#ifndef EMUGL_PROTOCOL_UTILS_H
#define EMUGL_PROTOCOL_UTILS_H

#include <stddef.h>
#include <stdint.h>

namespace emugl {

// Helper macro
#define COMPILE_ASSERT(cond)  static char kAssert##__LINE__[1 - 2 * !(cond)] __attribute__((unused)) = { 0 }

// Helper template: is_pointer.
// is_pointer<T>::value is true iff |T| is a pointer type.
template <typename T> struct is_pointer {
    static const bool value = false;
};

template <typename T> struct is_pointer<T*> {
    static const bool value = true;
};

// A helper template to extract values form the wire protocol stream
// and convert them to appropriate host values.
//
// The wire protocol uses 32-bit exclusively when transferring
// GLintptr or GLsizei values, as well as opaque handles like GLeglImage,
// from the guest (even when the guest is 64-bit).
//
// The corresponding host definitions depend on the host bitness. For
// example, GLintptr is 64-bit on linux-x86_64. The following is a set
// of templates that can simplify the conversion of protocol values
// into host ones.
//
// The most important one is:
//
//     unpack<HOST_TYPE,SIZE_TYPE>(const void* ptr)
//
// Which reads bytes from |ptr|, using |SIZE_TYPE| as the underlying
// sized-integer specifier (e.g. 'uint32_t'), and converting the result
// into a |HOST_TYPE| value. For example:
//
//     unpack<EGLImage,uint32_t>(ptr + 12);
//
// will read a 4-byte value from |ptr + 12| and convert it into
// an EGLImage, which is a host void*. The template detects host
// pointer types to perform proper type casting.
//
// TODO(digit): Add custom unpackers to handle generic opaque void* values.
//              and map them to unique 32-bit values.

template <typename T, typename S, bool IS_POINTER>
struct UnpackerT {};

template <typename T, typename S>
struct UnpackerT<T,S,false> {
    static inline T unpack(const void* ptr) {
        COMPILE_ASSERT(sizeof(T) == sizeof(S));
        return (T)(*(S*)(ptr));
    }
};

template <typename T, typename S>
struct UnpackerT<T,S,true> {
    static inline T unpack(const void* ptr) {
        return (T)(uintptr_t)(*(S*)(ptr));
    }
};

template <>
struct UnpackerT<float,uint32_t,false> {
    static inline float unpack(const void* ptr) {
        union {
            float f;
            uint32_t u;
        } v;
        v.u = *(uint32_t*)(ptr);
        return v.f;
    }
};

template <>
struct UnpackerT<double,uint64_t,false> {
    static inline double unpack(const void* ptr) {
        union {
            double d;
            uint32_t u;
        } v;
        v.u = *(uint64_t*)(ptr);
        return v.d;
    }
};

template <>
struct UnpackerT<ssize_t,uint32_t,false> {
    static inline ssize_t unpack(const void* ptr) {
        return (ssize_t)*(int32_t*)(ptr);
    }
};

template <typename T, typename S>
inline T Unpack(const void* ptr) {
    return UnpackerT<T, S, is_pointer<T>::value>::unpack(ptr);
}

}  // namespace emugl

#endif  // EMUGL_PROTOCOL_UTILS_H