/*
 * Copyright 2018-2020 Justas Masiulis
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

 // documentation is available at https://github.com/JustasMasiulis/lazy_importer

#ifndef LAZY_IMPORTER_HPP
#define LAZY_IMPORTER_HPP

#define LI_FN(name) \
    ::li::detail::lazy_function<::li::detail::khash(#name), decltype(&name)>()

#define LI_FN_DEF(name) ::li::detail::lazy_function<::li::detail::khash(#name), name>()

#define LI_MODULE(name) ::li::detail::lazy_module<::li::detail::khash(name)>()



// NOTE only std::forward is used from this header.
// If there is a need to eliminate this dependency the function itself is very small.
#include <utility>
#include <cstddef>
#include <intrin.h>

#ifndef LAZY_IMPORTER_NO_FORCEINLINE
#if defined(_MSC_VER)
#define LAZY_IMPORTER_FORCEINLINE __forceinline
#elif defined(__GNUC__) && __GNUC__ > 3
#define LAZY_IMPORTER_FORCEINLINE inline __attribute__((__always_inline__))
#else
#define LAZY_IMPORTER_FORCEINLINE inline
#endif
#else
#define LAZY_IMPORTER_FORCEINLINE inline
#endif

#ifdef LAZY_IMPORTER_CASE_INSENSITIVE
#define LAZY_IMPORTER_TOLOWER(c) (c >= 'A' && c <= 'Z' ? (c | (1 << 5)) : c)
#else
#define LAZY_IMPORTER_TOLOWER(c) (c)
#endif

namespace li {
    namespace detail {

        template<class First, class Second>
        struct pair {
            First  first;
            Second second;
        };

        namespace win {

            struct LIST_ENTRY_T {
                const char* Flink;
                const char* Blink;
            };

            struct UNICODE_STRING_T {
                unsigned short Length;
                unsigned short MaximumLength;
                wchar_t* Buffer;
            };

            struct PEB_LDR_DATA_T {
                unsigned long Length;
                unsigned long Initialized;
                const char* SsHandle;
                LIST_ENTRY_T  InLoadOrderModuleList;
            };

            struct PEB_T {
                unsigned char   Reserved1[2];
                unsigned char   BeingDebugged;
                unsigned char   Reserved2[1];
                const char* Reserved3[2];
                PEB_LDR_DATA_T* Ldr;
            };

            struct LDR_DATA_TABLE_ENTRY_T {
                LIST_ENTRY_T InLoadOrderLinks;
                LIST_ENTRY_T InMemoryOrderLinks;
                LIST_ENTRY_T InInitializationOrderLinks;
                const char* DllBase;
                const char* EntryPoint;
                union {
                    unsigned long SizeOfImage;
                    const char* _dummy;
                };
                UNICODE_STRING_T FullDllName;
                UNICODE_STRING_T BaseDllName;

                LAZY_IMPORTER_FORCEINLINE const LDR_DATA_TABLE_ENTRY_T*
                    load_order_next() const noexcept
                {
                    return reinterpret_cast<const LDR_DATA_TABLE_ENTRY_T*>(
                        InLoadOrderLinks.Flink);
                }
            };

            struct IMAGE_DOS_HEADER { // DOS .EXE header
                unsigned short e_magic; // Magic number
                unsigned short e_cblp; // Bytes on last page of file
                unsigned short e_cp; // Pages in file
                unsigned short e_crlc; // Relocations
                unsigned short e_cparhdr; // Size of header in paragraphs
                unsigned short e_minalloc; // Minimum extra paragraphs needed
                unsigned short e_maxalloc; // Maximum extra paragraphs needed
                unsigned short e_ss; // Initial (relative) SS value
                unsigned short e_sp; // Initial SP value
                unsigned short e_csum; // Checksum
                unsigned short e_ip; // Initial IP value
                unsigned short e_cs; // Initial (relative) CS value
                unsigned short e_lfarlc; // File address of relocation table
                unsigned short e_ovno; // Overlay number
                unsigned short e_res[4]; // Reserved words
                unsigned short e_oemid; // OEM identifier (for e_oeminfo)
                unsigned short e_oeminfo; // OEM information; e_oemid specific
                unsigned short e_res2[10]; // Reserved words
                long           e_lfanew; // File address of new exe header
            };

            struct IMAGE_FILE_HEADER {
                unsigned short Machine;
                unsigned short NumberOfSections;
                unsigned long  TimeDateStamp;
                unsigned long  PointerToSymbolTable;
                unsigned long  NumberOfSymbols;
                unsigned short SizeOfOptionalHeader;
                unsigned short Characteristics;
            };

            struct IMAGE_EXPORT_DIRECTORY {
                unsigned long  Characteristics;
                unsigned long  TimeDateStamp;
                unsigned short MajorVersion;
                unsigned short MinorVersion;
                unsigned long  Name;
                unsigned long  Base;
                unsigned long  NumberOfFunctions;
                unsigned long  NumberOfNames;
                unsigned long  AddressOfFunctions; // RVA from base of image
                unsigned long  AddressOfNames; // RVA from base of image
                unsigned long  AddressOfNameOrdinals; // RVA from base of image
            };

            struct IMAGE_DATA_DIRECTORY {
                unsigned long VirtualAddress;
                unsigned long Size;
            };

            struct IMAGE_OPTIONAL_HEADER64 {
                unsigned short       Magic;
                unsigned char        MajorLinkerVersion;
                unsigned char        MinorLinkerVersion;
                unsigned long        SizeOfCode;
                unsigned long        SizeOfInitializedData;
                unsigned long        SizeOfUninitializedData;
                unsigned long        AddressOfEntryPoint;
                unsigned long        BaseOfCode;
                unsigned long long   ImageBase;
                unsigned long        SectionAlignment;
                unsigned long        FileAlignment;
                unsigned short       MajorOperatingSystemVersion;
                unsigned short       MinorOperatingSystemVersion;
                unsigned short       MajorImageVersion;
                unsigned short       MinorImageVersion;
                unsigned short       MajorSubsystemVersion;
                unsigned short       MinorSubsystemVersion;
                unsigned long        Win32VersionValue;
                unsigned long        SizeOfImage;
                unsigned long        SizeOfHeaders;
                unsigned long        CheckSum;
                unsigned short       Subsystem;
                unsigned short       DllCharacteristics;
                unsigned long long   SizeOfStackReserve;
                unsigned long long   SizeOfStackCommit;
                unsigned long long   SizeOfHeapReserve;
                unsigned long long   SizeOfHeapCommit;
                unsigned long        LoaderFlags;
                unsigned long        NumberOfRvaAndSizes;
                IMAGE_DATA_DIRECTORY DataDirectory[16];
            };

            struct IMAGE_OPTIONAL_HEADER32 {
                unsigned short       Magic;
                unsigned char        MajorLinkerVersion;
                unsigned char        MinorLinkerVersion;
                unsigned long        SizeOfCode;
                unsigned long        SizeOfInitializedData;
                unsigned long        SizeOfUninitializedData;
                unsigned long        AddressOfEntryPoint;
                unsigned long        BaseOfCode;
                unsigned long        BaseOfData;
                unsigned long        ImageBase;
                unsigned long        SectionAlignment;
                unsigned long        FileAlignment;
                unsigned short       MajorOperatingSystemVersion;
                unsigned short       MinorOperatingSystemVersion;
                unsigned short       MajorImageVersion;
                unsigned short       MinorImageVersion;
                unsigned short       MajorSubsystemVersion;
                unsigned short       MinorSubsystemVersion;
                unsigned long        Win32VersionValue;
                unsigned long        SizeOfImage;
                unsigned long        SizeOfHeaders;
                unsigned long        CheckSum;
                unsigned short       Subsystem;
                unsigned short       DllCharacteristics;
                unsigned long        SizeOfStackReserve;
                unsigned long        SizeOfStackCommit;
                unsigned long        SizeOfHeapReserve;
                unsigned long        SizeOfHeapCommit;
                unsigned long        LoaderFlags;
                unsigned long        NumberOfRvaAndSizes;
                IMAGE_DATA_DIRECTORY DataDirectory[16];
            };

            struct IMAGE_NT_HEADERS {
                unsigned long     Signature;
                IMAGE_FILE_HEADER FileHeader;
#ifdef _WIN64
                IMAGE_OPTIONAL_HEADER64 OptionalHeader;
#else
                IMAGE_OPTIONAL_HEADER32 OptionalHeader;
#endif
            };

        } // namespace win

        // hashing stuff
        struct hash_t {
            using value_type = unsigned long;
            constexpr static value_type         offset = 2166136261;
            constexpr static value_type         prime = 16777619;
            constexpr static unsigned long long prime64 = prime;

            LAZY_IMPORTER_FORCEINLINE constexpr static value_type single(value_type value,
                char c) noexcept
            {
                return static_cast<hash_t::value_type>(
                    (value ^ LAZY_IMPORTER_TOLOWER(c)) *
                    static_cast<unsigned long long>(prime));
            }
        };

        template<class CharT = char>
        LAZY_IMPORTER_FORCEINLINE constexpr hash_t::value_type
            khash(const CharT* str, hash_t::value_type value = hash_t::offset) noexcept
        {
            return (*str ? khash(str + 1, hash_t::single(value, *str)) : value);
        }

        template<class CharT = char>
        LAZY_IMPORTER_FORCEINLINE hash_t::value_type hash(const CharT* str) noexcept
        {
            hash_t::value_type value = hash_t::offset;

            for (;;) {
                char c = *str++;
                if (!c)
                    return value;
                value = hash_t::single(value, c);
            }
        }

        LAZY_IMPORTER_FORCEINLINE hash_t::value_type hash(
            const win::UNICODE_STRING_T& str) noexcept
        {
            auto       first = str.Buffer;
            const auto last = first + (str.Length / sizeof(wchar_t));
            auto       value = hash_t::offset;
            for (; first != last; ++first)
                value = hash_t::single(value, static_cast<char>(*first));

            return value;
        }

        LAZY_IMPORTER_FORCEINLINE pair<hash_t::value_type, hash_t::value_type> hash_forwarded(
            const char* str) noexcept
        {
            pair<hash_t::value_type, hash_t::value_type> module_and_function{
                hash_t::offset, hash_t::offset
            };

            for (; *str != '.'; ++str)
                module_and_function.first = hash_t::single(module_and_function.first, *str);

            ++str;

            for (; *str; ++str)
                module_and_function.second = hash_t::single(module_and_function.second, *str);

            return module_and_function;
        }


        // some helper functions
        LAZY_IMPORTER_FORCEINLINE const win::PEB_T* peb() noexcept
        {
#if defined(_WIN64)
            return reinterpret_cast<const win::PEB_T*>(__readgsqword(0x60));
#elif defined(_WIN32)
            return reinterpret_cast<const win::PEB_T*>(__readfsdword(0x30));
#else
#error Unsupported platform. Open an issue and I'll probably add support.
#endif
        }

        LAZY_IMPORTER_FORCEINLINE const win::PEB_LDR_DATA_T* ldr()
        {
            return reinterpret_cast<const win::PEB_LDR_DATA_T*>(peb()->Ldr);
        }

        LAZY_IMPORTER_FORCEINLINE const win::IMAGE_NT_HEADERS* nt_headers(
            const char* base) noexcept
        {
            return reinterpret_cast<const win::IMAGE_NT_HEADERS*>(
                base + reinterpret_cast<const win::IMAGE_DOS_HEADER*>(base)->e_lfanew);
        }

        LAZY_IMPORTER_FORCEINLINE const win::IMAGE_EXPORT_DIRECTORY* image_export_dir(
            const char* base) noexcept
        {
            return reinterpret_cast<const win::IMAGE_EXPORT_DIRECTORY*>(
                base + nt_headers(base)->OptionalHeader.DataDirectory->VirtualAddress);
        }

        LAZY_IMPORTER_FORCEINLINE const win::LDR_DATA_TABLE_ENTRY_T* ldr_data_entry() noexcept
        {
            return reinterpret_cast<const win::LDR_DATA_TABLE_ENTRY_T*>(
                ldr()->InLoadOrderModuleList.Flink);
        }

        struct exports_directory {
            const char* _base;
            const win::IMAGE_EXPORT_DIRECTORY* _ied;
            unsigned long                      _ied_size;

        public:
            using size_type = unsigned long;

            LAZY_IMPORTER_FORCEINLINE
                exports_directory(const char* base) noexcept : _base(base)
            {
                const auto ied_data_dir = nt_headers(base)->OptionalHeader.DataDirectory[0];
                _ied = reinterpret_cast<const win::IMAGE_EXPORT_DIRECTORY*>(
                    base + ied_data_dir.VirtualAddress);
                _ied_size = ied_data_dir.Size;
            }

            LAZY_IMPORTER_FORCEINLINE explicit operator bool() const noexcept
            {
                return reinterpret_cast<const char*>(_ied) != _base;
            }

            LAZY_IMPORTER_FORCEINLINE size_type size() const noexcept
            {
                return _ied->NumberOfNames;
            }

            LAZY_IMPORTER_FORCEINLINE const char* base() const noexcept { return _base; }
            LAZY_IMPORTER_FORCEINLINE const win::IMAGE_EXPORT_DIRECTORY* ied() const noexcept
            {
                return _ied;
            }

            LAZY_IMPORTER_FORCEINLINE const char* name(size_type index) const noexcept
            {
                return reinterpret_cast<const char*>(
                    _base + reinterpret_cast<const unsigned long*>(
                        _base + _ied->AddressOfNames)[index]);
            }

            LAZY_IMPORTER_FORCEINLINE const char* address(size_type index) const noexcept
            {
                const auto* const rva_table =
                    reinterpret_cast<const unsigned long*>(_base + _ied->AddressOfFunctions);

                const auto* const ord_table = reinterpret_cast<const unsigned short*>(
                    _base + _ied->AddressOfNameOrdinals);

                return _base + rva_table[ord_table[index]];
            }

            LAZY_IMPORTER_FORCEINLINE bool is_forwarded(const char* export_address) const
                noexcept
            {
                const auto ui_ied = reinterpret_cast<const char*>(_ied);
                return (export_address > ui_ied && export_address < ui_ied + _ied_size);
            }
        };

        struct safe_module_enumerator {
            using value_type = const detail::win::LDR_DATA_TABLE_ENTRY_T;
            value_type* value;
            value_type* const head;

            LAZY_IMPORTER_FORCEINLINE safe_module_enumerator() noexcept
                : value(ldr_data_entry()), head(value)
            {}

            LAZY_IMPORTER_FORCEINLINE void reset() noexcept { value = head; }

            LAZY_IMPORTER_FORCEINLINE bool next() noexcept
            {
                value = value->load_order_next();
                return value != head && value->DllBase;
            }
        };

        struct unsafe_module_enumerator {
            using value_type = const detail::win::LDR_DATA_TABLE_ENTRY_T*;
            value_type value;

            LAZY_IMPORTER_FORCEINLINE unsafe_module_enumerator() noexcept
                : value(ldr_data_entry())
            {}

            LAZY_IMPORTER_FORCEINLINE void reset() noexcept { value = ldr_data_entry(); }

            LAZY_IMPORTER_FORCEINLINE bool next() noexcept
            {
                value = value->load_order_next();
                return true;
            }
        };

        // provides the cached functions which use Derive classes methods
        template<class Derived, class DefaultType = void*>
        class lazy_base {
        protected:
            // This function is needed because every templated function
            // with different args has its own static buffer
            LAZY_IMPORTER_FORCEINLINE static void*& _cache() noexcept
            {
                static void* value = nullptr;
                return value;
            }

        public:
            template<class T = DefaultType>
            LAZY_IMPORTER_FORCEINLINE static T safe() noexcept
            {
                return Derived::template get<T, safe_module_enumerator>();
            }

            template<class T = DefaultType, class Enum = unsafe_module_enumerator>
            LAZY_IMPORTER_FORCEINLINE static T cached() noexcept
            {
                auto& cached = _cache();
                if (!cached)
                    cached = Derived::template get<void*, Enum>();

                return (T)(cached);
            }

            template<class T = DefaultType>
            LAZY_IMPORTER_FORCEINLINE static T safe_cached() noexcept
            {
                return cached<T, safe_module_enumerator>();
            }
        };

        template<hash_t::value_type Hash>
        struct lazy_module : lazy_base<lazy_module<Hash>> {
            template<class T = void*, class Enum = unsafe_module_enumerator>
            LAZY_IMPORTER_FORCEINLINE static T get() noexcept
            {
                Enum e;
                do {
                    if (hash(e.value->BaseDllName) == Hash)
                        return (T)(e.value->DllBase);
                } while (e.next());
                return {};
            }
        };

        template<hash_t::value_type Hash, class T>
        struct lazy_function : lazy_base<lazy_function<Hash, T>, T> {
            using base_type = lazy_base<lazy_function<Hash, T>, T>;

            template<class... Args>
            LAZY_IMPORTER_FORCEINLINE decltype(auto) operator()(Args&&... args) const
            {
#ifndef LAZY_IMPORTER_CACHE_OPERATOR_PARENS
                return get()(std::forward<Args>(args)...);
#else
                return this->cached()(std::forward<Args>(args)...);
#endif
            }

            template<class F = T, class Enum = unsafe_module_enumerator>
            LAZY_IMPORTER_FORCEINLINE static F get() noexcept
            {
                // for backwards compatability.
                // Before 2.0 it was only possible to resolve forwarded exports when
                // this macro was enabled
#ifdef LAZY_IMPORTER_RESOLVE_FORWARDED_EXPORTS
                return forwarded<F, Enum>();
#else
                Enum e;
                do {
                    const exports_directory exports(e.value->DllBase);

                    if (exports) {
                        auto export_index = exports.size();
                        while (export_index--)
                            if (hash(exports.name(export_index)) == Hash)
                                return (F)(exports.address(export_index));
                    }
                } while (e.next());
                return {};
#endif
            }

            template<class F = T, class Enum = unsafe_module_enumerator>
            LAZY_IMPORTER_FORCEINLINE static F forwarded() noexcept
            {
                detail::win::UNICODE_STRING_T name;
                hash_t::value_type            module_hash = 0;
                auto                          function_hash = Hash;

                Enum e;
                do {
                    name = e.value->BaseDllName;
                    name.Length -= 8; // get rid of .dll extension

                    if (!module_hash || hash(name) == module_hash) {
                        const exports_directory exports(e.value->DllBase);

                        if (exports) {
                            auto export_index = exports.size();
                            while (export_index--)
                                if (hash(exports.name(export_index)) == function_hash) {
                                    const auto addr = exports.address(export_index);

                                    if (exports.is_forwarded(addr)) {
                                        auto hashes = hash_forwarded(
                                            reinterpret_cast<const char*>(addr));

                                        function_hash = hashes.second;
                                        module_hash = hashes.first;

                                        e.reset();
                                        break;
                                    }
                                    return (F)(addr);
                                }
                        }
                    }
                } while (e.next());
                return {};
            }

            template<class F = T>
            LAZY_IMPORTER_FORCEINLINE static F forwarded_safe() noexcept
            {
                return forwarded<F, safe_module_enumerator>();
            }

            template<class F = T, class Enum = unsafe_module_enumerator>
            LAZY_IMPORTER_FORCEINLINE static F forwarded_cached() noexcept
            {
                auto& value = base_type::_cache();
                if (!value)
                    value = forwarded<void*, Enum>();
                return (F)(value);
            }

            template<class F = T>
            LAZY_IMPORTER_FORCEINLINE static F forwarded_safe_cached() noexcept
            {
                return forwarded_cached<F, safe_module_enumerator>();
            }

            template<class F = T, bool IsSafe = false, class Module>
            LAZY_IMPORTER_FORCEINLINE static F in(Module m) noexcept
            {
                if (IsSafe && !m)
                    return {};

                const exports_directory exports((const char*)(m));
                if (IsSafe && !exports)
                    return {};

                for (unsigned long i{};; ++i) {
                    if (IsSafe && i == exports.size())
                        break;

                    if (hash(exports.name(i)) == Hash)
                        return (F)(exports.address(i));
                }
                return {};
            }

            template<class F = T, class Module>
            LAZY_IMPORTER_FORCEINLINE static F in_safe(Module m) noexcept
            {
                return in<F, true>(m);
            }

            template<class F = T, bool IsSafe = false, class Module>
            LAZY_IMPORTER_FORCEINLINE static F in_cached(Module m) noexcept
            {
                auto& value = base_type::_cache();
                if (!value)
                    value = in<void*, IsSafe>(m);
                return (F)(value);
            }

            template<class F = T, class Module>
            LAZY_IMPORTER_FORCEINLINE static F in_safe_cached(Module m) noexcept
            {
                return in_cached<F, true>(m);
            }

            template<class F = T>
            LAZY_IMPORTER_FORCEINLINE static F nt() noexcept
            {
                return in<F>(ldr_data_entry()->load_order_next()->DllBase);
            }

            template<class F = T>
            LAZY_IMPORTER_FORCEINLINE static F nt_safe() noexcept
            {
                return in_safe<F>(ldr_data_entry()->load_order_next()->DllBase);
            }

            template<class F = T>
            LAZY_IMPORTER_FORCEINLINE static F nt_cached() noexcept
            {
                return in_cached<F>(ldr_data_entry()->load_order_next()->DllBase);
            }

            template<class F = T>
            LAZY_IMPORTER_FORCEINLINE static F nt_safe_cached() noexcept
            {
                return in_safe_cached<F>(ldr_data_entry()->load_order_next()->DllBase);
            }
        };

    }
} // namespace li::detail

#endif // include guard