/*
 * 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 IMPORT_HPP
#define IMPORT_HPP

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

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

#define import_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(_M_X64) || defined(__amd64__)
            return reinterpret_cast< const win::PEB_T* >( __readgsqword( 0x60 ) );
#elif defined(_M_IX86) || defined(__i386__)
            return reinterpret_cast< const win::PEB_T* >( __readfsdword( 0x30 ) );
#elif defined(_M_ARM) || defined(__arm__)
            return *reinterpret_cast< const win::PEB_T** >( _MoveFromCoprocessor( 15, 0, 13, 0, 2 ) + 0x30 );
#elif defined(_M_ARM64) || defined(__aarch64__)
            return *reinterpret_cast< const win::PEB_T** >( __getReg( 18 ) + 0x60 );
#elif defined(_M_IA64) || defined(__ia64__)
            return *reinterpret_cast< const win::PEB_T** >( static_cast< char* >( _rdteb( ) ) + 0x60 );
#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* head;

            LAZY_IMPORTER_FORCEINLINE safe_module_enumerator( ) noexcept
                : safe_module_enumerator( ldr_data_entry( ) )
            {}

            LAZY_IMPORTER_FORCEINLINE
                safe_module_enumerator( const detail::win::LDR_DATA_TABLE_ENTRY_T* ldr ) noexcept
                : value( ldr->load_order_next( ) ), head( value )
            {}

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

            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<class T = void*, class Ldr>
            LAZY_IMPORTER_FORCEINLINE static T in( Ldr ldr ) noexcept
            {
                safe_module_enumerator e( ( const detail::win::LDR_DATA_TABLE_ENTRY_T* ) ( ldr ) );
                do {
                    if ( hash( e.value->BaseDllName ) == Hash )
                        return ( T ) ( e.value->DllBase );
                } while ( e.next( ) );
                return {};
            }

            template<class T = void*, class Ldr>
            LAZY_IMPORTER_FORCEINLINE static T in_cached( Ldr ldr ) noexcept
            {
                auto& cached = lazy_base<lazy_module<Hash>>::_cache( );
                if ( !cached )
                    cached = in( ldr );

                return ( T ) ( cached );
            }
        };

        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 {
#ifdef LAZY_IMPORTER_HARDENED_MODULE_CHECKS
                    if ( !e.value->DllBase || !e.value->FullDllName.Length )
                        continue;
#endif

                    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