#include "90CN_op3_parent_fix.h"

#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <wchar.h>

namespace
{
constexpr uintptr_t kOp3ParentCallRva = 0x01988B9F; // 01D88B9F
constexpr uintptr_t kParentFunctionRva = 0x021B69E0; // 025B69E0

HMODULE g_selfModule = nullptr;
uintptr_t g_exeBase = 0;
uintptr_t g_parentFunction = 0;
uintptr_t g_continueAfterParentCall = 0;
volatile LONG g_bypassSequence = 0;

void BuildLogPath(wchar_t* output, size_t outputCount)
{
    if (!output || outputCount == 0) return;
    output[0] = L'\0';
    DWORD length = g_selfModule
        ? GetModuleFileNameW(g_selfModule, output, static_cast<DWORD>(outputCount))
        : 0;
    if (!length || length >= outputCount) {
        wcscpy_s(output, outputCount, L"90CN_fix.log");
        return;
    }
    wchar_t* slash = wcsrchr(output, L'\\');
    wchar_t* slash2 = wcsrchr(output, L'/');
    if (slash2 && (!slash || slash2 > slash)) slash = slash2;
    if (slash) {
        slash[1] = L'\0';
        wcscat_s(output, outputCount, L"90CN_fix.log");
    }
    else {
        wcscpy_s(output, outputCount, L"90CN_fix.log");
    }
}

void WriteLogLine(const char* text)
{
    if (!text) return;
    wchar_t path[MAX_PATH] = {};
    BuildLogPath(path, _countof(path));
    HANDLE file = CreateFileW(path, FILE_APPEND_DATA,
        FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
        nullptr, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, nullptr);
    if (file == INVALID_HANDLE_VALUE) return;
    DWORD written = 0;
    WriteFile(file, text, static_cast<DWORD>(strlen(text)), &written, nullptr);
    CloseHandle(file);
}

void __stdcall RecordNullBypass(uintptr_t actor)
{
    LONG sequence = InterlockedIncrement(&g_bypassSequence);
    // Prevent pathological log growth while retaining enough evidence for support.
    if (sequence > 64) return;

    SYSTEMTIME now = {};
    GetLocalTime(&now);
    char line[512] = {};
    sprintf_s(line,
        "op3-parent-readiness-fix seq=%ld time=%04u-%02u-%02u %02u:%02u:%02u.%03u "
        "tid=%lu actor=%08X action=bypass-null-parent continue=01D88BA4\r\n",
        sequence,
        now.wYear, now.wMonth, now.wDay,
        now.wHour, now.wMinute, now.wSecond, now.wMilliseconds,
        GetCurrentThreadId(), static_cast<unsigned int>(actor));
    WriteLogLine(line);
}

// Replaces only the single CALL at 01D88B9F.
// Normal path is untouched: restore incoming EFLAGS and tail-jump to 025B69E0.
// Null path skips the known-invalid call, removes CALL return address + 2 args
// (12 bytes), and resumes at the original continuation 01D88BA4.
__declspec(naked) void ProxyOp3ParentCall()
{
    __asm {
        pushfd
        test ecx, ecx
        jz parent_is_null
        popfd
        jmp dword ptr [g_parentFunction]

    parent_is_null:
        popfd
        pushfd
        pushad
        push esi
        call RecordNullBypass
        popad
        popfd
        add esp, 0Ch
        jmp dword ptr [g_continueAfterParentCall]
    }
}

DWORD WINAPI InstallOp3ParentReadinessFix(LPVOID)
{
    HMODULE executable = GetModuleHandleW(nullptr);
    g_exeBase = reinterpret_cast<uintptr_t>(executable);
    if (!g_exeBase) return 0;

    unsigned char* callSite = reinterpret_cast<unsigned char*>(
        g_exeBase + kOp3ParentCallRva);
    g_parentFunction = g_exeBase + kParentFunctionRva;
    g_continueAfterParentCall = reinterpret_cast<uintptr_t>(callSite + 5);

    bool verified = false;
    uintptr_t observedTarget = 0;
    __try {
        if (callSite[0] == 0xE8) {
            LONG currentRelative = *reinterpret_cast<LONG*>(callSite + 1);
            observedTarget = reinterpret_cast<uintptr_t>(callSite + 5) + currentRelative;
            verified = observedTarget == g_parentFunction;
        }
    }
    __except (EXCEPTION_EXECUTE_HANDLER) {
        verified = false;
    }

    if (!verified) {
        char line[512] = {};
        sprintf_s(line,
            "op3-parent-readiness-fix install_failed site=%08X opcode=%02X observed=%08X expected=%08X\r\n",
            static_cast<unsigned int>(reinterpret_cast<uintptr_t>(callSite)),
            static_cast<unsigned int>(callSite[0]),
            static_cast<unsigned int>(observedTarget),
            static_cast<unsigned int>(g_parentFunction));
        WriteLogLine(line);
        return 0;
    }

    const uintptr_t replacement = reinterpret_cast<uintptr_t>(&ProxyOp3ParentCall);
    LONG replacementRelative = static_cast<LONG>(
        replacement - reinterpret_cast<uintptr_t>(callSite + 5));

    DWORD oldProtection = 0;
    if (!VirtualProtect(callSite, 5, PAGE_EXECUTE_READWRITE, &oldProtection)) {
        WriteLogLine("op3-parent-readiness-fix install_failed reason=VirtualProtect\r\n");
        return 0;
    }

    *reinterpret_cast<LONG*>(callSite + 1) = replacementRelative;
    DWORD ignoredProtection = 0;
    VirtualProtect(callSite, 5, oldProtection, &ignoredProtection);
    FlushInstructionCache(GetCurrentProcess(), callSite, 5);

    WriteLogLine("op3-parent-readiness-fix installed site=01D88B9F native=025B69E0 continue=01D88BA4\r\n");
    return 0;
}
}

void StartOp3ParentReadinessFix(HMODULE module)
{
    g_selfModule = module;
    HANDLE worker = CreateThread(nullptr, 0, InstallOp3ParentReadinessFix, nullptr, 0, nullptr);
    if (worker) CloseHandle(worker);
}