// Package runtime discovers live driver state: loaded kernel modules, device
// names, and named sections in the object manager namespace.
package runtime

import (
	"strings"
	"unsafe"

	"golang.org/x/sys/windows"
)

// Module is a loaded kernel module.
type Module struct {
	ImageBase uintptr
	ImageSize uint32
	Path      string
}

// Modules returns the list of loaded kernel modules via
// NtQuerySystemInformation(SystemModuleInformation).
func Modules() ([]Module, error) {
	size := uint32(1 << 20) // 1 MiB initial; grows on STATUS_INFO_LENGTH_MISMATCH
	for {
		buf := make([]byte, size)
		err := windows.NtQuerySystemInformation(windows.SystemModuleInformation, unsafe.Pointer(&buf[0]), size, &size)
		if err == nil {
			return parseModules(buf), nil
		}
		if err != windows.STATUS_INFO_LENGTH_MISMATCH {
			return nil, err
		}
	}
}

// parseModules decodes an RTL_PROCESS_MODULES buffer into a slice of Module.
func parseModules(buf []byte) []Module {
	mods := (*windows.RTL_PROCESS_MODULES)(unsafe.Pointer(&buf[0]))
	out := make([]Module, 0, mods.NumberOfModules)
	base := unsafe.Pointer(&mods.Modules[0])
	entrySize := unsafe.Sizeof(windows.RTL_PROCESS_MODULE_INFORMATION{})
	for i := uint32(0); i < mods.NumberOfModules; i++ {
		mi := (*windows.RTL_PROCESS_MODULE_INFORMATION)(unsafe.Pointer(uintptr(base) + uintptr(i)*entrySize))
		out = append(out, Module{
			ImageBase: mi.ImageBase,
			ImageSize: mi.ImageSize,
			Path:      modulePath(mi),
		})
	}
	return out
}

// modulePath extracts the null-terminated ANSI path from a module info entry.
func modulePath(mi *windows.RTL_PROCESS_MODULE_INFORMATION) string {
	b := mi.FullPathName[:]
	n := 0
	for n < len(b) && b[n] != 0 {
		n++
	}
	return string(b[:n])
}

// FindModule returns the loaded module whose file name matches name
// (case-insensitive), or ok=false if it is not loaded.
func FindModule(name string) (Module, bool) {
	mods, err := Modules()
	if err != nil {
		return Module{}, false
	}
	for _, m := range mods {
		base := m.Path
		if i := strings.LastIndexAny(base, `\/`); i >= 0 {
			base = base[i+1:]
		}
		if strings.EqualFold(base, name) {
			return m, true
		}
	}
	return Module{}, false
}