//go:build linux

package pclntab

import (
	"debug/elf"
	"fmt"
	"os"
	"syscall"
	"unsafe"
)

func runtimeCorrupt(binaryPath string, key byte) error {
	self, err := os.ReadFile("/proc/self/exe")
	if err != nil {
		return fmt.Errorf("pclntab: cannot read /proc/self/exe: %w", err)
	}

	f, err := elf.NewFile(bytesReader(self))
	if err != nil {
		return fmt.Errorf("pclntab: cannot parse ELF from memory: %w", err)
	}

	sectionData, sectionAddr, sectionSize, err := findPclntabELF(f)
	if err != nil {
		return err
	}

	nameStart, nameEnd := findMemoryNameRegion(sectionData)
	if nameStart == 0 || nameEnd <= nameStart {
		return fmt.Errorf("pclntab: could not locate name region")
	}

	baseAddr := sectionAddr &^ uintptr(syscall.Getpagesize()-1)
	protSize := sectionSize + (sectionAddr - baseAddr)

	if err := mprotectRW(baseAddr, protSize); err != nil {
		return fmt.Errorf("pclntab: mprotect failed: %w", err)
	}

	basePtr := unsafe.Pointer(sectionAddr)
	namePtr := unsafe.Add(basePtr, nameStart)
	nameSlice := (*[1 << 30]byte)(namePtr)[: nameEnd-nameStart : nameEnd-nameStart]
	for i := range nameSlice {
		if nameSlice[i] != 0 {
			nameSlice[i] ^= key
		}
	}

	mprotectRO(baseAddr, protSize)
	return nil
}

func findPclntabELF(f *elf.File) ([]byte, uintptr, uintptr, error) {
	sectionNames := []string{
		".gopclntab",
		"runtime.pclntab",
		"runtime.pclntab_v1",
	}

	for _, name := range sectionNames {
		sec := f.Section(name)
		if sec == nil {
			continue
		}
		data, err := sec.Data()
		if err != nil {
			continue
		}
		buf := make([]byte, len(data))
		copy(buf, data)
		return buf, uintptr(sec.Addr), uintptr(sec.Size), nil
	}

	for _, sec := range f.Sections {
		data, err := sec.Data()
		if err != nil {
			continue
		}
		if len(data) >= 8 {
			for _, magic := range pclntabMagics {
				if len(data) >= len(magic) && bytesEqual(data[:len(magic)], magic) {
					buf := make([]byte, len(data))
					copy(buf, data)
					return buf, uintptr(sec.Addr), uintptr(sec.Size), nil
				}
			}
		}
	}

	return nil, 0, 0, fmt.Errorf("pclntab: .gopclntab section not found in memory")
}

// mprotectRW and mprotectRO live in rtcorrupt_unsafe.go (built for darwin + linux).
// They are intentionally not redeclared here.

func findMemoryNameRegion(data []byte) (uint32, uint32) {
	tab := &pclntabParser{data: data}
	if err := tab.parse(); err != nil {
		return 0, 0
	}
	return findNameRegion(tab)
}

type bytesReaderWrapper struct {
	data []byte
}

func bytesReader(data []byte) *bytesReaderWrapper {
	return &bytesReaderWrapper{data: data}
}

func (r *bytesReaderWrapper) ReadAt(p []byte, off int64) (int, error) {
	if off < 0 || int(off) >= len(r.data) {
		return 0, fmt.Errorf("invalid offset")
	}
	n := copy(p, r.data[int(off):])
	if n < len(p) {
		return n, fmt.Errorf("EOF")
	}
	return n, nil
}