// Extracts the address of a variable, dereferencing any pointers
func (thread *Thread) extractVariableDataAddress(entry *dwarf.Entry, rdr *reader.Reader) (int64, error) {
	instructions, err := rdr.InstructionsForEntry(entry)
	if err != nil {
		return 0, err
	}

	address, err := thread.executeStackProgram(instructions)
	if err != nil {
		return 0, err
	}

	// Dereference pointers to get down the concrete type
	for typeEntry, err := rdr.SeekToType(entry, true, false); typeEntry != nil; typeEntry, err = rdr.SeekToType(typeEntry, true, false) {
		if err != nil {
			return 0, err
		}

		if typeEntry.Tag != dwarf.TagPointerType {
			break
		}

		ptraddress := uintptr(address)

		ptr, err := thread.readMemory(ptraddress, thread.dbp.arch.PtrSize())
		if err != nil {
			return 0, err
		}
		address = int64(binary.LittleEndian.Uint64(ptr))
	}

	return address, nil
}

func (thread *Thread) evaluateStructMember(parentEntry *dwarf.Entry, rdr *reader.Reader, memberName string) (*Variable, error) {
	parentAddr, err := thread.extractVariableDataAddress(parentEntry, rdr)
	if err != nil {
		return nil, err
	}

	// Get parent variable name
	parentName, ok := parentEntry.Val(dwarf.AttrName).(string)
	if !ok {
		return nil, fmt.Errorf("unable to retrive variable name")
	}

	// Seek reader to the type information so members can be iterated
	_, err = rdr.SeekToType(parentEntry, true, true)
	if err != nil {
		return nil, err
	}

	// Iterate to find member by name
	for memberEntry, err := rdr.NextMemberVariable(); memberEntry != nil; memberEntry, err = rdr.NextMemberVariable() {
		if err != nil {
			return nil, err
		}

		name, ok := memberEntry.Val(dwarf.AttrName).(string)
		if !ok {
			continue
		}

		if name == memberName {
			// Nil ptr, wait until here to throw a nil pointer error to prioritize no such member error
			if parentAddr == 0 {
				return nil, fmt.Errorf("%s is nil", parentName)
			}

			memberInstr, err := rdr.InstructionsForEntry(memberEntry)
			if err != nil {
				return nil, err
			}

			offset, ok := memberEntry.Val(dwarf.AttrType).(dwarf.Offset)
			if !ok {
				return nil, fmt.Errorf("type assertion failed")
			}

			data := thread.dbp.dwarf
			t, err := data.Type(offset)
			if err != nil {
				return nil, err
			}

			baseAddr := make([]byte, 8)
			binary.LittleEndian.PutUint64(baseAddr, uint64(parentAddr))

			parentInstructions := append([]byte{op.DW_OP_addr}, baseAddr...)
			val, err := thread.extractValue(append(parentInstructions, memberInstr...), 0, t, true)
			if err != nil {
				return nil, err
			}
			return &Variable{Name: strings.Join([]string{parentName, memberName}, "."), Type: t.String(), Value: val}, nil
		}
	}

	return nil, fmt.Errorf("%s has no member %s", parentName, memberName)
}