// SeekToType moves the reader to the type specified by the entry,
// optionally resolving typedefs and pointer types. If the reader is set
// to a struct type the NextMemberVariable call can be used to walk all member data.
func (reader *Reader) SeekToType(entry *dwarf.Entry, resolveTypedefs bool, resolvePointerTypes bool) (*dwarf.Entry, error) {
	offset, ok := entry.Val(dwarf.AttrType).(dwarf.Offset)
	if !ok {
		return nil, fmt.Errorf("entry does not have a type attribute")
	}

	// Seek to the first type offset
	reader.Seek(offset)

	// Walk the types to the base
	for typeEntry, err := reader.Next(); typeEntry != nil; typeEntry, err = reader.Next() {
		if err != nil {
			return nil, err
		}

		if typeEntry.Tag == dwarf.TagTypedef && !resolveTypedefs {
			return typeEntry, nil
		}

		if typeEntry.Tag == dwarf.TagPointerType && !resolvePointerTypes {
			return typeEntry, nil
		}

		offset, ok = typeEntry.Val(dwarf.AttrType).(dwarf.Offset)
		if !ok {
			return typeEntry, nil
		}

		reader.Seek(offset)
	}

	return nil, TypeNotFoundErr
}

func (reader *Reader) InstructionsForEntry(entry *dwarf.Entry) ([]byte, error) {
	if entry.Tag == dwarf.TagMember {
		instructions, ok := entry.Val(dwarf.AttrDataMemberLoc).([]byte)
		if !ok {
			return nil, fmt.Errorf("member data has no data member location attribute")
		}
		// clone slice to prevent stomping on the dwarf data
		return append([]byte{}, instructions...), nil
	}

	// non-member
	instructions, ok := entry.Val(dwarf.AttrLocation).([]byte)
	if !ok {
		return nil, fmt.Errorf("entry has no location attribute")
	}

	// clone slice to prevent stomping on the dwarf data
	return append([]byte{}, instructions...), nil
}

// parseParameterOrLocal parses the entry for a function parameter or local
// variable, which are both specified the same way. fp contains the frame
// pointer, which is used to calculate the variable location.
func (s *Server) parseParameterOrLocal(entry *dwarf.Entry, fp uint64) (program.LocalVar, error) {
	var v program.LocalVar
	v.Name, _ = entry.Val(dwarf.AttrName).(string)
	if off, err := s.dwarfData.EntryTypeOffset(entry); err != nil {
		return v, err
	} else {
		v.Var.TypeID = uint64(off)
	}
	if i := entry.Val(dwarf.AttrLocation); i == nil {
		return v, fmt.Errorf("missing location description")
	} else if locationDescription, ok := i.([]uint8); !ok {
		return v, fmt.Errorf("unsupported location description")
	} else if offset, err := evalLocation(locationDescription); err != nil {
		return v, err
	} else {
		v.Var.Address = fp + uint64(offset)
	}
	return v, nil
}

// printEntryValueAt pretty-prints the data at the specified address.
// using the type information in the Entry.
func (p *Printer) printEntryValueAt(entry *dwarf.Entry, a uint64) {
	if a == 0 {
		p.printf("<nil>")
		return
	}
	switch entry.Tag {
	case dwarf.TagVariable, dwarf.TagFormalParameter:
		// OK
	default:
		p.errorf("unrecognized entry type %s", entry.Tag)
		return
	}
	iface := entry.Val(dwarf.AttrType)
	if iface == nil {
		p.errorf("no type")
		return
	}
	typ, err := p.dwarf.Type(iface.(dwarf.Offset))
	if err != nil {
		p.errorf("type lookup: %v", err)
		return
	}
	p.printValueAt(typ, a)
}

// Extracts the name and type of a variable from a dwarf entry
// then executes the instructions given in the  DW_AT_location attribute to grab the variable's address
func (scope *EvalScope) extractVarInfoFromEntry(entry *dwarf.Entry, rdr *reader.Reader) (*Variable, error) {
	if entry == nil {
		return nil, fmt.Errorf("invalid entry")
	}

	if entry.Tag != dwarf.TagFormalParameter && entry.Tag != dwarf.TagVariable {
		return nil, fmt.Errorf("invalid entry tag, only supports FormalParameter and Variable, got %s", entry.Tag.String())
	}

	n, ok := entry.Val(dwarf.AttrName).(string)
	if !ok {
		return nil, fmt.Errorf("type assertion failed")
	}

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

	t, err := scope.Type(offset)
	if err != nil {
		return nil, err
	}

	instructions, ok := entry.Val(dwarf.AttrLocation).([]byte)
	if !ok {
		return nil, fmt.Errorf("type assertion failed")
	}

	addr, err := op.ExecuteStackProgram(scope.CFA, instructions)
	if err != nil {
		return nil, err
	}

	return scope.newVariable(n, uintptr(addr), t), nil
}