trigger UpdateCase on CaseComment (before insert) {
    Map<String, String> keywordToStatus = new Map<String, String> {
        'resolved' => 'Closed',
        'fixed' => 'Closed',
        'completed' => 'Closed',
        'reopen' => 'Reopened',
        'reopened' => 'Reopened'
    };

    for (CaseComment comment : Trigger.New) {
        Case theCase = [
            SELECT Id, Status 
            FROM Case 
            WHERE Id = :comment.ParentId
        ];

        for (String keyword : keywordToStatus.keySet()) {
            if (comment.CommentBody.toLowerCase().contains(keyword.toLowerCase())) {
                theCase.Status = keywordToStatus.get(keyword);
                update theCase;
                break;
            }
        }
    }
}