>> requirement to read email message and creating case with the email content
Configure your email listener and use it with Activity pyCreateAndManageWorkFromEmail. This is an OOTB activity
>>Before creating any case, i have to verify wheather the case is already created for that week,month,year and so on
Since the activity is available, you can save as a copy in your local ruleset and do the required validation. For example if you want to check whether the case is created for the week or not, you can add a step which can check the work table to see whether any case is present with pxCreateDateTime=CurrentWeek.
>>Also I want to build the logic for identifying week, month and Year based on the email received date
As said earlier, you need to extend the OOTB activity only and then incorporate a logic to retrieve the week/month etc from the date of receiving the email. The service method that you use with your email listener has the provision of mapping the message details in various fields like TO, FROM, Date etc. Utilize these features to capture the details as required.