The famous Coachella music festival had to cancel its 2020 edition because of the pandemic. The festival team wants to hold the 2021 version in attendance as they have for several years. This festival is held over several days outdoors on stages that have been set up temporarily for the occasion. As it is a festival which usually welcomes a lot of spectators (200,000 spectators over a period of 2 weeks), the organizers want to respect the rules of public health. It was decided that the larger stages would only be accessible to people who have received 2 doses of a covid-19 vaccine. These areas must be controlled by a rigid access system as people inside this area will not need to obey distancing rules and may not wear masks. Certain secondary stages will be accessible to spectators who have not received a vaccine (as well as to those who have had it), but we must respect the rules of distancing and wear the mask at all times in these areas.

States

The spectator must present a pass equipped with an RFID chip in order to have access to the performances of each stage. A reader reads the pass and retrieves the following information:

• The type of package
• The date / time of the start of the package
• The date / time of the end of the package
• Information if the person has obtained their 2 doses of vaccine
• The time of the last use of the pass

A validation system must verify that the festival-goer's pass is valid and that he has access to the desired area. To achieve this, the system checks each rule successively, and moves on to the next one if it does not apply. The rules for checking packages are as follows:

• One show, one zone package (to see a single show - access to a single area): valid if the date / time of day is between the start date / time of the package and the end date / time of the package
• One-day package (valid all day, to access all areas): valid if the current date is equal to the start date of the package
• Evening pass (valid all evening, to access all areas): valid every day of the festival from 7 p.m. until closing
• Festival package (every day and evening of the festival, to access all areas): valid at all times for the duration of the festival

The pass verification is done locally at the barrier based on the pass information. While the other rules (eg: if the person has obtained their 2 doses of vaccine) are saved in a remote database. Thus the system must take charge of this remote request and behave as if the whole of the verification takes place locally.

In addition, fraud must be prevented. A case of fraud occurs when a person lends their ticket to a friend immediately after using it themselves.

In summary, the pass validation system must perform the following operations

• The system checks if the plan is valid using the listed plan verification rules. If the package is not valid, access is denied.
• The system checks whether the bundle has already been used during the last 30 minutes (case of fraud). If so, access is denied.

Note that other validation rules may be added in the future.

When a case of fraud is detected, a message should be sent to the gate attendant, to the administrative office, and to other responders, if applicable.

Questions

A) Draw a class diagram that shows a design to solve this problem. Your diagram should show the Reader, System and Pass classes. Your diagram should use 3 patterns that we have seen in class. For the sake of clarity, don't hesitate to divide your diagram over several pages if necessary.

B) For each part of the system to be designed, identify and justify the design patterns you applied. For each boss, you must:

clearly state and name the boss,

indicate the names of the classes participating in the boss, and

Indicate one benefit of using the pattern in the context of this problem.