exercism/elixir/library-fees/HINTS.md

Hints

General

• Review the functions available in the NaiveDateTime module, the Date module, and the Time module.

1. Parse the stored datetimes

• There is a built-in function that parses an ISO8601 datetime string and returns a NaiveDateTime struct.

2. Determine if a book was checked out before noon

• You can define a Time literal using the ~T sigil.
• There is a built-in function that changes a NaiveDateTime struct to a Time struct.
• There is a built-in function that checks which one of two Time structs is bigger.

3. Calculate the return date

• A day has 24 * 60 * 60 seconds.
• There is a built-in function that adds a given number of seconds to a NaiveDateTime struct.
• There is a built-in function that changes a NaiveDateTime struct to a Date struct.

4. Determine how late the return of the book was

• There is a built-in function that changes a NaiveDateTime struct to a Date struct.
• There is a built-in function that calculates the difference in days between two Date structs.

5. Determine if the book was returned on a Monday

• There is a built-in function that changes a NaiveDateTime struct to a Date struct.
• There is a built-in function that returns the day of week for a given Date struct.

6. Calculate the late fee

• Combine together all of the functions that you defined in previous steps.