47 lines
2.3 KiB
Markdown
47 lines
2.3 KiB
Markdown
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# Hints
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## General
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- Review the functions available in the [`NaiveDateTime` module][naive-date-time], the [`Date` module][date], and the [`Time` module][time].
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## 1. Parse the stored datetimes
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- There is a [built-in function][naive-date-time-from-iso8601] that parses an ISO8601 datetime string and returns a `NaiveDateTime` struct.
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## 2. Determine if a book was checked out before noon
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- You can define a `Time` literal using the [`~T` sigil][time-sigil].
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- There is a [built-in function][naive-date-time-to-time] that changes a `NaiveDateTime` struct to a `Time` struct.
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- There is a [built-in function][time-compare] that checks which one of two `Time` structs is bigger.
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## 3. Calculate the return date
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- A day has `24 * 60 * 60` seconds.
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- There is a [built-in function][naive-date-time-add] that adds a given number of seconds to a `NaiveDateTime` struct.
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- There is a [built-in function][naive-date-time-to-date] that changes a `NaiveDateTime` struct to a `Date` struct.
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## 4. Determine how late the return of the book was
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- There is a [built-in function][naive-date-time-to-date] that changes a `NaiveDateTime` struct to a `Date` struct.
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- There is a [built-in function][date-diff] that calculates the difference in days between two `Date` structs.
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## 5. Determine if the book was returned on a Monday
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- There is a [built-in function][naive-date-time-to-date] that changes a `NaiveDateTime` struct to a `Date` struct.
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- There is a [built-in function][date-day-of-week] that returns the day of week for a given `Date` struct.
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## 6. Calculate the late fee
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- Combine together all of the functions that you defined in previous steps.
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[naive-date-time]: https://hexdocs.pm/elixir/NaiveDateTime.html
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[time]: https://hexdocs.pm/elixir/Time.html
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[date]: https://hexdocs.pm/elixir/Date.html
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[naive-date-time-from-iso8601]: https://hexdocs.pm/elixir/NaiveDateTime.html#from_iso8601!/2
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[naive-date-time-to-time]: https://hexdocs.pm/elixir/NaiveDateTime.html#to_time/1
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[naive-date-time-to-date]: https://hexdocs.pm/elixir/NaiveDateTime.html#to_date/1
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[naive-date-time-add]: https://hexdocs.pm/elixir/NaiveDateTime.html#add/3
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[time-sigil]: https://hexdocs.pm/elixir/Kernel.html#sigil_T/2
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[time-compare]: https://hexdocs.pm/elixir/Time.html#compare/2
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[date-diff]: https://hexdocs.pm/elixir/Date.html#diff/2
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[date-day-of-week]: https://hexdocs.pm/elixir/Date.html#day_of_week/2
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