Timespan formatter kata

The problem

We have a system that processes tasks. Each task takes some amount of time. We know these durations in minutes, but we want to print them out in a more human-readable form, i.e., in weeks, days, hours, and minutes.

Objective

Write a function or method that takes as input an amount of time expressed as an arbitrary positive number of minutes, and returns a string with a human-readable description of that amount of time expressed in weeks, days, hours, and minutes.

For example: given 12345, return: "1 week 1 day 13 hours 45 minutes"

The solution must satisfy the following:

Zero values should generally not be output; for example, given 10345, return "1 week 4 hours 25 minutes" (i.e., skip days, as that would be 0)
There's only one exception to the rule above: for input 0, return "0 minutes"
Use singular and plural as needed
In the basic version, don't use commas or other conjuctions.

The kata should be solved in TDD. Optionally, use a functional programming language and try to keep it pure FP.

Optional tasks

1. Use conjunctions

Use commas and "and" properly, for example: "1 week, 1 day, 13 hours, and 45 minutes".

Note: follow the Oxford Comma rule, i.e., you must place a comma before the word "and" if you have more than two items. For example: "1 day, 2 hours, and 3 minutes", "1 day and 2 hours".

2. Provide a compact alternative

Write another method or function with the same behavior as above (or add an optional behavior to the original function) to produce a compact output using "w" for weeks, "d" for days, "h" for hours, and "m" for minutes, like this:

given 12345, return: "1w 1d 13h 45m"

Keep your original function, and try to end up with as little duplicated code as possible.

3. Round the less significant parts

Often, it makes little sense to use widely different units of time when describing time spans. For example, it makes sense to say that resolving a kata will take "2 minutes" or "2 weeks", but "2 weeks and 2 minutes" sounds weird. In order to make our timespan description more "human", we want to rule out weird sentences like that.

Let's start by looking at the stack of units of time we are using:

weeks
days
hours
minutes

Let's also define the depth of a timespan description as the distance (in "steps") between the largest and the smallest unit of time that is being used. For example, "weeks" are one step above "days", so "1 week 2 days" has depth 1; on the other hand, weeks are 3 steps above minutes, so "1 week 2 minutes" has depth 3.

Your goal: Add an argument to your function to specify the maximum depth allowed in the output. Then modify the function to omit the less significant parts of the description accordingly. Here's a few examples:

basic description	maximum depth	resulting description
1 week 1 day 1 minute	3	1 week 1 day 1 minute
1 week 1 day 1 minute	2	1 week 1 day
1 week 1 day 1 minute	1	1 week 1 day
1 week 1 day 1 minute	0	1 week
2 weeks 1 hour 13 minutes	2	2 weeks 1 hour
1 day 1 minute	1	1 day
1 day 1 minute	2	1 day 1 minute

When omitting parts of the timespan, round to the nearest value allowed by your maximum depth, i.e., if omitting minutes, increment the hours if minutes are >30; if omitting hours, increment the days if hours are >12; if omitting days, increment the weeks if days are >3. Here's a few more examples:

basic description	maximum depth	resulting description
1 week 1 day 13 hours 45 minutes	2	1 week 1 day 14 hours
1 week 1 day 13 hours 45 minutes	1	1 week 2 days
1 week 3 days 12 hours 31 minutes	0	2 weeks

The last example is the trickiest; make sure to have a test for it. Also, take care of carry-overs (hours should never be "24", days should never be "7").

3bis. Combine 2 and 3 :-)

TODO: Add description

Installation

If available in Hex, the package can be installed by adding timespanner to your list of dependencies in mix.exs:

def deps do
  [{:timespanner, "~> 0.1.0"}]
end

Documentation can be generated with ExDoc and published on HexDocs. Once published, the docs can be found at https://hexdocs.pm/timespanner.

Eseguire il container e lanciare i test

$ docker build -t es .
$ docker run --rm -itv $(pwd):/app -w /app es bash
$ mix deps.get
$ mix test
$ mix test.watch

danielemegna/elixirspanner