From 7a9cd81fb6a54c5e9cf32feca43cafd942cc7c11 Mon Sep 17 00:00:00 2001
From: Chris Hapgood <cch1@hapgood.com>
Date: Thu, 6 Jun 2024 17:29:49 -0400
Subject: [PATCH] Add README and example test

---
 README.md               | 51 +++++++++++++++++++++++++++++++++++++++++
 test/challenge_test.clj |  5 ++++
 2 files changed, 56 insertions(+)
 create mode 100644 README.md

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..390a4bf
--- /dev/null
+++ b/README.md
@@ -0,0 +1,51 @@
+### The Sun Tribe Code Challenge
+You are challenged to implement a date-interval difference function.  The arguments to the function `difference` will be clojure sets, each
+of which contains zero or more [LocalDateRange](https://www.threeten.org/threeten-extra/apidocs/org.threeten.extra/org/threeten/extra/LocalDateRange.html)
+objects.  The function must return a set of LocalDateRange objects that represent the [interval difference](http://mathinschool.com/page/8.html) of the 
+first set and all additional sets of the input.  This English sentence represents an example of the operation:
+
+"Remove the second week in January 2024 and New Years Day from the month of January 2024."
+
+### Context
+At Sun Tribe Trading we gather the energy production of solar generators from various sources (typically API from of the manufacturers
+of solar energy equipment) and submit the data to regulatory authorities.  It's important that we accurately determine the energy data we need
+to gather based on the data we already have on hand and the current reporting period.  Date interval operations are central to this
+computation.
+
+### Evaluation
+Your solution will be evaluated as follows, in decreasing order of importance:
+* Correctness.  Do all the tests pass?
+* Readability.  Can we understand your code?  Is it well organized?  Is it well documented?  Is it idiomatic?
+* Performance.  How long does it take to run the test suite?
+
+Correctness and performance will be evaluated by running this command in the root of your submitted repository:
+
+`time clojure -X:test`
+
+Readability will be evaluated by your potential future colleagues looking at the entire contents of the repository.  You may organize
+the code of your implementation in any way you deem appropriate, but you must not modify the `challenge-test` namespace.  You may
+add additional tests in separate namespaces.  You may introduce additional dependencies and make other modifications to the `deps.edn`
+file, but you must not modify the `:test` alias.
+
+### Scale of the Challenge
+We believe that a performance-optimized solution to the problem is difficult and we have not attempted to implement it.  We have 
+implemented a correct solution in less than fifty lines of documented Clojure code with no additional dependencies.  It takes ~15 seconds 
+to complete the test suite on a 2023 MacBook Pro with an Apple M2 Pro processor and 32G of RAM.
+
+### Hints, maybe helpful
+Our solution evolved from the observation that a LocalDateRange object can be represented (inefficiently) by a sequence of 
+[LocalDate](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/time/LocalDate.html) objects.  That representation can be
+input into a set difference operation, but the result must be "compressed" back into the minimal set of LocalDateRange 
+objects.
+
+Before coding, you should be comfortable with the concept of a [time interval](https://en.wikipedia.org/wiki/ISO_8601#Time_intervals), and
+more specifically a (local) date interval as implemented by
+the [backing Java library we use](https://www.threeten.org/threeten-extra/apidocs/org.threeten.extra/org/threeten/extra/LocalDateRange.html).
+
+### Submitting your response
+This git repository is the entire input you will need for the Sun Tribe code challenge.  Your submission should be a modified version 
+of this repository (including our initial commits and the commit(s) of your solution).  You may submit either:
+
+* a link to a public http(s) repository that can be cloned by `git clone <url>`.
+-or-
+* a repository compressed into a standard zip file that can be opened with `unzip <file>`.
diff --git a/test/challenge_test.clj b/test/challenge_test.clj
index b45832f..733b65e 100644
--- a/test/challenge_test.clj
+++ b/test/challenge_test.clj
@@ -46,6 +46,11 @@
                      #{week1}
                      #{week2 week3}))))
 
+(deftest example-from-readme
+  (is (= #{#st/local-date-range "2024-01-02/P6D" #st/local-date-range "2024-01-15/P17D"}
+         (difference #{month0}
+                     #{week1 #st/local-date-range "2024-01-01/P1D"}))))
+
 (deftest performance
   (is (= #{#st/local-date-range "2020-01-01/P4Y" #st/local-date-range "2024-01-05/P5Y11M27D"}
          (difference #{#st/local-date-range "2020-01-01/P10Y"}