Create initial project structure with tests and reader

.gitignore

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+.cpcache

.tool-versions

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+# https://asdf-vm.com/
+
+# Java:
+java temurin-17.0.7+7
+
+# Clojure:
+clojure 1.11.1.1342

deps.edn

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+{:deps    {org.clojure/clojure         {:mvn/version "1.11.2"}
+           org.threeten/threeten-extra {:mvn/version "1.8.0"}}
+ :paths   ["src"]
+ :aliases {:test {:extra-paths ["test"]
+                  :extra-deps {com.cognitect/test-runner      {:git/url "https://github.com/cognitect-labs/test-runner.git"
+                                                               :git/sha "dfb30dd"
+                                                               :git/tag "v0.5.1"}}
+                  :exec-fn    cognitect.test-runner.api/test}}}

src/challenge/core.clj

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+(ns challenge.core
+  (:require [clojure.set :as set])
+  (:import (java.time LocalDate Period)
+           (org.threeten.extra LocalDateRange)))
+
+(defn difference [& input])

src/challenge/readers.clj

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+(ns challenge.readers
+  (:import (org.threeten.extra LocalDateRange)))
+
+(defn local-date-range [s] (LocalDateRange/parse s))
+
+(defn local-date-range-as-iso-interval
+  "Print the given LocalDateRange `ldr` as an ISO 8601-1:2019 interval in
+  <start>/<duration> format."
+  [ldr]
+  {:pre [(instance? LocalDateRange ldr)]}
+  (let [start (.getStart ldr)
+        period (.toPeriod ldr)]
+    ;; NB: when the start date is the first day of the month and the duration is
+    ;; one month, consider printing the interval as "YYYY-MM/P1M".  This has the
+    ;; advantage of naturally segregating month intervals from day intervals in
+    ;; lexical sorts but has the disadvantage of not being parseable by the
+    ;; LocalDateRange class nor by its sibling Interval class.
+    (str start "/" period)))
+
+;; We elect to print a LocalDateRange using the ISO 8601-1:2019 <start>/<period>
+;; representation.  This is a compact and standardized representation that high-
+;; lights our expected use case of specific periods (one day and one month).
+;; The use of a LocalDate to represent the date-only start point is not well
+;; publicized, probably because the relevant ISO standard (ISO 8601-2:2019) is
+;; aggressively copyrighted and the use cases are few compared to other elements
+;; of the standard.
+(defmethod print-dup LocalDateRange
+  [o ^java.io.Writer w]
+  (doto w
+    (.write "#st/local-date-range \"")
+    (.write (local-date-range-as-iso-interval o))
+    (.write "\"")))
+
+(defmethod print-method LocalDateRange [o ^java.io.Writer w] (print-dup o w))

src/data_readers.clj

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+{st/local-date-range challenge.readers/local-date-range}

test/challenge_test.clj

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+(ns challenge-test
+  (:require [challenge.core :refer [difference]]
+            [challenge.readers]
+            [clojure.test :refer [deftest is testing]]))
+
+(def week0 #st/local-date-range "2024-01-01/P7D")
+(def week1 #st/local-date-range "2024-01-08/P7D")
+(def week2 #st/local-date-range "2024-01-15/P7D")
+(def week3 #st/local-date-range "2024-01-22/P7D")
+(def extra #st/local-date-range "2024-01-29/P3D")
+(def month0 #st/local-date-range "2024-01-01/P1M")
+
+(deftest unary
+  (is (= #{week0}
+         (difference #{week0})))
+  (testing "compresses results"
+    (is (= #{month0}
+           (difference #{week0 week1 week2 week3 extra})))))
+
+(deftest binary
+  (testing "equals"
+    (is (= #{}
+           (difference #{week0} #{week0})))
+    (is (= #{}
+           (difference #{week0 week1} #{week0 week1}))))
+  (testing "overlapped by"
+    (is (= #{#st/local-date-range "2024-01-01/P4D"}
+           (difference #{week0}
+                       #{#st/local-date-range "2024-01-05/P10D"})))
+    (is (= #{#st/local-date-range "2024-01-01/P4D"}
+           (difference #{week0 week1}
+                       #{#st/local-date-range "2024-01-05/P10D"}))))
+  (testing "met by"
+    (is (= #{week0}
+           (difference #{week0} #{week1}))))
+  (testing "contains"
+    (is (= #{week0 #st/local-date-range "2024-01-15/P17D"}
+           (difference #{month0} #{week1}))))
+  (testing "during"
+    (is (= #{}
+           (difference #{week1} #{month0})))))
+
+(deftest variadic
+  (is (= #{week0 extra}
+         (difference #{month0}
+                     #{week1}
+                     #{week2 week3}))))