Create initial project structure with tests and reader

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}