string_calculator.clj

(use 'speclj.core)
(require '[clojure.string :as str])

(defn- assert-positives [^String s]
  (if-let [neg (re-seq #"-\d+" s)]
    (throw (Exception. (str "Unexpected negative numbers: " (str/join ", " neg))))))

(defn- parse-input [^String s]
  (if-let [[[_ sep text]] (re-seq #"//(.+)\n(.+)" s)]
    [text sep]
    [(if (empty? s) "0" s) ",|\n"]))

(defn calc [^String s]
  (assert-positives s)
  (let [[text sep] (parse-input s)
        nums (str/split text (re-pattern sep))]
    (transduce (map read-string) + nums)))

(describe "String calculator"

  (context "given empty string on input"
    (it "should return zero"
        (should= 0 (calc ""))))

  (context "given single number on input"
    (it "should return that number"
        (should= 1 (calc "1"))
        (should= 2 (calc "2"))))

  (context "given numbers separated by comma"
    (it "should return sum of the numbers"
        (should= 2 (calc "1,1"))
        (should= 3 (calc "1,1,1"))))

  (context "given numbers separated by new line"
    (it "should return sum of the numbers"
        (should= 2 (calc "1\n1"))))

  (context "given separator and numbers separated by that separator"
    (it "should return sum of the numbers"
        (should= 2 (calc "//;\n1;1")))))

  (context "given negative numbers"
    (it "should throw"
        (should-throw (calc "-1")))
    (it "should throw with negative numbers in message"
        (should-throw Exception "Unexpected negative numbers: -1, -2" (calc "-1,1,-2"))))

(run-specs)