profitability_calculator.clj

(import '[java.math MathContext RoundingMode])

(comment
  (apply + (last
            (transpose
             (map (fn [i]
                    (concat (repeat i 0)
                            (map (partial * 1.75) (range 1 (- 12 i)))))
                  (range 11)))))
  )

(defn bd-round
  ([bd]
   (bd-round bd 2))
  ([bd accuracy]
   (bd-round bd accuracy RoundingMode/HALF_EVEN))
  ([bd accuracy mode]
   (if (bd? bd)
     (.stripTrailingZeros (.setScale bd accuracy mode))
     bd)))

(defn bd?
  [x]
  (instance? BigDecimal x))

(defn- bd-if-not
  [x]
  (if (bd? x)
    x
    (BigDecimal. x)))

(defn divide
  ([a b]
   (let [a' (bd-if-not a)
         b' (bd-if-not b)]
     (.stripTrailingZeros (.divide a' b' MathContext/DECIMAL32))))
  ([a b & tail]
   (reduce (fn [acc x]
             (divide acc x))
           (divide a b)
           tail)))

(def ydays
  [31 28 31 30 31 30 31 31 30 31 30 31])

(defn get-sec
  [x]
  (mapcat (fn [n]
            (cons x (repeat (dec n) 0)))
          ydays))

(comment

  (let [start 6300000
        secs (get-sec 240000)]
    (bd-round (* (- 1 0.15M)
                 (- (reduce (fn [acc x]
                              (+ x
                                 (bd-round (* acc (+ 1 (divide 19.5M 100 365))) 2)))
                            start
                            secs)
                    (+ start (apply + secs))))
              2))
  )