#!/usr/bin/env racket
#lang racket/base

;; burn-rate :: A little script to calculate my burn rate.
;;
;; Author: Ben Sima <bensima@gmail.com>
;; License: MIT

(require
 (only-in racket/cmdline command-line))

(define (burn safe rate days)
  (- safe (* rate days)))

(define (round-off z n) ; http://stackoverflow.com/a/16302176
  (let ((power (expt 10 n)))
    (/ (round (* power z)) power)))

(define (burn-fmt amount)
  (format "You have $~a remaining this pay period!\n" (round-off amount 2)))

;;; CLI

(define safe-to-spend 0)
(define burn-rate     0)
(define days-left     0)


(define main
  (command-line
   #:usage-help
   "Calculates your current burn rate, according to your Simple.com"
   "account balances and days until your next paycheck."
   #:once-each
   [("-s" "--safe-to-spend") s "The amount left in Safe-to-Spend"
    (set! safe-to-spend (string->number s))]

   [("-b" "--burn-rate") b "How much you spend each day."
    (set! burn-rate (string->number b))]

   [("-d" "--days-left") d "How many days until next payheck."
    (set! days-left (string->number d))]

   #:multi
   [("-o" "--offsets") o ("Additional money you know you have coming in later. Will simply be added to safe-to-spend.")
    (set! safe-to-spend (+ safe-to-spend (string->number o)))]
   #:args args
   (if (= 0 (length args))
       (printf "burn-rate :: A little script to calculate burn rate. Run with --help for instructions.\n")
       (printf (burn-fmt (burn safe-to-spend burn-rate days-left))))))