#lang plai-typed

(require [typed-in racket (substring : (string number number -> string))]
         [typed-in racket (string-length : (string -> number))])

; 2012

(define-type (tv-pair 'a 'b)
  [tv (tag : 'a) (value : 'b)])

(define (wc-map [file : (tv-pair string string)]) : (listof (tv-pair string number))
    (map (lambda ([word : string]) : (tv-pair string number)
           (tv word 1))
         (parse-words (tv-value file))))

(define (wc-reduce [word-counts : (tv-pair string (listof number))]) : (tv-pair string number)
  (tv (tv-tag word-counts)
           (length (tv-value word-counts))))

; words can be divided by any number of spaces
(define (parse-words [text : string]) : (listof string)
  (cond
    [(string=? "" text) empty]
    [else (local [(define word (take-til " " text))]
            (cons word
                (parse-words (rmv-spaces
                              (substring text (string-length word) (string-length text))))))]))

; removes spaces from front until a letter is hit
(define (rmv-spaces [str : string]) : string
  (cond  
    [(string=? "" str) ""]
    [(string=? (substring str 0 1) " ") (rmv-spaces (substring str 1 (string-length str)))]
    [else str]))

; takes from the front of a string until it hits c
(define (take-til [c : string] [str : string]) : string
  (cond
    [(string=? "" str) ""]
    [(string=? c (substring str 0 1)) ""]
    [else (string-append (substring str 0 1)
                         (take-til c (substring str 1 (string-length str))))]))