(define-module (dhhieft)
  #:use-module (srfi srfi-1)
  #:export (dhhieft
            string->vowels
            three-vowels?
            repeated-char?
            favorable-string?
            long-distance-match?))


(define (dhhieft str p2?)
  (count (lambda (x) x)
         (map (lambda (str)
                (favorable-string? str p2?))
              (string-split
               (string-trim-both str char-set:whitespace)
               #\newline))))

(define (favorable-string? str p2?)
  "Returns #t or #f depending on if STR
meets the requirements defined in the problem
definition.

If p2? is true, uses the problem two definition
of favorable."
  (let ((gap (if p2? 1 0)))
    (and (repeated-char? str gap)
         (if p2?
             (long-distance-match? str)
             (and (three-vowels? str)
                  (not (or (string-contains str "ab")
                           (string-contains str "cd")
                           (string-contains str "pq")
                           (string-contains str "xy"))))))))

(define (long-distance-match? str)
  "Given STR, returns #t if a substring
of size two is repeated multiple times in
STR, non-overlapping."
  (if (< (string-length str) 3)
      #f
      (let loop ((str (substring str 2)) (pair (substring str 0 2)))
        (cond
         ((string-contains str pair) #t)
         ((< (string-length str) 3) #f)
         (#t (loop (substring str 1)
                   (string-append (substring pair 1) (substring str 0 1))))))))

(define (repeated-char? str gapsize)
  "Given STR, returns a boolean
indicating if the string contains
a repeated character.

GAPSIZE is the number of characters to
skip when making repeated char comparisons."
  (let loop ((lst (string->list str)))
    (cond
     ((>= (1+ gapsize) (length lst)) #f)
     ((equal? (car lst) (list-ref lst (1+ gapsize))) #t)
     (#t (loop (cdr lst))))))

(define (three-vowels? str)
  "Given STR, returns a boolean
indicating if the string contains
at least three vowels."
  (>= (string-length
       (string->vowels (string-downcase str)))
      3))

(define (string->vowels str)
  "Given STR, returns STR with all
non-vowel characters removed."
  (string-filter (char-set #\a #\e #\i #\o #\u) str))