;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-intermediate-lambda-reader.ss" "lang")((modname lab10_starter_file) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f () #f)))

(define-struct child [name mother father])

;; Child is a (make-child String AT AT)
;; - name is the child's name
;; - mother is the maternal AncestorTree
;; - father is the paternal AncestorTree

;; AncestorTree (AT) is one of 
;; - ‘unknown
;; - (make-child String AT AT)


; EXAMPLES AncestorTree

(define Carmen (make-child "Carmen" 'unknown 'unknown))
(define John (make-child "John" 'unknown 'unknown))
(define Joel (make-child "Joel" 'unknown 'unknown))
(define Vladimir (make-child "Vladimir" 'unknown 'unknown))
(define Mike (make-child "Mike" Carmen John))
(define Lucy (make-child "Lucy" Joel Mike))
(define Terrence (make-child "Terrence" Joel Mike))
(define Priscilla (make-child "Priscilla" Lucy Vladimir))

;; -----------------------------------------------------------------------------
;; LIBRARY

;; at=?: AT AT -> Boolean
;; given two AT determines if they are the same AT

(check-expect (at=? 'unknown 'unkown) #true)
(check-expect (at=? Lucy Lucy) #true)
(check-expect (at=? Carmen Terrence) #false)
(check-expect (at=? Vladimir 'unknown) #false)

(define (at=? at1 at2)
  (cond [(symbol? at1) (symbol? at2)]
        [else (if (symbol? at2) #false
                  (and (string=? (child-name at1) (child-name at2))
                       (at=? (child-mother at1) (child-mother at2))
                       (at=? (child-father at1) (child-father at2))))]))

;; number->ordinal: Number -> String
;; given a number, returns the corresponding ordinal string 

(check-expect (number->ordinal 1) "1st")
(check-expect (number->ordinal 22) "22nd")
(check-expect (number->ordinal 12) "12th")
(check-expect (number->ordinal 4) "4th")
(check-expect (number->ordinal 103) "103rd")

(define (number->ordinal n)
  (local ((define n-string (number->string n))
          (define length (string-length n-string))
          ; String -> String
          ; retrieves the last 1String in a String
          (define (last-string s) (substring s (- length 1) length))
          (define suffix
            (cond [(or (= n 11) (= n 12) (= n 13)) "th"]
                  [(string=? "1" (last-string n-string)) "st"]
                  [(string=? "2" (last-string n-string)) "nd"]
                  [(string=? "3" (last-string n-string)) "rd"]
                  [else "th"])))
    (string-append n-string suffix)))