;; 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 week7_tu_full) (read-case-sensitive #t) (teachpacks ((lib "image.ss" "teachpack" "htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "image.ss" "teachpack" "htdp")))))
; an invention-event is a:
; - symbol inventor
; - symbol item
; - number year
(define-struct invention-event (inventor item year))

; examples:
(make-invention-event 'edison 'lightbulb 1879)
(make-invention-event 'watt 'steam-engine 1765)

; a list-of-invention-events is either:
; - empty
; - (cons invention-event list-of-invention-events)

(define myinventions (list 
                      (make-invention-event 'edison 'lightbulb 1879)
                      (make-invention-event 'edison 'phonograph 1877)
                      (make-invention-event 'watt 'steam-engine 1765)
                      (make-invention-event 'dr-evils-dad 'question-mark 1560)))


; Q1: It's time to get the credit you so richly deserve -- use lambda and map to write a (single) statement that outputs myinventions with all the inventors switched to be you.

(map (lambda (a) (make-invention-event 'doug (invention-event-item a) (invention-event-year a))) myinventions)

; Q2: Write a function select-in-years using filter that returns all inventions within a specified year range.

; select-in-years: list-of-invention-events number number -> list-of-invention-events
; returns all invention events that happened between specified years (inclusive)
(define (select-in-years loi ystart yend)
  (filter (lambda (x) (and (>= (invention-event-year x) ystart) (<= (invention-event-year x) yend))) loi))
                                                                    
(check-expect (select-in-years myinventions 1870 1890) (list (make-invention-event 'edison 'lightbulb 1879) (make-invention-event 'edison 'phonograph 1877)))
(check-expect (select-in-years myinventions 1970 1990) empty)


; a hq is a:
; - symbol company
; - symbol city
(define-struct hq (company city))

; examples:
(make-hq 'intel 'santa-clara)
(make-hq 'nvidia 'santa-clara)
(make-hq 'google 'mountain-view)

(define myhqs (list (make-hq 'intel 'santa-clara) (make-hq 'nvidia 'santa-clara) (make-hq 'google 'mountain-view)))

; Q3: Consider the following function, select-unique-city, which selects cities from a list-of-hq, eliminating duplicates:

; select-unique-city : list-of-hq -> list-of-symbol
; returns all cities in the input list, eliminating duplicates
(define (select-unique-city lohq)
  (remove-duplicates (map hq-city lohq)))

; remove-duplicates : list-of-X -> list-of-X
; Removes the symbols that appear more than once, leaving
; the relative order of the others unchanged
(define (remove-duplicates lox)
  (cond [(empty? lox) empty]
        [(cons? lox)
         (cons (first lox)
               (remove (first lox) (remove-duplicates (rest lox))))]))

(check-expect (select-unique-city myhqs) (list 'santa-clara 'mountain-view))
(check-expect (select-unique-city empty) empty)

;  Design a similar function select-unique-inventor, which selects unique inventors from a list-of-invention-events.



; select-unique-inventor : list-of-invention-event -> list-of-symbol
; returns all inventors in the input list, removing duplicates
(define (select-unique-inventor loie)
  (remove-duplicates (map invention-event-inventor loie)))

(check-expect (select-unique-inventor myinventions) (list 'edison 'watt 'dr-evils-dad))
(check-expect (select-unique-inventor empty) empty)

; Q4: Using select-unique-city and select-unique-inventor above, write an abstract function select-unique-values that can be used to return all
; unique values of some field (e.g. inventor, company) from a list of data of some type (e.g. invention-events, hqs).

; select-value : (X -> Y) list-of-X -> list-of-Y
; returns unique values produced by given selector to given list
(define (select-unique-values selector lox)
  (remove-duplicates (map selector lox)))

(check-expect (select-unique-values hq-city myhqs) (list 'santa-clara 'mountain-view))
(check-expect (select-unique-values hq-city empty) empty)
(check-expect (select-unique-values invention-event-inventor myinventions) (list 'edison 'watt 'dr-evils-dad))
(check-expect (select-unique-values invention-event-inventor empty) empty)