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#lang racket/base
(require "core.rkt" racket/match racket/contract racket/string racket/list sugar/unstable/container sugar/coerce)
(define/contract (css-unit? x)
(any/c . -> . boolean?)
(x . in? . '("%" "in" "cm" "mm" "em" "ex" "pt" "pc" "px" "rem")))
(struct cssq (num unit)
#:methods gen:custom-write
[(define write-proc
(λ(x port mode) (display (format "~a~a" (cssq-num x) (cssq-unit x)) port)))])
(define/contract (cssqish? x)
(any/c . -> . boolean?)
(->boolean (or (cssq? x) (string? x))))
(define/contract (string->unit x)
(string? . -> . css-unit?)
(if (css-unit? x)
(error 'string->unit "'~a' not a valid css unit" x)))
(define/contract (cssqish->cssq x)
(cssqish? . -> . cssq?)
[(cssq? x) x]
[else (begin
(define pieces (let* ([str (string-downcase x)]
[str (string-replace str " " "")]
[str (string-trim str "s" #:left? #f)])
(string-split str #px"(?<![A-Za-z])(?=[A-Za-z])")))
(apply cssq
(with-handlers ([exn:fail? (λ(e) (error 'string->cssq (exn-message e)))])
(list (string->number (first pieces))
(string->unit (second pieces))))))]))
(define/contract (css-math-op op left right)
(procedure? cssqish? cssqish? . -> . cssq?)
(let ([left (cssqish->cssq left)]
[right (cssqish->cssq right)])
(cssqish->cssq (format "~a~a" (apply op (list (cssq-num left) (cssq-num right)))(cssq-unit left)))))
(define-values (css+ css- css* css/)
(apply values (map (λ(op) (λ(left right) (css-math-op op left right))) (list + - * /))))
(module+ main
(css+ "10rem" "5rem"))