#lang typed/racket/base
(require racket/string
         typed/net/url-structs
         "pure-utils.rkt")
(require/typed web-server/http/request-structs
               [#:opaque Header header?])

(provide
 ; regex to match wiki names
 px-wikiname
 ; make a query string from an association list of strings
 params->query
 ; custom percent encoding (you probably want params->query instead)
 percent-encode
 ; sets for custom percent encoding
 path-set urlencoded-set filename-set
 ; make a proxied version of a fandom url
 u-proxy-url
 ; check whether a url is on a domain controlled by fandom
 is-fandom-url?
 ; pass in a header, headers, or something useless. they'll all combine into a list
 build-headers
 ; try to follow wikimedia's format for which characters should be encoded/replaced in page titles for the url
 page-title->path
 ; path/param eats semicolons into params, which need to be fixed back into semicolons
 fix-semicolons-url-path
 fix-semicolons-url)

(module+ test
  (require "typed-rackunit.rkt"))

(define px-wikiname "[a-zA-Z0-9-]{1,50}")

;; https://url.spec.whatwg.org/#urlencoded-serializing

(define path-set '(#\; ; semicolon is part of the userinfo set in the URL standard, but I'm putting it here
                   #\? #\` #\{ #\} ; path set
                   #\  #\" #\# #\< #\> ; query set
                   ; c0 controls included elsewhere
                   ; higher ranges included elsewhere
                   ))
(define urlencoded-set (append
                        '(#\! #\' #\( #\) #\~ ; urlencoded set
                          #\$ #\% #\& #\+ #\, ; component set
                          #\/ #\: #\= #\@ #\[ #\\ #\] #\^ #\| ; userinfo set
                          )
                        path-set))

(define filename-set '(#\< #\> #\: #\" #\/ #\\ #\| #\? #\* #\# #\~ #\&))

(: percent-encode (String (Listof Char) Boolean -> Bytes))
(define (percent-encode value set space-as-plus)
  (define b (string->bytes/utf-8 value))
  (apply bytes-append
         (for/list ([char b]) : (Listof Bytes)
                   (cond
                     [(and space-as-plus (eq? char 32))
                      #"+"]
                     [(or (member (integer->char char) set)
                          (char . > . #x7E)
                          (char . <= . #x1F))
                      (bytes-append #"%" (string->bytes/latin-1
                                          (string-upcase (number->string char 16))))]
                     [#t
                      (bytes char)]))))

(: params->query ((Listof (Pair String String)) -> String))
(define (params->query params)
  (string-join
   (map (λ ([p : (Pair String String)])
          (format "~a=~a"
                  (percent-encode (car p) urlencoded-set #t)
                  (percent-encode (cdr p) urlencoded-set #t)))
        params)
   "&"))
(module+ test
  (check-equal? (params->query '(("hello" . "world")))
                "hello=world")
  (check-equal? (params->query '(("a" . "hello world''") ("utf8" . "✓")))
                "a=hello+world%27%27&utf8=%E2%9C%93"))

(: is-fandom-url? (String -> Boolean))
(define (is-fandom-url? url)
  (regexp-match? (pregexp (format "^https://static\\.wikia\\.nocookie\\.net/|^https://~a\\.fandom\\.com/" px-wikiname)) url))
(module+ test
  (check-true (is-fandom-url? "https://static.wikia.nocookie.net/wikiname/images/2/2f/SomeImage.jpg/revision/latest?cb=20110210094136"))
  (check-true (is-fandom-url? "https://test.fandom.com/wiki/Some_Page"))
  (check-false (is-fandom-url? "https://cadence.moe")))

(: u-proxy-url (String -> String))
(define (u-proxy-url url)
  (u
   is-fandom-url?
   (λ ([v : String]) (string-append "/proxy?" (params->query `(("dest" . ,url)))))
   url))

(: build-headers ((U Header (Listof Header) False Void) * -> (Listof Header)))
(define (build-headers . fs)
  (apply
   append
   (map (λ ([f : (U Header (Listof Header) False Void)])
         (cond
           [(not f) null]
           [(void? f) null]
           [(null? f) null]
           [(header? f) (list f)]
           [(pair? f) f]))
       fs)))

(: page-title->path (String -> Bytes))
(define (page-title->path title)
  (percent-encode (regexp-replace* " " title "_") path-set #f))

(: fix-semicolons-url-path ((Listof Path/Param) -> (Listof Path/Param)))
(define (fix-semicolons-url-path pps)
  (for/list ([pp pps])
    (define path (path/param-path pp))
    (if (or (null? (path/param-param pp))
            (symbol? path))
        pp
        ;; path/param does have params, which need to be fixed into a semicolon.
        (path/param
         (string-append path ";" (string-join (path/param-param pp) ";"))
         null))))

(: fix-semicolons-url (URL -> URL))
(define (fix-semicolons-url orig-url)
  (struct-copy url orig-url [path (fix-semicolons-url-path (url-path orig-url))]))