#lang racket/base

(require racket/match racket/function racket/port racket/string
         net/url net/url-structs net/url-string)

(provide (struct-out gmi-rsp)
         (struct-out gmi-rsp:success)
         gemini-request-read
         gemini-parse-success-meta
         gemini-response-read
         gemini-request-write
         gemini-response-write
         gemini-make-success-meta)

;; protocol

(define gmi-codes
  (hash 'input 10
        'sensitive-input 11
        'success 20
        'redirect-temp 30
        'redirect-perm 31
        'failure-temp 40
        'server-unavailable 41
        'cgi-error 42
        'proxy-error 43
        'slow-down 44
        'failure-perm 50
        'not-found 51
        'gone 52
        'proxy-fail 53
        'bad-request 59
        'cert-required 60
        'cert-not-authorized 61
        'cert-not-valid 62))
(define gmi-rev-codes
  (for/hash ([(k v) (in-hash gmi-codes)])
    (values v k)))

;; Int Str
(struct gmi-rsp [status meta-line] #:transparent)
;; Str Hash Port
(struct gmi-rsp:success gmi-rsp [mime extra-fields body] #:transparent)

;; port -> url
;; reads a gemini request (returns the URL)
(define (gemini-request-read [port (current-input-port)])
  (let ([line (read-line port 'any)])
    (string->url port)))

;; util: parse success meta text
;; str -> mimetype fields-hash
(define (gemini-parse-success-meta meta)
  (match (regexp-split #px"; *" meta)
    [(list meta rst ...)
     (values meta (for/hash ([item (in-list rst)])
                  (match (regexp-match-positions "=" item)
                    [(list (cons pos _)) (values (substring item 0 pos) (substring item (add1 pos)))]
                    [_ (values item #t)])))]
    ['() (raise (exn:fail:network "gmi protocol error" (current-continuation-marks)))]))

;; port -> gmi-rsp
(define (gemini-response-read [port (current-input-port)])
  (let ([line (read-line port 'any)])
    (match (regexp-match #px"^([0-9]{2}) (.*?)$" line)
      [(list _ status-str meta)
       (let ([status (string->number status-str)])
         (match status
           [(? (curry = (hash-ref gmi-codes 'success)))
            (let-values ([(mime extra-fields) (gemini-parse-success-meta meta)])
              (gmi-rsp:success status meta mime extra-fields port))]
           [_
            (close-input-port port)
            (gmi-rsp status meta)]))]
      [_ (raise (exn:fail:network "gmi protocol error" (current-continuation-marks)))])))

;; url port ->
(define (gemini-request-write req-url [port (current-output-port)])
  (write-string (format "~a\r\n" (url->string req-url)) port))

;; gmi-rsp port ->
(define (gemini-response-write resp [port (current-output-port)])
  (write-string (format "~a ~a\r\n" (gmi-rsp-status resp) (gmi-rsp-meta-line resp)) port))

;; string hash -> string
(define (gemini-make-success-meta mime extra-fields)
  (string-join (cons mime (for/list ([(k v) (in-hash extra-fields)])
                            (match v
                              [#t k]
                              [_ (string-append k "=" v)])))
               "; "))

(module+ test
  (require rackunit))