;;; Copyright © 2015 David Thompson <address@hidden>
;;; Copyright © 2016-2017 Amirouche Boubekki <address@hidden>
;;;
;;; This program is free software: you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License as published by
;;; the Free Software Foundation, either version 3 of the License, or
;;; (at your option) any later version.
;;;
;;; This program is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this program.  If not, see <http://www.gnu.org/licenses/>.

;; ChangeLog:
;;
;; - 2017-XX-XX: add support for script tags
;;

(define-module (web html))

(use-modules (ice-9 rdelim))
(use-modules (sxml simple))
(use-modules (srfi srfi-26))
(use-modules (ice-9 match))
(use-modules (ice-9 format))
(use-modules (ice-9 hash-table))
(use-modules (srfi srfi-1))

(use-modules (web uri))
(use-modules ((sxml xpath) #:renamer (symbol-prefix-proc 'sxml:)))

;;;
;;; sxml->html
;;;

(define %void-elements
  '(area
    base
    br
    col
    command
    embed
    hr
    img
    input
    keygen
    link
    meta
    param
    source
    track
    wbr))

(define (void-element? tag)
  "Return #t if TAG is a void element."
  (pair? (memq tag %void-elements)))

(define %escape-chars
  (alist->hash-table
   '((#\" . "quot")
     (#\& . "amp")
     (#\' . "apos")
     (#\< . "lt")
     (#\> . "gt"))))

(define (string->escaped-html s port)
  "Write the HTML escaped form of S to PORT."
  (define (escape c)
    (let ((escaped (hash-ref %escape-chars c)))
      (if escaped
          (format port "&~a;" escaped)
          (display c port))))
  (string-for-each escape s))

(define (object->escaped-html obj port)
  "Write the HTML escaped form of OBJ to PORT."
  (string->escaped-html
   (call-with-output-string (cut display obj <>))
   port))

(define (attribute-value->html value port)
  "Write the HTML escaped form of VALUE to PORT."
  (if (string? value)
      (string->escaped-html value port)
      (object->escaped-html value port)))

(define (attribute->html attr value port)
  "Write ATTR and VALUE to PORT."
  (format port "~a=\"" attr)
  (attribute-value->html value port)
  (display #\" port))

(define (element->html tag attrs body port)
  "Write the HTML TAG to PORT, where TAG has the attributes in the
list ATTRS and the child nodes in BODY."
  (format port "<~a" tag)
  (for-each (match-lambda
             ((attr value)
              (display #\space port)
              (attribute->html attr value port)))
            attrs)
  (cond
   ((and (null? body) (void-element? tag)) (display " />" port))
   ((eqv? tag 'script) (display #\> port) (unless (null? body) (display (car body) port)) (display "</script>" port))
   (else (begin
           (display #\> port)
           (for-each (cut sxml->html <> port) body)
           (format port "</~a>" tag)))))

(define (doctype->html doctype port)
  (format port "<!DOCTYPE ~a>" doctype))

(define* (sxml->html tree #:optional (port (current-output-port)))
  "Write the serialized HTML form of TREE to PORT."
  (match tree
    (() *unspecified*)
    (('doctype type)
     (doctype->html type port))
    (((? symbol? tag) ('@ attrs ...) body ...)
     (element->html tag attrs body port))
    (((? symbol? tag) body ...)
     (element->html tag '() body port))
    ((nodes ...)
     (for-each (cut sxml->html <> port) nodes))
    ((? string? text)
     (string->escaped-html text port))
    ;; Render arbitrary Scheme objects, too.
    (obj (object->escaped-html obj port))))

(export sxml->html)