(in-package #:chatikbot)

(defstruct feed url title seen-guids next-fetch (period 300))
(defstruct feed-item guid link title description published)

(defparameter *rss-min-period* 60 "Min rss refresh period in seconds")
(defparameter *rss-max-period* 600 "Min rss refresh period in seconds")
(defparameter *rss-change-rate* 0.1 "Refresh period adjustment rata")

(defun http-default (url)
  (let ((uri (quri:uri url)))
    (quri:render-uri
     (if (null (quri:uri-scheme uri))
         (quri:uri (format nil "http://~A" url))
         uri))))

(defun find-rss-url (url)
  (ignore-errors
    (multiple-value-bind (body status headers uri stream)
        (dex:get (http-default url) :force-binary t)
      (declare (ignore status stream))
      (let ((root (plump:parse (flexi-streams:octets-to-string body :external-format :utf-8)))
            (content-type (gethash "content-type" headers)))
        (cond
          ((alexandria:starts-with-subseq "text/html" content-type)
           (loop for link in (plump:get-elements-by-tag-name root "link")
              when (string= "application/rss+xml" (plump:attribute link "type"))
              do (return (quri:render-uri
                          (quri:merge-uris (quri:uri (plump:attribute link "href"))
                                           uri)))))
          ((string= "rss" (plump:tag-name (plump:first-element root)))
           (quri:render-uri uri)))))))

(defun build-feed (url)
  (let ((root (plump:parse (flexi-streams:octets-to-string
                            (dex:get url :force-binary t) :external-format :utf-8))))
    (make-feed :url url :title (child-text root "title"))))

(defun adjust-period (feed had-new?)
  "Adjust the period of feed based on whenever there were new items. With clamping"
  (let* ((p (feed-period feed))
         (diff (round (* p *rss-change-rate*))))
    (setf (feed-period feed)
          (min *rss-max-period*
               (max *rss-min-period*
                    (if had-new? (- p diff) (+ p diff)))))))

(defun need-fetch-p (feed)
  (or (null (feed-next-fetch feed))
      (local-time:timestamp> (local-time:now) (feed-next-fetch feed))))

(defun fetch-new-items (feed)
  (let ((items
         (loop for item in (parse-rss (feed-url feed))
            unless (member (feed-item-guid item) (feed-seen-guids feed) :test #'equal)
            do (pushnew (feed-item-guid item) (feed-seen-guids feed) :test #'equal)
            and collect item)))
    (adjust-period feed (consp items))
    (setf (feed-next-fetch feed)
          (local-time:timestamp+ (local-time:now)
                                 (feed-period feed)
                                 :sec))
    items))

(defun trim-nil (text)
  (when text
    (let ((text (string-trim " " text)))
      (unless (zerop (length text))
        text))))

(defun text-with-cdata (node)
  "Compiles all text nodes within the nesting-node into one string."
  (with-output-to-string (stream)
    (labels ((r (node)
               (loop for child across (plump:children node)
                  do (typecase child
                       (plump:text-node (write-string (plump:text child) stream))
                       (plump:cdata (write-string (plump:text child) stream))
                       (plump:nesting-node (r child))))))
      (r node))))

(defun child-text (node tag)
  (alexandria:when-let (child (car (nreverse
                                    (plump:get-elements-by-tag-name node tag))))
    (trim-nil (text-with-cdata child))))

(defun clean-text (text)
  (when text (trim-nil (plump:text (plump:parse text)))))

(defun parse-rss (url)
  (let ((plump:*tag-dispatchers* plump:*xml-tags*))
    (loop for item in (plump:get-elements-by-tag-name
                       (plump:parse
                        (flexi-streams:octets-to-string
                         (dex:get url :force-binary t) :external-format :utf-8))
                       "item")
       collect (make-feed-item :guid (child-text item "guid")
                               :link (child-text item "link")
                               :title (clean-text (child-text item "title"))
                               :description (clean-text (child-text item "description"))
                               :published (local-time:universal-to-timestamp
                                           (date-time-parser:parse-date-time (child-text item "pubDate")))))))

(defun format-feed-item (item)
  (format nil "~A~@[ @ ~A~]~@[~%~%~A~]~%~%~A"
          (feed-item-title item)
          (alexandria:when-let (ts (feed-item-published item))
            (local-time:format-timestring
             nil ts
             :format '((:year 2) "-" (:month 2) "-" (:day 2) " " (:hour 2) ":" (:min 2))))
          (feed-item-description item)
          (feed-item-link item)))