(in-package #:chatikbot)

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

(defparameter *rss-min-period* 60 "Min rss refresh period in seconds")
(defparameter *rss-max-period* 1800 "Max rss refresh period in seconds")
(defparameter *rss-change-rate* 0.1 "Refresh period adjustment rate")

(defun find-rss-links (url)
  (handler-case
      (multiple-value-bind (root uri) (xml-request url)
        (loop for link in (get-by-tag root "link")
           when (string= "application/rss+xml" (plump:attribute link "type"))
           collect (list (plump:attribute link "title")
                         (puri:render-uri
                          (puri:merge-uris
                           (puri:uri (plump:attribute link "href"))
                           uri) nil))))
    (error (e) (log:error e))))

(defun build-feed (url)
  (let ((root (xml-request url)))
    (alexandria:when-let (rss (car (get-by-tag root "rss")))
      (make-feed :url url :title (child-text rss "title")))))

(defun adjust-period (period new-items)
  "Adjust the period of feed based on whenever there were new items. With clamping"
  (let ((diff (round (* period *rss-change-rate*))))
    (min *rss-max-period*
         (max *rss-min-period*
              (- period (* diff (if (zerop new-items) -1 new-items)))))))

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

(defun refresh-feed (feed &optional (skip-p #'not))
  (let* ((items
          (loop for item in (ignore-errors (fetch-feed-items feed))
             unless (funcall skip-p item)
             collect item))
         (new-period (adjust-period (feed-period feed) (length items))))
    (setf (feed-period feed) new-period
          (feed-next-fetch feed) (local-time:timestamp+ (local-time:now) new-period :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 (get-by-tag node tag)))
    (trim-nil (text-with-cdata child))))

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

(defun fetch-feed-items (feed)
  (let ((plump:*tag-dispatchers* plump:*xml-tags*))
    (loop for item in (get-by-tag (xml-request (feed-url feed)) "item")
       collect (make-feed-item :feed feed
                               :guid (or (child-text item "guid") (child-text item "link"))
                               :link (child-text item "link")
                               :title (clean-text (child-text item "title"))
                               :description (clean-text (child-text item "description"))
                               :published
                               (ignore-errors
                                 (alexandria:when-let
                                     (pub (or (child-text item "pubDate")
                                              (child-text item "published")))
                                   (local-time:universal-to-timestamp
                                    (date-time-parser:parse-date-time pub))))))))

(defun format-feed-item (item)
  (format nil "~A~@[ @ ~A~]~%~A~%~A"
          (feed-title (feed-item-feed 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-title item)
          (feed-item-link item)))

(defun feed-next-fetch-unix (feed)
  (alexandria:when-let (ts (feed-next-fetch feed))
    (local-time:timestamp-to-unix ts)))

(defun feed-item-published-unix (item)
  (alexandria:when-let (ts (feed-item-published item))
    (local-time:timestamp-to-unix ts)))