;; Copyright (C) 2023  Felisp
;;
;; This program is free software: you can redistribute it and/or modify
;; it under the terms of the GNU Affero General Public License as published by
;; the Free Software Foundation, version 3 of the License.
;;
;; 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 Affero General Public License for more details.
;;
;; You should have received a copy of the GNU Affero General Public License
;; along with this program.  If not, see <https://www.gnu.org/licenses/>.

(ns rss-thread-watch.feed-generator
  "Generates feed for requests"
  (:require [ring.middleware.params :as rp]
            [clj-rss.core :as rss]
            [clojure.string :as s]
            [rss-thread-watch.watcher :as cache])
  (:gen-class))


(defn indices
  ;; https://stackoverflow.com/questions/8641305/find-index-of-an-element-matching-a-predicate-in-clojure
  "Returns indexes of elements passing predicate"
  [pred coll]
   (keep-indexed #(when (pred %2) %1) coll))

(defn new-guid-always
  "Generates always unique GUID for Feed item.
   This is used when user wants notification on every server update,
   no matter whether thread actually changed it's position.

   This is done by always making new GUID - (concat thread-number UNIX-time-of-data-update)"
  [thread time]
  (assoc thread guid (str (:no thread)
                          "-"
                          time)))

(defn update-only-guid
  "Generates new GUID for feed item ONLY if the threads ChoD increased

   This is done by concating thread-number and it's rounded chod"
  [thread]
  (assoc thread :guid (format "%d-%.2f"
                              (:no thread)
                              :chod thread)))

(defn filter-chod-posts
  "Return list of all threads with equal or higher ChoD than requested"
  [query-vec chod-treshold repeat?]
  (let [time-of-generation (System/currentTimeMillis)
        guid-fn (if repeat? (fn [x] (new-guid-always x time-of-generation))
                    update-only-guid)
        cache-start-index (first (indices (fn [x] (>= x chod-treshold))
                                          @cache/chod-threads-cache))
        ;; So we don't have to search thru everything we have cached
        needed-cache-part (subvec @cache/chod-threads-cache cache-start-index)
        actuall-matches (keep (fn [t]
                                (let [title (:title t)]
                                  (when (some (fn [querry]
                                                (s/includes? title querry))
                                              query-vec)
                                    t)))
                              needed-cache-part)]
    ;; Finally generate and append GUIDs
    (map guid-fn actuall-matches)))

(defn http-handler
  "Handles HTTP requests, returns generated feed

   READS FROM GLOBALS:
     rss-thread-watch.watcher.chod-threads-cache
     rss-thread-watch.core.CONFIG"
  [rqst]
  {:status 200
   :header {"Content-Type" "text/html"}
   :body "All pony here ^:)"})