(ns microformats.parser
  (:require [net.cgrand.enlive-html :as html]
            [clojure.core.reducers :as r]
            [clojure.string :as str]))

(defn mf-names-from-class
  "Get microformat classnames from a class attribute"
  [prefix]
  #(.startsWith % prefix))

(defn remove-mf-prefix
  "Remove microformats prefixes from a class attribute"
  [prefix]
  #(apply str (drop (count prefix) %)))

(defn- split-ws-attribute
  "Split a whitespace-separated attribute."
  [class]
  (str/split class #"\s+"))

(defn classes-to-props
  "Convert class list to list of microformat property keywords"
  [prefix]
  (comp (r/map keyword)
        (r/map (remove-mf-prefix prefix))
        (r/filter (mf-names-from-class prefix))))

(defn element-to-classes
  "Get list of classes from an element"
  [el] (some-> el
               :attrs
               :class
               split-ws-attribute))

(defn element-to-rels
  "Get list of rels from an element"
  [el] (-> el
           :attrs
           :rel
           split-ws-attribute))

(defn- node-to-html
  "Turn a node into a list of HTML strings"
  [el]
  (map #(if (string? %)
          %
          (apply str (persistent! (html/emit-tag % (transient []))))) el))

(defn- node-to-text
  "Turn a node into a text string"
  [content]
  (->> content
       html/texts
       (map #(str/replace % #"\s+" " "))
       (apply str)
       str/trim))

(defn get-value-class
  "Get the value class of elements"
  [elements]
  (str/join " " (into [] ((comp (r/map (partial apply str))
                                (r/map node-to-text)
                                (r/map :content))
                          elements))))

(defn find-value-class
  "Find and get the value class of elements"
  [el]
  (when-let [values (seq (html/select el [html/root :> :.value]))]
    (get-value-class values)))

(defn get-p-value
  "Get the p-x property value of an element"
  [el]
  (str/trim (or (find-value-class el)
            (case (:tag el)
              :img (-> el :attrs :alt)
              :area (-> el :attrs :alt)
              :abbr (-> el :attrs :title)
              :data (-> el :attrs :value)
              :input (-> el :attrs :value)
              nil)
            (node-to-text (:content el))
            "")))

(defn get-u-value
  "Get the u-x property value of an element"
  [el]
  (str/trim (or (find-value-class el)
            (case (:tag el)
              :a (-> el :attrs :href)
              :area (-> el :attrs :href)
              :img (-> el :attrs :src)
              :object (-> el :attrs :data)
              (get-p-value el))
            (node-to-text (:content el))
            "")))

(defn get-dt-value
  "Get the dt-x property value of an element"
  [el]
  (str/trim (or (find-value-class el)
            (case (:tag el)
              :time (-> el :attrs :datetime)
              :ins  (-> el :attrs :datetime)
              :del  (-> el :attrs :datetime)
              :abbr (-> el :attrs :title)
              :data (-> el :attrs :value)
              :input (-> el :attrs :value))
            (node-to-text (:content el))
            "")))

(defn get-e-value
  "Get the e-x propery value of an element"
  [el]
  (let [content (:content el)]
    (list {:html (apply str (node-to-html content))
           :value (apply str (node-to-text content))})))

(defn parse-p
  "Parse p-* classes within HTML element."
  [element]
  (->> element
       element-to-classes
       ((classes-to-props "p-"))
       (r/map #(hash-map % (list (get-p-value element))))
       (into {})))

(defn parse-u
  "Parse u-* classes within HTML element"
  [element]
  (->> element
       element-to-classes
       ((classes-to-props "u-"))
       (r/map #(hash-map % (list (get-u-value element))))
       (into {})))

(defn parse-dt
  "Parse dt-* classes within HTML element"
  [element]
  (->> element
       element-to-classes
       ((classes-to-props "dt-"))
       (r/map #(hash-map % (list (get-dt-value element))))
       (into {})))

(defn parse-e
  "Parse e-* classes within HTML element"
  [element]
  (->> element
       element-to-classes
       ((classes-to-props "e-"))
       (r/map #(hash-map % (get-e-value element)))
       (into {})))

(defn- get-mf-names
  "Get the microformat names from an element"
  [element]
  (->> element
       element-to-classes
       (r/filter (mf-names-from-class "h-"))
       (into [])))

(defn- imply-name
  "Imply the name of an entity from the element"
  [element]
  (list (node-to-text (:content element))))

(defn parse-implied
  "Parse implied properties of a HTML element"
  [element]
  {:name (imply-name element)})

(defn parse-h
  "Parse h-* classes within a HTML element."
  [element]
  (let [el (first (html/select element [(html/union [(html/attr-starts :class "p-")
                                                     (html/attr-starts :class "u-")
                                                     (html/attr-starts :class "dt-")
                                                     (html/attr-starts :class "e-")])]))]
    (hash-map :type (get-mf-names element)
              :properties (merge (parse-implied element)
                                 (apply merge ((juxt parse-p parse-u parse-dt parse-e) el))))))

(defn select-h
  "Select h-* elements within a HTML document."
  [element]
  (html/select element [(html/attr-starts :class "h-")]))

(defn parse-rel
  "Parse rel attributes of an HTML link element"
  [element]
  (->> element
       element-to-rels
       (map keyword)
       (map #(hash-map % [(-> element :attrs :href)]))
       (into {})))

(defn select-rels
  "Select linking HTML elements with rel attributes"
  [html] (html/select html [[#{:a :link} (html/attr? :rel)]]))

(defn parse-rels
  "Parse rel attibutes of a set of HTML link elements"
  [elements]
  (or (apply merge-with into (map parse-rel (select-rels elements))) {}))

(defn parse
  "Parse a HTML string with microformats"
  [html]
  (let [document (html/html-snippet html)]
    {:items (mapv parse-h (select-h document)) :rels (parse-rels document)}))