expression-builder.clj

(require '[clojure.string :refer [join]])

(defprotocol ExpressionBuilderProtocol
  (ensureExprAttrName [this val])
  (ensureExprAttrVal  [this val])
  (ADD                [this attr amnt])
  (SET                [this attr val])
  (toArgs             [this]))

(defrecord ExpressionBuilder
  [expr-map expr-attr-vals expr-attr-names]

  ExpressionBuilderProtocol

  (ensureExprAttrName [this attr]
    (if (get expr-attr-names attr)
      expr-attr-names
      (assoc expr-attr-names
             attr
             (str "#attr" (count expr-attr-names)))))

  (ensureExprAttrVal [this val]
    (if (get expr-attr-vals val)
      expr-attr-vals
      (assoc expr-attr-vals
             val
             (str ":val" (count expr-attr-vals)))))

  (ADD [this attr amnt]
    (let [expr-attr-names (.ensureExprAttrName this attr)
          expr-attr-vals  (.ensureExprAttrVal this amnt)

          attr (get expr-attr-names attr)
          amnt (get expr-attr-vals amnt)

          add-expr (format "%s = %s + %s" attr attr amnt)
          expr-map (update expr-map ::ADD (fnil conj []) add-expr)]

      (ExpressionBuilder. expr-map expr-attr-vals expr-attr-names)))

  (SET [this attr val]
    (let [expr-attr-names (.ensureExprAttrName this attr)
          expr-attr-vals  (.ensureExprAttrVal this val)

          attr (get expr-attr-names attr)
          val (get expr-attr-vals val)

          add-expr (format "%s = %s" attr val)
          expr-map (update expr-map ::SET (fnil conj #{}) add-expr)]

      (ExpressionBuilder. expr-map expr-attr-vals expr-attr-names)))

  (toArgs
    [{:keys [expr-attr-vals expr-attr-names expr-map]}]
    {:expr-attr-vals  (clojure.set/map-invert expr-attr-vals)
     :expr-attr-names (clojure.set/map-invert expr-attr-names)
     :expr (join " " (map (fn [[k exprs]] (str (name k) " " (join "," exprs)))
                          expr-map))}))

(defn table-fn
  [_]
  "table_foo")

(defn part-key-fn
  [{:keys [host hour]}]
  (str host "::" hour))

(defn sort-key-fn
  [{:keys [source_path target_path]}]
  (str source_path "::" target_path))


(->>
  [{:host        "h1"
    :source_path "sp1"
    :target_path "tp1"
    :hour        7
    :minute      10
    :weight      100}
   {:host        "h2"
    :source_path "sp2"
    :target_path "tp2"
    :hour        7
    :minute      10
    :weight      100}
   {:host        "h1"
    :source_path "sp1"
    :target_path "tp1"
    :hour        7
    :minute      10
    :weight      200}
   {:host        "h1"
    :source_path "sp1"
    :target_path "tp1"
    :hour        7
    :minute      11
    :weight      100}]

  
  (reduce (fn [exprs click]
            (update exprs 
                    ((juxt table-fn part-key-fn sort-key-fn) click)
                    #(-> (or % (ExpressionBuilder. {} {} {}))
                         (.ADD (str "M" (:minute click)) (:weight click))
                         (.SET "SourcePath" (:source_path click))
                         (.SET "TargetPath" (:target_path click)))))
          {})
                    
  (map (fn [[[table-name part-key sort-key] expr]]
         (println "apply update to "
                  (merge {:table-name table-name
                          :part-key part-key
                          :sort-key sort-key}
                         (.toArgs expr))))))

;=> apply update to  {:table-name table_foo, :part-key h1::7, :sort-key sp1::tp1, :expr-attr-vals {:val0 100, :val1 sp1, :val2 tp1, :val3 200}, :expr-attr-names {#attr0 M10, #attr1 SourcePath, #attr2 TargetPath, #attr3 M11}, :expr ADD #attr0 = #attr0 + :val0,#attr0 = #attr0 + :val3,#attr3 = #attr3 + :val0 SET #attr1 = :val1,#attr2 = :val2}
;=> apply update to  {:table-name table_foo, :part-key h2::7, :sort-key sp2::tp2, :expr-attr-vals {:val0 100, :val1 sp2, :val2 tp2}, :expr-attr-names {#attr0 M10, #attr1 SourcePath, #attr2 TargetPath}, :expr ADD #attr0 = #attr0 + :val0 SET #attr1 = :val1,#attr2 = :val2}