(ns clojure-sql.dsl
  (:refer-clojure :exclude [sort-by])
  (:require [clojure.set :as set]
            [clojure.walk]
            [clojure-sql.query :as q]
            [clojure-sql.util :as u]))


;; ==============================================================
;; The DSL for making query maps
;; ==============================================================

;; important sections:
;;   -PROJECTION-
;;   -TABLES-
;;   -FILTERS-
;;   GROUPING
;;   GROUPED FILTERS
;;   -SORTING-

;; {
;;  :table => tablename -> table_alias,
;;  :fields => (table_alias, fieldname) -> field_alias
;;  :joins => [tablename -> (type, table_alias, on)]
;;  :where => expression
;;  :sort-by => [(field, direction)]
;; }

(defn table [arg]
  (into (q/->Query)
        (if (map? arg)
          {:table arg}
          {:table {arg arg}})))

(defn ^:private ambiguous-error [field & [query]]
  (throw (ex-info (str "Ambiguous field " field " in query with more than one table")
                  {:field field
                   :query query})))

(defn ^:private resolve-field [table aliases field]
  (let [field-alias-lookup (u/flip-map aliases)]
    (or (field-alias-lookup field)
        (if table
          [table field]
          (ambiguous-error field)))))

(defn ^:private resolve-fields [table aliases expression]
  (cond (list? expression) (map (partial resolve-fields table aliases) expression)
        (vector? expression) (mapv (partial resolve-fields table aliases) expression)
        (keyword? expression) (resolve-field table aliases expression)
        :else expression))

(defn project [query fields]
  (let [table (if-not (:joins query)
                (-> query :table first val))
        alias-lookup (u/flip-map (:fields query))
        original-name #(resolve-fields table (:fields query) %)]
    (assoc query
      :fields (->> (for [[key val] (if (map? fields)
                                     fields
                                     (zipmap fields fields))]
                     [(original-name key) val])
                   (into {})))))

(defn rename [query field-renames]
  {:pre [(map? field-renames)
         ;; the intersection of the new aliases with the old aliases NOT renamed by this operation
         (empty? (set/intersection (set (vals field-renames))
                                   (set/difference (set (vals (:fields query)))
                                                   (set (keys field-renames)))))]}
  (let [fields (:fields query)
        alias-lookup (u/flip-map (:fields query)) 
        original-name (fn [field]
                        (cond (vector? field) field
                              (contains? alias-lookup field) (get alias-lookup field)
                              :else (throw (ex-info (str "Cannot rename field " (pr-str field) ". Field does not exist in query.")
                                                    {:field field
                                                     :query query
                                                     :renames field-renames})))
                        (get alias-lookup field))]
    (update-in query
               [:fields] #(->> (for [[key val] field-renames]
                                 ;(if (contains? val (:fields query)))
                                 [(original-name key) val])
                               (into %)))))

(defn ^:private combine-wheres [& wheres]
  (reduce (fn [acc where]
            (cond (nil? acc) where
                  (nil? where) acc
                  :else (or (if (and (sequential? where)
                                     (= (name (first where)) "and"))
                              `(and ~acc ~@(next where)))
                            (if (and (sequential? acc)
                                     (= (name (first acc)) "and"))
                              `(and ~@(next acc) ~where))
                            `(and ~acc ~where))))
          nil wheres))

(defn join [left right & {:keys [on type]}]
  (let [joins-vector (or (:join left) []) 
        common-fields (set/intersection (set (vals (:fields left)))
                                        (set (vals (:fields right))))
        joined-fields (if (:type :right) 
                        (merge (->> (:fields left)
                                    (filter (comp not common-fields val))
                                    (into {}))
                               (:fields right))
                        (merge (:fields left)
                               (->> (:fields right)
                                    (filter (comp not common-fields val))
                                    (into {}))))
        implicit-on (if (seq common-fields)
                      (map (fn [field]
                             `(= ~(resolve-field (:table left) (:fields left) field)
                                 ~(resolve-field (:table right) (:fields right) field)))
                           common-fields))
        on (if on
             [(resolve-fields nil joined-fields on)])
        join-condition (if-let [condition (seq (concat implicit-on on))]
                         `(and ~@condition)
                         true)]
    (-> left
        (assoc :fields joined-fields)
        (assoc :joins (into (conj joins-vector
                                  [(or type :inner) (:table right) join-condition])
                            (:joins right)))
        (assoc :where (combine-wheres (:where left) (:where right))))))

(defn select [query expression]
  (let [table-name (if-not (:joins query)
                     (-> query :table first val))
        old-where (:where query)
        resolved-expression (resolve-fields table-name (:fields query) expression)
        new-where (combine-wheres old-where resolved-expression)]
    (assoc query :where new-where)))

(defn sort-by [query fields]
  (let [table-name (if-not (:joins query)
                     (-> query :table first val))
        fields-seq (if (sequential? fields)
                     fields
                     [fields])]
    (assoc query
      :sort-by (for [field fields-seq]
                 (if (vector? field)
                   (resolve-field table-name (:fields query) field)
                   [(resolve-field table-name (:fields query) field) :asc])))))