(ns clojure-sql.compiler
  (:refer-clojure :exclude [compile sequence])
  (:require [clojure.string :as string]
            [clojure-sql.query :refer [query?]]
            [clojure-sql.util :as u :refer [named?]]
            [clojure-sql.writer :as w :refer [return lift p-lift sequence do-m tell >>]]))

(defn no-args-operator-error [op]
  (throw (ex-info (str "Argument called with no args doesn't have identity value: " op)
                  {:operator op})))



(defn add-parentheses [s]
  (str \( s \)))


;; ==============================================================
;; DB specific escaping methods
;; ==============================================================

(defmulti field-name (fn [db _] db))
(defmethod field-name :default [_ field]
  (str \" (name field) \"))

(defmulti table-name (fn [db _] db))
(defmethod table-name :default [_ table]
  (str \" (name table) \"))

(defmulti function-name (fn [db _] db))
(defmethod function-name :default [_ function]
  (str \" (name function) \"))




;; we use the $ prefix to denote a lifted function
(def $add-parentheses (lift add-parentheses))
(def $str (lift str))




;; ==============================================================
;; Utility functions for the compile-* functions
;; ==============================================================

(def ^:private boolean? (some-fn true? false?))
(def ^:private regex? (partial instance? (class #"")))
(def ^:private operator-name (some-fn (comp {"$" "~"} name) name))

(def quote? (comp boolean '#{"quote"} name))
(def unary? (comp boolean '#{"not" "exists" "-"} name))
(def binary? (comp boolean '#{"=" "<" ">" "<=" ">=" "is" "in" "like" "~"} name))
(def n-ary? (comp boolean '#{"and" "or" "+" "-" "/" "*"} name))
(def operator-identity (comp {"and" true
                              "or" false
                              "+" 0
                              "*" 1} name))


;; ==============================================================
;; compile-* functions (turning a map into a query string)
;; ==============================================================

;; compile-* multimethods are of the signature:
;;  (db, expr) -> [args] -> [sql & args]

(declare compile-query compile-expression)

(defmulti compile-expression-list (fn [db _] db))
(defmethod compile-expression-list :default [db ex]
  (->> (map (partial compile-expression db) ex)
       (apply sequence)
       ((p-lift string/join ","))
       $add-parentheses))

(defmulti compile-expression-sequential (fn [db _] db))
(defmethod compile-expression-sequential :default [db ex]
  (let [compile-exprs #(map (partial compile-expression db) %)
        op-name (operator-name (first ex))
        num-args (dec (count ex))]
    (-> (condp u/funcall op-name
          quote?    (do (assert (= num-args 1) "`quote` must only take one argument")
                        (if (sequential? (second ex))
                          (compile-expression-list db (second ex))
                          (>> (tell (second ex)) (return "?"))))
          n-ary?    (do-m :let [[op & exprs] (compile-exprs ex)]
                          vals <- (apply sequence (interpose op exprs))
                          (condp = (count vals)
                            0 (if-let [id (operator-identity op-name)]
                                (compile-expression db id)
                                (no-args-operator-error (name (first ex))))
                            1 (if (unary? op-name)
                                (do-m compiled-op <- op
                                      (return (str compiled-op (first vals))))
                                (return (first vals))) 
                            (return (string/join " " vals))))
          unary?    (do (assert (= num-args 1) (str "Unary operator `" (first ex) "` must take one argument"))
                        (do-m :let [exprs (compile-exprs ex)]
                              vals <- (apply sequence exprs)
                              (return (string/join "" vals))))
          binary?   (do (assert (= num-args 2) (str "Binary operator `" (first ex) "` must take two arguments"))
                        (do-m :let [[op left right] (compile-exprs ex)]
                              vals <- (sequence left op right)
                              (return (string/join " " vals))))
          (do-m :let [fn-name (function-name db (first ex))
                      exprs (compile-exprs (rest ex))]
                vals <- (apply sequence exprs)
                (return (str fn-name
                             (add-parentheses (string/join "," vals))))))
        $add-parentheses)))

(defmulti compile-expression (fn [db _] db))
(defmethod compile-expression :default [db ex]
  (condp u/funcall ex
    boolean?     (return (string/upper-case (str ex)))
    query?       ($add-parentheses (compile-query db ex))
    nil?         (return "NULL")
    vector?      (return (str (table-name db (first ex)) \. (field-name db (second ex))))
    keyword?     (return (field-name db ex))
    regex?       (>> (tell (str ex)) (return "?"))
    string?      (>> (tell ex) (return "?")) ;;(sql-string db ex)
    symbol?      (return (string/upper-case (operator-name ex)))
    sequential?  (compile-expression-sequential db ex)
    (return ex)))

(defn ^:private make-table-name [db table & [alias]]
  (if (or (= table alias) (nil? alias))
    (return (table-name db table))
    ($str (condp #(%1 %2) table
            query? ($add-parentheses (compile-query db table))
            named? (return (table-name db table))
            (compile-expression db table))
          (return " AS ")
          (return (table-name db alias)))))

(defn ^:private make-field-name [db field & [alias]]
  (if (and (vector? field) (or (= field alias) (nil? alias)))
    (compile-expression db field)
    ($str (compile-expression db field)
          (return " AS ")
          (return (field-name db alias)))))

(defmulti compile-fields (fn [db _] db))
(defmethod compile-fields :default [db fields-map]
  (if (seq fields-map)
    (->> (for [[alias field] fields-map]
           (make-field-name db field alias))
         (apply sequence)
         ((p-lift string/join ", ")))
    (return "*")))

(def ^:private join-type-names
  {:inner "INNER"
   :outer "LEFT OUTER"
   :full-outer "FULL OUTER"
   :cross "CROSS"})

(defmulti compile-tables (fn [db _ _] db))
(defmethod compile-tables :default [db join tables-map] 
  (if (vector? join) 
    (->> (for [table-alias join]
           (make-table-name db (get tables-map table-alias) table-alias))
         (apply sequence)
         ((p-lift string/join ", ")))
    (let [{:keys [left right type on]} join]
      (if (= type :cross)
        ($str (return "(")
              (compile-tables db left tables-map)
              (return " CROSS JOIN ")
              (compile-tables db right tables-map)
              (return ")"))
        ($str (return "(") 
              (compile-tables db left tables-map)
              (return (str " " (get join-type-names type (name type)) " JOIN "))
              (compile-tables db right tables-map) 
              (return " ON ")
              (if on
                (compile-expression db on)
                (return "TRUE"))
              (return ")"))))))

(defmulti compile-where (fn [db _] db))
(defmethod compile-where :default [db expr]
  (if expr
    ($str (return " WHERE ") (compile-expression db expr))
    (return nil)))

(defmulti compile-sort (fn [db _] db))
(defmethod compile-sort :default [db fields]
  (if fields
    (->> (for [[[table field] dir] fields]
           ($str (make-field-name db [table field])
                 (return (str \space (string/upper-case (name dir))))))
         (apply sequence)
         ((p-lift string/join ","))
         ($str (return " ORDER BY ")))
    (return nil)))

(defmulti compile-group (fn [db _] db))
(defmethod compile-group :default [db fields]
  (if fields
    (->> (for [[table field] fields]
           (make-field-name db [table field]))
         (apply sequence)
         ((p-lift string/join ","))
         ($str (return " GROUP BY ")))
    (return nil)))

(defmulti compile-having (fn [db _] db))
(defmethod compile-having :default [db expr]
  (if expr
    ($str (return " HAVING ") (compile-expression db expr))
    (return nil)))

(defmulti compile-query (fn [db _] db))
(defmethod compile-query :default [db {:keys [tables fields joins where sort group having union]}]
  (if union
    (->> union
         (map (partial compile-query db))
         (apply sequence)
         ((p-lift string/join " UNION ")))
    ($str (return "SELECT ")
          (compile-fields db fields)
          (if tables
            ($str (return " FROM ")
                  (compile-tables db joins tables))
            ($str ""))
          (compile-where db where)
          (compile-group db group)
          (compile-having db having)
          (compile-sort db sort))))




(defn compile [db query]
  (let [[sql vars] ((compile-query db query) [])]
    (vec (cons sql vars))))


;; ==============================================================
;; A few DB specific overrides
;; ==============================================================


;; SQL SERVER
(defmethod field-name :sql-server [_ field]
  (str \[ (name field) \]))

(defmethod table-name :sql-server [_ table]
  (str \[ (name table) \]))

;; mySQL
(defmethod field-name :mysql [_ field]
  (str \` (name field) \`))

(defmethod table-name :mysql [_ table]
  (str \` (name table) \`))


;;(compile nil {:table {:u :u}, :fields {[:v :x] :w}})




;; Utility functions

(defn insert! [db query & records]
  {:pre [(empty? (:joins query))]}
  ;; some code here
  )

(defn update! [db query & partial-records]
  {:pre [(empty? (:joins query))]}
  ;; some code here
  )

(defn delete! [db query]
  {:pre [(empty? (:joins query))]}
  ;; some code here
  )