;; copyright (c) 2018-2019 Sean Corfield, all rights reserved

(ns next.jdbc.result-set
  "An implementation of ResultSet handling functions."
  (:require [clojure.core.protocols :as core-p]
            [next.jdbc.prepare :as prepare]
            [next.jdbc.protocols :as p])
  (:import (java.sql PreparedStatement
                     ResultSet ResultSetMetaData
                     SQLException)))

(set! *warn-on-reflection* true)

(defn- get-column-names
  "Given a ResultSet, return a vector of columns names, each qualified by
  the table from which it came.

  If :identifiers was specified, apply that to both the table qualifier
  and the column name."
  [^ResultSet rs opts]
  (let [^ResultSetMetaData rsmeta (.getMetaData rs)
        idxs (range 1 (inc (.getColumnCount rsmeta)))]
    (if-let [ident-fn (:identifiers opts)]
      (mapv (fn [^Integer i]
              (keyword (when-let [qualifier (not-empty (.getTableName rsmeta i))]
                         (ident-fn qualifier))
                       (ident-fn (.getColumnLabel rsmeta i))))
            idxs)
      (mapv (fn [^Integer i]
              (keyword (not-empty (.getTableName rsmeta i))
                       (.getColumnLabel rsmeta i)))
            idxs))))

(defn- mapify-result-set
  "Given a result set, return an object that wraps the current row as a hash
  map. Note that a result set is mutable and the current row will change behind
  this wrapper so operations need to be eager (and fairly limited).

  Supports ILookup (keywords are treated as strings).

  Supports Associative (again, keywords are treated as strings). If you assoc,
  a full row will be realized (via seq/into).

  Supports Seqable which realizes a full row of the data."
  [^ResultSet rs opts]
  (let [cols (delay (get-column-names rs opts))]
    (reify

      clojure.lang.ILookup
      (valAt [this k]
             (try
               (.getObject rs (name k))
               (catch SQLException _)))
      (valAt [this k not-found]
             (try
               (.getObject rs (name k))
               (catch SQLException _
                 not-found)))

      clojure.lang.Associative
      (containsKey [this k]
                   (try
                     (.getObject rs (name k))
                     true
                     (catch SQLException _
                       false)))
      (entryAt [this k]
               (try
                 (clojure.lang.MapEntry. k (.getObject rs (name k)))
                 (catch SQLException _)))
      (assoc [this k v]
             (assoc (into {} (seq this)) k v))

      clojure.lang.Seqable
      (seq [this]
           (seq (mapv (fn [^Integer i]
                        (clojure.lang.MapEntry. (nth @cols (dec i))
                                                (.getObject rs i)))
                      (range 1 (inc (count @cols)))))))))

(defn- reduce-stmt
  "Execute the PreparedStatement, attempt to get either its ResultSet or
  its generated keys (as a ResultSet), and reduce that using the supplied
  function and initial value.

  If the statement yields neither a ResultSet nor generated keys, return
  a hash map containing ::update-count and the number of rows updated,
  with the supplied function and initial value applied."
  [^PreparedStatement stmt f init opts]
  (if-let [^ResultSet rs (if (.execute stmt)
                           (.getResultSet stmt)
                           (when (:return-keys opts)
                             (try
                               (.getGeneratedKeys stmt)
                               (catch Exception _))))]
    (let [rs-map (mapify-result-set rs opts)]
      (loop [init' init]
        (if (.next rs)
          (let [result (f init' rs-map)]
            (if (reduced? result)
              @result
              (recur result)))
          init')))
    (f init {::update-count (.getUpdateCount stmt)})))

(extend-protocol p/Executable
  java.sql.Connection
  (-execute [this sql-params opts]
    (let [factory (prepare/->factory opts)]
      (reify clojure.lang.IReduceInit
        (reduce [_ f init]
                (with-open [stmt (prepare/create this
                                                 (first sql-params)
                                                 (rest sql-params)
                                                 factory)]
                  (reduce-stmt stmt f init opts))))))
  javax.sql.DataSource
  (-execute [this sql-params opts]
    (let [factory (prepare/->factory opts)]
      (reify clojure.lang.IReduceInit
        (reduce [_ f init]
                (with-open [con (p/get-connection this opts)]
                  (with-open [stmt (prepare/create con
                                                   (first sql-params)
                                                   (rest sql-params)
                                                   factory)]
                    (reduce-stmt stmt f init opts)))))))
  java.sql.PreparedStatement
  (-execute [this _ opts]
    (reify clojure.lang.IReduceInit
      ;; we can't tell if this PreparedStatement will return generated
      ;; keys so we pass a truthy value to at least attempt it if we
      ;; do not get a ResultSet back from the execute call
      (reduce [_ f init]
              (reduce-stmt this f init (assoc opts :return-keys true)))))
  Object
  (-execute [this sql-params opts]
    (p/-execute (p/get-datasource this) sql-params opts)))

(declare navize-row)

(defn datafiable-row
  "Given a connectable object, return a function that knows how to turn a row
  into a datafiable object that can be 'nav'igated."
  [connectable opts]
  (fn [row]
    (into (with-meta {} {`core-p/datafy (navize-row connectable opts)}) row)))

(defn execute!
  "Given a connectable object and SQL and parameters, execute it and reduce it
  into a vector of processed hash maps (rows).

  By default, this will create datafiable rows but :row-fn can override that."
  [connectable sql-params opts]
  (into []
        (map (or (:row-fn opts) (datafiable-row connectable opts)))
        (p/-execute connectable sql-params opts)))

(defn execute-one!
  "Given a connectable object and SQL and parameters, execute it and return
  just the first processed hash map (row).

  By default, this will create a datafiable row but :row-fn can override that."
  [connectable sql-params opts]
  (let [row-fn (or (:row-fn opts) (datafiable-row connectable opts))]
    (reduce (fn [_ row]
              (reduced (row-fn row)))
            nil
            (p/-execute connectable sql-params opts))))

(defn- default-schema
  "The default schema lookup rule for column names.

  If a column name ends with _id or id, it is assumed to be a foreign key
  into the table identified by the first part of the column name."
  [col]
  (let [[_ table] (re-find #"(?i)^(.+)_?id$" (name col))]
    (when table
      [(keyword table) :id])))

(defn- navize-row
  "Given a connectable object, return a function that knows how to turn a row
  into a navigable object.

  A :schema option can provide a map of qualified column names (:table/column)
  to tuples that indicate which table they are a foreign key for, the name of
  the key within that table, and (optionality) the cardinality of that
  relationship (:many, :one).

  If no :schema item is provided for a column, the convention of <table>id or
  <table>_id is used, and the assumption is that such columns are foreign keys
  in the <table> portion of their name, the key is called 'id', and the
  cardinality is :one.

  Rows are looked up using 'execute!' or 'execute-one!' and the :entities
  function, if provided, is applied to both the assumed table name and the
  assumed foreign key column name."
  [connectable opts]
  (fn [row]
    (with-meta row
      {`core-p/nav (fn [coll k v]
                     (let [[table fk cardinality] (or (get-in opts [:schema k])
                                                      (default-schema k))]
                       (if fk
                         (try
                           (let [entity-fn (:entities opts identity)
                                 exec-fn!  (if (= :many cardinality)
                                             execute!
                                             execute-one!)]
                             (exec-fn! connectable
                                       [(str "SELECT * FROM "
                                             (entity-fn (name table))
                                             " WHERE "
                                             (entity-fn (name fk))
                                             " = ?")
                                        v]
                                       opts))
                           (catch Exception _
                             ;; assume an exception means we just cannot
                             ;; navigate anywhere, so return just the value
                             v))
                         v)))})))