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;;; Eclipse Public License 1.0, which can be found at 
;;; 
;;; http://opensource.org/licenses/eclipse-1.0.php
;;;
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;;; by the terms of this license. You must not remove this notice, or any 
;;; other, from this software. 

(ns railsy.migrations
  (:use (clojure.contrib
         [sql :only (insert-values
                     delete-rows
                     do-commands
                     with-connection
                     create-table
                     drop-table
                     transaction
                     with-query-results)]
         [logging :only (info warn)]
         [core :only (.?.)]
         [java-utils :only (as-str)]))
  (:import (java.sql SQLException)))

(def *application-db* {:classname "org.apache.derby.jdbc.EmbeddedDriver"
                       :subprotocol "derby"
                       :subname "MyDB"
                       :create true
                       })

(defn- execute-migration [direction]
  (fn [[version { migration-fn direction
                  doc :doc }]]
    (info (str (direction {:up "Applying migration "
                           :down "Undoing migration "}) version " " doc))
    (transaction
     (migration-fn)
     (if (= :up direction)
       (insert-values :SchemaVersion
                      [:version]
                      [version])
       (delete-rows :SchemaVersion ["version=?" version])))))

(defn- run-migrations [direction from to]
  "Run the specified migrations on the database"
  (dorun (map (execute-migration direction) (if (= :up direction)
                                              (take (- to from) (nthnext migrations from))
                                              (reverse (take (- from to) (nthnext migrations to)))))))

(defn- create-schema-table-if-needed [direction to]
  (try
   (info "Attempting to create SchemaVersion table")
   (create-table :SchemaVersion [:version :int "NOT NULL UNIQUE"])
   (info "No SchemaVersion table exists - first run installing migrations")
   (try 
    (run-migrations direction 0 to)
    (catch Exception ex
      (warn "Error running migrations: " ex)))
   (catch Exception e
     (when-not (= java.sql.BatchUpdateException (.?. e getCause getClass))
       (throw (SQLException. "Unknown error whilst creating SchemaVersion table" e))))))

(defn migrate
  "Pass it :up or :down and a version to migrate to.  If no arguments
are supplied we assume application of all migrations."
  ([] (migrate :up (count migrations)))
  ([direction to]
     (with-connection *application-db*
       (when (= :up direction)
         (create-schema-table-if-needed direction to))
       (let [current-version (or (with-query-results rs
                                   ["SELECT MAX(version) as version FROM SchemaVersion"]
                                   (:version (first rs)))
                                 0)]
         (run-migrations direction current-version to)))))