1 files changed, 89 insertions, 0 deletions
diff --git a/lib/click_house/migration.rb b/lib/click_house/migration.rb
new file mode 100644
index 00000000000..410a7ec86bc
--- /dev/null
+++ b/lib/click_house/migration.rb
@@ -0,0 +1,89 @@
+# frozen_string_literal: true
+
+module ClickHouse
+  class Migration
+    cattr_accessor :verbose, :client_configuration
+    attr_accessor :name, :version
+
+    class << self
+      attr_accessor :delegate
+    end
+
+    def initialize(name = self.class.name, version = nil)
+      @name    = name
+      @version = version
+    end
+
+    self.client_configuration = ClickHouse::Client.configuration
+    self.verbose = true
+    # instantiate the delegate object after initialize is defined
+    self.delegate = new
+
+    MIGRATION_FILENAME_REGEXP = /\A([0-9]+)_([_a-z0-9]*)\.?([_a-z0-9]*)?\.rb\z/
+
+    def database
+      self.class.constants.include?(:SCHEMA) ? self.class.const_get(:SCHEMA, false) : :main
+    end
+
+    def execute(query)
+      ClickHouse::Client.execute(query, database, self.class.client_configuration)
+    end
+
+    def up
+      self.class.delegate = self
+
+      return unless self.class.respond_to?(:up)
+
+      self.class.up
+    end
+
+    def down
+      self.class.delegate = self
+
+      return unless self.class.respond_to?(:down)
+
+      self.class.down
+    end
+
+    # Execute this migration in the named direction
+    def migrate(direction)
+      return unless respond_to?(direction)
+
+      case direction
+      when :up   then announce 'migrating'
+      when :down then announce 'reverting'
+      end
+
+      time = Benchmark.measure do
+        exec_migration(direction)
+      end
+
+      case direction
+      when :up   then announce format("migrated (%.4fs)", time.real)
+                      write
+      when :down then announce format("reverted (%.4fs)", time.real)
+                      write
+      end
+    end
+
+    private
+
+    def exec_migration(direction)
+      # noinspection RubyCaseWithoutElseBlockInspection
+      case direction
+      when :up then up
+      when :down then down
+      end
+    end
+
+    def write(text = '')
+      $stdout.puts(text) if verbose
+    end
+
+    def announce(message)
+      text = "#{version} #{name}: #{message}"
+      length = [0, 75 - text.length].max
+      write format('== %s %s', text, '=' * length)
+    end
+  end
+end