[APPINT-1146] Fix database encoding configuration

Sometimes the database is created with an character set different that
the one specified in `config/database.yml`.
This causes some issue when the database is created in non utf8 charset
(eg: latin1).

This commit adds an initializer that warn the user in case of mismatch
between the configured and actual encoding.
It also provides a migration generator to facilitate charset migration.

config/initializers/db_encoding.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+# Only applicable for MySQL
+if ActiveRecord::Base.connection_config[:adapter] == 'mysql2'
+  # Get the configured encoding
+  configured_encoding = ActiveRecord::Base.connection_config[:encoding]
+
+  # Get the actual character set from the DB
+  database_charset = ActiveRecord::Base.connection.exec_query("SELECT @@character_set_database as charset").first['charset']
+
+  msg = <<-LOG
+WARNING: The configured db encoding `#{configured_encoding}` is different from the actual one `#{database_charset}`!
+         This is likely to cause issues with special characters.
+         Please see https://maestrano.atlassian.net/wiki/x/rQ0nBg or run:
+           $ rails g connector:charset_migration
+  LOG
+
+  if configured_encoding != database_charset
+    Rails.logger.warn msg
+    warn msg
+  end
+end

lib/generators/connector/charset_migration/charset_migration_generator.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+require 'rails/generators/named_base'
+require 'rails/generators/active_record/migration'
+
+module Connector
+  module Generators
+    class CharsetMigrationGenerator < ::Rails::Generators::Base
+      include ActiveRecord::Generators::Migration
+
+      source_root File.expand_path('templates', __dir__)
+
+      def copy_migration
+        migration_template "migration.rb", "db/migrate/convert_tables_to_utf8.rb"
+      end
+    end
+  end
+end

lib/generators/connector/charset_migration/templates/migration.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+class ConvertTablesToUtf8 < ActiveRecord::Migration
+  def change_encoding(encoding,collation)
+    # Allow for different adapter in different environment
+    unless ActiveRecord::Base.connection_config[:adapter] == 'mysql2'
+      say "Skipping conversion as non MySQL database (#{ActiveRecord::Base.connection_config[:adapter]})"
+      return
+    end
+    tables = connection.tables
+    dbname = ActiveRecord::Base.connection_config[:database]
+    say_with_time "Converting database to #{encoding}" do
+      execute <<-SQL
+        ALTER DATABASE `#{dbname}` CHARACTER SET #{encoding} COLLATE #{collation};
+      SQL
+    end
+    tables.each do |tablename|
+      say_with_time "Converting table `#{tablename}` to #{encoding}" do
+        execute <<-SQL
+        ALTER TABLE `#{dbname}`.`#{tablename}` CONVERT TO CHARACTER SET #{encoding} COLLATE #{collation};
+        SQL
+      end
+    end
+  end
+
+  def change
+    reversible do |dir|
+      dir.up do
+        change_encoding('utf8','utf8_general_ci')
+      end
+      dir.down do
+        change_encoding('latin1','latin1_swedish_ci')
+      end
+    end
+  end
+end