SoundSoftware Code Site

# Generates a migration which migrates all plugins to their latest versions

# within the database.

class PluginMigrationGenerator < Rails::Generator::Base

  # 255 characters max for Windows NTFS (http://en.wikipedia.org/wiki/Filename)

  # minus 14 for timestamp, minus some extra chars for dot, underscore, file 

  # extension. So let's have 230.

  MAX_FILENAME_LENGTH = 230

  def initialize(runtime_args, runtime_options={})

    super

    @options = {:assigns => {}}

    ensure_schema_table_exists    

    get_plugins_to_migrate(runtime_args)

    if @plugins_to_migrate.empty?

      puts "All plugins are migrated to their latest versions"

      exit(0)

    end

    @options[:migration_file_name] = build_migration_name

    @options[:assigns][:class_name] = build_migration_name.classify

  end

  def manifest

    record do |m|

      m.migration_template 'plugin_migration.erb', 'db/migrate', @options

    end

  end

  protected

    # Create the schema table if it doesn't already exist.

    def ensure_schema_table_exists

      ActiveRecord::Base.connection.initialize_schema_migrations_table

    end

    # Determine all the plugins which have migrations that aren't present

    # according to the plugin schema information from the database.

    def get_plugins_to_migrate(plugin_names)

      # First, grab all the plugins which exist and have migrations

      @plugins_to_migrate = if plugin_names.empty?

        Engines.plugins

      else

        plugin_names.map do |name| 

          Engines.plugins[name] ? Engines.plugins[name] : raise("Cannot find the plugin '#{name}'")

        end

      end

      @plugins_to_migrate.reject! { |p| !p.respond_to?(:latest_migration) || p.latest_migration.nil? }

      # Then find the current versions from the database    

      @current_versions = {}

      @plugins_to_migrate.each do |plugin|

        @current_versions[plugin.name] = Engines::Plugin::Migrator.current_version(plugin)

      end

      # Then find the latest versions from their migration directories

      @new_versions = {}      

      @plugins_to_migrate.each do |plugin|

        @new_versions[plugin.name] = plugin.latest_migration

      end

      # Remove any plugins that don't need migration

      @plugins_to_migrate.map { |p| p.name }.each do |name|

        @plugins_to_migrate.delete(Engines.plugins[name]) if @current_versions[name] == @new_versions[name]

      end

      @options[:assigns][:plugins] = @plugins_to_migrate

      @options[:assigns][:new_versions] = @new_versions

      @options[:assigns][:current_versions] = @current_versions

    end

    # Returns a migration name. If the descriptive migration name based on the 

    # plugin names involved is shorter than 230 characters that one will be

    # used. Otherwise a shorter name will be returned.

    def build_migration_name

      descriptive_migration_name.tap do |name|        

        name.replace short_migration_name if name.length > MAX_FILENAME_LENGTH

      end

    end

    # Construct a unique migration name based on the plugins involved and the

    # versions they should reach after this migration is run. The name constructed

    # needs to be lowercase

    def descriptive_migration_name

      @plugins_to_migrate.map do |plugin| 

        "#{plugin.name}_to_version_#{@new_versions[plugin.name]}" 

      end.join("_and_").downcase

    end

    # Short migration name that will be used if the descriptive_migration_name

    # exceeds 230 characters

    def short_migration_name

      'plugin_migrations'

    end

end