require 'ostruct'

module PDK
  class TemplateFile < OpenStruct
    # Initialises the TemplateFile object with the path to the template file
    # and the data to be used when rendering the template.
    #
    # @param template_file [String] The path on disk to the template file.
    # @param data [Hash{Symbol => Object}] The data that should be provided to
    # the template when rendering.
    # @option data [Object] :configs The value of this key will be provided to
    # the template as an instance variable `@configs` in order to maintain
    # compatibility with modulesync.
    #
    # @api public
    def initialize(template_file, data = {})
      @template_file = template_file

      if data.key?(:configs)
        @configs = data[:configs]
      end

      super(data)
    end

    # Renders the template by calling the appropriate engine based on the file
    # extension.
    #
    # If the template has an `.erb` extension, the content of the template
    # file will be treated as an ERB template. All other extensions are treated
    # as plain text.
    #
    # @return [String] The rendered template
    #
    # @raise (see #template_content)
    #
    # @api public
    def render
      case File.extname(@template_file)
      when '.erb'
        render_erb
      else
        render_plain
      end
    end

    private

    # Reads the content of the template file into memory.
    #
    # @return [String] The content of the template file.
    #
    # @raise [ArgumentError] If the template file does not exist or can not be
    # read.
    #
    # @api private
    def template_content
      if File.file?(@template_file) && File.readable?(@template_file)
        return File.read(@template_file)
      end

      raise ArgumentError, _("'%{template}' is not a readable file") % { template: @template_file }
    end

    # Renders the content of the template file as an ERB template.
    #
    # @return [String] The rendered template.
    #
    # @raise (see #template_content)
    #
    # @api private
    def render_erb
      renderer = ERB.new(template_content, nil, '-')
      renderer.filename = @template_file
      renderer.result(binding)
    end

    # Renders the content of the template file as plain text.
    #
    # @return [String] The rendered template.
    #
    # @raise (see #template_content)
    #
    # @api private
    def render_plain
      template_content
    end
  end
end