require 'base64'
require 'action_view/helpers'
require 'sewing_kit/webpack/manifest'

module SewingKit
  module Webpack
    module Helper
      include ActionView::Helpers

      class UnknownJavaScriptAssetError < StandardError
      end

      def sewing_kit_asset_paths(source, extension: 'js')
        return '' unless source.present?
        return '/webpack/assets/dll/vendor.js' if Rails.env.development? && 'vendor' == source && extension == 'js'
        return '' if ['runtime', 'vendor'].include?(source) && !Rails.env.production?

        paths = SewingKit::Webpack::Manifest.asset_paths(source)
        return '' unless paths[extension]

        [paths[extension]].flatten.reject { |path| path =~ /.*\.map$/ }
      end

      def sewing_kit_link_tag(*paths)
        return '' unless Rails.env.production?

        options = paths.extract_options!

        tags = paths.uniq.map { |path|
          create_asset_tag(:link, path, options)
        }

        safe_join(tags, "\n")
      end

      def sewing_kit_script_tag(*paths)
        options = paths.extract_options!

        tags = paths.uniq.map { |path|
          if path == ''
            next '' unless Rails.env.production?
            raise UnknownJavaScriptAssetError.new('Empty JavaSscript path passed to sewing_kit')
          end

          create_asset_tag(:script, path, options)
        }

        safe_join(tags, "\n")
      end

      private

      def create_asset_tag(tag_type, path, tag_options)
        raise ArgumentError, "Invalid tag type: #{tag_type}" unless [:script, :link].include? tag_type

        options = tag_options.clone

        if tag_options[:integrity]
          file_hash = extract_hash(path)
          options[:integrity] = file_hash ? encode_hash(file_hash) : nil
        end

        case tag_type
        when :script
          content_tag(:script, '', options.reverse_merge(src: path))
        when :link
          tag(:link, options.reverse_merge(href: path, rel: 'stylesheet'))
        end
      end

      def encode_hash(hash)
        # sewing-kit's default config places a sha256 hash in the filename. Browsers expect integrity
        # to be the Base64 encoded version of the binary hash prefixed with the hashing algorithm
        binary_hash = Array(hash).pack('H*')
        "sha256-#{Base64.strict_encode64(binary_hash)}"
      end

      def extract_hash(path)
        # Consumes sewing-kit's [name]-[chunkhash].[ext] format
        return unless path =~ /.*-[A-Za-z0-9]{64}\.(js|css)/
        path.rpartition('-').last.split('.').first
      end
    end
  end
end