module Katello
  module Util
    class CdnVarSubstitutor
      attr_reader :good_listings
      attr_reader :bad_listings
      # cdn_resource - an object providing access to CDN. It has to
      # provide a get method that takes a path (e.g.
      # /content/rhel/6.2/listing) and returns the body response)
      def initialize(cdn_resource)
        @resource = cdn_resource
        @substitutions = Thread.current[:cdn_var_substitutor_cache] || {}
        @good_listings = Set.new
        @bad_listings = Set.new
      end

      # using substitutor from whithin the block makes sure that every
      # request is made only once.
      def self.with_cache(&_block)
        Thread.current[:cdn_var_substitutor_cache] = {}
        yield
      ensure
        Thread.current[:cdn_var_substitutor_cache] = nil
      end

      # precalcuclate all paths at once - let's you discover errors and stop
      # before it causes more pain
      def precalculate(paths_with_vars)
        paths_with_vars.uniq.reduce({}) do |ret, path_with_vars|
          ret[path_with_vars] = substitute_vars(path_with_vars)
          ret
        end
      end

      # takes path e.g. "/rhel/server/5/$releasever/$basearch/os"
      # returns hash substituting variables:
      #
      #  { {"releasever" => "6Server", "basearch" => "i386"} =>  "/rhel/server/5/6Server/i386/os",
      #    {"releasever" => "6Server", "basearch" => "x86_64"} =>  "/rhel/server/5/6Server/x84_64/os"}
      #
      # values are loaded from CDN
      def substitute_vars(path_with_vars)
        if path_with_vars =~ /^(.*\$\w+)(.*)$/
          prefix_with_vars, suffix_without_vars =  Regexp.last_match[1], Regexp.last_match[2]
        else
          prefix_with_vars, suffix_without_vars = "", path_with_vars
        end

        prefixes_without_vars = substitute_vars_in_prefix(prefix_with_vars)
        paths_without_vars = prefixes_without_vars.reduce({}) do |h, (substitutions, prefix_without_vars)|
          h[substitutions] = prefix_without_vars + suffix_without_vars
          h
        end
        return paths_without_vars
      end

      # prefix_with_vars is the part of url containing some vars. We can cache
      # calcualted values for this parts. So for example for:
      #   "/a/$b/$c/d"
      #   "/a/$b/$c/e"
      # prefix_with_vars is "/a/$b/$c" and we store the result after resolving
      # for the first path.
      def substitute_vars_in_prefix(prefix_with_vars)
        paths_with_vars = { {} => prefix_with_vars}
        prefixes_without_vars = @substitutions[prefix_with_vars]

        unless prefixes_without_vars
          prefixes_without_vars = {}
          until paths_with_vars.empty?
            substitutions, path = paths_with_vars.shift

            if substituable? path
              for_each_substitute_of_next_var substitutions, path do |new_substitution, new_path|
                begin
                  paths_with_vars[new_substitution] = new_path
                rescue Errors::SecurityViolation
                  # Some paths may not be accessible
                  @resource.log :warn, "#{new_path} is not accessible, ignoring"
                end
              end
            else
              prefixes_without_vars[substitutions] = path
            end
          end
          @substitutions[prefix_with_vars] = prefixes_without_vars
        end
        return prefixes_without_vars
      end

      def substituable?(path)
        path.include?("$")
      end

      def valid_substitutions(content, substitutions)
        validate_all_substitutions_accepted(content, substitutions)
        content_url = content.contentUrl
        real_path = gsub_vars(content_url, substitutions)

        if substituable?(real_path)
          fail Errors::CdnSubstitutionError, _("%{substitutions} are not valid substitutions for %{content_url}") %
              { substitutions: substitutions, content_url: content.contentUrl }
        else
          is_valid = valid_path?(real_path, 'repodata/repomd.xml') || valid_path?(real_path, 'PULP_MANIFEST')
          unless is_valid
            @resource.log :error, "No valid metadata files found for #{real_path}"
            fail Errors::CdnSubstitutionError, _("%{substitutions} are not valid substitutions for %{content_url}."\
                   " No valid metadata files found for %{real_path}") %
              { substitutions: substitutions, content_url: content.contentUrl, real_path: real_path}
          end
        end
      end

      protected

      def validate_all_substitutions_accepted(content, substitutions)
        unaccepted_substitutions = substitutions.keys.reject do |key|
          content.contentUrl.include?("$#{key}")
        end
        if unaccepted_substitutions.size > 0
          fail Errors::CdnSubstitutionError, _("%{unaccepted_substitutions} cannot be specified for %{content_name}"\
                 " as that information is not substituable in %{content_url} ") %
              { unaccepted_substitutions: unaccepted_substitutions, content_name: content.name, content_url: content.contentUrl }
        end
      end

      def valid_path?(path, postfix)
        @resource.get(File.join(path, postfix)).present?
      rescue RestClient::MovedPermanently
        return true
      rescue Errors::NotFound
        return false
      end

      def gsub_vars(content_url, substitutions)
        substitutions.reduce(content_url) do |url, (key, value)|
          url.gsub("$#{key}", value)
        end
      end

      def for_each_substitute_of_next_var(substitutions, path)
        if path =~ /^(.*?)\$([^\/]*)/
          base_path, var = Regexp.last_match[1], Regexp.last_match[2]
          get_substitutions_from(base_path).compact.each do |value|
            new_substitutions = substitutions.merge(var => value)
            new_path = path.sub("$#{var}", value)

            yield new_substitutions, new_path
          end
        end
      end

      def get_substitutions_from(base_path)
        ret = @resource.get(File.join(base_path, "listing")).split("\n")
        @good_listings << base_path
        ret
      rescue Errors::NotFound => e # some of listing file points to not existing content
        @bad_listings << base_path
        @resource.log :error, e.message
        [] # return no substitution for unreachable listings
      end
    end
  end
end