require 'active_support/core_ext/file'

module ActionView
  class AssetPaths #:nodoc:
    attr_reader :config, :controller

    def initialize(config, controller)
      @config = config
      @controller = controller
    end

    # Add the extension +ext+ if not present. Return full or scheme-relative URLs otherwise untouched.
    # Prefix with <tt>/dir/</tt> if lacking a leading +/+. Account for relative URL
    # roots. Rewrite the asset path for cache-busting asset ids. Include
    # asset host, if configured, with the correct request protocol.
    def compute_public_path(source, dir, ext = nil, include_host = true)
      source = source.to_s
      return source if is_uri?(source)

      source = rewrite_extension(source, dir, ext) if ext
      source = rewrite_asset_path(source, dir)

      if controller && include_host
        has_request = controller.respond_to?(:request)
        source = rewrite_host_and_protocol(source, has_request)
      end

      source
    end

    def is_uri?(path)
      path =~ %r{^[-a-z]+://|^cid:|^//}
    end

  private

    def rewrite_extension(source, dir, ext)
      raise NotImplementedError
    end

    def rewrite_asset_path(source, path = nil)
      raise NotImplementedError
    end

    def rewrite_relative_url_root(source, relative_url_root)
      relative_url_root && !source.starts_with?("#{relative_url_root}/") ? "#{relative_url_root}#{source}" : source
    end

    def rewrite_host_and_protocol(source, has_request)
      source = rewrite_relative_url_root(source, controller.config.relative_url_root) if has_request
      host = compute_asset_host(source)
      if has_request && host && !is_uri?(host)
        host = "#{controller.request.protocol}#{host}"
      end
      "#{host}#{source}"
    end

    # Pick an asset host for this source. Returns +nil+ if no host is set,
    # the host if no wildcard is set, the host interpolated with the
    # numbers 0-3 if it contains <tt>%d</tt> (the number is the source hash mod 4),
    # or the value returned from invoking call on an object responding to call
    # (proc or otherwise).
    def compute_asset_host(source)
      if host = config.asset_host
        if host.respond_to?(:call)
          case host.is_a?(Proc) ? host.arity : host.method(:call).arity
          when 2
            request = controller.respond_to?(:request) && controller.request
            host.call(source, request)
          else
            host.call(source)
          end
        else
          (host =~ /%d/) ? host % (source.hash % 4) : host
        end
      end
    end
  end
end