joeyates/middleman-caching-proxy

require "autostruct/wrap"
require "fileutils"

require "middleman/caching_proxy/version"

module Middleman::CachingProxy
  class CacheManifest
    FILENAME = ".manifest.json"
    KEY = "key"
    ITEMS = "items"
    VERSION = "version"

    def initialize(path:, key:)
      @manifest = nil
      @items = nil
    end
    include Autostruct::Wrap

    def has?(item)
      items[item.path] == item.fingerprint
    end

    def add(item)
      items[item.path] = item.fingerprint
    end

    def save
      ensure_cache_directory

      File.write manifest_path, build(items: items).to_json
    end

    private 

    def items
      @items ||= manifest[ITEMS]
    end

    def manifest_path
      ::File.join(path, FILENAME)
    end

    def manifest
      return @manifest if @manifest
      @manifest = build
      if File.exist?(manifest_path)
        from_disk = JSON.load(File.read(manifest_path))
        if is_ok?(from_disk)
          @manifest = from_disk
        end
      end
      @manifest
    end

    def is_ok?(manifest)
      return false if manifest.nil?
      return false if manifest[VERSION] != version
      # Clear cache if key changes
      return false if manifest[KEY] != key
      return false if !manifest[ITEMS].is_a?(Hash)
      true
    end

    def build(items: {})
      {
        KEY => key,
        ITEMS => items,
        VERSION => version
      }
    end

    def version
      Middleman::CachingProxy::VERSION
    end

    def ensure_cache_directory
      FileUtils.mkdir_p path
    end
  end
end