require 'rest-client'
require 'zlib'
require 'json'

class NvdDownloader
    attr_accessor :version, :base_url, :base_filename, :years

    MIN_YEAR = '2002'
    MAX_YEAR = '2019'
    AVAILABLE_YEARS = (MIN_YEAR..MAX_YEAR).to_a

    def initialize
        @version = "1.0"
        @base_url = "https://nvd.nist.gov/feeds/json/cve/#{version}/"
        @base_filename = "nvdcve-#{version}-"
        @years = self.years
    end

    def years
        year = NvdDownloader::AVAILABLE_YEARS.map do |year|
            [year.to_i, year]
        end.to_h
    end

    def filenames(extension)
        year_filenames = years.map do |k, year|
            "#{base_filename}#{year}.#{extension}"
        end

        other_filenames = [ 
            "#{base_filename}recent.#{extension}",
            "#{base_filename}modified.#{extension}"
        ]

        year_filenames + other_filenames
    end

    def get(url)
        r = RestClient.get "#{base_url}#{url}"
        r.body if r.code == 200
    end

    def read_gzip_stream(gzip_stream)
        io_stream = StringIO.new(gzip_stream)
        gz = Zlib::GzipReader.new(io_stream)
        gz.read
    end

    def write_to_file(parsed_json, file_path)
        File.write(file_path, parsed_json)
    end

    def parse_json(json_string)
        JSON.parse(json_string)
    end

    def one_time_import
        # this should be a method that does a one-time import
        # of all of the json.gz from each year + recent + modified json feeds
    end

    def modified_meta
        # this should be a method that builds 
        # the modified filename with the meta file extension included
    end

    def check_metafile(metafile)
        # open the metafile, build a hash of k/v pairs of the data inside of the file
        # check each k/v pair against the file on disk
        # return a new hash with the same k as before, but the value being a boolean true or false if the value from the k/v pair
    end

    def detect_changes(metafile)
        # this should be a method that detects changes in the metafile. 
        # run the check_metafile method against the current metafile on disk.
        # if there is a change, return true, if not return false
    end
end