module Disco
  module Data
    def load_movielens
      item_path = download_file("ml-100k/u.item", "https://files.grouplens.org/datasets/movielens/ml-100k/u.item",
        file_hash: "553841ebc7de3a0fd0d6b62a204ea30c1e651aacfb2814c7a6584ac52f2c5701")
      data_path = download_file("ml-100k/u.data", "https://files.grouplens.org/datasets/movielens/ml-100k/u.data",
        file_hash: "06416e597f82b7342361e41163890c81036900f418ad91315590814211dca490")

      movies = {}
      File.foreach(item_path) do |line|
        row = line.encode("UTF-8", "ISO-8859-1").split("|")
        movies[row[0]] = row[1]
      end

      data = []
      File.foreach(data_path) do |line|
        row = line.split("\t")
        data << {
          user_id: row[0].to_i,
          item_id: movies[row[1]],
          rating: row[2].to_i
        }
      end

      data
    end

    private

    def download_file(fname, origin, file_hash:)
      require "digest"
      require "fileutils"
      require "net/http"
      require "tmpdir"

      # TODO handle this better
      raise "No HOME" unless ENV["HOME"]
      dest = "#{ENV["HOME"]}/.disco/#{fname}"
      FileUtils.mkdir_p(File.dirname(dest))

      return dest if File.exist?(dest)

      temp_path = "#{Dir.tmpdir}/disco-#{Time.now.to_f}" # TODO better name

      digest = Digest::SHA2.new

      uri = URI(origin)

      # Net::HTTP automatically adds Accept-Encoding for compression
      # of response bodies and automatically decompresses gzip
      # and deflateresponses unless a Range header was sent.
      # https://ruby-doc.org/stdlib-2.6.4/libdoc/net/http/rdoc/Net/HTTP.html
      Net::HTTP.start(uri.host, uri.port, use_ssl: uri.scheme == "https") do |http|
        request = Net::HTTP::Get.new(uri)

        puts "Downloading data from #{origin}"
        File.open(temp_path, "wb") do |f|
          http.request(request) do |response|
            response.read_body do |chunk|
              f.write(chunk)
              digest.update(chunk)
            end
          end
        end
      end

      if digest.hexdigest != file_hash
        raise Error, "Bad hash: #{digest.hexdigest}"
      end

      puts "Hash verified: #{file_hash}"

      FileUtils.mv(temp_path, dest)

      dest
    end
  end
end