# frozen_string_literal: true
require "fileutils"
require "stringio"
require "tmpdir"
require "zlib"

class Bundler::CompactIndexClient
  class Updater
    class MisMatchedChecksumError < Error
      def initialize(path, server_checksum, local_checksum)
        @path = path
        @server_checksum = server_checksum
        @local_checksum = local_checksum
      end

      def message
        "The checksum of /#{@path} does not match the checksum provided by the server! Something is wrong " \
          "(local checksum is #{@local_checksum.inspect}, was expecting #{@server_checksum.inspect})."
      end
    end

    def initialize(fetcher)
      @fetcher = fetcher
    end

    def update(local_path, remote_path, retrying = nil)
      headers = {}

      Dir.mktmpdir("bundler-compact-index-") do |local_temp_dir|
        local_temp_path = Pathname.new(local_temp_dir).join(local_path.basename)

        # first try to fetch any new bytes on the existing file
        if retrying.nil? && local_path.file?
          FileUtils.cp local_path, local_temp_path
          headers["If-None-Match"] = etag_for(local_temp_path)
          headers["Range"] = "bytes=#{local_temp_path.size}-"
        else
          # Fastly ignores Range when Accept-Encoding: gzip is set
          headers["Accept-Encoding"] = "gzip"
        end

        response = @fetcher.call(remote_path, headers)
        return if response.is_a?(Net::HTTPNotModified)

        content = response.body
        if response["Content-Encoding"] == "gzip"
          content = Zlib::GzipReader.new(StringIO.new(content)).read
        end

        mode = response.is_a?(Net::HTTPPartialContent) ? "a" : "w"
        local_temp_path.open(mode) {|f| f << content }

        response_etag = response["ETag"].gsub(%r{\AW/}, "")
        if etag_for(local_temp_path) == response_etag
          FileUtils.mv(local_temp_path, local_path)
          return
        end

        if retrying.nil?
          update(local_path, remote_path, :retrying)
        else
          raise MisMatchedChecksumError.new(remote_path, response_etag, etag_for(local_temp_path))
        end
      end
    end

    def etag_for(path)
      sum = checksum_for_file(path)
      sum ? %("#{sum}") : nil
    end

    def checksum_for_file(path)
      return nil unless path.file?
      # This must use IO.read instead of Digest.file().hexdigest
      # because we need to preserve \n line endings on windows when calculating
      # the checksum
      Digest::MD5.hexdigest(IO.read(path))
    end
  end
end
