Simple logfmt logger in Ruby

logger.rb

# frozen_string_literal: true

require "logger"
require "values"

module App
  module Logger
    class ContextualLogger < Value.new(:logger, :context)
      def log(**kwargs)
        logger.info(context.merge(kwargs))
      end

      def with(additional_context)
        super(context: context.merge(additional_context))
      end
    end

    @logger = ::Logger.new(STDERR)
    @logger.formatter = proc do |_severity, datetime, _progname, payload|
      entry = {
        ts: datetime.strftime("%Y-%m-%dT%H:%M:%S.%NZ"),
        tid: Thread.current.object_id,
      }.merge(payload)
      entry.reduce("") { |a, (k, v)| a + "#{k}=\"#{v.to_s.gsub('"', '\\"')}\" " } + "\n"
    end

    def self.with(**context)
      ContextualLogger.new(@logger, context)
    end

    def self.log(**kwargs)
      @logger.info(kwargs)
    end

    def log(**kwargs)
      @logger.info(kwargs)
    end
  end
end