Log errors to a file, warnings to stderr

require 'logger'
require 'multi_io'

# 1. Open the file for error logs
error_log_file = File.open('errors.log', File::WRONLY | File::APPEND | File::CREAT)

# 2. Create the primary logger instance
# By default, this logger sends everything to STDOUT (or whichever IO object you provide initially).
# We will adjust its output for errors later.
$logger = Logger.new(STDOUT)

# 3. Configure a custom formatter if needed
$logger.formatter = proc do |severity, datetime, progname, msg|
  "#{datetime.strftime('%Y-%m-%d %H:%M:%S')} [#{severity}] #{msg}\n"
end

# 4. Define the outputs using multi_io
# Errors will go to both stderr and the file for simplicity, but only the file will save them persistently.
# We use a custom method or condition to manage this behavior.

# A simple approach without multi_io:

# Configure the main logger to output all warnings to STDERR
$logger.level = Logger::WARN
$logger.instance_variable_set(:@logdev, Logger::LogDevice.new(STDERR))

# Create a separate, dedicated logger for ERROR level and higher that writes to the file
$error_logger = Logger.new(error_log_file)
$error_logger.level = Logger::ERROR
$error_logger.formatter = $logger.formatter # Use the same formatter

# Define a helper method to handle different levels
def log(level, message)
  case level
  when :error, :fatal
    $error_logger.add(Logger.const_get(level.to_s.upcase), message)
  when :warn, :info, :debug
    $logger.add(Logger.const_get(level.to_s.upcase), message)
  else
    $logger.info(message)
  end
end

puts "Logger configured. Running tests..."

log(:info, "This is an informational message (goes to STDOUT - but our level is WARN+ so it is suppressed)")
log(:warn, "This is a warning (goes to STDERR)")
log(:error, "This is an error (goes to errors.log)")
log(:fatal, "This is a fatal error (goes to errors.log)")

# 5. Ensure the file is closed when the script exits
at_exit { error_log_file.close }