# frozen_string_literal: true

require "yog/logfmt"

# Writes structured log lines.
class Yog

  # Get ready to do some yogging.
  def initialize(generator: Logfmt, output: $stdout, context: {})
    @context = context
    @generator = generator
    @output = output

    freeze
  end

  # Log a message. Logs any given block's duration as `elapsed=float` ms.
  def info(msg, **fields)
    if @output.nil?
      return (yield if block_given?)
    end

    if msg.is_a?(Hash)
      msg, fields = nil, fields.merge(msg)
    end

    start = Time.now.utc
    prefix = { now: start }
    result = nil

    if msg
      prefix[:msg] = msg
    end

    if block_given?
      result = yield
      prefix[:duration] = (Time.now - start) * 1000
    end

    combined = prefix.merge(@context).merge(fields)
    @output.puts(@generator.generate(combined))

    result
  end

  # Log an error.
  def error(ex, **fields)
    info(error: ex.message, type: ex.class, **fields)
  end

  # Update the context.
  def set(**fields)
    tap { @context.merge!(fields) }
  end

  # Create a new log with more context.
  def with(**fields)
    self.class.new \
      context: @context.merge(fields),
      generator: @generator,
      output: @output
  end

  ### Helpers for the default log

  # The log for Yog(), Yog.set(), and Yog.with().
  def self.default
    logs.first
  end

  # A stack of receivers with the default log first.
  def self.logs
    Thread.current[:logs] ||= [new]
  end

  # Add fields to all Yog() calls in the given block.
  def self.context(**fields)
    yield logs.unshift(with(fields))
  ensure
    logs.shift
  end

  # Update the context of the default log.
  def self.set(**fields)
    default.set(fields)
  end

  # Create a new log by extending the context of the default log.
  def self.with(**fields)
    default.with(fields)
  end

  # Write a line to the default log.
  def self.info(msg, **fields, &block)
    default.info(msg, fields, &block)
  end

  # Log an error to the default log.
  def self.error(ex, **fields)
    default.error(ex, fields)
  end
end

# Write a line to the default log.
def Yog(msg, **fields, &block)
  case msg
  when Exception
    Yog.error(msg, fields)
  else
    Yog.info(msg, fields, &block)
  end
end