require 'logger'
require 'time'
require 'json'

require 'colorize'


# Extending the base Logger with TRACE capabilities.
class Logger

  # Adding the new severity level
  SEV_LABEL << 'TRACE'

  # So we can reference it by name
  TRACE = SEV_LABEL.index('TRACE')

  # Send a TRACE-level log
  def trace progname, &block
    return true unless @trace
    add TRACE, nil, progname, &block
  end

end



module Slog

  # A colorful structured logger.
  class Logger < Logger

    DEFAULT_LEVEL = ::Logger::INFO

    # Create a new Logger.
    #
    # A little different than the canonical Logger. Add options to set the
    # log level and to disable both colorization and pretty JSON output. In
    # this form, it's perfect for use with either Logstash or Franz.
    def initialize \
      out:$stdout,                     # Output handle
      shift_age:7,                     # Max seven logs
      shift_size:1_048_576,            # 1024 KiB
      colorize:true,                   # Disable for files
      prettify:true,                   # Disable for files
      level:DEFAULT_LEVEL,             # INFO
      level_transform:'downcase',      # Any String method
      level_field:'level',             # nil to disable
      message_field: 'message',        # nil to disable
      timestamp_field:'@timestamp',    # nil to disable
      timestamp_format:'%FT%T.%3N%:z', # ISO-8601
      color_map: {
        'debug' => [ :blue,    :default ],
        'info'  => [ :green,   :default ],
        'warn'  => [ :yellow,  :default ],
        'error' => [ :red,     :default ],
        'fatal' => [ :red,     :black   ],
        'trace' => [ :magenta, :default ]
      }

      @prettify = prettify
      @colorize = colorize
      @color_map = color_map
      @level_field = level_field
      @level_transform = level_transform
      @message_field = message_field
      @timestamp_field = timestamp_field
      @timestamp_format = timestamp_format

      super out, shift_age, shift_size
      self.level = level

      set_formatter
    end


    # Set the formatter to work our magic
    def set_formatter
      self.formatter = proc do |severity, datetime, _, message|
        severity.downcase!

        # If it ain't a structured log, it is now.
        event = structure_event severity, datetime, message

        # When debugging, mark the location in Hoss's source
        unless level == DEFAULT_LEVEL
          event.merge! marker: File.basename(caller[4])
        end

        # Apply colorization and prettification as required
        format_json event, severity
      end
    end


    # Turn a call to the formatter into a Hash structure
    def structure_event severity, datetime, message
      message = { @message_field => message } unless message.is_a? Hash
      event = {
        @level_field => severity.send(@level_transform),
        @timestamp_field => datetime.strftime(@timestamp_format)
      }
      event.merge! message
      event.delete nil # ignore @field if @field.nil?
      event
    end


    # Convert the structured event into it's JSON representation
    def format_json event, severity
      generator = @prettify ? :pretty_generate : :generate
      event = JSON.send(generator, event) + "\n"
      return event unless @colorize
      event.colorize \
        color: @color_map[severity][0],
        background: @color_map[severity][1]
    end


    # Override the level setter to allow symbols and TRACE
    def level= l
      l = ::Logger.const_get l.upcase if l.is_a? Symbol
      @trace = l == ::Logger::TRACE # TRACE is really a fancy DEBUG
      l = ::Logger::DEBUG if @trace # Here's the proof.
      super l
    end

  end
end