module Logging

open System

/// Log levels.
let Error = 0
let Warning = 1
let Information = 2
let Debug = 3

let LevelToString level =
  match level with
    | 0 -> "Error"
    | 1 -> "Warning"
    | 2 -> "Information"
    | 3 -> "Debug"
    | _ -> "Unknown"

/// The current log level.
let mutable current_log_level = Debug

/// The inteface loggers need to implement.
type ILogger = abstract Log : int -> Printf.StringFormat<'a,unit> -> 'a

/// Writes to console.
let ConsoleLogger = { 
  new ILogger with
    member __.Log level format =
      Printf.kprintf (printfn "[%s][%A] %s" (LevelToString level) System.DateTime.Now) format
 }

/// Defines which logger to use.
let mutable DefaultLogger = ConsoleLogger

/// Logs a message with the specified logger.
let logUsing (logger: ILogger) = logger.Log

/// Logs a message using the default logger.
let log level message = logUsing DefaultLogger level message