using Unosquare.Swan.Abstractions;
using System;
using System.Collections.Concurrent;
using System.Text;
using System.Threading;

namespace Unosquare.Swan {
  /// <summary>
  /// A console terminal helper to create nicer output and receive input from the user. 
  /// This class is thread-safe :).
  /// </summary>
  public static partial class Terminal {
    #region Private Declarations

    private const Int32 OutputFlushInterval = 15;
    private static readonly ExclusiveTimer DequeueOutputTimer;
    private static readonly Object SyncLock = new Object();
    private static readonly ConcurrentQueue<OutputContext> OutputQueue = new ConcurrentQueue<OutputContext>();

    private static readonly ManualResetEventSlim OutputDone = new ManualResetEventSlim(false);
    private static readonly ManualResetEventSlim InputDone = new ManualResetEventSlim(true);

    private static Boolean? _isConsolePresent;

    #endregion

    #region Constructors

    /// <summary>
    /// Initializes static members of the <see cref="Terminal"/> class.
    /// </summary>
    static Terminal() {
      lock(SyncLock) {
        if(DequeueOutputTimer != null) {
          return;
        }

        if(IsConsolePresent) {
#if !NET452
                    Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
#endif
          Console.CursorVisible = false;
        }

        // Here we start the output task, fire-and-forget
        DequeueOutputTimer = new ExclusiveTimer(DequeueOutputCycle);
        DequeueOutputTimer.Resume(OutputFlushInterval);
      }
    }

    #endregion

    #region Synchronized Cursor Movement

    /// <summary>
    /// Gets or sets the cursor left position.
    /// </summary>
    /// <value>
    /// The cursor left.
    /// </value>
    public static Int32 CursorLeft {
      get {
        if(IsConsolePresent == false) {
          return -1;
        }

        lock(SyncLock) {
          Flush();
          return Console.CursorLeft;
        }
      }
      set {
        if(IsConsolePresent == false) {
          return;
        }

        lock(SyncLock) {
          Flush();
          Console.CursorLeft = value;
        }
      }
    }

    /// <summary>
    /// Gets or sets the cursor top position.
    /// </summary>
    /// <value>
    /// The cursor top.
    /// </value>
    public static Int32 CursorTop {
      get {
        if(IsConsolePresent == false) {
          return -1;
        }

        lock(SyncLock) {
          Flush();
          return Console.CursorTop;
        }
      }
      set {
        if(IsConsolePresent == false) {
          return;
        }

        lock(SyncLock) {
          Flush();
          Console.CursorTop = value;
        }
      }
    }

    #endregion

    #region Properties

    /// <summary>
    /// Gets a value indicating whether the Console is present.
    /// </summary>
    /// <value>
    /// <c>true</c> if this instance is console present; otherwise, <c>false</c>.
    /// </value>
    public static Boolean IsConsolePresent {
      get {
        if(Settings.OverrideIsConsolePresent) {
          return true;
        }

        if(_isConsolePresent == null) {
          _isConsolePresent = true;
          try {
            Int32 windowHeight = Console.WindowHeight;
            _isConsolePresent = windowHeight >= 0;
          } catch {
            _isConsolePresent = false;
          }
        }

        return _isConsolePresent.Value;
      }
    }

    /// <summary>
    /// Gets a value indicating whether a debugger is attached.
    /// </summary>
    /// <value>
    ///   <c>true</c> if this instance is debugger attached; otherwise, <c>false</c>.
    /// </value>
    public static Boolean IsDebuggerAttached => System.Diagnostics.Debugger.IsAttached;

    /// <summary>
    /// Gets the available output writers in a bitwise mask.
    /// </summary>
    /// <value>
    /// The available writers.
    /// </value>
    public static TerminalWriters AvailableWriters {
      get {
        TerminalWriters writers = TerminalWriters.None;
        if(IsConsolePresent) {
          writers = TerminalWriters.StandardError | TerminalWriters.StandardOutput;
        }

        if(IsDebuggerAttached) {
          writers |= TerminalWriters.Diagnostics;
        }

        return writers;
      }
    }

    /// <summary>
    /// Gets or sets the output encoding for the current console.
    /// </summary>
    /// <value>
    /// The output encoding.
    /// </value>
    public static Encoding OutputEncoding {
      get => Console.OutputEncoding;
      set => Console.OutputEncoding = value;
    }

    #endregion

    #region Methods

    /// <summary>
    /// Waits for all of the queued output messages to be written out to the console.
    /// Call this method if it is important to display console text before
    /// quitting the application such as showing usage or help.
    /// Set the timeout to null or TimeSpan.Zero to wait indefinitely.
    /// </summary>
    /// <param name="timeout">The timeout. Set the amount of time to black before this method exits.</param>
    public static void Flush(TimeSpan? timeout = null) {
      if(timeout == null) {
        timeout = TimeSpan.Zero;
      }

      DateTime startTime = DateTime.UtcNow;

      while(OutputQueue.Count > 0) {
        // Manually trigger a timer cycle to run immediately
        DequeueOutputTimer.Change(0, OutputFlushInterval);

        // Wait for the output to finish
        if(OutputDone.Wait(OutputFlushInterval)) {
          break;
        }

        // infinite timeout
        if(timeout.Value == TimeSpan.Zero) {
          continue;
        }

        // break if we have reached a timeout condition
        if(DateTime.UtcNow.Subtract(startTime) >= timeout.Value) {
          break;
        }
      }
    }

    /// <summary>
    /// Sets the cursor position.
    /// </summary>
    /// <param name="left">The left.</param>
    /// <param name="top">The top.</param>
    public static void SetCursorPosition(Int32 left, Int32 top) {
      if(IsConsolePresent == false) {
        return;
      }

      lock(SyncLock) {
        Flush();
        Console.SetCursorPosition(left.Clamp(0, left), top.Clamp(0, top));
      }
    }

    /// <summary>
    /// Moves the output cursor one line up starting at left position 0
    /// Please note that backlining the cursor does not clear the contents of the 
    /// previous line so you might need to clear it by writing an empty string the 
    /// length of the console width.
    /// </summary>
    public static void BacklineCursor() => SetCursorPosition(0, CursorTop - 1);

    /// <summary>
    /// Enqueues the output to be written to the console
    /// This is the only method that should enqueue to the output
    /// Please note that if AvailableWriters is None, then no output will be enqueued.
    /// </summary>
    /// <param name="context">The context.</param>
    private static void EnqueueOutput(OutputContext context) {
      lock(SyncLock) {
        TerminalWriters availableWriters = AvailableWriters;

        if(availableWriters == TerminalWriters.None || context.OutputWriters == TerminalWriters.None) {
          OutputDone.Set();
          return;
        }

        if((context.OutputWriters & availableWriters) == TerminalWriters.None) {
          return;
        }

        OutputDone.Reset();
        OutputQueue.Enqueue(context);
      }
    }

    /// <summary>
    /// Runs a Terminal I/O cycle in the <see cref="ThreadPool"/> thread.
    /// </summary>
    private static void DequeueOutputCycle() {
      if(AvailableWriters == TerminalWriters.None) {
        OutputDone.Set();
        return;
      }

      InputDone.Wait();

      if(OutputQueue.Count <= 0) {
        OutputDone.Set();
        return;
      }

      OutputDone.Reset();

      while(OutputQueue.Count > 0) {
        if(OutputQueue.TryDequeue(out OutputContext context) == false) {
          continue;
        }

        // Process Console output and Skip over stuff we can't display so we don't stress the output too much.
        if(IsConsolePresent && (Settings.OverrideIsConsolePresent || OutputQueue.Count <= Console.BufferHeight)) {
          // Output to the standard output
          if(context.OutputWriters.HasFlag(TerminalWriters.StandardOutput)) {
            Console.ForegroundColor = context.OutputColor;
            Console.Out.Write(context.OutputText);
            Console.ResetColor();
            Console.ForegroundColor = context.OriginalColor;
          }

          // output to the standard error
          if(context.OutputWriters.HasFlag(TerminalWriters.StandardError)) {
            Console.ForegroundColor = context.OutputColor;
            Console.Error.Write(context.OutputText);
            Console.ResetColor();
            Console.ForegroundColor = context.OriginalColor;
          }
        }

        // Process Debugger output
        if(IsDebuggerAttached && context.OutputWriters.HasFlag(TerminalWriters.Diagnostics)) {
          System.Diagnostics.Debug.Write(new String(context.OutputText));
        }
      }
    }

    #endregion

    #region Output Context

    /// <summary>
    /// Represents an asynchronous output context.
    /// </summary>
    private sealed class OutputContext {
      /// <summary>
      /// Initializes a new instance of the <see cref="OutputContext"/> class.
      /// </summary>
      public OutputContext() {
        this.OriginalColor = Settings.DefaultColor;
        this.OutputWriters = IsConsolePresent
            ? TerminalWriters.StandardOutput
            : IsDebuggerAttached
                ? TerminalWriters.Diagnostics
                : TerminalWriters.None;
      }

      public ConsoleColor OriginalColor {
        get;
      }
      public ConsoleColor OutputColor {
        get; set;
      }
      public Char[] OutputText {
        get; set;
      }
      public TerminalWriters OutputWriters {
        get; set;
      }
    }

    #endregion
  }
}