using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;

namespace Swan.Diagnostics {
  /// <summary>
  /// A simple benchmarking class.
  /// </summary>
  /// <example>
  /// The following code demonstrates how to create a simple benchmark.
  /// <code>
  /// namespace Examples.Benchmark.Simple
  /// {
  ///     using Swan.Diagnostics;
  /// 
  ///     public class SimpleBenchmark
  ///     {
  ///         public static void Main()
  ///         {
  ///              using (Benchmark.Start("Test"))
  ///              {
  ///                 // do some logic in here
  ///              }
  ///              
  ///             // dump results into a string
  ///             var results = Benchmark.Dump();
  ///         }
  ///     }
  ///     
  /// }
  /// </code>
  /// </example>
  public static partial class Benchmark {
    private static readonly Object SyncLock = new Object();
    private static readonly Dictionary<String, List<TimeSpan>> Measures = new Dictionary<String, List<TimeSpan>>();

    /// <summary>
    /// Starts measuring with the given identifier.
    /// </summary>
    /// <param name="identifier">The identifier.</param>
    /// <returns>A disposable object that when disposed, adds a benchmark result.</returns>
    public static IDisposable Start(String identifier) => new BenchmarkUnit(identifier);

    /// <summary>
    /// Outputs the benchmark statistics.
    /// </summary>
    /// <returns>A string containing human-readable statistics.</returns>
    public static String Dump() {
      StringBuilder builder = new StringBuilder();

      lock(SyncLock) {
        foreach(KeyValuePair<String, List<TimeSpan>> kvp in Measures) {
          _ = builder.Append($"BID: {kvp.Key,-30} | ").Append($"CNT: {kvp.Value.Count,6} | ").Append($"AVG: {kvp.Value.Average(t => t.TotalMilliseconds),8:0.000} ms. | ").Append($"MAX: {kvp.Value.Max(t => t.TotalMilliseconds),8:0.000} ms. | ").Append($"MIN: {kvp.Value.Min(t => t.TotalMilliseconds),8:0.000} ms. | ").Append(Environment.NewLine);
        }
      }

      return builder.ToString().TrimEnd();
    }

    /// <summary>
    /// Measures the elapsed time of the given action as a TimeSpan
    /// This method uses a high precision Stopwatch if it is available.
    /// </summary>
    /// <param name="target">The target.</param>
    /// <returns>
    /// A  time interval that represents a specified time, where the specification is in units of ticks.
    /// </returns>
    /// <exception cref="ArgumentNullException">target.</exception>
    public static TimeSpan BenchmarkAction(Action target) {
      if(target == null) {
        throw new ArgumentNullException(nameof(target));
      }

      Stopwatch sw = Stopwatch.IsHighResolution ? new HighResolutionTimer() : new Stopwatch();

      try {
        sw.Start();
        target.Invoke();
      } catch {
        // swallow
      } finally {
        sw.Stop();
      }

      return TimeSpan.FromTicks(sw.ElapsedTicks);
    }

    /// <summary>
    /// Adds the specified result to the given identifier.
    /// </summary>
    /// <param name="identifier">The identifier.</param>
    /// <param name="elapsed">The elapsed.</param>
    private static void Add(String identifier, TimeSpan elapsed) {
      lock(SyncLock) {
        if(Measures.ContainsKey(identifier) == false) {
          Measures[identifier] = new List<TimeSpan>(1024 * 1024);
        }

        Measures[identifier].Add(elapsed);
      }
    }
  }
}