using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;

namespace Glass.PerformanceTests
{
    /// <summary>
    /// Runs a benchmark once over a small text with its output thrown away, so the compiling and first-use setup of the
    /// code it times is done before the run that counts.  Without it the first slice or frame of every run carries tens
    /// of milliseconds that the later ones don't.
    /// </summary>
    public static class WarmStart
    {
        public const int Chars = 200000;

        /// <summary>
        /// Gets whether a warm-up is running, when a row needs only enough calls to compile what it times.
        /// </summary>
        public static bool IsWarming { get; private set; }

        /// <summary>
        /// Returns the arguments with every text size, which starts with a digit, set to the warm-up's, adding one
        /// after the benchmark's name when there is none.
        /// </summary>
        public static string[] Shrunk(string[] args)
        {
            string size = Chars.ToString(CultureInfo.InvariantCulture);
            var returnMe = new List<string>();
            bool sized = false;
            foreach (string argument in args)
            {
                if (argument.Length > 0 && char.IsDigit(argument[0]))
                {
                    returnMe.Add(size);
                    sized = true;
                }
                else
                {
                    returnMe.Add(argument);
                }
            }

            if (!sized)
            {
                returnMe.Insert(1, size);
            }

            return returnMe.ToArray();
        }

        /// <summary>
        /// Warms up, and then runs a benchmark for real.  A warm-up that fails ends the run, since it has already said
        /// why.
        /// </summary>
        public static int Run(Func<string[], int> benchmark, string[] args)
        {
            TextWriter output = Console.Out;
            int warmExit;
            IsWarming = true;
            Console.SetOut(TextWriter.Null);
            try
            {
                warmExit = benchmark(Shrunk(args));
            }
            finally
            {
                Console.SetOut(output);
                IsWarming = false;
            }

            if (warmExit != 0)
            {
                return warmExit;
            }

            GC.Collect();
            GC.WaitForPendingFinalizers();
            GC.Collect();

            return benchmark(args);
        }
    }
}