using System;
using System.Diagnostics;
using System.IO;
using System.Text;
using System.Threading.Tasks;

namespace Cosmos.Build.Builder.BuildTasks
{
    internal abstract class ProcessBuildTaskBase : IBuildTask
    {
        public abstract string Name { get; }

        private readonly bool _waitForExit;
        private readonly bool _createWindow;

        protected ProcessBuildTaskBase(bool waitForExit, bool createWindow)
        {
            _waitForExit = waitForExit;
            _createWindow = createWindow;
        }

        public Task RunAsync(ILogger logger)
        {
            var exePath = GetExePath();
            var args = GetArguments();

            logger.LogMessage($"\"{exePath}\" {args}");

            var process = new Process();
            var processStartInfo = new ProcessStartInfo(exePath, args);

            processStartInfo.CreateNoWindow = !_createWindow;
            processStartInfo.UseShellExecute = false;

            processStartInfo.RedirectStandardError = true;
            processStartInfo.RedirectStandardOutput = true;
            processStartInfo.StandardErrorEncoding = Encoding.GetEncoding(858);
            processStartInfo.StandardOutputEncoding = Encoding.GetEncoding(858);

            process.StartInfo = processStartInfo;
            process.Start();

            if (_waitForExit)
            {
                var standardOutputReaderTask = Task.Run(() => ReadOutputAsync(process.StandardOutput, logger));
                var standardErrorReaderTask = Task.Run(() => ReadOutputAsync(process.StandardError, logger));

                var waitForExitTask = Task.Run(() => WaitForExit(process));

                return Task.WhenAll(waitForExitTask, standardOutputReaderTask, standardErrorReaderTask);
            }

            return Task.CompletedTask;
        }

        protected abstract string GetExePath();
        protected abstract string GetArguments();

        private static void WaitForExit(Process process)
        {
            process.WaitForExit();

            if (process.ExitCode != 0)
            {
                throw new Exception("The process failed to execute!");
            }
        }

        private static async Task ReadOutputAsync(StreamReader reader, ILogger logger)
        {
            while (true)
            {
                var line = await reader.ReadLineAsync().ConfigureAwait(false);

                if (line == null)
                {
                    return;
                }

                logger.LogMessage(line);
            }
        }
    }
}