using System;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;

namespace MalwareMultiScan.Backends.Backends.Abstracts
{
    public abstract class AbstractLocalProcessScanBackend : AbstractScanBackend
    {
        private readonly ILogger _logger;

        protected AbstractLocalProcessScanBackend(ILogger logger)
        {
            _logger = logger;
        }

        protected abstract Regex MatchRegex { get; }
        protected abstract string BackendPath { get; }
        protected virtual bool ParseStdErr { get; } = false;
        protected virtual bool ThrowOnNonZeroExitCode { get; } = true;

        protected abstract string GetBackendArguments(string path);

        public override async Task<string[]> ScanAsync(string path, CancellationToken cancellationToken)
        {
            var process = new Process
            {
                StartInfo = new ProcessStartInfo(BackendPath, GetBackendArguments(path))
                {
                    RedirectStandardError = true,
                    RedirectStandardOutput = true,
                    WorkingDirectory = Path.GetDirectoryName(BackendPath) ?? Directory.GetCurrentDirectory()
                }
            };

            _logger.LogInformation(
                $"Starting process {process.StartInfo.FileName} " +
                $"with arguments {process.StartInfo.Arguments} " +
                $"in working directory {process.StartInfo.WorkingDirectory}");

            process.Start();

            cancellationToken.Register(() =>
            {
                if (!process.HasExited)
                    process.Kill(true);
            });

            process.WaitForExit();

            _logger.LogInformation($"Process has exited with code {process.ExitCode}");

            var standardOutput = await process.StandardOutput.ReadToEndAsync();
            var standardError = await process.StandardError.ReadToEndAsync();

            _logger.LogDebug($"Process standard output: {standardOutput}");
            _logger.LogDebug($"Process standard error: {standardError}");

            if (ThrowOnNonZeroExitCode && process.ExitCode != 0)
                throw new ApplicationException($"Process has terminated with an exit code {process.ExitCode}");

            return MatchRegex
                .Matches(ParseStdErr ? standardError : standardOutput)
                .Where(x => x.Success)
                .Select(x => x.Groups["threat"].Value)
                .ToArray();
        }
    }
}