ffmpeg and ffprobe validation fixes (#63)

* abort building playout if any collection contains a zero-duration item

* surface errors calling ffprobe

* improve ffmpeg/ffprobe path validation

ErsatzTV.Application/FFmpegProfiles/Commands/UpdateFFmpegSettings.cs

@@ -1,6 +1,7 @@
-using MediatR;
+using ErsatzTV.Core;
+using LanguageExt;
 
 namespace ErsatzTV.Application.FFmpegProfiles.Commands
 {
-    public record UpdateFFmpegSettings(FFmpegSettingsViewModel Settings) : IRequest;
+    public record UpdateFFmpegSettings(FFmpegSettingsViewModel Settings) : MediatR.IRequest<Either<BaseError, Unit>>;
 }

ErsatzTV.Application/FFmpegProfiles/Commands/UpdateFFmpegSettingsHandler.cs

@@ -1,21 +1,74 @@
-using System.Threading;
+using System.Diagnostics;
+using System.Threading;
 using System.Threading.Tasks;
+using ErsatzTV.Core;
 using ErsatzTV.Core.Domain;
+using ErsatzTV.Core.Interfaces.Metadata;
 using ErsatzTV.Core.Interfaces.Repositories;
 using LanguageExt;
-using MediatR;
-using Unit = MediatR.Unit;
 
 namespace ErsatzTV.Application.FFmpegProfiles.Commands
 {
-    public class UpdateFFmpegSettingsHandler : IRequestHandler<UpdateFFmpegSettings>
+    public class UpdateFFmpegSettingsHandler : MediatR.IRequestHandler<UpdateFFmpegSettings, Either<BaseError, Unit>>
     {
         private readonly IConfigElementRepository _configElementRepository;
+        private readonly ILocalFileSystem _localFileSystem;
 
-        public UpdateFFmpegSettingsHandler(IConfigElementRepository configElementRepository) =>
+        public UpdateFFmpegSettingsHandler(
+            IConfigElementRepository configElementRepository,
+            ILocalFileSystem localFileSystem)
+        {
             _configElementRepository = configElementRepository;
+            _localFileSystem = localFileSystem;
+        }
 
-        public async Task<Unit> Handle(UpdateFFmpegSettings request, CancellationToken cancellationToken)
+        public Task<Either<BaseError, Unit>> Handle(
+            UpdateFFmpegSettings request,
+            CancellationToken cancellationToken) =>
+            Validate(request)
+                .MapT(_ => ApplyUpdate(request))
+                .Bind(v => v.ToEitherAsync());
+
+        private async Task<Validation<BaseError, Unit>> Validate(UpdateFFmpegSettings request) =>
+            (await FFmpegMustExist(request), await FFprobeMustExist(request))
+            .Apply((_, _) => Unit.Default);
+
+        private Task<Validation<BaseError, Unit>> FFmpegMustExist(UpdateFFmpegSettings request) =>
+            ValidateToolPath(request.Settings.FFmpegPath, "ffmpeg");
+
+        private Task<Validation<BaseError, Unit>> FFprobeMustExist(UpdateFFmpegSettings request) =>
+            ValidateToolPath(request.Settings.FFprobePath, "ffprobe");
+
+        private async Task<Validation<BaseError, Unit>> ValidateToolPath(string path, string name)
+        {
+            if (!_localFileSystem.FileExists(path))
+            {
+                return BaseError.New($"{name} path does not exist");
+            }
+
+            var startInfo = new ProcessStartInfo
+            {
+                FileName = path,
+                Arguments = "-version",
+                RedirectStandardOutput = true,
+                RedirectStandardError = true,
+                UseShellExecute = false
+            };
+
+            var test = new Process
+            {
+                StartInfo = startInfo
+            };
+
+            test.Start();
+            string output = await test.StandardOutput.ReadToEndAsync();
+            await test.WaitForExitAsync();
+            return test.ExitCode == 0 && output.Contains($"{name} version")
+                ? Unit.Default
+                : BaseError.New($"Unable to verify {name} version");
+        }
+
+        private async Task<Unit> ApplyUpdate(UpdateFFmpegSettings request)
         {
             Option<ConfigElement> ffmpegPath = await _configElementRepository.Get(ConfigElementKey.FFmpegPath);
             Option<ConfigElement> ffprobePath = await _configElementRepository.Get(ConfigElementKey.FFprobePath);
@@ -64,7 +117,7 @@ namespace ErsatzTV.Application.FFmpegProfiles.Commands
                     _configElementRepository.Add(ce);
                 });
 
-            return Unit.Value;
+            return Unit.Default;
         }
     }
 }