using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Junction.Core.Plugins;
using Junction.Domain;
using Junction.Domain.Models;
using Junction.Domain.Protocols;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using Xunit;

namespace Junction.Tests.Unit
{
    /// <summary>
    /// Tests for <see cref="PluginLoader"/>. A real loadable plugin is synthesized at test
    /// time from THIS test assembly: a temp plugin dir gets a copy of the test dll plus a
    /// <c>plugin.manifest.json</c> whose EntryTypeName points at <see cref="FakeFactory"/>
    /// below. Because the copy shares the already-loaded test assembly's identity,
    /// <c>Assembly.LoadFrom</c> resolves the running assembly and the type is found.
    /// </summary>
    public sealed class PluginLoaderTests : IDisposable
    {
        // ---- Fake plugin types defined IN the test project ----

        /// <summary>Valid, loadable factory used for the happy path.</summary>
        public sealed class FakeFactory : IProtocolDriverFactory
        {
            public string ProtocolId => "fake";

            public Result<IProtocolDriver> Create(Machine machine) =>
                Result<IProtocolDriver>.Ok(new FakeDriver());
        }

        public sealed class FakeDriver : IProtocolDriver
        {
            public string ProtocolId => "fake";

            public Task<Result<MachineSnapshot>> ReadCurrentAsync(CancellationToken cancellationToken) =>
                Task.FromResult(Result<MachineSnapshot>.Ok(
                    new MachineSnapshot(
                        Guid.NewGuid(),
                        DateTimeOffset.UtcNow,
                        ConnectionState.Connected,
                        Array.Empty<DataItem>())));
        }

        /// <summary>Type that does NOT implement the factory contract.</summary>
        public sealed class NotAFactory
        {
        }

        /// <summary>Factory whose ctor throws (activation failure path).</summary>
        public sealed class ThrowingFactory : IProtocolDriverFactory
        {
            public ThrowingFactory() => throw new InvalidOperationException("boom");
            public string ProtocolId => "throwing";
            public Result<IProtocolDriver> Create(Machine machine) => throw new NotImplementedException();
        }

        private static readonly string TestAssemblyPath =
            typeof(PluginLoaderTests).Assembly.Location;

        private static readonly string TestAssemblyFileName =
            Path.GetFileName(TestAssemblyPath);

        private readonly string _root;

        public PluginLoaderTests()
        {
            _root = Path.Combine(Path.GetTempPath(), "junction-plugintests-" + Guid.NewGuid().ToString("N"));
            Directory.CreateDirectory(_root);
        }

        public void Dispose()
        {
            try
            {
                if (Directory.Exists(_root))
                    Directory.Delete(_root, recursive: true);
            }
            catch
            {
                // best-effort cleanup
            }
        }

        // ---- helpers ----

        private static PluginLoader NewLoader(ILogger<PluginLoader>? logger = null) =>
            new PluginLoader(logger ?? NullLogger<PluginLoader>.Instance);

        /// <summary>
        /// Create a plugin subdir with a copy of the test dll (so AssemblyFile resolves)
        /// and a manifest pointing at <paramref name="entryTypeName"/>.
        /// </summary>
        private string CreatePluginDir(string dirName, string entryTypeName, string protocolId = "fake", bool copyDll = true)
        {
            var dir = Path.Combine(_root, dirName);
            Directory.CreateDirectory(dir);

            if (copyDll)
                File.Copy(TestAssemblyPath, Path.Combine(dir, TestAssemblyFileName), overwrite: true);

            var manifest =
                "{\n" +
                $"  \"protocolId\": \"{protocolId}\",\n" +
                "  \"displayName\": \"Fake Plugin\",\n" +
                $"  \"assemblyFile\": \"{TestAssemblyFileName}\",\n" +
                $"  \"entryTypeName\": \"{entryTypeName}\",\n" +
                "  \"apiVersion\": \"1.0\"\n" +
                "}";
            File.WriteAllText(Path.Combine(dir, PluginLoader.ManifestFileName), manifest);
            return dir;
        }

        private void CreateBadJsonPluginDir(string dirName)
        {
            var dir = Path.Combine(_root, dirName);
            Directory.CreateDirectory(dir);
            File.Copy(TestAssemblyPath, Path.Combine(dir, TestAssemblyFileName), overwrite: true);
            File.WriteAllText(Path.Combine(dir, PluginLoader.ManifestFileName), "{ this is : not valid json ]");
        }

        // ---- tests ----

        [Fact]
        public void LoadFrom_ValidPlugin_ReturnsLoadedPluginWithWorkingFactory()
        {
            CreatePluginDir("good", typeof(FakeFactory).FullName!);

            var result = NewLoader().LoadFrom(_root);

            Assert.True(result.IsSuccess);
            var plugin = Assert.Single(result.Value);
            Assert.Equal("fake", plugin.Descriptor.Manifest.ProtocolId);
            Assert.Equal("fake", plugin.Factory.ProtocolId);
            Assert.True(File.Exists(plugin.Descriptor.AssemblyPath));

            var machine = new Machine(Guid.NewGuid(), "M1", "fake", null, TimeSpan.FromSeconds(1));
            var created = plugin.Factory.Create(machine);
            Assert.True(created.IsSuccess);
            Assert.Equal("fake", created.Value.ProtocolId);
        }

        [Fact]
        public void LoadFrom_RootManifest_IsDiscovered()
        {
            // manifest + dll directly in root (no subdir)
            File.Copy(TestAssemblyPath, Path.Combine(_root, TestAssemblyFileName), overwrite: true);
            File.WriteAllText(
                Path.Combine(_root, PluginLoader.ManifestFileName),
                "{ \"protocolId\": \"fake\", \"displayName\": \"d\", " +
                $"\"assemblyFile\": \"{TestAssemblyFileName}\", " +
                $"\"entryTypeName\": \"{typeof(FakeFactory).FullName}\", \"apiVersion\": \"1.0\" }}");

            var result = NewLoader().LoadFrom(_root);

            Assert.True(result.IsSuccess);
            Assert.Single(result.Value);
        }

        [Fact]
        public void LoadFrom_BadJson_SkipsThatPlugin_LoadsOthers()
        {
            CreateBadJsonPluginDir("bad");
            CreatePluginDir("good", typeof(FakeFactory).FullName!);

            var logger = new CapturingLogger<PluginLoader>();
            var result = NewLoader(logger).LoadFrom(_root);

            Assert.True(result.IsSuccess);
            var plugin = Assert.Single(result.Value); // only the good one
            Assert.Equal("fake", plugin.Descriptor.Manifest.ProtocolId);
            Assert.Contains(logger.Entries, e => e.Level == LogLevel.Error);
        }

        [Fact]
        public void LoadFrom_MissingDll_SkipsPlugin_NoThrow()
        {
            // manifest present, but do not copy the dll
            CreatePluginDir("nodll", typeof(FakeFactory).FullName!, copyDll: false);

            var logger = new CapturingLogger<PluginLoader>();
            var result = NewLoader(logger).LoadFrom(_root);

            Assert.True(result.IsSuccess);
            Assert.Empty(result.Value);
            Assert.Contains(logger.Entries, e => e.Level == LogLevel.Error);
        }

        [Fact]
        public void LoadFrom_UnknownEntryType_SkipsPlugin_NoThrow()
        {
            CreatePluginDir("badtype", "Junction.Tests.Unit.NoSuchType");

            var logger = new CapturingLogger<PluginLoader>();
            var result = NewLoader(logger).LoadFrom(_root);

            Assert.True(result.IsSuccess);
            Assert.Empty(result.Value);
            Assert.Contains(logger.Entries, e => e.Level == LogLevel.Error);
        }

        [Fact]
        public void LoadFrom_EntryTypeNotAFactory_SkipsPlugin()
        {
            CreatePluginDir("wrongcontract", typeof(NotAFactory).FullName!);

            var result = NewLoader().LoadFrom(_root);

            Assert.True(result.IsSuccess);
            Assert.Empty(result.Value);
        }

        [Fact]
        public void LoadFrom_FactoryCtorThrows_SkipsPlugin()
        {
            CreatePluginDir("throwctor", typeof(ThrowingFactory).FullName!);

            var result = NewLoader().LoadFrom(_root);

            Assert.True(result.IsSuccess);
            Assert.Empty(result.Value);
        }

        [Fact]
        public void LoadFrom_MissingDirectory_ReturnsFail()
        {
            var missing = Path.Combine(_root, "does-not-exist");

            var result = NewLoader().LoadFrom(missing);

            Assert.False(result.IsSuccess);
            Assert.Contains(result.Errors, e => e.Code == "PLUGIN_DIR_MISSING");
        }

        [Fact]
        public void LoadFrom_EmptyPath_ReturnsFail()
        {
            var result = NewLoader().LoadFrom("");

            Assert.False(result.IsSuccess);
            Assert.Contains(result.Errors, e => e.Code == "PLUGIN_DIR_MISSING");
        }

        [Fact]
        public void LoadFrom_MultiplePlugins_LoadsAllValid()
        {
            CreatePluginDir("p1", typeof(FakeFactory).FullName!);
            CreatePluginDir("p2", typeof(FakeFactory).FullName!);
            CreateBadJsonPluginDir("bad");

            var result = NewLoader().LoadFrom(_root);

            Assert.True(result.IsSuccess);
            Assert.Equal(2, result.Value.Count);
        }

        // ---- capturing logger ----

        private sealed class CapturingLogger<T> : ILogger<T>
        {
            public readonly List<(LogLevel Level, string Message)> Entries = new();

            public IDisposable BeginScope<TState>(TState state) where TState : notnull => NullScope.Instance;

            public bool IsEnabled(LogLevel logLevel) => true;

            public void Log<TState>(
                LogLevel logLevel,
                EventId eventId,
                TState state,
                Exception? exception,
                Func<TState, Exception?, string> formatter)
            {
                Entries.Add((logLevel, formatter(state, exception)));
            }

            private sealed class NullScope : IDisposable
            {
                public static readonly NullScope Instance = new();
                public void Dispose() { }
            }
        }
    }
}