using System.Net;
using Microsoft.Data.Sqlite;
using Microsoft.Extensions.Logging.Abstractions;
using NSubstitute;
using ScadaLink.Commons.Entities.ExternalSystems;
using ScadaLink.Commons.Interfaces.Repositories;
using ScadaLink.StoreAndForward;

namespace ScadaLink.ExternalSystemGateway.Tests;

/// <summary>
/// WP-6/7: Tests for ExternalSystemClient — HTTP client, call modes, error handling.
/// </summary>
public class ExternalSystemClientTests
{
    private readonly IExternalSystemRepository _repository = Substitute.For<IExternalSystemRepository>();
    private readonly IHttpClientFactory _httpClientFactory = Substitute.For<IHttpClientFactory>();

    [Fact]
    public async Task Call_SystemNotFound_ReturnsError()
    {
        _repository.GetAllExternalSystemsAsync().Returns(new List<ExternalSystemDefinition>());

        var client = new ExternalSystemClient(
            _httpClientFactory, _repository,
            NullLogger<ExternalSystemClient>.Instance);

        var result = await client.CallAsync("nonexistent", "method");

        Assert.False(result.Success);
        Assert.Contains("not found", result.ErrorMessage);
    }

    [Fact]
    public async Task Call_MethodNotFound_ReturnsError()
    {
        var system = new ExternalSystemDefinition("TestAPI", "https://api.example.com", "none") { Id = 1 };
        _repository.GetAllExternalSystemsAsync().Returns(new List<ExternalSystemDefinition> { system });
        _repository.GetMethodsByExternalSystemIdAsync(1).Returns(new List<ExternalSystemMethod>());

        var client = new ExternalSystemClient(
            _httpClientFactory, _repository,
            NullLogger<ExternalSystemClient>.Instance);

        var result = await client.CallAsync("TestAPI", "missingMethod");

        Assert.False(result.Success);
        Assert.Contains("not found", result.ErrorMessage);
    }

    [Fact]
    public async Task Call_SuccessfulHttp_ReturnsResponse()
    {
        var system = new ExternalSystemDefinition("TestAPI", "https://api.example.com", "none") { Id = 1 };
        var method = new ExternalSystemMethod("getData", "GET", "/data") { Id = 1, ExternalSystemDefinitionId = 1 };

        _repository.GetAllExternalSystemsAsync().Returns(new List<ExternalSystemDefinition> { system });
        _repository.GetMethodsByExternalSystemIdAsync(1).Returns(new List<ExternalSystemMethod> { method });

        var handler = new MockHttpMessageHandler(HttpStatusCode.OK, "{\"result\": 42}");
        var httpClient = new HttpClient(handler);
        _httpClientFactory.CreateClient(Arg.Any<string>()).Returns(httpClient);

        var client = new ExternalSystemClient(
            _httpClientFactory, _repository,
            NullLogger<ExternalSystemClient>.Instance);

        var result = await client.CallAsync("TestAPI", "getData");

        Assert.True(result.Success);
        Assert.Contains("42", result.ResponseJson!);
    }

    [Fact]
    public async Task Call_Transient500_ReturnsTransientError()
    {
        var system = new ExternalSystemDefinition("TestAPI", "https://api.example.com", "none") { Id = 1 };
        var method = new ExternalSystemMethod("failMethod", "POST", "/fail") { Id = 1, ExternalSystemDefinitionId = 1 };

        _repository.GetAllExternalSystemsAsync().Returns(new List<ExternalSystemDefinition> { system });
        _repository.GetMethodsByExternalSystemIdAsync(1).Returns(new List<ExternalSystemMethod> { method });

        var handler = new MockHttpMessageHandler(HttpStatusCode.InternalServerError, "server error");
        var httpClient = new HttpClient(handler);
        _httpClientFactory.CreateClient(Arg.Any<string>()).Returns(httpClient);

        var client = new ExternalSystemClient(
            _httpClientFactory, _repository,
            NullLogger<ExternalSystemClient>.Instance);

        var result = await client.CallAsync("TestAPI", "failMethod");

        Assert.False(result.Success);
        Assert.Contains("Transient error", result.ErrorMessage);
    }

    [Fact]
    public async Task Call_Permanent400_ReturnsPermanentError()
    {
        var system = new ExternalSystemDefinition("TestAPI", "https://api.example.com", "none") { Id = 1 };
        var method = new ExternalSystemMethod("badMethod", "POST", "/bad") { Id = 1, ExternalSystemDefinitionId = 1 };

        _repository.GetAllExternalSystemsAsync().Returns(new List<ExternalSystemDefinition> { system });
        _repository.GetMethodsByExternalSystemIdAsync(1).Returns(new List<ExternalSystemMethod> { method });

        var handler = new MockHttpMessageHandler(HttpStatusCode.BadRequest, "bad request");
        var httpClient = new HttpClient(handler);
        _httpClientFactory.CreateClient(Arg.Any<string>()).Returns(httpClient);

        var client = new ExternalSystemClient(
            _httpClientFactory, _repository,
            NullLogger<ExternalSystemClient>.Instance);

        var result = await client.CallAsync("TestAPI", "badMethod");

        Assert.False(result.Success);
        Assert.Contains("Permanent error", result.ErrorMessage);
    }

    [Fact]
    public async Task CachedCall_SystemNotFound_ReturnsError()
    {
        _repository.GetAllExternalSystemsAsync().Returns(new List<ExternalSystemDefinition>());

        var client = new ExternalSystemClient(
            _httpClientFactory, _repository,
            NullLogger<ExternalSystemClient>.Instance);

        var result = await client.CachedCallAsync("nonexistent", "method");

        Assert.False(result.Success);
        Assert.Contains("not found", result.ErrorMessage);
    }

    [Fact]
    public async Task CachedCall_Success_ReturnsDirectly()
    {
        var system = new ExternalSystemDefinition("TestAPI", "https://api.example.com", "none") { Id = 1 };
        var method = new ExternalSystemMethod("getData", "GET", "/data") { Id = 1, ExternalSystemDefinitionId = 1 };

        _repository.GetAllExternalSystemsAsync().Returns(new List<ExternalSystemDefinition> { system });
        _repository.GetMethodsByExternalSystemIdAsync(1).Returns(new List<ExternalSystemMethod> { method });

        var handler = new MockHttpMessageHandler(HttpStatusCode.OK, "{\"ok\": true}");
        var httpClient = new HttpClient(handler);
        _httpClientFactory.CreateClient(Arg.Any<string>()).Returns(httpClient);

        var client = new ExternalSystemClient(
            _httpClientFactory, _repository,
            NullLogger<ExternalSystemClient>.Instance);

        var result = await client.CachedCallAsync("TestAPI", "getData");

        Assert.True(result.Success);
        Assert.False(result.WasBuffered);
    }

    // ── ExternalSystemGateway-001: buffered-call delivery handler ──

    private static ScadaLink.StoreAndForward.StoreAndForwardMessage BufferedCall(
        string systemName, string methodName) =>
        new()
        {
            Id = Guid.NewGuid().ToString("N"),
            Category = ScadaLink.Commons.Types.Enums.StoreAndForwardCategory.ExternalSystem,
            Target = systemName,
            PayloadJson =
                $$"""{"SystemName":"{{systemName}}","MethodName":"{{methodName}}","Parameters":null}""",
        };

    [Fact]
    public async Task DeliverBuffered_SuccessfulHttp_ReturnsTrue()
    {
        var system = new ExternalSystemDefinition("TestAPI", "https://api.example.com", "none") { Id = 1 };
        var method = new ExternalSystemMethod("getData", "GET", "/data") { Id = 1, ExternalSystemDefinitionId = 1 };
        _repository.GetAllExternalSystemsAsync().Returns(new List<ExternalSystemDefinition> { system });
        _repository.GetMethodsByExternalSystemIdAsync(1).Returns(new List<ExternalSystemMethod> { method });

        var httpClient = new HttpClient(new MockHttpMessageHandler(HttpStatusCode.OK, "{\"ok\":true}"));
        _httpClientFactory.CreateClient(Arg.Any<string>()).Returns(httpClient);

        var client = new ExternalSystemClient(
            _httpClientFactory, _repository, NullLogger<ExternalSystemClient>.Instance);

        var delivered = await client.DeliverBufferedAsync(BufferedCall("TestAPI", "getData"));

        Assert.True(delivered);
    }

    [Fact]
    public async Task DeliverBuffered_SystemNoLongerExists_ReturnsFalseSoMessageParks()
    {
        _repository.GetAllExternalSystemsAsync().Returns(new List<ExternalSystemDefinition>());

        var client = new ExternalSystemClient(
            _httpClientFactory, _repository, NullLogger<ExternalSystemClient>.Instance);

        var delivered = await client.DeliverBufferedAsync(BufferedCall("GoneAPI", "method"));

        Assert.False(delivered); // permanent — the S&F engine parks the message
    }

    [Fact]
    public async Task DeliverBuffered_Transient500_ThrowsSoEngineRetries()
    {
        var system = new ExternalSystemDefinition("TestAPI", "https://api.example.com", "none") { Id = 1 };
        var method = new ExternalSystemMethod("failMethod", "POST", "/fail") { Id = 1, ExternalSystemDefinitionId = 1 };
        _repository.GetAllExternalSystemsAsync().Returns(new List<ExternalSystemDefinition> { system });
        _repository.GetMethodsByExternalSystemIdAsync(1).Returns(new List<ExternalSystemMethod> { method });

        var httpClient = new HttpClient(new MockHttpMessageHandler(HttpStatusCode.InternalServerError, "boom"));
        _httpClientFactory.CreateClient(Arg.Any<string>()).Returns(httpClient);

        var client = new ExternalSystemClient(
            _httpClientFactory, _repository, NullLogger<ExternalSystemClient>.Instance);

        await Assert.ThrowsAsync<TransientExternalSystemException>(
            () => client.DeliverBufferedAsync(BufferedCall("TestAPI", "failMethod")));
    }

    // ── ExternalSystemGateway-003: CachedCall must not double-dispatch ──

    [Fact]
    public async Task CachedCall_TransientFailure_DoesNotImmediatelyRedispatchViaRegisteredHandler()
    {
        var system = new ExternalSystemDefinition("TestAPI", "https://api.example.com", "none") { Id = 1 };
        var method = new ExternalSystemMethod("postData", "POST", "/post") { Id = 1, ExternalSystemDefinitionId = 1 };
        _repository.GetAllExternalSystemsAsync(Arg.Any<CancellationToken>())
            .Returns(new List<ExternalSystemDefinition> { system });
        _repository.GetMethodsByExternalSystemIdAsync(1, Arg.Any<CancellationToken>())
            .Returns(new List<ExternalSystemMethod> { method });

        // The HTTP layer always fails transiently (500).
        var httpClient = new HttpClient(new MockHttpMessageHandler(HttpStatusCode.InternalServerError, "boom"));
        _httpClientFactory.CreateClient(Arg.Any<string>()).Returns(httpClient);

        // A real S&F service with a registered delivery handler that counts invocations.
        var dbName = $"EsgDoubleDispatch_{Guid.NewGuid():N}";
        var connStr = $"Data Source={dbName};Mode=Memory;Cache=Shared";
        using var keepAlive = new SqliteConnection(connStr);
        keepAlive.Open();
        var storage = new StoreAndForwardStorage(connStr, NullLogger<StoreAndForwardStorage>.Instance);
        await storage.InitializeAsync();
        var sfOptions = new StoreAndForwardOptions
        {
            DefaultRetryInterval = TimeSpan.FromMinutes(10),
            RetryTimerInterval = TimeSpan.FromMinutes(10),
        };
        var sf = new StoreAndForwardService(storage, sfOptions, NullLogger<StoreAndForwardService>.Instance);

        var handlerInvocations = 0;
        sf.RegisterDeliveryHandler(
            ScadaLink.Commons.Types.Enums.StoreAndForwardCategory.ExternalSystem,
            _ => { Interlocked.Increment(ref handlerInvocations); return Task.FromResult(false); });

        var client = new ExternalSystemClient(
            _httpClientFactory, _repository,
            NullLogger<ExternalSystemClient>.Instance,
            storeAndForward: sf);

        var result = await client.CachedCallAsync("TestAPI", "postData");

        // The call already made one HTTP attempt; EnqueueAsync must NOT invoke the
        // registered handler again synchronously (which would dispatch a 2nd request).
        Assert.True(result.WasBuffered);
        Assert.Equal(0, handlerInvocations);
    }

    // ── ExternalSystemGateway-002: per-system call timeout ──

    [Fact]
    public async Task Call_SlowSystem_TimesOutAsTransientErrorWithinConfiguredWindow()
    {
        var system = new ExternalSystemDefinition("TestAPI", "https://api.example.com", "none") { Id = 1 };
        var method = new ExternalSystemMethod("getData", "GET", "/data") { Id = 1, ExternalSystemDefinitionId = 1 };
        _repository.GetAllExternalSystemsAsync(Arg.Any<CancellationToken>())
            .Returns(new List<ExternalSystemDefinition> { system });
        _repository.GetMethodsByExternalSystemIdAsync(1, Arg.Any<CancellationToken>())
            .Returns(new List<ExternalSystemMethod> { method });

        // Handler that hangs far longer than the configured timeout and the test budget.
        var httpClient = new HttpClient(new HangingHttpMessageHandler(TimeSpan.FromMinutes(10)));
        _httpClientFactory.CreateClient(Arg.Any<string>()).Returns(httpClient);

        // Configure a short timeout so the call must fail quickly.
        var options = new ExternalSystemGatewayOptions { DefaultHttpTimeout = TimeSpan.FromMilliseconds(200) };
        var client = new ExternalSystemClient(
            _httpClientFactory, _repository,
            NullLogger<ExternalSystemClient>.Instance,
            options: Microsoft.Extensions.Options.Options.Create(options));

        var sw = System.Diagnostics.Stopwatch.StartNew();
        var result = await client.CallAsync("TestAPI", "getData");
        sw.Stop();

        Assert.False(result.Success);
        Assert.Contains("Transient error", result.ErrorMessage);
        Assert.Contains("Timeout", result.ErrorMessage);
        // Must fail near the configured 200ms, well before HttpClient's default 100s.
        Assert.True(sw.Elapsed < TimeSpan.FromSeconds(10),
            $"Call took {sw.Elapsed}, expected to time out near the configured 200ms window");
    }

    [Fact]
    public async Task Call_CallerCancellation_IsNotMisreportedAsTimeout()
    {
        var system = new ExternalSystemDefinition("TestAPI", "https://api.example.com", "none") { Id = 1 };
        var method = new ExternalSystemMethod("getData", "GET", "/data") { Id = 1, ExternalSystemDefinitionId = 1 };
        _repository.GetAllExternalSystemsAsync(Arg.Any<CancellationToken>())
            .Returns(new List<ExternalSystemDefinition> { system });
        _repository.GetMethodsByExternalSystemIdAsync(1, Arg.Any<CancellationToken>())
            .Returns(new List<ExternalSystemMethod> { method });

        var httpClient = new HttpClient(new HangingHttpMessageHandler(TimeSpan.FromMinutes(10)));
        _httpClientFactory.CreateClient(Arg.Any<string>()).Returns(httpClient);

        var options = new ExternalSystemGatewayOptions { DefaultHttpTimeout = TimeSpan.FromMinutes(5) };
        var client = new ExternalSystemClient(
            _httpClientFactory, _repository,
            NullLogger<ExternalSystemClient>.Instance,
            options: Microsoft.Extensions.Options.Options.Create(options));

        using var cts = new CancellationTokenSource(TimeSpan.FromMilliseconds(200));

        // Caller-initiated cancellation must surface as OperationCanceledException,
        // not be swallowed as a transient timeout error.
        await Assert.ThrowsAnyAsync<OperationCanceledException>(
            () => client.CallAsync("TestAPI", "getData", cancellationToken: cts.Token));
    }

    /// <summary>
    /// Test helper: mock HTTP message handler.
    /// </summary>
    private class MockHttpMessageHandler : HttpMessageHandler
    {
        private readonly HttpStatusCode _statusCode;
        private readonly string _body;

        public MockHttpMessageHandler(HttpStatusCode statusCode, string body)
        {
            _statusCode = statusCode;
            _body = body;
        }

        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            return Task.FromResult(new HttpResponseMessage(_statusCode)
            {
                Content = new StringContent(_body)
            });
        }
    }

    /// <summary>
    /// Test helper: an HTTP handler that hangs until cancelled (simulates a slow/hung system).
    /// </summary>
    private class HangingHttpMessageHandler : HttpMessageHandler
    {
        private readonly TimeSpan _delay;

        public HangingHttpMessageHandler(TimeSpan delay) => _delay = delay;

        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            await Task.Delay(_delay, cancellationToken);
            return new HttpResponseMessage(HttpStatusCode.OK) { Content = new StringContent("{}") };
        }
    }
}