using Microsoft.Data.Sqlite;
using Microsoft.Extensions.Logging.Abstractions;
using ScadaLink.Commons.Types.Enums;

namespace ScadaLink.StoreAndForward.Tests;

/// <summary>
/// WP-10/12/13/14: Tests for the StoreAndForwardService retry engine and management.
/// </summary>
public class StoreAndForwardServiceTests : IAsyncLifetime, IDisposable
{
    private readonly SqliteConnection _keepAlive;
    private readonly StoreAndForwardStorage _storage;
    private readonly StoreAndForwardService _service;
    private readonly StoreAndForwardOptions _options;

    public StoreAndForwardServiceTests()
    {
        var dbName = $"SvcTests_{Guid.NewGuid():N}";
        var connStr = $"Data Source={dbName};Mode=Memory;Cache=Shared";
        _keepAlive = new SqliteConnection(connStr);
        _keepAlive.Open();

        _storage = new StoreAndForwardStorage(connStr, NullLogger<StoreAndForwardStorage>.Instance);

        _options = new StoreAndForwardOptions
        {
            DefaultRetryInterval = TimeSpan.Zero,
            DefaultMaxRetries = 3,
            RetryTimerInterval = TimeSpan.FromMinutes(10)
        };

        _service = new StoreAndForwardService(
            _storage, _options, NullLogger<StoreAndForwardService>.Instance);
    }

    public async Task InitializeAsync() => await _storage.InitializeAsync();

    public Task DisposeAsync() => Task.CompletedTask;

    public void Dispose() => _keepAlive.Dispose();

    // ── WP-10: Immediate delivery ──

    [Fact]
    public async Task EnqueueAsync_ImmediateDeliverySuccess_ReturnsAcceptedNotBuffered()
    {
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ => Task.FromResult(true));

        var result = await _service.EnqueueAsync(
            StoreAndForwardCategory.ExternalSystem, "api.example.com",
            """{"method":"Test"}""", "Pump1");

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

    [Fact]
    public async Task EnqueueAsync_PermanentFailure_ReturnsNotAccepted()
    {
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ => Task.FromResult(false));

        var result = await _service.EnqueueAsync(
            StoreAndForwardCategory.ExternalSystem, "api.example.com",
            """{"method":"Test"}""");

        Assert.False(result.Accepted);
        Assert.False(result.WasBuffered);
    }

    [Fact]
    public async Task EnqueueAsync_TransientFailure_BuffersForRetry()
    {
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ => throw new HttpRequestException("Connection refused"));

        var result = await _service.EnqueueAsync(
            StoreAndForwardCategory.ExternalSystem, "api.example.com",
            """{"method":"Test"}""", "Pump1");

        Assert.True(result.Accepted);
        Assert.True(result.WasBuffered);

        var msg = await _storage.GetMessageByIdAsync(result.MessageId);
        Assert.NotNull(msg);
        Assert.Equal(StoreAndForwardMessageStatus.Pending, msg!.Status);
        // StoreAndForward-003: RetryCount counts sweep retries only; the immediate
        // attempt is attempt 0, so a freshly buffered message has RetryCount 0.
        Assert.Equal(0, msg.RetryCount);
    }

    [Fact]
    public async Task EnqueueAsync_NoHandler_BuffersForLater()
    {
        var result = await _service.EnqueueAsync(
            StoreAndForwardCategory.Notification, "alerts@company.com",
            """{"subject":"Alert"}""");

        Assert.True(result.Accepted);
        Assert.True(result.WasBuffered);
    }

    // ── WP-10: Retry engine ──

    [Fact]
    public async Task RetryPendingMessagesAsync_SuccessfulRetry_RemovesMessage()
    {
        int callCount = 0;
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ =>
            {
                callCount++;
                if (callCount == 1) throw new HttpRequestException("fail");
                return Task.FromResult(true);
            });

        var result = await _service.EnqueueAsync(
            StoreAndForwardCategory.ExternalSystem, "api", """{}""");
        Assert.True(result.WasBuffered);

        await _service.RetryPendingMessagesAsync();

        var msg = await _storage.GetMessageByIdAsync(result.MessageId);
        Assert.Null(msg);
    }

    [Fact]
    public async Task RetryPendingMessagesAsync_MaxRetriesReached_ParksMessage()
    {
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ => throw new HttpRequestException("always fails"));

        var result = await _service.EnqueueAsync(
            StoreAndForwardCategory.ExternalSystem, "api", """{}""",
            maxRetries: 2);

        // StoreAndForward-003: MaxRetries bounds sweep retries (not the immediate
        // attempt), so a message with MaxRetries=2 needs two retry sweeps to park.
        await _service.RetryPendingMessagesAsync();
        var afterFirst = await _storage.GetMessageByIdAsync(result.MessageId);
        Assert.Equal(StoreAndForwardMessageStatus.Pending, afterFirst!.Status);

        await _service.RetryPendingMessagesAsync();

        var msg = await _storage.GetMessageByIdAsync(result.MessageId);
        Assert.NotNull(msg);
        Assert.Equal(StoreAndForwardMessageStatus.Parked, msg!.Status);
    }

    // ── StoreAndForward-003: retry-count accounting ──

    [Fact]
    public async Task RetryPendingMessagesAsync_MaxRetriesOne_PerformsExactlyOneRetryBeforeParking()
    {
        // The immediate attempt is attempt 0; MaxRetries=1 must allow exactly one
        // retry sweep before parking. The pre-fix off-by-one parked with zero retries.
        var attempts = 0;
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ => { Interlocked.Increment(ref attempts); throw new HttpRequestException("always fails"); });

        var result = await _service.EnqueueAsync(
            StoreAndForwardCategory.ExternalSystem, "api", """{}""",
            maxRetries: 1);

        // After the immediate failed attempt the message is buffered, not parked.
        var buffered = await _storage.GetMessageByIdAsync(result.MessageId);
        Assert.Equal(StoreAndForwardMessageStatus.Pending, buffered!.Status);
        Assert.Equal(1, attempts); // only the immediate attempt so far

        await _service.RetryPendingMessagesAsync();

        var msg = await _storage.GetMessageByIdAsync(result.MessageId);
        Assert.Equal(StoreAndForwardMessageStatus.Parked, msg!.Status);
        Assert.Equal(2, attempts);      // immediate attempt + exactly one retry
        Assert.Equal(1, msg.RetryCount); // one sweep retry recorded
    }

    // ── StoreAndForward-005: sweep-vs-management race hardening ──

    [Fact]
    public async Task RetryMessageAsync_StatusChangedDuringDelivery_SweepParkWriteIsSkipped()
    {
        // StoreAndForward-005: the retry sweep's state-changing writes must be
        // conditional on the status it observed, so a concurrent operator action that
        // moved the row out of Pending (e.g. between the sweep's snapshot load and its
        // park write) is not silently overwritten by the sweep's stale view.
        var result = await _service.EnqueueAsync(
            StoreAndForwardCategory.ExternalSystem, "api", """{}""",
            attemptImmediateDelivery: false, maxRetries: 1);

        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            async msg =>
            {
                // Simulate an operator action winning the race: the row leaves Pending
                // (here: parked) while the sweep is still mid-delivery. The sweep would
                // otherwise unconditionally re-write this row from its stale snapshot.
                var parkedOutFromUnderTheSweep = new StoreAndForwardMessage
                {
                    Id = msg.Id, Category = msg.Category, Target = msg.Target,
                    PayloadJson = msg.PayloadJson, RetryCount = 7,
                    MaxRetries = msg.MaxRetries, RetryIntervalMs = msg.RetryIntervalMs,
                    CreatedAt = msg.CreatedAt, LastAttemptAt = DateTimeOffset.UtcNow,
                    Status = StoreAndForwardMessageStatus.Parked,
                    LastError = "operator/other writer"
                };
                await _storage.UpdateMessageAsync(parkedOutFromUnderTheSweep);
                throw new HttpRequestException("transient — sweep will try to park");
            });

        await _service.RetryPendingMessagesAsync();

        // The sweep observed Pending; the row is now Parked with the other writer's
        // RetryCount (7), not the sweep's (1). The sweep's conditional write was skipped.
        var msg = await _storage.GetMessageByIdAsync(result.MessageId);
        Assert.NotNull(msg);
        Assert.Equal(StoreAndForwardMessageStatus.Parked, msg!.Status);
        Assert.Equal(7, msg.RetryCount);
        Assert.Equal("operator/other writer", msg.LastError);
    }

    [Fact]
    public async Task RetryPendingMessagesAsync_PermanentFailureOnRetry_ParksMessage()
    {
        int callCount = 0;
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ =>
            {
                callCount++;
                if (callCount == 1) throw new HttpRequestException("transient");
                return Task.FromResult(false);
            });

        var result = await _service.EnqueueAsync(
            StoreAndForwardCategory.ExternalSystem, "api", """{}""");

        await _service.RetryPendingMessagesAsync();

        var msg = await _storage.GetMessageByIdAsync(result.MessageId);
        Assert.NotNull(msg);
        Assert.Equal(StoreAndForwardMessageStatus.Parked, msg!.Status);
    }

    // ── WP-12: Parked message management ──

    [Fact]
    public async Task RetryParkedMessageAsync_MovesBackToQueue()
    {
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ => throw new HttpRequestException("fail"));

        var result = await _service.EnqueueAsync(
            StoreAndForwardCategory.ExternalSystem, "api", """{}""",
            maxRetries: 1);

        await _service.RetryPendingMessagesAsync();

        var msg = await _storage.GetMessageByIdAsync(result.MessageId);
        Assert.Equal(StoreAndForwardMessageStatus.Parked, msg!.Status);

        var retried = await _service.RetryParkedMessageAsync(result.MessageId);
        Assert.True(retried);

        msg = await _storage.GetMessageByIdAsync(result.MessageId);
        Assert.Equal(StoreAndForwardMessageStatus.Pending, msg!.Status);
        Assert.Equal(0, msg.RetryCount);
    }

    [Fact]
    public async Task DiscardParkedMessageAsync_PermanentlyRemoves()
    {
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ => throw new HttpRequestException("fail"));

        var result = await _service.EnqueueAsync(
            StoreAndForwardCategory.ExternalSystem, "api", """{}""",
            maxRetries: 1);

        await _service.RetryPendingMessagesAsync();

        var discarded = await _service.DiscardParkedMessageAsync(result.MessageId);
        Assert.True(discarded);

        var msg = await _storage.GetMessageByIdAsync(result.MessageId);
        Assert.Null(msg);
    }

    [Fact]
    public async Task GetParkedMessagesAsync_ReturnsPaginatedResults()
    {
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ => throw new HttpRequestException("fail"));

        for (int i = 0; i < 3; i++)
        {
            await _service.EnqueueAsync(
                StoreAndForwardCategory.ExternalSystem, $"api{i}", """{}""",
                maxRetries: 1);
        }

        await _service.RetryPendingMessagesAsync();

        var (messages, total) = await _service.GetParkedMessagesAsync(
            StoreAndForwardCategory.ExternalSystem, 1, 2);

        Assert.Equal(2, messages.Count);
        Assert.True(total >= 3);
    }

    // ── WP-13: Messages survive instance deletion ──

    [Fact]
    public async Task MessagesForInstance_SurviveAfterDeletion()
    {
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ => throw new HttpRequestException("fail"));

        await _service.EnqueueAsync(
            StoreAndForwardCategory.ExternalSystem, "api", """{}""", "Pump1");
        await _service.EnqueueAsync(
            StoreAndForwardCategory.ExternalSystem, "api2", """{}""", "Pump1");

        var count = await _service.GetMessageCountForInstanceAsync("Pump1");
        Assert.Equal(2, count);
    }

    // ── WP-14: Health metrics ──

    [Fact]
    public async Task GetBufferDepthAsync_ReturnsCorrectDepth()
    {
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ => throw new HttpRequestException("fail"));
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.Notification,
            _ => throw new HttpRequestException("fail"));

        await _service.EnqueueAsync(StoreAndForwardCategory.ExternalSystem, "api1", """{}""");
        await _service.EnqueueAsync(StoreAndForwardCategory.ExternalSystem, "api2", """{}""");
        await _service.EnqueueAsync(StoreAndForwardCategory.Notification, "email", """{}""");

        var depth = await _service.GetBufferDepthAsync();
        Assert.True(depth.GetValueOrDefault(StoreAndForwardCategory.ExternalSystem) >= 2);
        Assert.True(depth.GetValueOrDefault(StoreAndForwardCategory.Notification) >= 1);
    }

    [Fact]
    public async Task OnActivity_RaisedOnEnqueue()
    {
        var activities = new List<string>();
        _service.OnActivity += (action, _, _) => activities.Add(action);

        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ => Task.FromResult(true));

        await _service.EnqueueAsync(StoreAndForwardCategory.ExternalSystem, "api", """{}""");

        Assert.Contains("Delivered", activities);
    }

    [Fact]
    public async Task OnActivity_RaisedOnBuffer()
    {
        var activities = new List<string>();
        _service.OnActivity += (action, _, _) => activities.Add(action);

        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ => throw new HttpRequestException("fail"));

        await _service.EnqueueAsync(StoreAndForwardCategory.ExternalSystem, "api", """{}""");

        Assert.Contains("Queued", activities);
    }

    // ── WP-10: Per-source-entity retry settings ──

    [Fact]
    public async Task EnqueueAsync_CustomRetrySettings_Respected()
    {
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ => throw new HttpRequestException("fail"));

        var result = await _service.EnqueueAsync(
            StoreAndForwardCategory.ExternalSystem, "api", """{}""",
            maxRetries: 100,
            retryInterval: TimeSpan.FromSeconds(60));

        var msg = await _storage.GetMessageByIdAsync(result.MessageId);
        Assert.Equal(100, msg!.MaxRetries);
        Assert.Equal(60000, msg.RetryIntervalMs);
    }

    // ── attemptImmediateDelivery: false — caller already attempted delivery ──

    [Fact]
    public async Task EnqueueAsync_AttemptImmediateDeliveryFalse_BuffersWithoutInvokingHandler()
    {
        // A caller that has already made its own delivery attempt passes
        // attemptImmediateDelivery: false so the request is not dispatched twice.
        var handlerCalls = 0;
        _service.RegisterDeliveryHandler(StoreAndForwardCategory.ExternalSystem,
            _ => { Interlocked.Increment(ref handlerCalls); return Task.FromResult(true); });

        var result = await _service.EnqueueAsync(
            StoreAndForwardCategory.ExternalSystem, "api", """{}""",
            attemptImmediateDelivery: false);

        Assert.Equal(0, handlerCalls);   // handler NOT invoked at enqueue time
        Assert.True(result.WasBuffered);

        var msg = await _storage.GetMessageByIdAsync(result.MessageId);
        Assert.NotNull(msg);
        Assert.Equal(StoreAndForwardMessageStatus.Pending, msg!.Status);
        // StoreAndForward-003: the caller's own attempt is attempt 0; RetryCount
        // counts only sweep retries, so a freshly buffered message has RetryCount 0.
        Assert.Equal(0, msg.RetryCount);
    }
}