using System.Reflection;
using Microsoft.Data.Sqlite;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using NSubstitute;
using ZB.MOM.WW.Audit;
using ZB.MOM.WW.ScadaBridge.AuditLog.Site;
using ZB.MOM.WW.ScadaBridge.AuditLog.Tests.TestSupport;
using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Services;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Audit;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
using IAuditWriter = ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Services.IAuditWriter;

namespace ZB.MOM.WW.ScadaBridge.AuditLog.Tests.Site;

/// <summary>
/// Regression coverage. <see cref="SqliteAuditWriter.FlushBatch"/>
/// used to call <c>pending.Completion.TrySetResult()</c> per row BEFORE
/// <c>transaction.Commit()</c> ran. A later failure in the SAME batch — another row's insert
/// throwing, or the commit itself failing (SQLITE_FULL, IOERR) — rolled the whole transaction
/// back, but the earlier row's <see cref="System.Threading.Tasks.Task"/> had already completed
/// successfully: the caller, and <see cref="FallbackAuditWriter"/> (whose ring-buffer fallback
/// exists precisely for this outage), both saw false success while the row was actually gone
/// from the database — <c>TrySetException</c> in the outer catch is a no-op against an
/// already-completed <see cref="System.Threading.Tasks.TaskCompletionSource"/>.
/// </summary>
/// <remarks>
/// A committed transaction can't practically be made to fail via public SQLite surface without
/// exhausting disk or injecting a custom VFS, so these tests force a genuine, non-swallowed
/// mid-batch INSERT failure instead (the "bonus defect" the finding also calls out: a mid-batch
/// insert failure on a later row loses the rows that inserted fine before it, the same way).
/// That failure is reached through a real SQLite trigger + a custom scalar function registered
/// directly on the writer's own connection (via reflection — <see cref="SqliteAuditWriter"/>
/// deliberately doesn't expose it), so the whole path under test — transaction, per-row
/// try/catch, rollback, TrySetException — is the writer's real production code, not a mock.
/// </remarks>
public class SqliteAuditWriterCommitFailureTests
{
    private const string FailMarker = "P4-2-FORCED-FAILURE";

    private static AuditEvent NewEvent(string target) => ScadaBridgeAuditEventFactory.Create(
        channel: AuditChannel.ApiOutbound,
        kind: AuditKind.ApiCall,
        status: AuditStatus.Delivered,
        eventId: Guid.NewGuid(),
        occurredAtUtc: DateTime.UtcNow,
        target: target);

    /// <summary>
    /// Installs a BEFORE INSERT trigger on <c>audit_event</c> that calls a custom scalar
    /// function throwing whenever the inserted row's <c>Target</c> is <see cref="FailMarker"/>.
    /// An exception thrown from a Microsoft.Data.Sqlite custom function surfaces as a generic
    /// SQLITE_ERROR (code 1), NOT SQLITE_CONSTRAINT (code 19) — so it is NOT caught by
    /// FlushBatch's duplicate-EventId swallow (which matches only code 19) and instead reaches
    /// the outer catch exactly like a real disk-outage commit failure would.
    /// </summary>
    private static void InstallFailureTrigger(SqliteAuditWriter writer)
    {
        var connectionField = typeof(SqliteAuditWriter).GetField(
            "_connection", BindingFlags.NonPublic | BindingFlags.Instance)
            ?? throw new InvalidOperationException("SqliteAuditWriter._connection not found — test seam broke.");
        var connection = (SqliteConnection)connectionField.GetValue(writer)!;

        connection.CreateFunction<string, long>("throw_if_marker", target =>
        {
            if (target == FailMarker)
            {
                throw new InvalidOperationException("P4-2 test-forced insert failure");
            }
            return 0;
        });

        using var cmd = connection.CreateCommand();
        cmd.CommandText = $"""
            CREATE TRIGGER test_fail_marker
            BEFORE INSERT ON audit_event
            FOR EACH ROW WHEN NEW.Target = '{FailMarker}'
            BEGIN
                SELECT throw_if_marker(NEW.Target);
            END;
            """;
        cmd.ExecuteNonQuery();
    }

    private static (SqliteAuditWriter writer, string dataSource) CreateWriter(string testName)
    {
        var dataSource = $"file:{testName}-{Guid.NewGuid():N}?mode=memory&cache=shared";
        var opts = new SqliteAuditWriterOptions
        {
            DatabasePath = dataSource,
            // Generous flush window: both writes below are enqueued back-to-back with no
            // await between them, so they are already both in the channel long before the
            // background loop's first drain attempt — this just gives extra margin so the
            // test can't flake into two separate flushes on a slow CI box.
            FlushIntervalMs = 1000,
        };
        var writer = new SqliteAuditWriter(
            Options.Create(opts),
            NullLogger<SqliteAuditWriter>.Instance,
            new FakeNodeIdentityProvider(),
            connectionStringOverride: $"Data Source={dataSource};Cache=Shared");
        return (writer, dataSource);
    }

    /// <summary>Verifies that a mid-batch insert failure faults every row in the batch, not just the failing row.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task FlushBatch_MidBatchInsertFailure_FaultsEveryRowInBatch_NotJustTheFailingRow()
    {
        var (writer, dataSource) = CreateWriter(
            nameof(FlushBatch_MidBatchInsertFailure_FaultsEveryRowInBatch_NotJustTheFailingRow));
        await using var _ = writer;

        InstallFailureTrigger(writer);

        // evt1 is an ordinary row — its own two INSERTs succeed. evt2 carries the marker and
        // throws mid-batch, from WITHIN the same transaction as evt1's already-successful
        // inserts. Fired without individually awaiting so both land in the channel before the
        // background loop's first drain — i.e. the same FlushBatch transaction.
        var evt1 = NewEvent("normal-row");
        var evt2 = NewEvent(FailMarker);

        var t1 = writer.WriteAsync(evt1);
        var t2 = writer.WriteAsync(evt2);

        try
        {
            await Task.WhenAll(t1, t2).WaitAsync(TimeSpan.FromSeconds(10));
        }
        catch
        {
            // Expected: both tasks fault. Individually asserted below so a failure here
            // reports which one didn't behave as expected, not just "something threw".
        }

        // THE regression assertion: evt1's own inserts succeeded, but the batch it shared
        // with evt2 rolled back — its Task must fault, not silently report success. Pre-fix,
        // t1 would already be RanToCompletion at this point (TrySetResult ran inside the loop
        // before evt2's insert threw), and the later TrySetException in the outer catch would
        // be a silent no-op against the already-completed TaskCompletionSource.
        Assert.True(t1.IsFaulted,
            "evt1's row was rolled back along with the rest of the batch, so its Task must fault instead of reporting false success.");
        Assert.True(t2.IsFaulted, "evt2's own insert threw directly and must fault its Task.");

        // No commit ever happened for this batch.
        Assert.Equal(0, writer.FlushCountForTests);

        // And the database genuinely holds neither row — proves the rollback actually
        // happened, not just that the Task-completion contract changed.
        using var verify = new SqliteConnection($"Data Source={dataSource};Cache=Shared");
        verify.Open();
        using var countCmd = verify.CreateCommand();
        countCmd.CommandText = "SELECT COUNT(*) FROM audit_event;";
        Assert.Equal(0L, (long)countCmd.ExecuteScalar()!);
    }

    /// <summary>Verifies that the fallback writer rings every faulted row of a mid-batch insert failure and increments the failure counter once per row.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task FallbackAuditWriter_MidBatchInsertFailure_RingsEveryFaultedRow_AndIncrementsFailureCounterForEach()
    {
        // End-to-end proof the fix actually closes the loop the finding describes:
        // FallbackAuditWriter composes the REAL SqliteAuditWriter as its primary. Before the
        // fix, evt1's primary write would appear to SUCCEED (its Task completed before the
        // rollback), so FallbackAuditWriter would never route it to the ring or count it as a
        // failure — the whole batch would be silently lost with SiteAuditWriteFailures staying
        // at 0, exactly as the finding describes.
        var (writer, _) = CreateWriter(
            nameof(FallbackAuditWriter_MidBatchInsertFailure_RingsEveryFaultedRow_AndIncrementsFailureCounterForEach));
        await using var _w = writer;

        InstallFailureTrigger(writer);

        var ring = new RingBufferFallback(capacity: 16);
        var counter = Substitute.For<IAuditWriteFailureCounter>();
        var fallback = new FallbackAuditWriter(
            writer, ring, counter, NullLogger<FallbackAuditWriter>.Instance);

        var evt1 = NewEvent("normal-row");
        var evt2 = NewEvent(FailMarker);

        // FallbackAuditWriter.WriteAsync never throws (audit failures are always swallowed at
        // that layer) — fired concurrently, same reasoning as above, so both land in one
        // FlushBatch transaction.
        var t1 = fallback.WriteAsync(evt1);
        var t2 = fallback.WriteAsync(evt2);
        await Task.WhenAll(t1, t2).WaitAsync(TimeSpan.FromSeconds(10));

        // Both rows — including the one whose own INSERT succeeded before the batch rolled
        // back — must have been routed to the ring and counted as a primary failure.
        Assert.Equal(2, ring.Count);
        counter.Received(2).Increment();
    }
}