using Microsoft.Data.Sqlite;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using Xunit.Abstractions;

namespace ZB.MOM.WW.ScadaBridge.SiteEventLogging.Tests;

/// <summary>
/// Register row 81 — the storage cap measures <c>site_events</c>' own pages, not the whole
/// consolidated LocalDb file.
/// </summary>
/// <remarks>
/// <para>
/// The defect these tests close: <c>site_events</c> shares one SQLite file with nine other
/// tables plus LocalDb's <c>__localdb_oplog</c> / <c>__localdb_row_version</c> bookkeeping, and
/// the cap used to compare <c>MaxStorageMb</c> against <c>page_count - freelist_count</c> over
/// that whole file. On a replication-enabled node the trim therefore fought itself — each
/// 1000-row delete freed ~390 KB of event pages while adding ~1000 oplog rows and ~1000
/// tombstones to the same file — and stopped 2.5x over a 64 MB cap with 226 k rows still
/// present (<c>docs/plans/2026-08-15-site-events-purge-burst-measurement.md</c> §5).
/// </para>
/// <para>
/// A real replication pair is not needed to pin the semantics: what matters is that OTHER pages
/// in the same file neither consume nor block the event log's budget. A plain ballast table
/// stands in for the oplog, tombstones and the other nine tables alike.
/// </para>
/// </remarks>
public class EventLogStorageCapScopeTests : IDisposable
{
    private readonly ITestOutputHelper _output;
    private readonly SiteEventLogger _eventLogger;
    private readonly TestLocalDb _localDb;
    private readonly string _dbPath;

    public EventLogStorageCapScopeTests(ITestOutputHelper output)
    {
        _output = output;
        _dbPath = Path.Combine(Path.GetTempPath(), $"test_capscope_{Guid.NewGuid()}.db");
        _localDb = TestLocalDb.Create(_dbPath);
        _eventLogger = new SiteEventLogger(
            Options.Create(new SiteEventLogOptions { DatabasePath = _dbPath }),
            NullLogger<SiteEventLogger>.Instance,
            _localDb.Db);
    }

    public void Dispose()
    {
        _eventLogger.Dispose();
        _localDb.Dispose();
        TestLocalDb.DeleteFiles(_dbPath);
        GC.SuppressFinalize(this);
    }

    private EventLogPurgeService CreatePurgeService(SiteEventLogOptions options, ILogger<EventLogPurgeService>? logger = null) =>
        new(_eventLogger, Options.Create(options), logger ?? NullLogger<EventLogPurgeService>.Instance);

    private SiteEventLogOptions CapOptions(int maxStorageMb) => new()
    {
        DatabasePath = _dbPath,
        // Far enough in the past that the retention purge never fires — these tests are about
        // the cap trim in isolation, and a shared tick budget would otherwise blur the two.
        RetentionDays = 3650,
        MaxStorageMb = maxStorageMb,
    };

    /// <summary>Seeds <paramref name="count"/> events, each ~256 bytes of payload.</summary>
    private void SeedEvents(int count)
    {
        var details = new string('x', 200);
        _eventLogger.WithConnection(connection =>
        {
            using var tx = connection.BeginTransaction();
            using var cmd = connection.CreateCommand();
            cmd.Transaction = tx;
            cmd.CommandText = """
                INSERT INTO site_events (id, timestamp, event_type, severity, instance_id, source, message, details)
                VALUES ($id, $ts, 'script', 'Info', $inst, 'SiteRuntime', 'Bulk event', $details)
                """;
            var id = cmd.Parameters.Add("$id", SqliteType.Text);
            var ts = cmd.Parameters.Add("$ts", SqliteType.Text);
            var inst = cmd.Parameters.Add("$inst", SqliteType.Text);
            var det = cmd.Parameters.Add("$details", SqliteType.Text);
            var start = new DateTimeOffset(2026, 1, 1, 0, 0, 0, TimeSpan.Zero);
            for (var i = 0; i < count; i++)
            {
                id.Value = Guid.NewGuid().ToString("N");
                ts.Value = start.AddSeconds(i).ToString("o");
                inst.Value = i % 3 == 0 ? DBNull.Value : Guid.NewGuid().ToString();
                det.Value = details;
                cmd.ExecuteNonQuery();
            }
            tx.Commit();
        });
    }

    /// <summary>
    /// Fills a non-event table in the SAME file, standing in for LocalDb's oplog and
    /// row-version tables and the nine other consolidated tables.
    /// </summary>
    private void SeedBallast(int rows, int bytesPerRow)
    {
        var payload = new string('b', bytesPerRow);
        _eventLogger.WithConnection(connection =>
        {
            using var create = connection.CreateCommand();
            create.CommandText = "CREATE TABLE IF NOT EXISTS test_ballast (seq INTEGER PRIMARY KEY, row_json TEXT)";
            create.ExecuteNonQuery();

            using var tx = connection.BeginTransaction();
            using var cmd = connection.CreateCommand();
            cmd.Transaction = tx;
            cmd.CommandText = "INSERT INTO test_ballast (row_json) VALUES ($p)";
            var p = cmd.Parameters.Add("$p", SqliteType.Text);
            for (var i = 0; i < rows; i++)
            {
                p.Value = payload;
                cmd.ExecuteNonQuery();
            }
            tx.Commit();
        });
    }

    private long EventCount() => _eventLogger.WithConnection(connection =>
    {
        using var cmd = connection.CreateCommand();
        cmd.CommandText = "SELECT COUNT(*) FROM site_events";
        return (long)cmd.ExecuteScalar()!;
    });

    [Fact]
    public void EstimatedSize_ExcludesOtherTablesInTheSameFile()
    {
        // A small ballast is seeded up front so the whole-file clamp inside the estimator is
        // slack in BOTH readings — otherwise the first would be pinned to the file size and the
        // comparison would be measuring the clamp rather than the model.
        SeedBallast(rows: 4_000, bytesPerRow: 400);
        SeedEvents(4000);

        var purge = CreatePurgeService(CapOptions(1024));
        var eventsOnly = purge.EstimateSiteEventsSize().EstimatedBytes;
        var fileBefore = purge.GetDatabaseSizeBytes();

        SeedBallast(rows: 40_000, bytesPerRow: 500);

        var eventsAfterBallast = purge.EstimateSiteEventsSize().EstimatedBytes;
        var fileAfter = purge.GetDatabaseSizeBytes();

        _output.WriteLine($"site_events estimate {eventsOnly} -> {eventsAfterBallast}; file {fileBefore} -> {fileAfter}");

        // The file grew several-fold; the event log's own measured footprint did not move at all.
        Assert.True(fileAfter > fileBefore * 2,
            $"Ballast must visibly grow the file ({fileBefore} -> {fileAfter}).");
        Assert.Equal(eventsOnly, eventsAfterBallast);
    }

    [Fact]
    public void PurgeByStorageCap_WithLargeBallastInTheSameFile_DoesNotTrimAnUnderCapEventLog()
    {
        // The most direct expression of row 81: on a replicated node with an undrained oplog the
        // file dwarfs site_events. Under the old whole-file cap the trim would run — and delete
        // events — purely because of bytes the event log does not own.
        SeedEvents(4000);

        var sizingProbe = CreatePurgeService(CapOptions(1024));
        var eventBytes = sizingProbe.EstimateSiteEventsSize().EstimatedBytes;

        SeedBallast(rows: 40_000, bytesPerRow: 500);

        // Cap comfortably above site_events but far BELOW the whole file.
        var capMb = (int)Math.Max(1, (eventBytes * 2) / (1024 * 1024));
        var purge = CreatePurgeService(CapOptions(capMb));

        Assert.True(purge.GetDatabaseSizeBytes() > (long)capMb * 1024 * 1024,
            "Precondition: the whole file must exceed the cap, so a file-scoped cap would trim.");

        purge.RunPurge();

        Assert.Equal(4000, EventCount());
    }

    [Fact]
    public void PurgeByStorageCap_WithLargeBallastInTheSameFile_StillEnforcesTheCapOnEventsAndDoesNotEmptyTheTable()
    {
        // The other half: the cap must still be MET. Under the old whole-file measurement this
        // was impossible with unreclaimable ballast present — the trim either emptied the table
        // chasing a file size it could not reach, or (as measured) tripped the progress guard
        // and left the log 2.5x over cap.
        SeedEvents(6000);
        SeedBallast(rows: 40_000, bytesPerRow: 500);

        var sizingProbe = CreatePurgeService(CapOptions(1024));
        var eventBytes = sizingProbe.EstimateSiteEventsSize().EstimatedBytes;

        var capBytes = eventBytes / 2;
        var capMb = (int)Math.Max(1, capBytes / (1024 * 1024));
        var purge = CreatePurgeService(CapOptions(capMb));

        purge.RunPurge();

        var remaining = EventCount();
        var finalEstimate = purge.EstimateSiteEventsSize().EstimatedBytes;
        var finalCapBytes = (long)capMb * 1024 * 1024;

        _output.WriteLine($"remaining={remaining} estimate={finalEstimate} cap={finalCapBytes} file={purge.GetDatabaseSizeBytes()}");

        Assert.True(remaining > 0, "The cap trim must not empty the event table.");
        Assert.True(remaining < 6000, "The cap trim must remove events when the event log is over cap.");
        Assert.True(finalEstimate <= finalCapBytes,
            $"site_events estimate {finalEstimate} must be at or below the cap {finalCapBytes}.");

        // And the proof that the cap is table-scoped: the FILE is still way over it, and that is
        // correct — those bytes belong to LocalDb bookkeeping and the other consolidated tables.
        Assert.True(purge.GetDatabaseSizeBytes() > finalCapBytes,
            "The whole file is expected to stay over the cap — the cap no longer measures it.");
    }

    // ── size-model accuracy ──

    public static TheoryData<string, int, int, double> Workloads => new()
    {
        // name, rows, details length (0 = no details column), details on every row
        { "narrow rows, no details", 8000, 0, 1.0 },
        { "typical rows, 200B details", 6000, 200, 1.0 },
        { "wide rows, 2KB details", 3000, 2048, 1.0 },
    };

    [Theory]
    [MemberData(nameof(Workloads))]
    public void EstimateSiteEventsSize_TracksTheRealFootprint(string name, int rows, int detailsLength, double detailsFraction)
    {
        // Calibration guard for the modelled estimate. site_events' true page count is obtained
        // DIFFERENTIALLY: the file is measured with ballast only, the events are then added, and
        // the growth is what the table and its four indexes actually cost. Seeding the ballast
        // first also keeps the estimator's whole-file clamp slack, so this scores the model
        // itself rather than the clamp.
        //
        // The band is deliberately asymmetric. The model is tuned to run somewhat high, because
        // a cap that fires early wastes a slice of the budget whereas one that reads low lets
        // the log overrun the disk allowance the cap exists to defend.
        SeedBallast(rows: 4_000, bytesPerRow: 400);

        var purge = CreatePurgeService(CapOptions(1024));
        var baselineBytes = purge.GetDatabaseSizeBytes();

        var details = detailsLength > 0 ? new string('d', detailsLength) : null;
        _eventLogger.WithConnection(connection =>
        {
            using var tx = connection.BeginTransaction();
            using var cmd = connection.CreateCommand();
            cmd.Transaction = tx;
            cmd.CommandText = """
                INSERT INTO site_events (id, timestamp, event_type, severity, instance_id, source, message, details)
                VALUES ($id, $ts, 'ScriptExecution', 'Information', $inst, 'SiteRuntime', $msg, $details)
                """;
            var id = cmd.Parameters.Add("$id", SqliteType.Text);
            var ts = cmd.Parameters.Add("$ts", SqliteType.Text);
            var inst = cmd.Parameters.Add("$inst", SqliteType.Text);
            var msg = cmd.Parameters.Add("$msg", SqliteType.Text);
            var det = cmd.Parameters.Add("$details", SqliteType.Text);
            var start = new DateTimeOffset(2026, 1, 1, 0, 0, 0, TimeSpan.Zero);
            var rnd = new Random(7);
            for (var i = 0; i < rows; i++)
            {
                id.Value = Guid.NewGuid().ToString();
                ts.Value = start.AddSeconds(i).ToString("o");
                inst.Value = i % 3 == 0 ? DBNull.Value : Guid.NewGuid().ToString();
                msg.Value = $"Script 'Recipe{i % 50}' completed in {rnd.Next(1, 900)} ms";
                det.Value = details is not null && rnd.NextDouble() < detailsFraction ? details : (object)DBNull.Value;
                cmd.ExecuteNonQuery();
            }
            tx.Commit();
        });

        var estimated = purge.EstimateSiteEventsSize().EstimatedBytes;
        var actual = purge.GetDatabaseSizeBytes() - baselineBytes;
        var error = (estimated - (double)actual) / actual;

        _output.WriteLine($"{name}: rows={rows} estimated={estimated} actual={actual} error={error:P1}");

        Assert.InRange(error, -0.05, 0.25);
    }

    // ── wipe-prevention backstops ──

    /// <summary>Purge service whose size estimate and row count can be pinned by a test.</summary>
    private sealed class StubbedEstimatePurgeService(
        SiteEventLogger eventLogger,
        IOptions<SiteEventLogOptions> options,
        ILogger<EventLogPurgeService> logger,
        EventLogPurgeService.SiteEventsSizeEstimate? estimate,
        long? frozenRowCount)
        : EventLogPurgeService(eventLogger, options, logger)
    {
        internal override EventLogPurgeService.SiteEventsSizeEstimate EstimateSiteEventsSize() =>
            estimate ?? base.EstimateSiteEventsSize();

        internal override long GetSiteEventsRowCount() =>
            frozenRowCount ?? base.GetSiteEventsRowCount();
    }

    [Fact]
    public void PurgeByStorageCap_WhenRowWidthCannotBeSampled_DeletesNothingAndWarns()
    {
        // First backstop. A zero row width makes "how many rows put us under cap" unanswerable.
        // The old loop's answer to an unanswerable cap was to keep deleting until the file
        // shrank, which is precisely how a cap that can never be met empties a table.
        SeedEvents(2000);

        var logger = new CapturingLogger();
        var purge = new StubbedEstimatePurgeService(
            _eventLogger,
            Options.Create(CapOptions(0)),
            logger,
            new EventLogPurgeService.SiteEventsSizeEstimate(RowCount: 2000, BytesPerRow: 0),
            frozenRowCount: null);

        purge.RunPurge();

        Assert.Equal(2000, EventCount());
        Assert.Contains(logger.Entries, e =>
            e.Level == LogLevel.Warning && e.Message.Contains("row width could not be sampled", StringComparison.Ordinal));
    }

    [Fact]
    public void PurgeByStorageCap_WhenTheTableStopsShrinking_StopsRatherThanEmptyingTheLog()
    {
        // Second backstop, carried over from the old "size did not decrease" guard but re-based
        // onto the table-scoped metric. It can no longer be tripped by replication bookkeeping;
        // a frozen row count is what it now models — writers arriving as fast as the trim deletes.
        SeedEvents(5000);

        var logger = new CapturingLogger();
        var purge = new StubbedEstimatePurgeService(
            _eventLogger,
            Options.Create(CapOptions(0)),   // a 0 MB cap would otherwise delete every row
            logger,
            estimate: null,
            frozenRowCount: 5000);

        purge.RunPurge();

        var remaining = EventCount();
        Assert.True(remaining > 0, "The guard must stop the trim before the table is emptied.");
        Assert.True(remaining >= 4000, $"Only one batch should have been deleted; {5000 - remaining} rows went.");
        Assert.Contains(logger.Entries, e =>
            e.Level == LogLevel.Warning && e.Message.Contains("did not decrease", StringComparison.Ordinal));
    }

    private sealed record LogEntry(LogLevel Level, string Message);

    private sealed class CapturingLogger : ILogger<EventLogPurgeService>
    {
        public List<LogEntry> Entries { get; } = [];

        public IDisposable? BeginScope<TState>(TState state) where TState : notnull => null;

        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(new LogEntry(logLevel, formatter(state, exception)));
    }
}