using Microsoft.Data.SqlClient;
using Microsoft.EntityFrameworkCore;
using ZB.MOM.WW.Audit;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Audit;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
using ZB.MOM.WW.ScadaBridge.ConfigurationDatabase.Maintenance;
using ZB.MOM.WW.ScadaBridge.ConfigurationDatabase.Repositories;
using ZB.MOM.WW.ScadaBridge.ConfigurationDatabase.Tests.Migrations;

namespace ZB.MOM.WW.ScadaBridge.ConfigurationDatabase.Tests.Maintenance;

/// <summary>
/// SQL Server tests for the chain-head export store (ScadaBridge#107 item 1): heads read with
/// their counts, and exported heads checked against the database. The key case is the forgery
/// the export exists for: rows rewritten AND every later link and the head recomputed — which
/// <c>verify-chain</c> accepts — is caught because the exported hash no longer matches.
/// </summary>
/// <remarks>Each test owns one month (partition) of the shared fixture database.</remarks>
public sealed class AuditChainHeadStoreTests : IClassFixture<MsSqlMigrationFixture>
{
    private readonly MsSqlMigrationFixture _fixture;

    /// <summary>Creates the test class with the shared migrated SQL Server fixture.</summary>
    /// <param name="fixture">The shared migration fixture.</param>
    public AuditChainHeadStoreTests(MsSqlMigrationFixture fixture) => _fixture = fixture;

    /// <summary>The head snapshot carries the chain end and the live row + tombstone counts.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [SkippableFact]
    public async Task ReadHeads_ReportsTheChainEnd_AndRowAndTombstoneCounts()
    {
        Skip.IfNot(_fixture.Available, _fixture.SkipReason);
        var month = Month(2026, 3);
        await InsertAsync(Enumerable.Range(1, 5).Select(i => NewEvent(month.AddDays(i))));
        await InsertAsync([NewEvent(month.AddHours(1), AuditChannel.DbOutbound)]);
        await DrainAsync();
        await using (var ctx = CreateContext())
        {
            Assert.Equal(1, await new AuditLogRepository(ctx).PurgeChannelOlderThanAsync("DbOutbound", month.AddDays(1), 100));
        }

        var head = await HeadAsync(month);

        Assert.Equal(6, head.LastSeq);
        Assert.Equal(5, head.ChainedRows);
        Assert.Equal(1, head.Tombstones);
        Assert.Null(head.PurgedThroughSeq);
    }

    /// <summary>
    /// Unchanged chain: Matches. The chain grew: Extended. Both centrals' duplicate exports
    /// collapse to one check.
    /// </summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [SkippableFact]
    public async Task ExportedHeads_MatchTheUnchangedChain_AndAreExtendedByLaterLinks()
    {
        Skip.IfNot(_fixture.Available, _fixture.SkipReason);
        var month = Month(2026, 4);
        await InsertAsync(Enumerable.Range(1, 4).Select(i => NewEvent(month.AddDays(i))));
        await DrainAsync();
        var exported = Export(await HeadAsync(month));

        var same = await VerifyAsync(exported, exported with { Node = "central-b" });
        Assert.True(same.Verified);
        Assert.Equal(AuditChainHeadStatus.Matches, Assert.Single(same.Checks).Status);

        await InsertAsync([NewEvent(month.AddDays(10))]);
        await DrainAsync();
        var grown = await VerifyAsync(exported);
        Assert.True(grown.Verified);
        var check = Assert.Single(grown.Checks);
        Assert.Equal(AuditChainHeadStatus.Extended, check.Status);
        Assert.Equal(5, check.DatabaseSeq);
    }

    /// <summary>
    /// The forgery: a chained row's content is rewritten and every link from it plus the head
    /// are recomputed with the real hasher. <c>VerifyMonthAsync</c> reports the forged chain
    /// Intact (positive control: the in-database chain alone cannot see it); the exported head
    /// does not match it.
    /// </summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [SkippableFact]
    public async Task ARewrittenAndRehashedChain_PassesVerifyChain_ButFailsTheExportedHead()
    {
        Skip.IfNot(_fixture.Available, _fixture.SkipReason);
        var month = Month(2026, 5);
        await InsertAsync(Enumerable.Range(1, 6).Select(i => NewEvent(month.AddDays(i))));
        await DrainAsync();
        var exported = Export(await HeadAsync(month));

        await ForgeChainAsync(month, fromSeq: 3);

        await using (var ctx = CreateContext())
        {
            var chain = await new AuditLogHashChain(ctx).VerifyMonthAsync(month);
            Assert.Equal(AuditChainStatus.Intact, chain.Status);
        }

        var result = await VerifyAsync(exported);
        Assert.False(result.Verified);
        Assert.Equal(AuditChainHeadStatus.Mismatch, Assert.Single(result.Checks).Status);
    }

    /// <summary>Each structural tampering maps to its own verdict.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [SkippableFact]
    public async Task TamperedHeadsAndRows_AreReported_WithTheirOwnVerdicts()
    {
        Skip.IfNot(_fixture.Available, _fixture.SkipReason);

        // Head rolled back below the export (tail deletion + head rewrite).
        var regressed = Month(2026, 6);
        await InsertAsync(Enumerable.Range(1, 3).Select(i => NewEvent(regressed.AddDays(i))));
        await DrainAsync();
        var regressedExport = Export(await HeadAsync(regressed));
        await ExecAsync("UPDATE dbo.AuditLogChainHead SET LastSeq = LastSeq - 1 WHERE ChainMonth = @m;", regressed);

        // Head row deleted.
        var missingHead = Month(2026, 7);
        await InsertAsync([NewEvent(missingHead.AddDays(1))]);
        await DrainAsync();
        var missingHeadExport = Export(await HeadAsync(missingHead));
        await ExecAsync("DELETE FROM dbo.AuditLogChainHead WHERE ChainMonth = @m;", missingHead);

        // A chained row deleted with no tombstone, head unchanged: counts no longer add up.
        var counted = Month(2026, 8);
        await InsertAsync(Enumerable.Range(1, 3).Select(i => NewEvent(counted.AddDays(i))));
        await DrainAsync();
        var countedExport = Export(await HeadAsync(counted));
        await ExecAsync("DELETE FROM dbo.AuditLog WHERE ChainSeq = 2 AND OccurredAtUtc >= @m AND OccurredAtUtc < DATEADD(MONTH, 1, @m);", counted);

        // The exported link itself deleted after the chain grew past it.
        var missingLink = Month(2026, 9);
        await InsertAsync(Enumerable.Range(1, 2).Select(i => NewEvent(missingLink.AddDays(i))));
        await DrainAsync();
        var missingLinkExport = Export(await HeadAsync(missingLink));
        await InsertAsync([NewEvent(missingLink.AddDays(5))]);
        await DrainAsync();
        await ExecAsync("DELETE FROM dbo.AuditLog WHERE ChainSeq = 2 AND OccurredAtUtc >= @m AND OccurredAtUtc < DATEADD(MONTH, 1, @m);", missingLink);

        var result = await VerifyAsync(regressedExport, missingHeadExport, countedExport, missingLinkExport);

        Assert.False(result.Verified);
        var byMonth = result.Checks.ToDictionary(c => c.Month, c => c.Status);
        Assert.Equal(AuditChainHeadStatus.Regressed, byMonth["2026-06"]);
        Assert.Equal(AuditChainHeadStatus.MissingHead, byMonth["2026-07"]);
        Assert.Equal(AuditChainHeadStatus.CountMismatch, byMonth["2026-08"]);
        Assert.Equal(AuditChainHeadStatus.MissingLink, byMonth["2026-09"]);
    }

    /// <summary>
    /// Sanctioned purges are not tamper evidence: a per-channel purge (row to tombstone) keeps
    /// Matches; after a partition switch the exported head is the anchor, so the check still
    /// passes, and an older exported sequence the switch removed is reported Purged.
    /// </summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [SkippableFact]
    public async Task SanctionedPurges_AreNotFailures()
    {
        Skip.IfNot(_fixture.Available, _fixture.SkipReason);
        var month = Month(2026, 10);
        await InsertAsync(Enumerable.Range(1, 3).Select(i => NewEvent(month.AddDays(i))));
        await DrainAsync();
        var early = Export(await HeadAsync(month));
        await InsertAsync([NewEvent(month.AddDays(5), AuditChannel.Notification)]);
        await DrainAsync();
        var late = Export(await HeadAsync(month));

        await using (var ctx = CreateContext())
        {
            Assert.Equal(1, await new AuditLogRepository(ctx).PurgeChannelOlderThanAsync("Notification", month.AddDays(6), 100));
        }

        Assert.Equal(AuditChainHeadStatus.Matches, Assert.Single((await VerifyAsync(late)).Checks).Status);

        await using (var ctx = CreateContext())
        {
            await new AuditLogRepository(ctx).SwitchOutPartitionAsync(month);
        }

        var afterSwitch = await VerifyAsync(late, early);
        Assert.True(afterSwitch.Verified);
        var statuses = afterSwitch.Checks.ToDictionary(c => c.ExportedSeq, c => c.Status);
        Assert.Equal(AuditChainHeadStatus.Matches, statuses[4]);
        Assert.Equal(AuditChainHeadStatus.Purged, statuses[3]);
    }

    private static AuditChainHeadRecord Export(AuditChainHeadSnapshot head) => new(
        AuditChainHeadRecord.CurrentVersion,
        AuditChainHasher.PartitionLabel(head.Month),
        head.LastSeq,
        AuditChainHeadComparer.ToHex(head.LastHash),
        head.PurgedThroughSeq,
        head.PurgedThroughHash is null ? null : AuditChainHeadComparer.ToHex(head.PurgedThroughHash),
        head.ChainedRows,
        head.Tombstones,
        head.UpdatedAtUtc,
        DateTime.UtcNow,
        "central-a");

    private async Task<AuditChainHeadSnapshot> HeadAsync(DateTime month)
    {
        await using var ctx = CreateContext();
        var heads = await new AuditLogHashChain(ctx).ReadHeadsAsync();
        return Assert.Single(heads, h => h.Month == month);
    }

    private async Task<AuditChainHeadVerificationResult> VerifyAsync(params AuditChainHeadRecord[] records)
    {
        await using var ctx = CreateContext();
        return await new AuditLogHashChain(ctx).VerifyExportedHeadsAsync(records);
    }

    /// <summary>
    /// Rewrites the row at <paramref name="fromSeq"/> and re-links it and every later row plus the
    /// head with the production hasher — what a principal with full write access could do.
    /// </summary>
    private async Task ForgeChainAsync(DateTime month, long fromSeq)
    {
        await using var conn = _fixture.OpenConnection();
        await using (var edit = new SqlCommand(
            "UPDATE dbo.AuditLog SET Target = N'forged' WHERE ChainSeq = @s AND OccurredAtUtc >= @m AND OccurredAtUtc < DATEADD(MONTH, 1, @m);", conn))
        {
            edit.Parameters.AddWithValue("@s", fromSeq);
            edit.Parameters.Add(new SqlParameter("@m", System.Data.SqlDbType.DateTime2) { Scale = 7, Value = month });
            Assert.Equal(1, await edit.ExecuteNonQueryAsync());
        }

        var rows = new List<AuditChainRow>();
        await using (var read = new SqlCommand(
            $"SELECT {AuditLogHashChain.RowColumns}, ChainSeq, RowHash FROM dbo.AuditLog " +
            "WHERE ChainSeq IS NOT NULL AND OccurredAtUtc >= @m AND OccurredAtUtc < DATEADD(MONTH, 1, @m) ORDER BY ChainSeq;", conn))
        {
            read.Parameters.Add(new SqlParameter("@m", System.Data.SqlDbType.DateTime2) { Scale = 7, Value = month });
            await using var reader = await read.ExecuteReaderAsync();
            while (await reader.ReadAsync())
            {
                rows.Add(AuditLogHashChain.ReadRow(reader, withLink: true));
            }
        }

        var previous = rows.Single(r => r.ChainSeq == fromSeq - 1).RowHash!;
        foreach (var row in rows.Where(r => r.ChainSeq >= fromSeq))
        {
            var hash = AuditChainHasher.ComputeRowHash(previous, month, row.ChainSeq!.Value, row);
            await using var update = new SqlCommand("UPDATE dbo.AuditLog SET RowHash = @h WHERE EventId = @e AND OccurredAtUtc = @o;", conn);
            update.Parameters.AddWithValue("@h", hash);
            update.Parameters.AddWithValue("@e", row.EventId);
            update.Parameters.Add(new SqlParameter("@o", System.Data.SqlDbType.DateTime2) { Scale = 7, Value = row.OccurredAtUtc });
            Assert.Equal(1, await update.ExecuteNonQueryAsync());
            previous = hash;
        }

        await using var head = new SqlCommand("UPDATE dbo.AuditLogChainHead SET LastHash = @h WHERE ChainMonth = @m;", conn);
        head.Parameters.AddWithValue("@h", previous);
        head.Parameters.Add(new SqlParameter("@m", System.Data.SqlDbType.Date) { Value = month });
        Assert.Equal(1, await head.ExecuteNonQueryAsync());
    }

    private async Task ExecAsync(string sql, DateTime month)
    {
        await using var conn = _fixture.OpenConnection();
        await using var cmd = new SqlCommand(sql, conn);
        cmd.Parameters.Add(new SqlParameter("@m", System.Data.SqlDbType.DateTime2) { Scale = 7, Value = month });
        Assert.True(await cmd.ExecuteNonQueryAsync() >= 1);
    }

    private async Task InsertAsync(IEnumerable<AuditEvent> events)
    {
        await using var ctx = CreateContext();
        var repo = new AuditLogRepository(ctx);
        foreach (var e in events)
        {
            await repo.InsertIfNotExistsAsync(e);
        }
    }

    private async Task DrainAsync()
    {
        await using var ctx = CreateContext();
        var chain = new AuditLogHashChain(ctx);
        for (var i = 0; i < 1000; i++)
        {
            var r = await chain.ChainPendingAsync(500);
            if (r.RowsChained == 0 && !r.LockBusy)
            {
                return;
            }
        }

        throw new InvalidOperationException("Chain did not drain.");
    }

    private static DateTime Month(int year, int month) => new(year, month, 1, 0, 0, 0, DateTimeKind.Utc);

    private ScadaBridgeDbContext CreateContext()
        => new(new DbContextOptionsBuilder<ScadaBridgeDbContext>().UseSqlServer(_fixture.ConnectionString).Options);

    private static AuditEvent NewEvent(DateTime occurredAtUtc, AuditChannel channel = AuditChannel.ApiOutbound) =>
        ScadaBridgeAuditEventFactory.Create(
            channel: channel,
            kind: channel == AuditChannel.DbOutbound ? AuditKind.DbWrite : AuditKind.ApiCall,
            status: AuditStatus.Delivered,
            occurredAtUtc: occurredAtUtc,
            actor: "head-test",
            target: "erp",
            sourceNode: "central-a",
            sourceSiteId: "head-test",
            correlationId: Guid.NewGuid());
}