using System.Threading.Channels;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using ZB.MOM.WW.LocalDb.Contracts;
using ZB.MOM.WW.LocalDb.Internal;
using ZB.MOM.WW.LocalDb.Replication;
using ZB.MOM.WW.LocalDb.Replication.Internal;

namespace ZB.MOM.WW.LocalDb.Tests;

public sealed class SyncSessionTests : IDisposable
{
    private const string OrdersSql = "CREATE TABLE orders (id INTEGER PRIMARY KEY, sku TEXT, qty INTEGER)";
    private static readonly TimeSpan RunTimeout = TimeSpan.FromSeconds(15);

    private readonly List<string> _paths = [];
    private readonly List<IDisposable> _disposables = [];

    public void Dispose()
    {
        foreach (var d in _disposables)
            d.Dispose();
        SqliteConnection_ClearAllPools();
        foreach (var p in _paths)
        {
            if (File.Exists(p)) File.Delete(p);
            if (File.Exists(p + "-wal")) File.Delete(p + "-wal");
            if (File.Exists(p + "-shm")) File.Delete(p + "-shm");
        }
    }

    private static void SqliteConnection_ClearAllPools() => Microsoft.Data.Sqlite.SqliteConnection.ClearAllPools();

    private sealed record Side(
        SqliteLocalDb Db, OplogStore Store, LwwApplier Applier, SyncSession Session);

    private async Task<Side> NewSideAsync(
        string createSql = OrdersSql,
        string table = "orders",
        ReplicationOptions? options = null,
        ILogger? logger = null,
        Func<DateTimeOffset>? utcNow = null)
    {
        var path = Path.Combine(Path.GetTempPath(), Guid.NewGuid() + ".db");
        _paths.Add(path);
        var db = new SqliteLocalDb(new LocalDbOptions { Path = path });
        _disposables.Add(db);
        await db.ExecuteAsync(createSql);
        db.RegisterReplicated(table);

        options ??= new ReplicationOptions { FlushInterval = TimeSpan.FromMilliseconds(20) };
        var store = new OplogStore(db, options, utcNow);
        var applier = new LwwApplier(db, utcNow);
        var session = new SyncSession(db, store, applier, options, logger ?? NullLogger.Instance, utcNow);
        return new Side(db, store, applier, session);
    }

    private static (SyncDuplex A, SyncDuplex B) DuplexPair()
    {
        var aToB = Channel.CreateUnbounded<SyncMessage>();
        var bToA = Channel.CreateUnbounded<SyncMessage>();
        var a = new SyncDuplex
        {
            Send = (m, ct) => aToB.Writer.WriteAsync(m, ct).AsTask(),
            Inbox = bToA.Reader,
        };
        var b = new SyncDuplex
        {
            Send = (m, ct) => bToA.Writer.WriteAsync(m, ct).AsTask(),
            Inbox = aToB.Reader,
        };
        return (a, b);
    }

    private static (SyncDuplex Duplex, ChannelWriter<SyncMessage> ToSession, ChannelReader<SyncMessage> FromSession) ScriptedPeer()
    {
        var toSession = Channel.CreateUnbounded<SyncMessage>();
        var fromSession = Channel.CreateUnbounded<SyncMessage>();
        var duplex = new SyncDuplex
        {
            Send = (m, ct) => fromSession.Writer.WriteAsync(m, ct).AsTask(),
            Inbox = toSession.Reader,
        };
        return (duplex, toSession.Writer, fromSession.Reader);
    }

    private static Handshake MatchingHandshake(SqliteLocalDb sessionDb, string peerNodeId, uint version = 1, long lastAppliedRemoteSeq = 0)
    {
        var h = new Handshake { NodeId = peerNodeId, LibSchemaVersion = version, LastAppliedRemoteSeq = lastAppliedRemoteSeq };
        foreach (var t in sessionDb.ReplicatedTables.Values.OrderBy(t => t.Name, StringComparer.Ordinal))
            h.Tables.Add(new TableDigest { TableName = t.Name, Digest = t.Digest });
        return h;
    }

    private static async Task<SyncMessage> NextAsync(ChannelReader<SyncMessage> reader, CancellationToken ct)
    {
        await reader.WaitToReadAsync(ct);
        reader.TryRead(out var msg);
        return msg!;
    }

    private static async Task SwallowAsync(Task task)
    {
        try { await task; }
        catch (OperationCanceledException) { }
    }

    private static async Task WaitForAsync(Func<Task<bool>> predicate, TimeSpan timeout)
    {
        var deadline = DateTime.UtcNow + timeout;
        while (DateTime.UtcNow < deadline)
        {
            if (await predicate()) return;
            await Task.Delay(20);
        }
        throw new TimeoutException("Condition not reached within " + timeout);
    }

    private static async Task<List<(long Id, string? Sku, long? Qty)>> ReadOrders(SqliteLocalDb db)
    {
        var rows = await db.QueryAsync(
            "SELECT id, sku, qty FROM orders ORDER BY id",
            x => (x.GetInt64(0), x.IsDBNull(1) ? null : x.GetString(1), (long?)(x.IsDBNull(2) ? null : x.GetInt64(2))));
        return rows.ToList();
    }

    private static async Task<long> OplogCount(SqliteLocalDb db)
    {
        var r = await db.QueryAsync("SELECT COUNT(*) FROM __localdb_oplog", x => x.GetInt64(0));
        return r[0];
    }

    private static async Task<long> LastAckedSeq(SqliteLocalDb db)
    {
        var r = await db.QueryAsync("SELECT last_acked_seq FROM __localdb_peer_state WHERE id = 1", x => x.GetInt64(0));
        return r[0];
    }

    [Fact]
    public async Task Handshake_Exchanged_BothProceed()
    {
        var a = await NewSideAsync();
        var b = await NewSideAsync();
        var (da, db) = DuplexPair();

        using var cts = new CancellationTokenSource(RunTimeout);
        var runA = a.Session.RunAsync(da, cts.Token);
        var runB = b.Session.RunAsync(db, cts.Token);

        await WaitForAsync(() => Task.FromResult(a.Session.PeerNodeId is not null && b.Session.PeerNodeId is not null), RunTimeout);

        Assert.Equal(b.Db.NodeId, a.Session.PeerNodeId);
        Assert.Equal(a.Db.NodeId, b.Session.PeerNodeId);

        cts.Cancel();
        await SwallowAsync(runA);
        await SwallowAsync(runB);
    }

    [Fact]
    public async Task Handshake_DigestMismatch_FailsClosed()
    {
        var a = await NewSideAsync();
        var b = await NewSideAsync("CREATE TABLE orders (id INTEGER PRIMARY KEY, sku TEXT, qty INTEGER, extra TEXT)");
        await a.Db.ExecuteAsync("INSERT INTO orders (id, sku, qty) VALUES (1, 'A', 5)");
        var (da, db) = DuplexPair();

        using var cts = new CancellationTokenSource(RunTimeout);
        var runA = a.Session.RunAsync(da, cts.Token);
        var runB = b.Session.RunAsync(db, cts.Token);

        var exA = await Assert.ThrowsAsync<LocalDbSchemaMismatchException>(() => runA);
        var exB = await Assert.ThrowsAsync<LocalDbSchemaMismatchException>(() => runB);
        Assert.Contains("orders", exA.Message);
        Assert.Contains("orders", exB.Message);

        // No delta crossed the handshake: B never received A's row.
        Assert.Empty(await ReadOrders(b.Db));
    }

    [Fact]
    public async Task Handshake_SchemaVersionMismatch_FailsClosed()
    {
        var a = await NewSideAsync();
        var (duplex, toSession, _) = ScriptedPeer();

        using var cts = new CancellationTokenSource(RunTimeout);
        var run = a.Session.RunAsync(duplex, cts.Token);

        await toSession.WriteAsync(new SyncMessage { Handshake = MatchingHandshake(a.Db, "peer", version: 2) }, cts.Token);

        await Assert.ThrowsAsync<LocalDbSchemaMismatchException>(() => run);
    }

    [Fact]
    public async Task Deltas_FlowBothDirections_AcksAdvanceWatermarks()
    {
        var a = await NewSideAsync();
        var b = await NewSideAsync();
        await a.Db.ExecuteAsync("INSERT INTO orders (id, sku, qty) VALUES (1, 'FROM_A', 10)");
        await b.Db.ExecuteAsync("INSERT INTO orders (id, sku, qty) VALUES (2, 'FROM_B', 20)");
        var (da, db) = DuplexPair();

        using var cts = new CancellationTokenSource(RunTimeout);
        var runA = a.Session.RunAsync(da, cts.Token);
        var runB = b.Session.RunAsync(db, cts.Token);

        async Task<bool> Converged()
        {
            var ra = await ReadOrders(a.Db);
            var rb = await ReadOrders(b.Db);
            return ra.Count == 2 && rb.Count == 2
                && await OplogCount(a.Db) == 0 && await OplogCount(b.Db) == 0;
        }

        await WaitForAsync(Converged, RunTimeout);

        var rowsA = await ReadOrders(a.Db);
        var rowsB = await ReadOrders(b.Db);
        Assert.Equal(rowsA, rowsB);
        Assert.Equal([(1L, "FROM_A", (long?)10), (2L, "FROM_B", (long?)20)], rowsA);
        Assert.True(await LastAckedSeq(a.Db) >= 1);
        Assert.True(await LastAckedSeq(b.Db) >= 1);

        cts.Cancel();
        await SwallowAsync(runA);
        await SwallowAsync(runB);
    }

    [Fact]
    public async Task Backlog_DrainsWithoutWaitingFlushInterval()
    {
        var options = new ReplicationOptions { MaxBatchSize = 5, FlushInterval = TimeSpan.FromSeconds(30) };
        var a = await NewSideAsync(options: options);
        var b = await NewSideAsync(options: options);

        const int rows = 15; // 3 x MaxBatchSize
        for (var i = 1; i <= rows; i++)
            await a.Db.ExecuteAsync("INSERT INTO orders (id, sku, qty) VALUES (@id, 'R', @id)", new { id = i });

        var (da, db) = DuplexPair();
        using var cts = new CancellationTokenSource(RunTimeout);
        var runA = a.Session.RunAsync(da, cts.Token);
        var runB = b.Session.RunAsync(db, cts.Token);

        // FlushInterval is 30 s: reaching convergence in a couple seconds proves the pump loops
        // immediately on backlog instead of waiting a flush tick between batches.
        var sw = System.Diagnostics.Stopwatch.StartNew();
        await WaitForAsync(async () => (await ReadOrders(b.Db)).Count == rows, TimeSpan.FromSeconds(5));
        sw.Stop();
        Assert.True(sw.Elapsed < TimeSpan.FromSeconds(5), $"drain took {sw.Elapsed}");

        cts.Cancel();
        await SwallowAsync(runA);
        await SwallowAsync(runB);
    }

    [Fact]
    public async Task HlcDriftAhead_Warns()
    {
        var logger = new ListLogger();
        var a = await NewSideAsync(
            options: new ReplicationOptions { FlushInterval = TimeSpan.FromMilliseconds(20), FailClosedOnDrift = false },
            logger: logger);
        var (duplex, toSession, fromSession) = ScriptedPeer();

        using var cts = new CancellationTokenSource(RunTimeout);
        var run = a.Session.RunAsync(duplex, cts.Token);

        await DriveHandshakeAsync(a.Db, toSession, fromSession, cts.Token);

        var aheadHlc = (DateTimeOffset.UtcNow.AddMinutes(10).ToUnixTimeMilliseconds() << 16);
        await toSession.WriteAsync(new SyncMessage
        {
            DeltaBatch = new DeltaBatch
            {
                Entries = { new OplogEntry
                {
                    Seq = 1, TableName = "orders", PkJson = "{\"id\":1}",
                    RowJson = "{\"id\":1,\"sku\":\"AHEAD\",\"qty\":9}", Hlc = aheadHlc, NodeId = "peer", IsTombstone = false,
                } },
            },
        }, cts.Token);

        // Drain the DeltaAck the session emits after applying.
        SyncMessage ack;
        do { ack = await NextAsync(fromSession, cts.Token); } while (ack.MsgCase != SyncMessage.MsgOneofCase.DeltaAck);
        Assert.Equal(1, ack.DeltaAck.AppliedThruSeq);

        Assert.Single(await ReadOrders(a.Db)); // applied despite drift
        Assert.Contains(logger.Entries, e => e.Level == LogLevel.Warning);

        cts.Cancel();
        await SwallowAsync(run);
    }

    [Fact]
    public async Task HlcDriftAhead_FailClosed_Throws()
    {
        var a = await NewSideAsync(
            options: new ReplicationOptions { FlushInterval = TimeSpan.FromMilliseconds(20), FailClosedOnDrift = true });
        var (duplex, toSession, fromSession) = ScriptedPeer();

        using var cts = new CancellationTokenSource(RunTimeout);
        var run = a.Session.RunAsync(duplex, cts.Token);

        await DriveHandshakeAsync(a.Db, toSession, fromSession, cts.Token);

        var aheadHlc = (DateTimeOffset.UtcNow.AddMinutes(10).ToUnixTimeMilliseconds() << 16);
        await toSession.WriteAsync(new SyncMessage
        {
            DeltaBatch = new DeltaBatch
            {
                Entries = { new OplogEntry
                {
                    Seq = 1, TableName = "orders", PkJson = "{\"id\":1}",
                    RowJson = "{\"id\":1,\"sku\":\"AHEAD\",\"qty\":9}", Hlc = aheadHlc, NodeId = "peer", IsTombstone = false,
                } },
            },
        }, cts.Token);

        await Assert.ThrowsAsync<InvalidOperationException>(() => run);
        Assert.Empty(await ReadOrders(a.Db)); // rejected, not applied
    }

    [Fact]
    public async Task PeerNeedsSnapshot_InvokesSnapshotHooks()
    {
        // (a) peer's HandshakeAck.snapshot_required = true -> our SnapshotSender fires.
        {
            var a = await NewSideAsync();
            var (duplex, toSession, fromSession) = ScriptedPeer();
            var sent = new TaskCompletionSource();
            a.Session.SnapshotSender = (_, _) => { sent.TrySetResult(); return Task.CompletedTask; };

            using var cts = new CancellationTokenSource(RunTimeout);
            var run = a.Session.RunAsync(duplex, cts.Token);

            await NextAsync(fromSession, cts.Token); // session Handshake
            await toSession.WriteAsync(new SyncMessage { Handshake = MatchingHandshake(a.Db, "peer") }, cts.Token);
            await NextAsync(fromSession, cts.Token); // session HandshakeAck
            await toSession.WriteAsync(new SyncMessage { HandshakeAck = new HandshakeAck { NodeId = "peer", SnapshotRequired = true } }, cts.Token);

            await sent.Task.WaitAsync(RunTimeout);
            cts.Cancel();
            await SwallowAsync(run);
        }

        // (b) inbound SnapshotBegin -> our SnapshotReceiver fires.
        {
            var a = await NewSideAsync();
            var (duplex, toSession, fromSession) = ScriptedPeer();
            var received = new TaskCompletionSource();
            a.Session.SnapshotReceiver = (_, _, _) => { received.TrySetResult(); return Task.CompletedTask; };

            using var cts = new CancellationTokenSource(RunTimeout);
            var run = a.Session.RunAsync(duplex, cts.Token);

            await DriveHandshakeAsync(a.Db, toSession, fromSession, cts.Token);
            await toSession.WriteAsync(new SyncMessage { SnapshotBegin = new SnapshotBegin { AsOfSeq = 0 } }, cts.Token);

            await received.Task.WaitAsync(RunTimeout);
            cts.Cancel();
            await SwallowAsync(run);
        }

        // (c) snapshot required but no sender hook -> NotSupportedException.
        {
            var a = await NewSideAsync();
            var (duplex, toSession, fromSession) = ScriptedPeer();

            using var cts = new CancellationTokenSource(RunTimeout);
            var run = a.Session.RunAsync(duplex, cts.Token);

            await NextAsync(fromSession, cts.Token);
            await toSession.WriteAsync(new SyncMessage { Handshake = MatchingHandshake(a.Db, "peer") }, cts.Token);
            await NextAsync(fromSession, cts.Token);
            await toSession.WriteAsync(new SyncMessage { HandshakeAck = new HandshakeAck { NodeId = "peer", SnapshotRequired = true } }, cts.Token);

            await Assert.ThrowsAsync<NotSupportedException>(() => run);
        }

        // (d) inbound SnapshotBegin but no receiver hook -> NotSupportedException.
        {
            var a = await NewSideAsync();
            var (duplex, toSession, fromSession) = ScriptedPeer();

            using var cts = new CancellationTokenSource(RunTimeout);
            var run = a.Session.RunAsync(duplex, cts.Token);

            await DriveHandshakeAsync(a.Db, toSession, fromSession, cts.Token);
            await toSession.WriteAsync(new SyncMessage { SnapshotBegin = new SnapshotBegin { AsOfSeq = 0 } }, cts.Token);

            await Assert.ThrowsAsync<NotSupportedException>(() => run);
        }
    }

    [Fact]
    public async Task SecondHandshake_MidStream_IsProtocolError()
    {
        var a = await NewSideAsync();
        var (duplex, toSession, fromSession) = ScriptedPeer();

        using var cts = new CancellationTokenSource(RunTimeout);
        var run = a.Session.RunAsync(duplex, cts.Token);

        await DriveHandshakeAsync(a.Db, toSession, fromSession, cts.Token);
        await toSession.WriteAsync(new SyncMessage { Handshake = MatchingHandshake(a.Db, "peer") }, cts.Token);

        await Assert.ThrowsAsync<InvalidOperationException>(() => run);
    }

    // Completes the two-phase handshake against a real session: consumes its Handshake + HandshakeAck
    // and replies with a matching Handshake + a no-snapshot HandshakeAck, leaving the session in steady state.
    private static async Task DriveHandshakeAsync(
        SqliteLocalDb sessionDb, ChannelWriter<SyncMessage> toSession, ChannelReader<SyncMessage> fromSession, CancellationToken ct)
    {
        var hs = await NextAsync(fromSession, ct);
        Assert.Equal(SyncMessage.MsgOneofCase.Handshake, hs.MsgCase);
        await toSession.WriteAsync(new SyncMessage { Handshake = MatchingHandshake(sessionDb, "peer") }, ct);
        var ack = await NextAsync(fromSession, ct);
        Assert.Equal(SyncMessage.MsgOneofCase.HandshakeAck, ack.MsgCase);
        await toSession.WriteAsync(new SyncMessage { HandshakeAck = new HandshakeAck { NodeId = "peer", SnapshotRequired = false } }, ct);
    }

    private sealed class ListLogger : ILogger
    {
        public List<(LogLevel Level, string Message)> Entries { get; } = [];

        public IDisposable BeginScope<TState>(TState state) where TState : notnull => NullScope.Instance;
        public bool IsEnabled(LogLevel logLevel) => true;

        public void Log<TState>(
            LogLevel logLevel, EventId eventId, TState state, Exception? exception, Func<TState, Exception?, string> formatter)
        {
            lock (Entries)
                Entries.Add((logLevel, formatter(state, exception)));
        }

        private sealed class NullScope : IDisposable
        {
            public static readonly NullScope Instance = new();
            public void Dispose() { }
        }
    }
}