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using System.Globalization;
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using Microsoft.Data.Sqlite;
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using ZB.MOM.WW.LocalDb.Internal;
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using ZB.MOM.WW.LocalDb.Registration;
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namespace ZB.MOM.WW.LocalDb.Replication.Internal;
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/// <summary>Outcome of applying one inbound batch. <see cref="AppliedThruSeq"/> is the batch's highest seq regardless of per-entry disposition, so the watermark advances even over discarded/dead-lettered entries.</summary>
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internal sealed record ApplyResult(long AppliedThruSeq, int Applied, int Discarded, int DeadLettered);
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/// <summary>
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/// Applies a peer's oplog batch under last-writer-wins in one transaction: the applying guard is
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/// raised so capture triggers skip these writes, per-entry LWW resolves against the local
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/// row-version (hlc, then node_id ordinal tie-break), poison rows are dead-lettered while the
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/// batch continues, and the remote watermark advances in the SAME transaction as the data so a
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/// crash-replay of the batch is a no-op (LWW's strict-greater compare loses on equal versions).
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/// This never writes <c>__localdb_oplog</c>: the 2-node topology does not re-forward applied deltas.
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/// </summary>
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internal sealed class LwwApplier(SqliteLocalDb db)
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{
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public async Task<ApplyResult> ApplyBatchAsync(IReadOnlyList<OplogEntryRecord> entries, CancellationToken ct)
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{
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if (entries.Count == 0)
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return new ApplyResult(0, 0, 0, 0);
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// Validated before opening the transaction: an unknown table is a schema disagreement
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// between the peers (a protocol violation), not a per-row poison — reject the whole batch
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// so nothing is half-applied.
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foreach (var entry in entries)
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if (!db.ReplicatedTables.ContainsKey(entry.TableName))
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throw new LocalDbSchemaMismatchException(
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$"Received an oplog entry for table '{entry.TableName}', which is not registered for replication on this node.");
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var utcNow = DateTimeOffset.UtcNow.UtcDateTime.ToString(OplogStore.TombstoneUtcFormat, CultureInfo.InvariantCulture);
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var maxSeq = 0L;
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var maxHlc = 0L;
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foreach (var entry in entries)
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{
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if (entry.Seq > maxSeq) maxSeq = entry.Seq;
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if (entry.Hlc > maxHlc) maxHlc = entry.Hlc;
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}
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var sqlByTable = new Dictionary<string, (string Delete, string Upsert)>(StringComparer.Ordinal);
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var applied = 0;
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var discarded = 0;
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var deadLettered = 0;
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await using var tx = await db.BeginTransactionAsync(ct);
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await tx.ExecuteAsync("UPDATE __localdb_applying SET applying = 1 WHERE id = 1", null, ct);
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foreach (var entry in entries)
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{
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var local = await tx.QueryAsync(
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"SELECT hlc, node_id FROM __localdb_row_version WHERE table_name = @t AND pk_json = @pk",
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static r => (Hlc: r.GetInt64(0), NodeId: r.GetString(1)),
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new { t = entry.TableName, pk = entry.PkJson }, ct);
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var remoteWins = local.Count == 0
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|| entry.Hlc > local[0].Hlc
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|| (entry.Hlc == local[0].Hlc && string.CompareOrdinal(entry.NodeId, local[0].NodeId) > 0);
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if (!remoteWins)
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{
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discarded++;
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continue;
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}
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if (!sqlByTable.TryGetValue(entry.TableName, out var sql))
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{
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sql = BuildTableSql(db.ReplicatedTables[entry.TableName]);
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sqlByTable[entry.TableName] = sql;
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}
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try
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{
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if (entry.IsTombstone)
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await tx.ExecuteAsync(sql.Delete, new { pk = entry.PkJson }, ct);
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else
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await tx.ExecuteAsync(sql.Upsert, new { row = entry.RowJson }, ct);
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await tx.ExecuteAsync(
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"INSERT OR REPLACE INTO __localdb_row_version " +
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"(table_name, pk_json, hlc, node_id, is_tombstone, tombstone_utc) " +
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"VALUES (@t, @pk, @hlc, @node, @tomb, @tut)",
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new
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{
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t = entry.TableName,
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pk = entry.PkJson,
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hlc = entry.Hlc,
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node = entry.NodeId,
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tomb = entry.IsTombstone ? 1 : 0,
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tut = entry.IsTombstone ? utcNow : null,
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}, ct);
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applied++;
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}
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catch (SqliteException ex)
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{
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// A statement-level SQLite error (e.g. json_extract on malformed row_json) aborts only
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// that statement, not the transaction, so the batch continues after dead-lettering.
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await tx.ExecuteAsync(
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"INSERT INTO __localdb_dead_letter " +
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"(received_utc, table_name, pk_json, row_json, hlc, node_id, error) " +
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"VALUES (@utc, @t, @pk, @row, @hlc, @node, @err)",
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new
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{
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utc = utcNow,
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t = entry.TableName,
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pk = entry.PkJson,
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row = entry.RowJson,
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hlc = entry.Hlc,
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node = entry.NodeId,
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err = ex.Message,
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}, ct);
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deadLettered++;
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}
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}
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await tx.ExecuteAsync(
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"UPDATE __localdb_peer_state SET " +
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"last_applied_remote_seq = MAX(last_applied_remote_seq, @maxSeq), " +
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"last_seen_hlc = MAX(last_seen_hlc, @maxHlc), last_sync_utc = @utc WHERE id = 1",
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new { maxSeq, maxHlc, utc = utcNow }, ct);
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await tx.ExecuteAsync("UPDATE __localdb_applying SET applying = 0 WHERE id = 1", null, ct);
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await tx.CommitAsync(ct);
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db.Clock.Observe(maxHlc);
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return new ApplyResult(maxSeq, applied, discarded, deadLettered);
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}
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private static (string Delete, string Upsert) BuildTableSql(ReplicatedTable table)
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{
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var name = Ident(table.Name);
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var pkMatch = string.Join(" AND ", table.PkColumns.Select(p => $"{Ident(p)} = json_extract(@pk, {JsonPath(p)})"));
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var delete = $"DELETE FROM {name} WHERE {pkMatch}";
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var columns = string.Join(", ", table.Columns.Select(c => Ident(c.Name)));
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var values = string.Join(", ", table.Columns.Select(c => $"json_extract(@row, {JsonPath(c.Name)})"));
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var upsert = $"INSERT OR REPLACE INTO {name} ({columns}) VALUES ({values})";
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return (delete, upsert);
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}
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// Local copy of TriggerSqlGenerator's convention (that helper lives in the core assembly).
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private static string Ident(string name) => "\"" + name.Replace("\"", "\"\"") + "\"";
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// A single-quoted JSON path with a quoted key member, so a column name with reserved characters
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// still resolves: $."col". The key's double quotes are backslash-escaped per JSON path grammar.
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private static string JsonPath(string column) => "'$.\"" + column.Replace("\"", "\\\"") + "\"'";
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}
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Joseph Doherty