using System.Text;

using Microsoft.Extensions.Logging;

using Npgsql;

using NpgsqlRest;

namespace NpgsqlRestClient;

/// <summary>

/// Database change detection for watch mode. There is no filesystem to watch for routine-source

/// endpoints — instead, the poller runs the SAME discovery query the routine source uses (same

/// configured filters — see <see cref="RoutineSource.CreateFingerprintCommand"/>), hashed server-side

/// into one scalar, on a dedicated non-pooled connection. If the hash changes, the discovered

/// endpoints changed — by definition: create/replace/drop/alter of functions and procedures, grants,

/// COMMENT ON (annotations), schema renames, and changes to the composite/table types their signatures

/// use. Anything the query does not read (an unrelated table, temp objects, data) can never trigger.

/// </summary>

public sealed class WatchDbPoller(

string connectionString,

TimeSpan interval,

Action onChange,

ILogger? logger,

IReadOnlyList<RoutineSource> sources)

{

private readonly string _connString = new NpgsqlConnectionStringBuilder(connectionString) { Pooling = false }.ConnectionString;

private NpgsqlConnection? _conn;

private string? _baseline;

private volatile bool _rebaseline;

/// <summary>Fingerprint of one source's discovery result on an open connection (also used by tests).</summary>

public static string? GetFingerprint(NpgsqlConnection connection, RoutineSource source)

{

using var cmd = source.CreateFingerprintCommand(connection);

return cmd.ExecuteScalar() as string;

}

/// <summary>

/// Forget the baseline so the next tick captures a fresh one WITHOUT firing. Called after work

/// that legitimately changes the database (a test rerun with committed fixtures, a restart) so

/// self-inflicted changes never trigger.

/// </summary>

public void Rebaseline() => _rebaseline = true;

/// <summary>Poll loop; runs until cancelled. Connection failures skip the tick and retry.</summary>

public async Task RunAsync(CancellationToken ct)

{

if (sources.Count == 0)

{

return;

}

while (ct.IsCancellationRequested is false)

{

try

{

await Task.Delay(interval, ct);

}

catch (OperationCanceledException)

{

break;

}

try

{

if (_conn is null || _conn.State != System.Data.ConnectionState.Open)

{

_conn?.Dispose();

_conn = new NpgsqlConnection(_connString);

await _conn.OpenAsync(ct);

}

var sb = new StringBuilder();

foreach (var source in sources)

{

await using var cmd = source.CreateFingerprintCommand(_conn);

sb.Append(await cmd.ExecuteScalarAsync(ct) as string).Append('|');

}

var current = sb.ToString();

if (_rebaseline)

{

_rebaseline = false;

_baseline = current;

continue;

}

if (_baseline is null)

{

_baseline = current;

continue;

}

if (string.Equals(_baseline, current, StringComparison.Ordinal) is false)

{

_baseline = current;

onChange();

}

}

catch (OperationCanceledException)

{

break;

}

catch (Exception ex)

{

// DB down / restarting: skip this tick, reconnect on the next one.

logger?.LogDebug("watch: database poll failed ({Message}) — retrying", ex.Message);

try { _conn?.Dispose(); } catch { }

_conn = null;

}

}

try { _conn?.Dispose(); } catch { }

}

}