ScadaBridge/src/ScadaLink.ExternalSystemGateway/DatabaseGateway.cs

using System.Data.Common;
using System.Text.Json;
using Microsoft.Data.SqlClient;
using Microsoft.Extensions.Logging;
using ScadaLink.Commons.Entities.ExternalSystems;
using ScadaLink.Commons.Interfaces.Repositories;
using ScadaLink.Commons.Interfaces.Services;
using ScadaLink.Commons.Types.Enums;
using ScadaLink.StoreAndForward;

namespace ScadaLink.ExternalSystemGateway;

/// <summary>
/// WP-9: Database access from scripts.
/// Database.Connection("name") — returns ADO.NET SqlConnection (connection pooling).
/// Database.CachedWrite("name", "sql", params) — submits to S&amp;F engine.
/// </summary>
public class DatabaseGateway : IDatabaseGateway
{
    private readonly IExternalSystemRepository _repository;
    private readonly StoreAndForwardService? _storeAndForward;
    private readonly ILogger<DatabaseGateway> _logger;

    public DatabaseGateway(
        IExternalSystemRepository repository,
        ILogger<DatabaseGateway> logger,
        StoreAndForwardService? storeAndForward = null)
    {
        _repository = repository;
        _logger = logger;
        _storeAndForward = storeAndForward;
    }

    /// <summary>
    /// Returns an open SqlConnection from the named database connection definition.
    /// Connection pooling is managed by the underlying ADO.NET provider.
    /// </summary>
    public async Task<DbConnection> GetConnectionAsync(
        string connectionName,
        CancellationToken cancellationToken = default)
    {
        var definition = await ResolveConnectionAsync(connectionName, cancellationToken);
        if (definition == null)
        {
            throw new InvalidOperationException($"Database connection '{connectionName}' not found");
        }

        var connection = new SqlConnection(definition.ConnectionString);
        await connection.OpenAsync(cancellationToken);
        return connection;
    }

    /// <summary>
    /// Submits a SQL write to the store-and-forward engine for reliable delivery.
    /// </summary>
    public async Task CachedWriteAsync(
        string connectionName,
        string sql,
        IReadOnlyDictionary<string, object?>? parameters = null,
        string? originInstanceName = null,
        CancellationToken cancellationToken = default)
    {
        var definition = await ResolveConnectionAsync(connectionName, cancellationToken);
        if (definition == null)
        {
            throw new InvalidOperationException($"Database connection '{connectionName}' not found");
        }

        if (_storeAndForward == null)
        {
            throw new InvalidOperationException("Store-and-forward service not available for cached writes");
        }

        var payload = JsonSerializer.Serialize(new
        {
            ConnectionName = connectionName,
            Sql = sql,
            Parameters = parameters
        });

        await _storeAndForward.EnqueueAsync(
            StoreAndForwardCategory.CachedDbWrite,
            connectionName,
            payload,
            originInstanceName,
            definition.MaxRetries > 0 ? definition.MaxRetries : null,
            definition.RetryDelay > TimeSpan.Zero ? definition.RetryDelay : null);
    }

    private async Task<DatabaseConnectionDefinition?> ResolveConnectionAsync(
        string connectionName,
        CancellationToken cancellationToken)
    {
        var connections = await _repository.GetAllDatabaseConnectionsAsync(cancellationToken);
        return connections.FirstOrDefault(c =>
            c.Name.Equals(connectionName, StringComparison.OrdinalIgnoreCase));
    }
}