Campaign_Tracker/Campaign_Tracker.Server/LegacyData/Schema/ILegacySchemaInspector.cs

namespace Campaign_Tracker.Server.LegacyData.Schema;

/// <summary>
/// Abstraction for reading the *current* legacy schema at runtime.
///
/// In production this is implemented against the live Access database (OleDb
/// schema rowsets). In development and testing it is implemented in-memory and
/// seeded from the baseline so the default state is "no drift". Tests inject
/// mutated inspectors to simulate drift.
/// </summary>
public interface ILegacySchemaInspector
{
    Task<IReadOnlyList<LegacyTableDefinition>> GetCurrentSchemaAsync(
        CancellationToken cancellationToken = default);
}

/// <summary>
/// Default development/test inspector. Returns whatever table list it was
/// constructed with (defaulting to the baseline tables — no drift).
/// </summary>
public sealed class InMemoryLegacySchemaInspector : ILegacySchemaInspector
{
    private readonly IReadOnlyList<LegacyTableDefinition> _tables;

    public InMemoryLegacySchemaInspector(IReadOnlyList<LegacyTableDefinition> tables)
    {
        _tables = tables ?? throw new ArgumentNullException(nameof(tables));
    }

    public Task<IReadOnlyList<LegacyTableDefinition>> GetCurrentSchemaAsync(
        CancellationToken cancellationToken = default) =>
        Task.FromResult(_tables);
}