using ErsatzTV.Core.Domain;
using ErsatzTV.Core.Errors;

namespace ErsatzTV.Core;

public static class VersionedAggregateExtensions
{
    /// <summary>
    ///     Optimistic-concurrency pre-check (issue #253). When the caller supplied an expected
    ///     version (from <c>If-Match</c>), fail with <see cref="PreconditionFailedError" /> (→ 412)
    ///     if it no longer matches the loaded aggregate. An absent expectation is a force-write
    ///     (Phase 1 back-compat). This returns a standalone <see cref="Either{L,R}" /> so the 412
    ///     is introduced AFTER the validation pipeline and never flattened to 422 by
    ///     <see cref="LanguageExtensions.Apply{T,TR}" /> (see api-conventions §7a).
    /// </summary>
    public static Either<BaseError, T> CheckVersion<T>(this T aggregate, Option<int> expectedVersion)
        where T : IVersionedAggregate =>
        expectedVersion.Match(
            Some: expected => aggregate.Version == expected
                ? Right<BaseError, T>(aggregate)
                : Left<BaseError, T>(new PreconditionFailedError(
                    "The resource was modified by another request. Reload and try again.")),
            None: () => Right<BaseError, T>(aggregate));
}