namespace Distribution.Features.Notifications;

public class NotificationRecipientResolver(INotificationRepository repo)
{
    /// <summary>
    /// Expands the rules into a de-duplicated list of active user ids, never including
    /// <paramref name="actingUserId"/>.
    /// </summary>
    public async Task<List<Guid>> ResolveAsync(IEnumerable<RecipientRule> rules, Guid? actingUserId)
    {
        var ids = new HashSet<Guid>();

        foreach (var rule in rules)
            ids.UnionWith(await ResolveRuleAsync(rule));

        if (actingUserId is { } actor)
            ids.Remove(actor);

        if (ids.Count == 0) return [];
        return await repo.FilterActiveUserIdsAsync(ids);
    }

    private async Task<IEnumerable<Guid>> ResolveRuleAsync(RecipientRule rule)
    {
        switch (rule)
        {
            case UsersRule r:
                return r.Ids;

            case PermissionRule r:
                return await repo.GetUserIdsByPermissionAsync(r.Code);

            case ScopeRule r:
                return await repo.GetUserIdsByScopeAsync(r.Kind, r.Id);

            case PermissionInScopeRule r:
                var withPermission = await repo.GetUserIdsByPermissionAsync(r.Code);
                var inScope = await repo.GetUserIdsByScopeAsync(r.Kind, r.Id);
                return withPermission.Intersect(inScope);

            case ReportsToRule r:
                var supervisor = await repo.GetReportsToUserIdAsync(r.UserId);
                return supervisor is { } s ? [s] : [];

            case RouteOwnerRule r:
                var owner = await repo.GetRouteOwnerUserIdAsync(r.Kind, r.Id);
                return owner is { } o ? [o] : [];

            default:
                throw new NotSupportedException($"Unknown recipient rule {rule.GetType().Name}.");
        }
    }
}