using System.Security.Cryptography;
using System.Text;

namespace Shared.Excel;

public static class ImportSourceSignature
{
    public static string Create(IEnumerable<string> columns)
    {
        var canonical = string.Join("|", columns.Select(Normalize).Order(StringComparer.Ordinal));
        return Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(canonical))).ToLowerInvariant();
    }

    private static string Normalize(string value) =>
        new(value.Where(char.IsLetterOrDigit).Select(char.ToLowerInvariant).ToArray());
}

public interface IImportMappingSuggester
{
    Task<IReadOnlyList<ImportMapping>> SuggestAsync(
        IReadOnlyList<string> unmappedColumns,
        ImportDefinition definition,
        CancellationToken ct);
}

/// <summary>
/// Safe default. A production AI adapter can replace this registration. The adapter must return
/// only target fields present in ImportDefinition and never mutate data or persist a mapping by itself.
/// </summary>
public sealed class NoopImportMappingSuggester : IImportMappingSuggester
{
    public Task<IReadOnlyList<ImportMapping>> SuggestAsync(
        IReadOnlyList<string> unmappedColumns,
        ImportDefinition definition,
        CancellationToken ct) => Task.FromResult<IReadOnlyList<ImportMapping>>([]);
}