namespace WxAgent.Core;

public static class WechatAttachmentInput
{
    public const int MaxBatchSize = 10;
    private static readonly HashSet<string> ImageExtensions = new([".png", ".jpg", ".jpeg", ".gif", ".bmp", ".webp"], StringComparer.OrdinalIgnoreCase);

    public static bool IsImagePath(string? path) =>
        !string.IsNullOrWhiteSpace(path) && ImageExtensions.Contains(Path.GetExtension(path));

    public static IReadOnlyList<string> PrepareFilePaths(IReadOnlyList<string>? paths)
    {
        if (paths is null || paths.Count is < 2 or > MaxBatchSize)
            throw new WxAgentException(WxAgentErrorCode.InvalidArgument, $"File batches must contain 2-{MaxBatchSize} attachments.");

        var normalized = new string[paths.Count];
        for (var index = 0; index < paths.Count; index++)
        {
            var path = paths[index];
            if (string.IsNullOrWhiteSpace(path))
                throw new WxAgentException(WxAgentErrorCode.InvalidArgument, "Attachment paths must not be empty.");

            string fullPath;
            try { fullPath = Path.GetFullPath(path); }
            catch (Exception exception) when (exception is ArgumentException or NotSupportedException or PathTooLongException)
            {
                throw new WxAgentException(WxAgentErrorCode.InvalidArgument, "An attachment path is invalid.");
            }

            if (!File.Exists(fullPath))
                throw new WxAgentException(WxAgentErrorCode.InvalidArgument, "An attachment file does not exist.");
            normalized[index] = fullPath;
        }

        return normalized;
    }
}