using PureHDF;
using PureHDF.Selections;

namespace GeoVLog.Core.Hdf5;

internal static class H5Extensions
{
    /// <summary>
    /// Creates a group at the specified path if it does not exist, or opens it if it already exists.
    /// All intermediate groups in the path are created as needed.
    /// </summary>
    public static H5Group CreateOrOpenGroup(this H5File file, string path)
    {
        if (string.IsNullOrWhiteSpace(path) || path == "/")
        {
            // Root or empty path: return the root group (file itself)
            return file;
        }
        string normalizedPath = path.Trim('/');
        string[] parts = normalizedPath.Split('/', StringSplitOptions.RemoveEmptyEntries);
        H5Group current = file;
        foreach (string part in parts)
        {
            IH5Object? item;
            try
            {
                // Try to get an existing child object with this name
                item = ((IH5Group)current).Get<IH5Object>(part);
            }
            catch
            {
                item = null;
            }
            if (item is H5Group subgroup)
            {
                // If a subgroup exists, descend into it
                current = subgroup;
            }
            else if (item is null)
            {
                // Create a new subgroup if none exists at this path segment
                var newGroup = new H5Group();
                current[part] = newGroup;
                current = newGroup;
            }
            else
            {
                throw new InvalidOperationException(
                    $"Cannot create group \"{part}\" in path \"{path}\" because an object with that name already exists and is not a group.");
            }
        }
        return current;
    }

    /// <summary>
    /// Creates a variable-length UTF-8 string dataset at the specified path if it does not exist, or opens it if it exists.
    /// The dataset is one-dimensional, chunked, and can grow without bound (unlimited dimension).
    /// </summary>
    public static H5Dataset<string> CreateOrOpenVLStringDataset(this H5File file, string path)
    {
        // Ensure parent group exists first
        int lastSlashIndex = path.LastIndexOf('/');
        if (lastSlashIndex > 0)
        {
            string parentPath = path[..lastSlashIndex];
            file.CreateOrOpenGroup(parentPath);
        }

        // Check if an object already exists at the target path
        IH5Object? existing;
        try
        {
            existing = ((IH5Group)file).Get<IH5Object>(path.TrimStart('/'));
        }
        catch
        {
            existing = null;
        }
        if (existing is H5Dataset<string> dataset)
        {
            // Dataset already exists, return it
            return dataset;
        }
        if (existing is not null)
        {
            throw new InvalidOperationException(
                $"Cannot create dataset at \"{path}\" because a different object already exists at that path.");
        }

        // Define a new 1D dataset of variable-length strings, initially empty (0 length).
        ulong[] dims = { 0 };               // Initial dimension size is 0 (no entries yet).
        // Note: We omit maxDims because PureHDF 2.1.1 no longer requires it – 
        // unlimited growth is handled by using chunked storage and extending on write:contentReference[oaicite:3]{index=3}.
        ulong[] chunkDims = { 1024 };       // Use chunking (chunks of 1024 elements) to allow resizing.
        uint[] chunkDims32 = Array.ConvertAll(chunkDims, x => (uint)x);

        // Create the new dataset with the specified initial dims and chunk layout.
        // PureHDF 2.1.1: H5Dataset constructor takes fileDims and chunks, but no maxDims:contentReference[oaicite:4]{index=4}.
        var newDataset = new H5Dataset<string>(fileDims: dims, chunks: chunkDims32);

        // Attach the new dataset to the file structure at the specified path.
        string datasetName = (lastSlashIndex >= 0) ? path[(lastSlashIndex + 1)..] : path;
        H5Group parentGroup = file;
        if (lastSlashIndex > 0)
        {
            string parentGroupPath = path[..lastSlashIndex];
            parentGroup = file.CreateOrOpenGroup(parentGroupPath);
        }
        parentGroup[datasetName] = newDataset;

        return newDataset;
    }
}