namespace VoiceCat.Windows;

/// <summary>A channel and its ordered children as displayed by the Windows client.</summary>
public sealed record ChannelHierarchyItem(
    ChannelInfo Channel,
    IReadOnlyList<ChannelHierarchyItem> Children);

public static class ChannelHierarchy
{
    /// <summary>
    /// Builds the server-defined channel hierarchy. SortOrder orders siblings; LINQ's stable
    /// ordering preserves the server's sequence when siblings have the same value.
    /// </summary>
    public static IReadOnlyList<ChannelHierarchyItem> Build(IReadOnlyList<ChannelInfo> channels)
    {
        var byParent = channels
            .GroupBy(channel => channel.ParentId)
            .ToDictionary(group => group.Key, group => group.OrderBy(channel => channel.SortOrder).ToArray());

        IReadOnlyList<ChannelHierarchyItem> AddChildren(uint parentId)
        {
            if (!byParent.TryGetValue(parentId, out ChannelInfo[]? children))
                return [];

            return children
                .Select(channel => new ChannelHierarchyItem(channel, AddChildren(channel.Id)))
                .ToArray();
        }

        return AddChildren(0);
    }
}