using Explorer.Domain;

namespace Explorer.Application;

public static class FolderStatusText
{
    public static string Format(IEnumerable<FileSystemItem> folderItems, IEnumerable<FileSystemItem> selectedItems)
    {
        var selected = selectedItems as IReadOnlyCollection<FileSystemItem> ?? selectedItems.ToList();
        var isSelection = selected.Count > 0;
        var totals = Measure(isSelection ? selected : folderItems);
        var noun = totals.Count == 1 ? "item" : "items";
        var prefix = isSelection
            ? $"{totals.Count:N0} {noun} selected"
            : $"{totals.Count:N0} {noun}";
        if (!ShouldShowSize(totals))
        {
            return prefix;
        }

        return $"{prefix}  ·  {FormatSize(totals.KnownBytes)}";
    }

    public static FolderStatusTotals Measure(IEnumerable<FileSystemItem> items)
    {
        var count = 0;
        var files = 0;
        var knownBytes = 0L;
        var hasKnownSize = false;
        foreach (var item in items)
        {
            count++;
            if (!item.IsDirectory)
            {
                files++;
            }

            if (item.SizeKnowledge == SizeKnowledge.Unknown)
            {
                continue;
            }

            knownBytes += Math.Max(0, item.SizeBytes);
            hasKnownSize = true;
        }

        return new FolderStatusTotals(count, files, knownBytes, hasKnownSize);
    }

    private static bool ShouldShowSize(FolderStatusTotals totals)
        => totals.HasKnownSize && (totals.KnownBytes > 0 || totals.Files > 0);

    private static string FormatSize(long bytes)
    {
        if (bytes < 0)
        {
            return string.Empty;
        }

        string[] units = ["B", "KB", "MB", "GB", "TB", "PB"];
        double value = bytes;
        var unit = 0;
        while (value >= 1024 && unit < units.Length - 1)
        {
            value /= 1024;
            unit++;
        }

        return unit == 0 ? $"{bytes} B" : $"{value:0.##} {units[unit]}";
    }
}

public readonly record struct FolderStatusTotals(int Count, int Files, long KnownBytes, bool HasKnownSize);