using System.Runtime.InteropServices;

namespace Theriapolis.Game.Platform;

/// <summary>
/// OS-aware save directory resolution. Per the implementation plan §4.2,
/// saves live under the platform-appropriate user data directory.
/// </summary>
public static class SavePaths
{
    /// <summary>Top-level Theriapolis save directory. Created on first call if missing.</summary>
    public static string SavesDir
    {
        get
        {
            string dir = ResolveBase();
            Directory.CreateDirectory(dir);
            return dir;
        }
    }

    public static string SlotPath(int slot) => Path.Combine(SavesDir, $"slot_{slot:D2}.trps");
    public static string AutosavePath() => Path.Combine(SavesDir, "autosave.trps");

    private static string ResolveBase()
    {
        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
            return Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
                                 "Theriapolis", "Saves");
        if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
            return Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.UserProfile),
                                 "Library", "Application Support", "Theriapolis", "Saves");
        // Linux + others: respect XDG_DATA_HOME, fall back to ~/.local/share.
        string xdg = Environment.GetEnvironmentVariable("XDG_DATA_HOME") ?? "";
        if (string.IsNullOrEmpty(xdg))
            xdg = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.UserProfile),
                                ".local", "share");
        return Path.Combine(xdg, "Theriapolis", "saves");
    }

    /// <summary>Atomic-rename file write so a crash mid-save can't corrupt the slot.</summary>
    public static void WriteAtomic(string path, byte[] bytes)
    {
        string dir = Path.GetDirectoryName(path)!;
        Directory.CreateDirectory(dir);
        string tmp = path + ".tmp";
        File.WriteAllBytes(tmp, bytes);
        if (File.Exists(path)) File.Replace(tmp, path, destinationBackupFileName: null);
        else                    File.Move(tmp, path);
    }
}
