using System.IO;

namespace ytLive.Helpers;

/// <summary>
/// Minimal file logger used to diagnose startup/shutdown crashes on Windows,
/// where the WPF app has no visible console. Writes to
/// %APPDATA%\ytLlive\startup.log (or a per-instance subfolder in DEBUG — see
/// InstanceProfile), appending synchronously so entries survive a hard crash.
/// </summary>
public static class AppLog
{
    /// <summary>The cap for the live log file. Past this, it rolls to <c>startup.1.log</c>.</summary>
    private const long DefaultMaxBytes = 5 * 1024 * 1024;

    /// <summary>How many rolled copies to keep (startup.1.log, startup.2.log, …).</summary>
    private const int RetainedFiles = 1;

    private static readonly string DefaultLogPath = Path.Combine(
        InstanceProfile.DataRoot, "startup.log");

    private static readonly object Gate = new();

    /// <summary>Test seam: point the log somewhere else. Null = the real profile's log.</summary>
    internal static string? PathOverride { get; set; }

    /// <summary>Test seam: the cap that triggers a roll.</summary>
    internal static long MaxBytes { get; set; } = DefaultMaxBytes;

    private static string LogPath => PathOverride ?? DefaultLogPath;

    public static void Write(string message)
    {
        try
        {
            lock (Gate)
            {
                var path = LogPath;
                Directory.CreateDirectory(Path.GetDirectoryName(path)!);
                LogRotation.RollIfNeeded(path, MaxBytes, RetainedFiles);
                File.AppendAllText(path, $"{DateTime.Now:yyyy-MM-dd HH:mm:ss.fff} {message}{Environment.NewLine}");
            }
        }
        catch
        {
            // Never let logging itself crash the app.
        }
    }

    public static void Write(Exception exception, string message)
    {
        Write($"{message}: {exception}");
    }
}