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;
    private const int CurrentLaunchEntryLimit = 500;

    /// <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();
    private static readonly List<AppLogEntry> CurrentLaunchEntries = new();
    private static long _nextSequence;

    /// <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;

    internal static IReadOnlyList<AppLogEntry> SnapshotCurrentLaunch()
    {
        lock (Gate)
            return CurrentLaunchEntries.ToArray();
    }

    public static void Write(string message)
    {
        try
        {
            lock (Gate)
            {
                var entry = new AppLogEntry(
                    ++_nextSequence,
                    $"{DateTime.Now:yyyy-MM-dd HH:mm:ss.fff} {message}");
                CurrentLaunchEntries.Add(entry);
                if (CurrentLaunchEntries.Count > CurrentLaunchEntryLimit)
                    CurrentLaunchEntries.RemoveAt(0);

                var path = LogPath;
                Directory.CreateDirectory(Path.GetDirectoryName(path)!);
                LogRotation.RollIfNeeded(path, MaxBytes, RetainedFiles);
                File.AppendAllText(path, $"{entry.Text}{Environment.NewLine}");
            }
        }
        catch
        {
            // Never let logging itself crash the app.
        }
    }

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

public sealed record AppLogEntry(long Sequence, string Text);