using System.Collections.Concurrent;

namespace TuneRipper.Api.Services;

public class SessionService : ISessionService
{
    private readonly IWebHostEnvironment _environment;
    private readonly ILogger<SessionService> _logger;
    private readonly ConcurrentDictionary<string, DateTime> _sessions = new();
    private readonly Timer _cleanupTimer;
    
    // Session expires after 24 hours of inactivity
    private readonly TimeSpan _sessionTimeout = TimeSpan.FromHours(24);

    public SessionService(IWebHostEnvironment environment, ILogger<SessionService> logger)
    {
        _environment = environment;
        _logger = logger;
        
        // Clean up expired sessions every hour
        _cleanupTimer = new Timer(
            callback: _ => CleanupExpiredSessions(),
            state: null,
            dueTime: TimeSpan.FromHours(1),
            period: TimeSpan.FromHours(1)
        );
    }

    /// <summary>
    /// Creates a new session with a unique ID. 
    /// Note: The session directory is NOT created at this point - it will be created 
    /// lazily when the first MP3 file is saved using EnsureSessionDirectoryExists().
    /// </summary>
    /// <returns>The unique session ID</returns>
    public string CreateSession()
    {
        var sessionId = Guid.NewGuid().ToString("N")[..16]; // Use first 16 characters for shorter IDs
        _sessions[sessionId] = DateTime.UtcNow;
        
        // Don't create directory here - it will be created when first MP3 is saved
        _logger.LogInformation("Created new session: {SessionId}", sessionId);
        return sessionId;
    }

    public string GetOrCreateSession(string? sessionId)
    {
        if (!string.IsNullOrWhiteSpace(sessionId) && IsValidSession(sessionId))
        {
            // Update last activity time
            _sessions[sessionId] = DateTime.UtcNow;
            return sessionId;
        }

        return CreateSession();
    }

    public bool IsValidSession(string sessionId)
    {
        if (string.IsNullOrWhiteSpace(sessionId))
            return false;

        if (_sessions.TryGetValue(sessionId, out var lastActivity))
        {
            // Check if session has expired
            if (DateTime.UtcNow - lastActivity > _sessionTimeout)
            {
                _sessions.TryRemove(sessionId, out _);
                return false;
            }
            return true;
        }

        return false;
    }

    public void CleanupExpiredSessions()
    {
        try
        {
            var expiredSessions = _sessions
                .Where(kvp => DateTime.UtcNow - kvp.Value > _sessionTimeout)
                .Select(kvp => kvp.Key)
                .ToList();

            foreach (var sessionId in expiredSessions)
            {
                if (_sessions.TryRemove(sessionId, out _))
                {
                    // Clean up session directory if it exists
                    var sessionPath = GetSessionDownloadsPath(sessionId);
                    if (Directory.Exists(sessionPath))
                    {
                        try
                        {
                            Directory.Delete(sessionPath, recursive: true);
                            _logger.LogInformation("Cleaned up expired session directory: {SessionId}", sessionId);
                        }
                        catch (Exception ex)
                        {
                            _logger.LogWarning(ex, "Failed to delete expired session directory: {SessionId}", sessionId);
                        }
                    }
                    else
                    {
                        _logger.LogDebug("No directory to clean up for expired session: {SessionId} (no MP3 files were downloaded)", sessionId);
                    }
                }
            }

            if (expiredSessions.Count > 0)
            {
                _logger.LogInformation("Cleaned up {Count} expired sessions", expiredSessions.Count);
            }
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error during session cleanup");
        }
    }

    public string GetSessionDownloadsPath(string sessionId)
    {
        var downloadsRoot = Path.Combine(_environment.WebRootPath, "downloads");
        return Path.Combine(downloadsRoot, sessionId);
    }

    /// <summary>
    /// Ensures that the session directory exists, creating it if necessary.
    /// This method should be called just before saving the first MP3 file in a session.
    /// </summary>
    /// <param name="sessionId">The session ID</param>
    /// <exception cref="ArgumentException">Thrown when sessionId is null or empty</exception>
    /// <exception cref="InvalidOperationException">Thrown when session is invalid or expired</exception>
    public void EnsureSessionDirectoryExists(string sessionId)
    {
        if (string.IsNullOrWhiteSpace(sessionId))
        {
            throw new ArgumentException("Session ID cannot be null or empty", nameof(sessionId));
        }

        if (!IsValidSession(sessionId))
        {
            throw new InvalidOperationException($"Invalid session ID: {sessionId}");
        }

        var sessionPath = GetSessionDownloadsPath(sessionId);
        
        if (!Directory.Exists(sessionPath))
        {
            Directory.CreateDirectory(sessionPath);
            _logger.LogInformation("Created session directory for session: {SessionId} at {Path}", sessionId, sessionPath);
        }
    }

    public void Dispose()
    {
        _cleanupTimer?.Dispose();
    }
}