using Newtonsoft.Json;
using System;
using System.IO;

namespace GB5Shared.Config
{
    /// <summary>
    /// Singleton that loads GB5Shared library defaults from the physical
    /// <c>gb5shared.json</c> file published alongside every GB5 module binary.
    ///
    /// Why a physical file (not embedded resource):
    ///   Operations teams and clients can change settings such as
    ///   <see cref="SessionExpiryMinutes"/> by editing <c>gb5shared.json</c>
    ///   in the deployment directory and restarting the service — no recompile needed.
    ///
    /// File location at runtime:
    ///   <c>{AppContext.BaseDirectory}/gb5shared.json</c>
    ///   The .NET SDK copies this file to the publish output automatically because
    ///   it is declared as a <c>Content</c> item with <c>CopyToPublishDirectory=PreserveNewest</c>
    ///   in GB5Shared.csproj.
    ///
    /// Override behaviour (priority, highest first):
    ///   1. Module's own <c>appsettings.json → Gb5SystemDTO:SessionExpiryMinutes &gt; 0</c>
    ///   2. <c>gb5shared.json</c> (this file) in the deployment directory
    ///   3. Code default (15 minutes) — used when the file is absent or unreadable
    ///
    /// Usage (read-only):
    ///   <code>int minutes = GB5SharedSettings.Instance.SessionExpiryMinutes;</code>
    /// </summary>
    public sealed class GB5SharedSettings
    {
        private static GB5SharedSettings? _instance;
        private static readonly object _lock = new();

        // ── Settings ─────────────────────────────────────────────────────────

        /// <summary>
        /// Master on/off switch for the session heartbeat check.
        /// "Y" (default) — enforce sliding session expiry on every API call.
        /// "N"           — skip session check entirely (useful during debugging).
        /// Change in gb5shared.json and restart the service.
        /// </summary>
        public string SessionHeartbeatEnabled { get; set; } = "Y";

        /// <summary>
        /// Session idle timeout in minutes.
        /// <see cref="GB5Shared.Middleware.SessionHeartbeatMiddleware"/> uses this value
        /// when the host module has not overridden <c>Gb5SystemDTO:SessionExpiryMinutes</c>
        /// in its own <c>appsettings.json</c>.
        /// Default (in gb5shared.json): 15.
        /// </summary>
        public int SessionExpiryMinutes { get; set; } = 15;

        // ── Singleton access ──────────────────────────────────────────────────

        /// <summary>
        /// The shared instance, lazily loaded from <c>gb5shared.json</c> on first access.
        /// Cached for the lifetime of the process; restart the service after editing the file.
        /// </summary>
        public static GB5SharedSettings Instance
        {
            get
            {
                if (_instance is not null) return _instance;
                lock (_lock)
                {
                    if (_instance is not null) return _instance;
                    _instance = Load();
                }
                return _instance;
            }
        }

        // ── Loader ────────────────────────────────────────────────────────────

        private static GB5SharedSettings Load()
        {
            try
            {
                // AppContext.BaseDirectory is the publish output folder at runtime —
                // the same directory where gb5shared.json is copied during dotnet publish.
                string filePath = Path.Combine(AppContext.BaseDirectory, "gb5shared.json");

                if (!File.Exists(filePath))
                    return new GB5SharedSettings(); // file absent — use in-code defaults

                string json = File.ReadAllText(filePath);
                return JsonConvert.DeserializeObject<GB5SharedSettings>(json)
                       ?? new GB5SharedSettings();
            }
            catch
            {
                // File unreadable or JSON malformed — fall back to in-code defaults.
                // The middleware always has a valid expiry value regardless.
                return new GB5SharedSettings();
            }
        }
    }
}