// <copyright file="ConfigurationHelper.cs" company="PlaceholderCompany">
// Copyright (c) PlaceholderCompany. All rights reserved.
// </copyright>

namespace Emby.Server.Implementations.AppBase
{
    using System;
    using System.IO;
    using System.Text.Json;
    using Jellyfin.Extensions.Json;
    using MediaBrowser.Model.Serialization;

    /// <summary>
    /// Class ConfigurationHelper.
    /// </summary>
    public static class ConfigurationHelper
    {
        /// <summary>
        /// Reads an xml configuration file from the file system
        /// It will immediately re-serialize and save if new serialization data is available due to property changes.
        /// </summary>
        /// <param name="type">The type.</param>
        /// <param name="path">The path.</param>
        /// <param name="xmlSerializer">The XML serializer.</param>
        /// <returns>System.Object.</returns>
        public static object GetXmlConfiguration(Type type, string path, IXmlSerializer xmlSerializer)
        {
            object configuration;

            byte[]? buffer = null;

            // Use try/catch to avoid the extra file system lookup using File.Exists
            try
            {
                buffer = File.ReadAllBytes(path);

                configuration = xmlSerializer.DeserializeFromBytes(type, buffer);
            }
            catch (Exception)
            {
                // Note: CreateInstance returns null for Nullable<T>, e.g. CreateInstance(typeof(int?)) returns null.
                configuration = Activator.CreateInstance(type)!;
            }

            using var stream = new MemoryStream(buffer?.Length ?? 0);
            xmlSerializer.SerializeToStream(configuration, stream);

            // Take the object we just got and serialize it back to bytes
            Span<byte> newBytes = stream.GetBuffer().AsSpan(0, (int)stream.Length);

            // If the file didn't exist before, or if something has changed, re-save
            if (buffer is null || !newBytes.SequenceEqual(buffer))
            {
                var directory = Path.GetDirectoryName(path) ?? throw new ArgumentException($"Provided path ({path}) is not valid.", nameof(path));

                Directory.CreateDirectory(directory);

                // Save it after load in case we got new items
#pragma warning disable IDE0063 // Use simple 'using' statement
                using (var fs = new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.None))
                {
                    fs.Write(newBytes);
                }
#pragma warning restore IDE0063 // Use simple 'using' statement
            }

            return configuration;
        }

        /// <summary>
        /// Reads a JSON configuration file from the file system using System.Text.Json.
        /// It will immediately re-serialize and save if new serialization data is available due to property changes.
        /// </summary>
        /// <typeparam name="T">The type of configuration to deserialize.</typeparam>
        /// <param name="path">The path to the JSON configuration file.</param>
        /// <returns>The deserialized configuration object.</returns>
        public static T GetJsonConfiguration<T>(string path)
            where T : class, new()
        {
            T configuration;
            byte[]? buffer = null;

            // Use try/catch to avoid the extra file system lookup using File.Exists
            try
            {
                buffer = File.ReadAllBytes(path);
                configuration = JsonSerializer.Deserialize<T>(buffer, JsonDefaults.Options) ?? new T();
            }
            catch (Exception)
            {
                // If file doesn't exist or deserialization fails, create a new instance with defaults
                configuration = new T();
            }

            // Re-serialize to ensure proper formatting and any new defaults are captured
            byte[] newBytes = JsonSerializer.SerializeToUtf8Bytes(configuration, JsonDefaults.Options);

            // If the file didn't exist before, or if something has changed, re-save
            if (buffer is null || !newBytes.AsSpan().SequenceEqual(buffer))
            {
                var directory = Path.GetDirectoryName(path) ?? throw new ArgumentException($"Provided path ({path}) is not valid.", nameof(path));

                Directory.CreateDirectory(directory);

                // Save it after load in case we got new items or formatting changed
                File.WriteAllBytes(path, newBytes);
            }

            return configuration;
        }
    }
}