JsonGlobalSettingsStore.cs

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using System;
using System.IO;
using System.Text.Json;
using System.Threading;
using System.Threading.Tasks;
using WeddingThankYou.Models;
 
namespace WeddingThankYou.Services
{
    public sealed class JsonGlobalSettingsStore : IGlobalSettingsStore
    {
        private readonly string _path;
        private static readonly SemaphoreSlim _gate = new(1, 1);
        private GlobalSettings? _cache;

        private static readonly JsonSerializerOptions _jsonOpts = new() { WriteIndented = true };

        public JsonGlobalSettingsStore(WeddingOptions opts)
        {
            var dataRoot = Path.GetDirectoryName(opts.ResolvedDataPath.TrimEnd(Path.DirectorySeparatorChar))
                ?? Path.Combine(AppContext.BaseDirectory, "App_Data");
            Directory.CreateDirectory(dataRoot);
            _path = Path.Combine(dataRoot, "global-settings.json");
        }

        public async Task<GlobalSettings> GetAsync(CancellationToken ct = default)
        {
            if (_cache is not null) return _cache;
 
            await _gate.WaitAsync(ct).ConfigureAwait(false);
            try
            {
                if (_cache is not null) return _cache;
 
                if (!File.Exists(_path))
                {
                    _cache = new GlobalSettings();
                    return _cache;
                }
 
                await using var fs = File.OpenRead(_path);
                _cache = await JsonSerializer.DeserializeAsync<GlobalSettings>(fs, _jsonOpts, ct).ConfigureAwait(false)
                    ?? new GlobalSettings();
                _cache.Normalize();
                return _cache;
            }
            finally { _gate.Release(); }
        }

        public async Task SaveAsync(GlobalSettings settings, CancellationToken ct = default)
        {
            settings.Normalize();
            await _gate.WaitAsync(ct).ConfigureAwait(false);
            try
            {
                var tmp = _path + ".tmp";
                await using (var fs = File.Create(tmp))
                    await JsonSerializer.SerializeAsync(fs, settings, _jsonOpts, ct).ConfigureAwait(false);
 
                File.Copy(tmp, _path, overwrite: true);
                File.Delete(tmp);
                _cache = settings;
            }
            finally { _gate.Release(); }
        }
    }
}