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FinlyticAssets/Services/SettingsDbService.cs

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+using FinlyticAssets.Database;
+using FinlyticAssets.Entities;
+using Microsoft.EntityFrameworkCore;
+
+namespace FinlyticAssets.Services;
+
+/// <summary>
+/// Defines the business logic for managing global application settings.
+/// Supports retrieving and updating (upserting) the central single-row configuration record.
+/// </summary>
+public interface ISettingsDbService
+{
+    /// <summary>
+    /// Retrieves the current global settings from the database.
+    /// </summary>
+    /// <returns>
+    /// A task that represents the asynchronous operation. The task result contains the current <see cref="Settings"/>.
+    /// If no settings exist in the database yet, a new instance initialized with default values is returned.
+    /// </returns>
+    public Task<Settings> GetSettings();
+
+    /// <summary>
+    /// Persists the provided settings by updating the existing record or inserting the first one if the table is empty.
+    /// </summary>
+    /// <param name="settings">The new configuration values to be persisted.</param>
+    /// <returns>
+    /// A task that represents the asynchronous operation. The task result contains the freshly saved 
+    /// and tracked <see cref="Settings"/> instance.
+    /// </returns>
+    public Task<Settings> SaveSettings(Settings settings);
+}
+
+/// <summary>
+/// Implements the <see cref="ISettingsDbService"/> utilizing Entity Framework Core.
+/// This service is designed for a single-row table architecture to maintain stateful global configurations.
+/// </summary>
+public class SettingsDbService : ISettingsDbService
+{
+    private readonly AssetsDbContext _context;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SettingsDbService"/> class with the required database context.
+    /// </summary>
+    /// <param name="context">The EF Core context used to access the assets database.</param>
+    public SettingsDbService(AssetsDbContext context)
+    {
+        _context = context;
+    }
+
+    /// <inheritdoc />
+    public async Task<Settings> GetSettings()
+    {
+        var settings = await _context.Settings.AsNoTracking().FirstOrDefaultAsync();
+
+        if (settings == null)
+        {
+            settings = new Settings
+            {
+                Id = Guid.NewGuid()
+            };
+            
+            await SaveSettings(settings);
+        }
+        
+        return settings;
+    }
+
+    /// <inheritdoc />
+    public async Task<Settings> SaveSettings(Settings settings)
+    {
+        var existing = await _context.Settings.FirstOrDefaultAsync();
+
+        if (existing == null)
+        {
+            if (settings.Id == Guid.Empty)
+            {
+                settings.Id = Guid.NewGuid();
+            }
+            await _context.Settings.AddAsync(settings);
+            await _context.SaveChangesAsync();
+            return settings;
+        }
+        else
+        {
+            _context.Entry(existing).CurrentValues.SetValues(settings);
+        
+            await _context.SaveChangesAsync();
+            return existing;
+        }
+    }
+}