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;
        }
    }
}