using System.Collections.Generic;
using System.Threading.Tasks;
using GameAuthApi.Models;
using Microsoft.Extensions.Configuration;
using MongoDB.Driver;
using System;
using System.Linq;

namespace GameAuthApi.Services;

public class UserService
{
    private readonly IMongoCollection<User> _users;

    public UserService(IConfiguration config)
    {
        var client = new MongoClient(config["MongoDB:ConnectionString"]);
        var database = client.GetDatabase(config["MongoDB:DatabaseName"]);
        _users = database.GetCollection<User>("Users");
    }

    public virtual async Task<User> GetByUsernameAsync(string username) =>
        await _users.Find(u => u.Username == username).FirstOrDefaultAsync();

    public virtual async Task<User> GetByLoginAsync(string login)
    {
        var normalized = Normalize(login);
        return await _users.Find(u =>
            u.NormalizedUsername == normalized ||
            u.NormalizedEmail == normalized ||
            u.Username == login ||
            u.Email == login).FirstOrDefaultAsync();
    }

    public virtual async Task<User> GetByIdAsync(string id) =>
        await _users.Find(u => u.Id == id).FirstOrDefaultAsync();

    public virtual async Task<List<User>> GetAllAsync() =>
        await _users.Find(_ => true).ToListAsync();

    public virtual async Task<bool> DeleteAsync(string username)
    {
        var result = await _users.DeleteOneAsync(u => u.Username == username);
        return result.DeletedCount > 0;
    }

    public virtual async Task CreateAsync(User user)
    {
        ApplyNormalizedFields(user);
        await _users.InsertOneAsync(user);
    }

    public virtual async Task UpdateAsync(User user)
    {
        ApplyNormalizedFields(user);
        await _users.ReplaceOneAsync(u => u.Id == user.Id, user);
    }

    public virtual async Task EnsureIndexesAsync()
    {
        var username = new CreateIndexModel<User>(
            Builders<User>.IndexKeys.Ascending(u => u.NormalizedUsername),
            new CreateIndexOptions { Unique = true, Sparse = true, Name = "normalized_username_unique" });
        var email = new CreateIndexModel<User>(
            Builders<User>.IndexKeys.Ascending(u => u.NormalizedEmail),
            new CreateIndexOptions { Unique = true, Sparse = true, Name = "normalized_email_unique" });
        await _users.Indexes.CreateManyAsync(new[] { username, email });
    }

    public virtual async Task BackfillNormalizedFieldsAsync()
    {
        var users = await _users.Find(_ => true).ToListAsync();
        var duplicateUsername = users.GroupBy(u => Normalize(u.Username)).FirstOrDefault(g => g.Key != string.Empty && g.Count() > 1);
        var duplicateEmail = users.Where(u => !string.IsNullOrWhiteSpace(u.Email)).GroupBy(u => Normalize(u.Email)).FirstOrDefault(g => g.Count() > 1);
        if (duplicateUsername != null || duplicateEmail != null)
            throw new InvalidOperationException("Duplicate normalized usernames or emails must be resolved before starting the authentication service.");
        foreach (var user in users)
        {
            var normalizedUsername = Normalize(user.Username);
            var normalizedEmail = string.IsNullOrWhiteSpace(user.Email) ? null : Normalize(user.Email);
            if (user.NormalizedUsername == normalizedUsername && user.NormalizedEmail == normalizedEmail) continue;
            user.NormalizedUsername = normalizedUsername;
            user.NormalizedEmail = normalizedEmail;
            await _users.ReplaceOneAsync(u => u.Id == user.Id, user);
        }
    }

    public static string Normalize(string value) => value?.Trim().ToUpperInvariant() ?? string.Empty;

    private static void ApplyNormalizedFields(User user)
    {
        user.NormalizedUsername = Normalize(user.Username);
        user.NormalizedEmail = string.IsNullOrWhiteSpace(user.Email) ? null : Normalize(user.Email);
    }
}