Phonebook/MainPage.xaml.cs

using Phonebook.Models;
using Phonebook.Services;
using Contact = Phonebook.Models.Contact;
using ClosedXML.Excel;
using Communication = Microsoft.Maui.ApplicationModel.Communication;
using Android.Content;

namespace Phonebook;

public partial class MainPage : ContentPage
{
    private readonly DatabaseService _databaseService;
    private List<Contact> _allContacts = [];

    public MainPage()
    {
        InitializeComponent();
        _databaseService = new DatabaseService();
    }

    protected override async void OnAppearing()
    {
        base.OnAppearing();
        await LoadContacts();
    }

    private async Task LoadContacts()
    {
        _allContacts = await GetAllContacts();

        contactsList.ItemsSource = _allContacts;
    }

    private async Task<List<Contact>> GetAllContacts()
    {
        var allContacts = await _databaseService.GetContactsAsync();
        
        if (!await IsPermissionGranted<Permissions.ContactsRead>()) 
            return allContacts;
        
        var contacts = GetContacts();

        await foreach (var contact in contacts)
        {
            allContacts.Add(contact);
        }

        return allContacts;
    }

    private async Task<bool> IsPermissionGranted<T>() where T : Permissions.BasePermission, new()
    {
        return await Permissions.RequestAsync<T>()  == PermissionStatus.Granted;
    }

    private async Task ExportToXlsx()
    {
        try
        {
            _allContacts = await GetAllContacts();

            if (_allContacts.Count <= 0)
            {
                return;
            }

            var fileName = $"contacts_{DateTime.Now:yyyyMMdd_HHmmss}.xlsx";
            var localPath = Path.Combine(FileSystem.CacheDirectory, fileName);

            using (var workbook = new XLWorkbook())
            {
                var worksheet = workbook.Worksheets.Add("Contacts");

                worksheet.Cell(1, 1).Value = "Id";
                worksheet.Cell(1, 2).Value = "Name";
                worksheet.Cell(1, 3).Value = "PhoneNumber";
                worksheet.Cell(1, 4).Value = "Email";
                worksheet.Cell(1, 5).Value = "Address";
                worksheet.Cell(1, 6).Value = "Description";
                worksheet.Cell(1, 7).Value = "PhotoPath";
                
                for (var i = 0; i < _allContacts.Count; i++)
                {
                    var contact = _allContacts[i];

                    worksheet.Cell(2 + i, 1).Value = contact.Id;
                    worksheet.Cell(2 + i, 2).Value = contact.Name;
                    worksheet.Cell(2 + i, 3).Value = contact.PhoneNumber;
                    worksheet.Cell(2 + i, 4).Value = contact.Email;
                    worksheet.Cell(2 + i, 5).Value = contact.Address;
                    worksheet.Cell(2 + i, 6).Value = contact.Description;
                    worksheet.Cell(2 + i, 7).Value = contact.PhotoPath;
                }
                
                workbook.SaveAs(localPath);
            }

            await Share.Default.RequestAsync(new ShareFileRequest
            {
                Title = "Сохранить контакты",
                File = new ShareFile(localPath)
            });

        }
        catch (Exception ex)
        {
            await DisplayAlert("Ошибка!", $"Не удалось экспортировать: {ex.Message}", "OK");
        }

    }

    private async IAsyncEnumerable<Contact> GetContacts()
    {
        var contacts = await Contacts.Default.GetAllAsync();
        
        foreach (var userContact in contacts)
        {
            var contact = new Contact();

            if(int.TryParse(userContact.Id, out var id))
                contact.Id = id;

            contact.Name = userContact.DisplayName;

            var firstPhoneNumber = userContact.Phones.FirstOrDefault();

            contact.PhoneNumber = firstPhoneNumber != null ? 
                firstPhoneNumber.PhoneNumber : "";
            
            var firstEmail = userContact.Emails.FirstOrDefault();

            contact.Email = firstEmail != null ? 
                firstEmail.EmailAddress : "";

            contact.Address = "";
            contact.Description = "";
            contact.PhotoPath = "";

            yield return contact;
        }

    }

    private async void OnContactSelected(object sender, SelectionChangedEventArgs e)
    {
        if (e.CurrentSelection.FirstOrDefault() is not Contact selectedContact) 
            return;
        await Navigation.PushAsync(new ContactDetailPage(selectedContact));
        contactsList.SelectedItem = null;
    }

    private async void OnSearchTextChanged(object sender, TextChangedEventArgs e)
    {
        var searchTerm = e.NewTextValue;
        var filteredContacts = await _databaseService.SearchContactsAsync(searchTerm);
        contactsList.ItemsSource = filteredContacts;
    }

    private async void OnAddContactClicked(object sender, EventArgs e)
    {
        await Navigation.PushAsync(new ContactDetailPage(new Contact()));
    }

    private async void OnExportContactClicked(object sender, EventArgs e)
    {
        await ExportToXlsx();
    }

    private async void SearchBar_TextChanged(object sender, TextChangedEventArgs e)
    {
        if (string.IsNullOrWhiteSpace(e.NewTextValue))
        {
            contactsList.ItemsSource = _allContacts;
        }
        else
        {
            contactsList.ItemsSource = await _databaseService.SearchContactsAsync(e.NewTextValue);
        }
    }
}