LehrerApp/LehrerApp.Desktop/ViewModels/Students/CreateLetterDialogViewModel.cs

using CommunityToolkit.Mvvm.ComponentModel;
using LehrerApp.Core.Interfaces;
using LehrerApp.Core.Models;
using LehrerApp.Desktop.Services;
using LehrerApp.Templating;
using System.Collections.ObjectModel;

namespace LehrerApp.Desktop.ViewModels.Students;

public partial class CreateLetterDialogViewModel : ObservableObject
{
    private readonly Student _student;
    private readonly TemplateStore _templates;
    private readonly ITemplateRenderer _renderer;

    [ObservableProperty] private LetterTemplateChoice? _selectedTemplate;
    [ObservableProperty] private LetterContactChoice? _selectedContact;
    [ObservableProperty] private LetterGroupChoice? _selectedGroup;
    [ObservableProperty] private DateTimeOffset? _letterDate = DateTimeOffset.Now;
    [ObservableProperty] private string _letterText = "";
    [ObservableProperty] private string _teacherName = "";
    [ObservableProperty] private string _generationError = "";
    [ObservableProperty] private bool _canGenerate;

    public string StudentName => _student.FullName;
    public ObservableCollection<LetterTemplateChoice> Templates { get; } = [];
    public ObservableCollection<LetterContactChoice> Contacts { get; } = [];
    public ObservableCollection<LetterGroupChoice> Groups { get; } = [];
    public ObservableCollection<LetterGenerationIssue> Issues { get; } = [];
    public bool HasIssues => Issues.Count > 0;
    public bool HasNoTemplates => Templates.Count == 0;
    public bool HasNoContacts => Contacts.Count == 0;
    public string SuggestedFileName => SanitizeFileName(
        $"{SelectedTemplate?.Name ?? "Elternbrief"}_{_student.LastName}_{_student.FirstName}.pdf");

    public CreateLetterDialogViewModel(Student student, TemplateStore templates, ITemplateRenderer renderer,
        IGroupMembershipRepository memberships, IGroupRepository groups)
    {
        _student = student; _templates = templates; _renderer = renderer;
        foreach (var template in templates.GetTemplates()) Templates.Add(new(template));
        foreach (var contact in student.Contacts.Where(c => !c.InvalidSince.HasValue).OrderBy(c => c.Name)) Contacts.Add(new(contact));
        foreach (var membership in memberships.GetByStudent(student.Id))
            if (groups.GetById(membership.GroupId) is { } group) Groups.Add(new(group));
        SelectedTemplate = Templates.FirstOrDefault(); SelectedContact = Contacts.FirstOrDefault(); SelectedGroup = Groups.FirstOrDefault();
        RefreshValidation();
    }

    partial void OnSelectedTemplateChanged(LetterTemplateChoice? value) { OnPropertyChanged(nameof(SuggestedFileName)); RefreshValidation(); }
    partial void OnSelectedContactChanged(LetterContactChoice? value) => RefreshValidation();
    partial void OnSelectedGroupChanged(LetterGroupChoice? value) => RefreshValidation();
    partial void OnLetterDateChanged(DateTimeOffset? value) => RefreshValidation();
    partial void OnLetterTextChanged(string value) => RefreshValidation();
    partial void OnTeacherNameChanged(string value) => RefreshValidation();

    public bool Generate(string outputPath)
    {
        RefreshValidation(); if (!CanGenerate || SelectedTemplate is null) return false;
        try
        {
            var pdf = _renderer.RenderToPdf(_templates.Load(SelectedTemplate.Model), new LetterDataProvider(BuildValues()));
            var directory = Path.GetDirectoryName(outputPath); if (!string.IsNullOrEmpty(directory)) Directory.CreateDirectory(directory);
            File.WriteAllBytes(outputPath, pdf); GenerationError = ""; return true;
        }
        catch (Exception ex) when (ex is IOException or InvalidDataException or UnauthorizedAccessException or TemplateValidationException)
        { GenerationError = $"Der Brief konnte nicht erzeugt werden: {ex.Message}"; return false; }
    }

    private void RefreshValidation()
    {
        Issues.Clear(); GenerationError = "";
        if (SelectedTemplate is null) Issues.Add(new("Bitte zuerst in den Einstellungen ein .lavorlage-Paket importieren.", true));
        if (SelectedContact is null) Issues.Add(new("Für den Schüler ist kein aktueller Kontakt ausgewählt.", true));
        if (LetterDate is null) Issues.Add(new("Bitte ein Briefdatum auswählen.", true));
        if (SelectedTemplate is not null)
        {
            try
            {
                var loaded = _templates.Load(SelectedTemplate.Model); var values = BuildValues();
                var validation = new TemplateLoader().Validate(loaded, values.ToDictionary(x => x.Key, x => x.Value.Type));
                foreach (var issue in validation.Issues) Issues.Add(new(issue.Message, issue.Severity == ValidationSeverity.Error));
                foreach (var required in loaded.Manifest.Placeholders.Where(x => !x.IsConstant && x.Required
                             && values.TryGetValue(x.Name, out var value) && IsEmpty(value)))
                    Issues.Add(new($"Für das Pflichtfeld „{required.Name}“ ist kein Wert vorhanden.", true));
            }
            catch (Exception ex) when (ex is IOException or InvalidDataException or TemplateValidationException)
            { Issues.Add(new($"Vorlage ist ungültig: {ex.Message}", true)); }
        }
        CanGenerate = SelectedTemplate is not null && SelectedContact is not null && LetterDate is not null && Issues.Count == 0;
        OnPropertyChanged(nameof(HasIssues));
    }

    private IReadOnlyDictionary<string, PlaceholderValue> BuildValues() => LetterPlaceholderBuilder.BuildStandardValues(
        _student, SelectedContact?.Model, SelectedGroup?.Model,
        DateOnly.FromDateTime((LetterDate ?? DateTimeOffset.Now).LocalDateTime), LetterText, TeacherName);

    private static bool IsEmpty(PlaceholderValue value) => LetterPlaceholderBuilder.IsEmpty(value);
    private static string SanitizeFileName(string value)
    { foreach (var character in Path.GetInvalidFileNameChars()) value = value.Replace(character, '_'); return value; }
}

internal sealed class LetterDataProvider(IReadOnlyDictionary<string, PlaceholderValue> values) : ITemplateDataProvider
{ public IReadOnlyDictionary<string, PlaceholderValue> GetValues() => values; }
public sealed class LetterTemplateChoice(InstalledTemplate model) { public InstalledTemplate Model { get; } = model; public string Name => Model.Name; }
public sealed class LetterContactChoice(Contact model) { public Contact Model { get; } = model; public string Display => string.IsNullOrWhiteSpace(Model.Relation) ? Model.Name : $"{Model.Name} · {Model.Relation}"; }
public sealed class LetterGroupChoice(LearningGroup model) { public LearningGroup Model { get; } = model; public string Display => $"{Model.Name} · {Model.SchoolYear}"; }
public sealed class LetterGenerationIssue(string message, bool isStrong)
{ public string Icon { get; } = isStrong ? "⚠" : "ⓘ"; public string Message { get; } = message; public string Color { get; } = isStrong ? "#D97706" : "#6B7280"; }