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;
    private readonly Func<AttendanceCalendarOptions, DrawingValue>? _attendanceCalendarFactory;
    private readonly Func<AttendanceCalendarOptions, DrawingValue>? _absenceDayListFactory;
    private AttendanceCalendarOptions _attendanceCalendarOptions = new(
        new DateOnly(DateTime.Today.Year, DateTime.Today.Month, 1), 1);

    [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;
    [ObservableProperty] private bool _usesAttendanceCalendar;
    [ObservableProperty] private bool _usesAbsenceDayList;
    [ObservableProperty] private bool _attendanceCalendarConfigured;
    [ObservableProperty] private string _attendanceCalendarSummary = "1 Monat · Standardgröße";

    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 ObservableCollection<LetterPlaceholderInput> CustomPlaceholders { get; } = [];
    public bool HasIssues => Issues.Count > 0;
    public bool HasCustomPlaceholders => CustomPlaceholders.Count > 0;
    public bool HasNoTemplates => Templates.Count == 0;
    public bool HasNoContacts => Contacts.Count == 0;
    public bool UsesAttendanceAdvancedContent => UsesAttendanceCalendar || UsesAbsenceDayList;
    public string SuggestedFileName => SanitizeFileName(
        $"{SelectedTemplate?.Name ?? "Elternbrief"}_{_student.LastName}_{_student.FirstName}.pdf");

    public CreateLetterDialogViewModel(Student student, TemplateStore templates, ITemplateRenderer renderer,
        IGroupMembershipRepository memberships, IGroupRepository groups,
        Func<AttendanceCalendarOptions, DrawingValue>? attendanceCalendarFactory = null,
        Func<AttendanceCalendarOptions, DrawingValue>? absenceDayListFactory = null)
    {
        _student = student; _templates = templates; _renderer = renderer;
        _attendanceCalendarFactory = attendanceCalendarFactory;
        _absenceDayListFactory = absenceDayListFactory;
        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));
        UsesAttendanceCalendar = TemplateUsesPlaceholder(value,
            StudentAttendanceCalendarDrawingBuilder.PlaceholderName);
        UsesAbsenceDayList = TemplateUsesPlaceholder(value,
            StudentAbsenceDayListDrawingBuilder.PlaceholderName);
        OnPropertyChanged(nameof(UsesAttendanceAdvancedContent));
        AttendanceCalendarConfigured = false;
        ResetAttendanceCalendarOptions();
        RebuildCustomPlaceholders(value);
        RefreshValidation();
    }
    partial void OnSelectedContactChanged(LetterContactChoice? value) => RefreshValidation();
    partial void OnSelectedGroupChanged(LetterGroupChoice? value) => RefreshValidation();
    partial void OnLetterDateChanged(DateTimeOffset? value)
    {
        if (!AttendanceCalendarConfigured) ResetAttendanceCalendarOptions();
        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()
    {
        var values = LetterPlaceholderBuilder.BuildStandardValues(
            _student, SelectedContact?.Model, SelectedGroup?.Model,
            DateOnly.FromDateTime((LetterDate ?? DateTimeOffset.Now).LocalDateTime), LetterText, TeacherName,
            UsesAttendanceCalendar ? _attendanceCalendarFactory?.Invoke(_attendanceCalendarOptions) : null,
            UsesAbsenceDayList ? _absenceDayListFactory?.Invoke(_attendanceCalendarOptions) : null);
        foreach (var custom in CustomPlaceholders) values[custom.Name] = custom.ToPlaceholderValue();
        return values;
    }

    private void RebuildCustomPlaceholders(LetterTemplateChoice? choice)
    {
        foreach (var existing in CustomPlaceholders) existing.PropertyChanged -= OnCustomPlaceholderChanged;
        CustomPlaceholders.Clear();
        if (choice is not null)
        {
            try
            {
                var loaded = _templates.Load(choice.Model);
                foreach (var placeholder in loaded.Manifest.Placeholders.Where(p => !p.IsConstant
                             && !StandardPlaceholderNames.Contains(p.Name) && p.Type is PlaceholderType.Text
                                 or PlaceholderType.Multiline or PlaceholderType.Date or PlaceholderType.Number))
                {
                    var input = new LetterPlaceholderInput(placeholder.Name, placeholder.Type);
                    input.PropertyChanged += OnCustomPlaceholderChanged;
                    CustomPlaceholders.Add(input);
                }
            }
            catch (Exception ex) when (ex is IOException or InvalidDataException or TemplateValidationException) { }
        }
        OnPropertyChanged(nameof(HasCustomPlaceholders));
    }

    private void OnCustomPlaceholderChanged(object? sender, System.ComponentModel.PropertyChangedEventArgs e) => RefreshValidation();

    private static readonly HashSet<string> StandardPlaceholderNames = new(StringComparer.Ordinal)
    {
        "Datum", "CurrentDate", "Empfaenger", "Anrede", "Brieftext", "LehrerName",
        "Student.FirstName", "Student.LastName", "Contact.Name", "Contact.Address", "Contact.Street",
        "Contact.PostalCode", "Contact.City", "Letter.Salutation", "Group.Name", "SchoolYear",
        StudentAttendanceCalendarDrawingBuilder.PlaceholderName, StudentAbsenceDayListDrawingBuilder.PlaceholderName,
    };

    public AttendanceCalendarOptions GetAttendanceCalendarOptions() => _attendanceCalendarOptions;

    public void SetAttendanceCalendarOptions(AttendanceCalendarOptions options)
    {
        _attendanceCalendarOptions = options with { StartMonth = options.NormalizedStartMonth,
            MonthCount = options.NormalizedMonthCount };
        AttendanceCalendarConfigured = true;
        AttendanceCalendarSummary = FormatAttendanceCalendarSummary(_attendanceCalendarOptions);
        RefreshValidation();
    }

    private void ResetAttendanceCalendarOptions()
    {
        var date = DateOnly.FromDateTime((LetterDate ?? DateTimeOffset.Now).LocalDateTime);
        _attendanceCalendarOptions = new AttendanceCalendarOptions(new(date.Year, date.Month, 1), 1);
        AttendanceCalendarSummary = FormatAttendanceCalendarSummary(_attendanceCalendarOptions);
    }

    private bool TemplateUsesPlaceholder(LetterTemplateChoice? choice, string placeholderName)
    {
        if (choice is null) return false;
        try
        {
            var loaded = _templates.Load(choice.Model);
            return UsesPlaceholder(loaded.Layout, placeholderName) ||
                   (loaded.ContinuationLayout is not null && UsesPlaceholder(loaded.ContinuationLayout, placeholderName));
        }
        catch (Exception ex) when (ex is IOException or InvalidDataException or TemplateValidationException)
        {
            return false;
        }
    }

    private static bool UsesPlaceholder(TemplateLayout layout, string placeholderName) =>
        layout.Elements.Concat(layout.PageTemplates.SelectMany(p => p.Elements))
            .Concat(layout.ContentFlows.SelectMany(f => f.Elements))
            .Any(e => e is DrawBoxElement draw && draw.Placeholder == placeholderName ||
                      e is FlowDrawBoxElement flow && flow.Placeholder == placeholderName);

    private static string FormatAttendanceCalendarSummary(AttendanceCalendarOptions options)
    {
        var month = options.NormalizedStartMonth.ToString("MMMM yyyy",
            System.Globalization.CultureInfo.GetCultureInfo("de-DE"));
        var size = options.Size switch
        {
            AttendanceCalendarSize.Small => "Klein",
            AttendanceCalendarSize.Large => "Groß",
            _ => "Standard",
        };
        return $"Ab {month} · {options.NormalizedMonthCount} Monat{(options.NormalizedMonthCount == 1 ? "" : "e")} · {size}";
    }

    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"; }

public sealed partial class LetterPlaceholderInput : ObservableObject
{
    public string Name { get; }
    public PlaceholderType Type { get; }
    public string Label => Type switch
    {
        PlaceholderType.Date => $"{Name} (Datum)",
        PlaceholderType.Number => $"{Name} (Zahl)",
        _ => Name,
    };
    public bool IsTextType => Type == PlaceholderType.Text;
    public bool IsMultilineType => Type == PlaceholderType.Multiline;
    public bool IsDateType => Type == PlaceholderType.Date;
    public bool IsNumberType => Type == PlaceholderType.Number;

    [ObservableProperty] private string _textValue = "";
    [ObservableProperty] private DateTimeOffset? _dateValue;
    [ObservableProperty] private decimal? _numberValue;

    public LetterPlaceholderInput(string name, PlaceholderType type) { Name = name; Type = type; }

    public PlaceholderValue ToPlaceholderValue() => Type switch
    {
        PlaceholderType.Multiline => new MultilineValue(TextValue),
        PlaceholderType.Date => new DateValue(DateValue.HasValue ? DateOnly.FromDateTime(DateValue.Value.LocalDateTime) : default),
        PlaceholderType.Number => new NumberValue(NumberValue ?? 0),
        _ => new TextValue(TextValue),
    };
}