using Nonemm.App.Configuration;
using System.Collections.ObjectModel;
using Avalonia;
using Avalonia.Collections;
using Avalonia.Controls;
using Avalonia.Controls.Primitives;
using Avalonia.Input;
using Avalonia.Interactivity;
using Avalonia.Threading;
using Avalonia.VisualTree;
using Nonemm.App.Dialogs;
using Nonemm.Contests;
using Nonemm.Core;
using Nonemm.Session;

namespace Nonemm.App.Windows;

/// The contacts of the contest in progress, newest last. Double-click a cell or
/// press Enter on it to change it; the Delete key removes the contact. Clicking a column header
/// sorts on it, right-clicking picks which columns are shown and dragging one
/// moves its column; see `LogWindow.Columns.cs`.
public sealed partial class LogWindow : RefreshableWindow
{
    private readonly AppSession session;
    /// The lines the grid is showing. They are kept and given the contact again
    /// when only the values changed, so that an edit does not rebuild the list
    /// and move the view.
    private ObservableCollection<LogRow> shownRows = [];
    /// The contacts the operator picked, by id. The grid is told to show them
    /// as picked only while this window is in front: a marked line in a window
    /// behind says nothing about where the keyboard is.
    private List<string> picked = [];
    /// True while this window is setting the selection itself, so that its own
    /// changes are not read back as the operator's.
    private bool picking;
    /// The contact quick edit is on, so that the picked line follows Ctrl+Q
    /// and Ctrl+A rather than being put back on every refresh.
    private string quickEditId = "";
    private string finding = "";

    public LogWindow(AppSession session)
    {
        this.session = session;
        InitializeComponent();
        // before the grid's own handling: the grid takes Enter to mean "move to
        // the next line", which would close the editing box as soon as it opens
        Rows.AddHandler(KeyDownEvent, OnKeyDown, RoutingStrategies.Tunnel);
        Rows.ColumnReordering += HideDragIndicator;
        Rows.AddHandler(PointerMovedEvent, ShowDragIndicator, RoutingStrategies.Tunnel);
        Rows.ColumnReordered += (_, _) => SaveColumnOrder();
        Rows.PreparingCellForEdit += SelectCellText;
        Rows.CellEditEnding += TakeCellEdit;
        Rows.AddHandler(ContextRequestedEvent, OnContextRequested, RoutingStrategies.Bubble);
        Rows.SelectionChanged += RememberPicked;
        Activated += (_, _) =>
        {
            Rows.Classes.Remove("away");
            ShowPicked();
        };
        Deactivated += (_, _) =>
        {
            Rows.Classes.Add("away");
            HidePicked();
        };
        Colour(Rows);
        Colour(Earlier);
        ApplyFontSize();
        _ = new FontZoom(this, new Settings().LogFontSize, () => session.Settings.LogFontSize, size =>
        {
            session.Save(session.Settings with { LogFontSize = size });
            ApplyFontSize();
            builtFor = "";
            Refresh();
        });
        Refresh();
    }

    /// The cells take their size from the `LogFontSize` resource, and the
    /// grids need it too because the column widths are measured from it.
    private void ApplyFontSize()
    {
        double size = session.Settings.LogFontSize;
        Resources["LogFontSize"] = size;
        Rows.FontSize = size;
        Earlier.FontSize = size;
    }

    /// What the operator picked. The grid raises this for the picks this window
    /// makes as well, and those are already known.
    private void RememberPicked(object? sender, SelectionChangedEventArgs e)
    {
        if (picking)
        {
            return;
        }
        picked = [.. Rows.SelectedItems.OfType<LogRow>().Select(r => r.Qso.Id)];
    }

    /// Marks the picked lines again. Only a window in front marks them, so the
    /// callers that are not the window coming to the front ask whether it is in
    /// front first.
    private void ShowPicked()
    {
        picking = true;
        Rows.SelectedItems.Clear();
        foreach (LogRow row in shownRows.Where(r => picked.Contains(r.Qso.Id)))
        {
            Rows.SelectedItems.Add(row);
        }
        picking = false;
    }

    /// Takes the marks off while another window has the keyboard. The contacts
    /// stay picked and are marked again when the window comes back.
    private void HidePicked()
    {
        picking = true;
        Rows.SelectedItems.Clear();
        picking = false;
    }

    /// Quick edit steps through the log from the entry window with Ctrl+Q and
    /// Ctrl+A. The contact in the entry boxes is the picked line here, and it
    /// is scrolled to whether or not this window is in front.
    private void FollowQuickEdit()
    {
        string id = session.Position?.Editing?.Id ?? "";
        if (id == quickEditId || id.Length == 0)
        {
            quickEditId = id;
            return;
        }
        quickEditId = id;
        picked = [id];
        if (IsActive)
        {
            ShowPicked();
        }
        if (shownRows.FirstOrDefault(r => r.Qso.Id == id) is { } row)
        {
            Rows.ScrollIntoView(row, null);
        }
    }

    /// A cell that has just opened for editing has all of its text selected, so
    /// typing replaces the value rather than adding to it.
    private static void SelectCellText(object? sender, DataGridPreparingCellForEditEventArgs e)
    {
        if (e.EditingElement is not TextBox box)
        {
            return;
        }
        box.SelectAll();
        // the grid hands the box back for the next cell, so the handler is
        // taken off before it is put on again
        box.RemoveHandler(KeyDownEvent, KeepCaretKeys);
        box.AddHandler(
            KeyDownEvent,
            KeepCaretKeys,
            RoutingStrategies.Direct | RoutingStrategies.Bubble,
            handledEventsToo: true);
    }

    /// Left, Right, Home and End stay in the editing box. The box marks a key
    /// as handled only when it moves the caret, and the grid reads a key the
    /// box left alone as "go to the next cell". Opening the box leaves the
    /// caret at the end of the text, so one press of Right closed the box.
    private static void KeepCaretKeys(object? sender, KeyEventArgs e)
    {
        if (e.Key is not (Key.Left or Key.Right or Key.Home or Key.End))
        {
            return;
        }
        // the box drops a selection by putting the caret at the start of it,
        // and does so after End has moved the caret to the end of the text, so
        // End on a box whose text is all selected lands at the start
        if (e.Key == Key.End && !e.KeyModifiers.HasFlag(KeyModifiers.Shift) && sender is TextBox box)
        {
            int end = (box.Text ?? "").Length;
            box.CaretIndex = end;
            box.SelectionStart = end;
            box.SelectionEnd = end;
        }
        e.Handled = true;
    }

    private void OnContextRequested(object? sender, ContextRequestedEventArgs e)
    {
        e.Handled = true;
        ContextMenu menu = IsColumnHeader(e.Source) ? ColumnMenu() : RowMenu();
        menu.PlacementTarget = Rows;
        menu.Placement = PlacementMode.Pointer;
        menu.Open(Rows);
    }

    private ContextMenu RowMenu()
    {
        MenuItem edit = new() { Header = "Edit contact…" };
        edit.Click += OnEditContact;
        MenuItem operators = new() { Header = "Change Operator…" };
        operators.Click += OnChangeOperator;
        MenuItem delete = new() { Header = "Delete contact", InputGesture = new KeyGesture(Key.Delete) };
        delete.Click += OnDelete;
        return new ContextMenu { ItemsSource = new List<MenuItem> { edit, operators, delete } };
    }

    public override void RefreshForEntry() => ShowEarlier();

    public override void Refresh()
    {
        if (session.Logging is null)
        {
            Rows.ItemsSource = Array.Empty<LogRow>();
            Earlier.ItemsSource = Array.Empty<LogRow>();
            return;
        }
        BuildColumns(session.Logging.Editor);
        IReadOnlyList<Qso> qsos = session.Logging.Log.Qsos;
        if (Rows.ItemsSource is DataGridCollectionView shown && shown.SourceCollection == shownRows && StartsWithShown(qsos))
        {
            // an edit, or contacts added at the end: the grid keeps its list, so
            // the view stays where it is and an open editing box stays open
            bool atBottom = ScrolledToBottom();
            for (int at = 0; at < shownRows.Count; at++)
            {
                // a contact that was not edited is the same object, and the
                // row has nothing to redraw
                if (!ReferenceEquals(shownRows[at].Qso, qsos[at]))
                {
                    shownRows[at].Show(qsos[at], VerdictFor(qsos[at]));
                }
            }
            bool grown = qsos.Count > shownRows.Count;
            for (int at = shownRows.Count; at < qsos.Count; at++)
            {
                // the grid puts the row where the sort says
                shownRows.Add(new LogRow(qsos[at], VerdictFor(qsos[at])));
            }
            Recolour(Rows);
            // the view follows a new contact only when it was at the foot of
            // the list; at the top the new row appears without a scroll
            if (grown && atBottom && Rows.ItemsSource is DataGridCollectionView view && view.Count > 0)
            {
                object last = view.GetItemAt(view.Count - 1);
                Dispatcher.UIThread.Post(() => Rows.ScrollIntoView(last, null), DispatcherPriority.Loaded);
            }
        }
        else
        {
            // a contact was deleted or moved: the list is built again, which
            // puts the view at the top, so it is wound back
            Qso? bottom = BottomOfView();
            shownRows = new ObservableCollection<LogRow>(qsos.Select(q => new LogRow(q, VerdictFor(q))));
            Rows.ItemsSource = Sorted(shownRows);
            ShowAgain(bottom, shownRows);
            // the new list comes with nothing picked
            if (IsActive)
            {
                ShowPicked();
            }
        }
        FollowQuickEdit();
        ShowEarlier();
    }

    /// True when the grid's lines are the first contacts of the log, in the
    /// same order. An edit leaves the list itself alone and logging a contact
    /// adds one at the end; deleting a contact does neither.
    private bool StartsWithShown(IReadOnlyList<Qso> qsos)
    {
        if (qsos.Count < shownRows.Count)
        {
            return false;
        }
        for (int at = 0; at < shownRows.Count; at++)
        {
            if (qsos[at].Id != shownRows[at].Qso.Id)
            {
                return false;
            }
        }
        return true;
    }

    /// The colour of a line is set as the grid draws it, so a line that is
    /// already on screen keeps the colour of the verdict it had before the
    /// edit until it is coloured again.
    private static void Recolour(DataGrid grid)
    {
        foreach (DataGridRow row in grid.GetVisualDescendants().OfType<DataGridRow>())
        {
            if (row.DataContext is LogRow item)
            {
                row.Foreground = item.Colour;
            }
        }
    }

    private ScrollBar? VerticalBar =>
        Rows.GetVisualDescendants().OfType<ScrollBar>()
            .FirstOrDefault(b => b.Orientation == Avalonia.Layout.Orientation.Vertical);

    /// True when the view is at the foot of the list, or when the list fits.
    private bool ScrolledToBottom() => VerticalBar is not { } bar || bar.Value >= bar.Maximum - 0.5;

    /// The contact drawn at the foot of the view, or null when the log is empty
    /// or has not been drawn yet. Setting `ItemsSource` puts the view back at
    /// the top, so this is what the view is wound back to afterwards.
    private Qso? BottomOfView()
    {
        Qso? found = null;
        double lowest = double.MinValue;
        foreach (DataGridRow row in Rows.GetVisualDescendants().OfType<DataGridRow>())
        {
            Point? foot = row.TranslatePoint(new Point(0, row.Bounds.Height), Rows);
            if (row.DataContext is not LogRow item
                || foot is null
                || foot.Value.Y > Rows.Bounds.Height + 1
                || foot.Value.Y <= lowest)
            {
                continue;
            }
            lowest = foot.Value.Y;
            found = item.Qso;
        }
        return found;
    }

    /// Scrolling a row into view from the top of the list leaves it at the foot
    /// of the view, which is where it was before the list was rebuilt. The grid
    /// puts the view back at the top itself as it takes the new list, so this
    /// waits for that to be over.
    private void ShowAgain(Qso? bottom, IReadOnlyList<LogRow> rows)
    {
        if (bottom is null)
        {
            return;
        }
        LogRow? row = rows.FirstOrDefault(r => r.Qso.Id == bottom.Id);
        if (row is not null)
        {
            Dispatcher.UIThread.Post(() => Rows.ScrollIntoView(row, null), DispatcherPriority.Loaded);
        }
    }

    /// The pane under the log: what has already been worked with the call being
    /// typed, so an apparent dupe can be read off the screen.
    private void ShowEarlier()
    {
        OperatingPosition? position = session.Position;
        if (position is null || session.Logging is null)
        {
            Earlier.ItemsSource = Array.Empty<LogRow>();
            return;
        }
        Earlier.ItemsSource = EarlierContacts
            .Matching(
                session.Logging.Log.Qsos,
                position.Entry.Call,
                position.Entry.ValueOf(ExchangeSlot.GridSquare))
            .Select(q => new LogRow(q, VerdictFor(q)))
            .ToList();
    }

    private static void Colour(DataGrid grid) =>
        grid.LoadingRow += (_, e) =>
        {
            if (e.Row.DataContext is LogRow row)
            {
                e.Row.Foreground = row.Colour;
            }
        };

    /// N1MM's Ctrl+F: shows the next contact with this call and selects it,
    /// starting again from the top once the last one has been shown. Null when
    /// the call is not in the log.
    public Qso? FindNextCall(string call)
    {
        string wanted = call.Trim();
        if (wanted.Length == 0 || Rows.ItemsSource is not DataGridCollectionView rows || rows.Count == 0)
        {
            return null;
        }
        int from = wanted.Equals(finding, StringComparison.OrdinalIgnoreCase) ? Rows.SelectedIndex + 1 : 0;
        finding = wanted;
        for (int step = 0; step < rows.Count; step++)
        {
            int at = (from + step) % rows.Count;
            if (rows.GetItemAt(at) is not LogRow row
                || !row.Qso.Call.Text.Equals(wanted, StringComparison.OrdinalIgnoreCase))
            {
                continue;
            }
            Rows.SelectedIndex = at;
            Rows.ScrollIntoView(row, null);
            return row.Qso;
        }
        return null;
    }

    /// The cell is written back when the operator takes the edit — Enter, or a
    /// click on another cell — and not before. The columns bind one way, so
    /// typing changes the box alone: Escape drops what was typed, and the value
    /// does not go into the log one character at a time.
    private void TakeCellEdit(object? sender, DataGridCellEditEndingEventArgs e)
    {
        if (e.EditAction != DataGridEditAction.Commit
            || e.EditingElement is not TextBox box
            || e.Row.DataContext is not LogRow row
            || !columnOf.TryGetValue(e.Column, out QsoColumn? column))
        {
            return;
        }
        string text = box.Text ?? "";
        // the edit rebuilds the rows, which the grid cannot take while it is
        // still closing the editing box
        Dispatcher.UIThread.Post(() => Edit(row.Qso, column.Field, text));
    }

    /// A refused edit leaves the cell as it was and shows the reason.
    private async void Edit(Qso qso, QsoField field, string text)
    {
        if (session.Logging is null)
        {
            return;
        }
        QsoEdit edit = session.Logging.Edit(qso.Id, field, text);
        if (!edit.IsAccepted)
        {
            await new AlertDialog("Edit refused", edit.Error).ShowDialog(this);
        }
    }

    private void OnKeyDown(object? sender, KeyEventArgs e)
    {
        if (e.Source is TextBox)
        {
            return;
        }
        switch (e.Key)
        {
            case Key.Delete:
                e.Handled = true;
                OnDelete(sender, new RoutedEventArgs());
                break;
            case Key.Enter:
                e.Handled = true;
                Rows.BeginEdit();
                break;
        }
    }

    private async void OnEditContact(object? sender, RoutedEventArgs e)
    {
        if (session.Logging is null || Rows.SelectedItem is not LogRow row)
        {
            return;
        }
        await new EditContactDialog(session.Logging, row.Qso.Id).ShowDialog(this);
    }

    /// Writes one callsign over the operator of every contact picked in the
    /// grid. A multi-operator station logs a whole shift under whoever was at
    /// the radio, so a shift logged under the wrong callsign is put right in
    /// one go rather than a contact at a time.
    private async void OnChangeOperator(object? sender, RoutedEventArgs e)
    {
        if (session.Logging is null)
        {
            return;
        }
        List<Qso> picked = [.. Rows.SelectedItems.OfType<LogRow>().Select(r => r.Qso)];
        if (picked.Count == 0)
        {
            return;
        }
        string was = picked[0].Operator.Length > 0 ? picked[0].Operator : session.Settings.CurrentOperator;
        List<string> known = [.. session.Settings.Operators.Select(o => o.Callsign)];
        if (await new ChangeOperatorDialog(picked.Count, was, known).ShowDialog<string?>(this) is not { } callsign)
        {
            return;
        }
        foreach (Qso qso in picked)
        {
            session.Logging.Edit(qso.Id, QsoField.Operator, callsign);
        }
        Refresh();
    }

    private async void OnDelete(object? sender, RoutedEventArgs e)
    {
        if (session.Logging is null || Rows.SelectedItem is not LogRow row)
        {
            return;
        }
        ConfirmDialog dialog = new(
            "Delete contact",
            $"Delete {row.Qso.Call.Text} at {row.Qso.TimestampUtc:yyyy-MM-dd HH:mm:ss}? " +
            "The other stations are told to delete it too.",
            "Delete");
        if (await dialog.ShowDialog<bool>(this))
        {
            session.Logging.Delete(row.Qso.Id);
            Refresh();
        }
    }

    /// A logged contact is coloured by what it turned out to be worth, not by
    /// judging it again as if it were new.
    private static Contests.Verdict VerdictFor(Qso qso) =>
        new(
            IsDupe: false,
            Points: qso.Points,
            NewMultipliers: qso.IsMultiplier1 || qso.IsMultiplier2 || qso.IsMultiplier3
                ? [new Contests.Multiplier(1, "", "")]
                : []);
}