using System.Collections;
using System.Globalization;
using Avalonia;
using Avalonia.Collections;
using Avalonia.Controls;
using Avalonia.Controls.Primitives;
using Avalonia.Data;
using Avalonia.Input;
using Avalonia.Media;
using Avalonia.VisualTree;
using Nonemm.Session;

namespace Nonemm.App.Windows;

/// Which columns the log shows, in which order, and which one it sorts on. The
/// contest gives the set the log opens with; a right click on a header adds or
/// removes one and a header can be dragged to move its column, both of which
/// are kept in the settings file. A click on a header sorts on that column and
/// lasts as long as the window is open.
public sealed partial class LogWindow
{
    /// What a cell takes either side of its text, in device pixels.
    private const double CellPadding = 30;

    private readonly Dictionary<DataGridColumn, QsoColumn> columnOf = [];
    private IReadOnlyList<QsoColumn> shown = [];
    private Control? hiddenDragIndicator;
    private string builtFor = "";

    /// Avalonia arranges the drag indicator once before it has worked out where
    /// the pointer is, and that first frame draws the header about a column's
    /// width to the left of where it belongs. The indicator is hidden until the
    /// next pointer move, which is the first frame that carries the offset.
    private void HideDragIndicator(object? sender, DataGridColumnReorderingEventArgs e)
    {
        hiddenDragIndicator = e.DragIndicator;
        if (hiddenDragIndicator is not null)
        {
            hiddenDragIndicator.Opacity = 0;
        }
    }

    private void ShowDragIndicator(object? sender, PointerEventArgs e)
    {
        if (hiddenDragIndicator is null)
        {
            return;
        }
        hiddenDragIndicator.Opacity = 1;
        hiddenDragIndicator = null;
    }

    private static bool IsColumnHeader(object? source) =>
        source is Visual visual && visual.GetSelfAndVisualAncestors().OfType<DataGridColumnHeader>().Any();

    /// One item per column the contest or this program can show, ticked when it
    /// is on screen. The last item puts the contest's own set back.
    private ContextMenu ColumnMenu()
    {
        List<Control> items = [];
        foreach (QsoColumn column in LogColumns.Choices(ContestColumns()))
        {
            MenuItem item = new()
            {
                Header = column.Label,
                ToggleType = MenuItemToggleType.CheckBox,
                IsChecked = shown.Any(c => c.Field == column.Field),
            };
            item.Click += (_, _) => Toggle(column);
            items.Add(item);
        }
        MenuItem reset = new() { Header = "Default columns" };
        reset.Click += (_, _) => Store([]);
        items.Add(new Separator());
        items.Add(reset);
        return new ContextMenu { ItemsSource = items };
    }

    /// Removing the last column would leave a grid nothing can be selected in,
    /// so the last one stays.
    private void Toggle(QsoColumn column)
    {
        List<QsoColumn> next = [.. shown];
        if (next.RemoveAll(c => c.Field == column.Field) == 0)
        {
            next.Add(column);
        }
        else if (next.Count == 0)
        {
            message = "the log needs at least one column";
            Refresh();
            return;
        }
        Store(LogColumns.Store(next));
    }

    private void SaveColumnOrder() =>
        Store(LogColumns.Store(Rows.Columns
            .OrderBy(c => c.DisplayIndex)
            .Select(c => columnOf[c])));

    private void Store(IReadOnlyList<string> columns)
    {
        session.Save(session.Settings with { LogColumns = columns });
        builtFor = "";
        Refresh();
    }

    private IReadOnlyList<QsoColumn> ContestColumns() =>
        session.Logging?.Editor.Columns ?? [];

    /// The columns follow the contest exchange and the operator's choice, so
    /// they are rebuilt when either changes. Both grids get the same columns: a
    /// value in the pane has to sit under the column it belongs to.
    private void BuildColumns(QsoEditor editor)
    {
        IReadOnlyList<QsoColumn> chosen = LogColumns.Chosen(editor.Columns, session.Settings.LogColumns);
        string wanted = string.Join('|', chosen.Select(c => $"{c.Field}:{c.Label}"));
        if (wanted == builtFor)
        {
            return;
        }
        builtFor = wanted;
        shown = chosen;
        FillColumns(Rows, chosen);
        FillColumns(Earlier, chosen);
        columnOf.Clear();
        for (int at = 0; at < chosen.Count; at++)
        {
            columnOf[Rows.Columns[at]] = chosen[at];
        }
    }

    /// N1MM gives each column the width of the longest value it can hold, and
    /// the last column what is left over. A fixed width also keeps a column from
    /// changing size as rows scroll into view.
    private static void FillColumns(DataGrid grid, IReadOnlyList<QsoColumn> columns)
    {
        grid.Columns.Clear();
        double Width(QsoColumn column) => WidthFor(column, grid);
        for (int at = 0; at < columns.Count; at++)
        {
            QsoColumn column = columns[at];
            grid.Columns.Add(new DataGridTextColumn
            {
                Header = column.Label,
                IsReadOnly = !column.IsEditable,
                Width = at == columns.Count - 1
                    ? new DataGridLength(1, DataGridLengthUnitType.Star)
                    : new DataGridLength(Width(column)),
                MinWidth = Width(column),
                Binding = column.IsEditable
                    ? new Binding($"[{column.Field}]") { Mode = BindingMode.TwoWay }
                    : new Binding($"[{column.Field}]"),
                CustomSortComparer = By(column.Field),
            });
        }
    }

    /// The grid sorts on the field itself rather than on the text of the cell,
    /// which is what `LogColumns.SortKey` gives.
    private static IComparer By(QsoField field) =>
        Comparer<LogRow>.Create((left, right) =>
            LogColumns.SortKey(left.Qso, field).CompareTo(LogColumns.SortKey(right.Qso, field)));

    /// A new view for each refresh, carrying over the sort the operator clicked.
    /// Without one the log shows the order the contacts were worked in.
    private DataGridCollectionView Sorted(IEnumerable<LogRow> rows)
    {
        DataGridCollectionView view = new(rows);
        if (Rows.ItemsSource is DataGridCollectionView old)
        {
            foreach (DataGridSortDescription sort in old.SortDescriptions)
            {
                view.SortDescriptions.Add(sort);
            }
        }
        return view;
    }

    /// Wide enough for both the longest value and the header. They are in
    /// different fonts — the values in the grid's monospace, the header in the
    /// theme's own font — so each is measured in the font it is drawn in.
    private static double WidthFor(QsoColumn column, DataGrid grid) =>
        Math.Max(
            TextWidth(new string('0', column.Width + 1), grid.FontFamily, grid.FontSize),
            TextWidth(column.Label + "0", FontFamily.Default, grid.FontSize)) + CellPadding;

    private static double TextWidth(string text, FontFamily family, double size) =>
        new FormattedText(
            text,
            CultureInfo.InvariantCulture,
            FlowDirection.LeftToRight,
            new Typeface(family),
            size,
            null).Width;
}