using Nonemm.Core;

namespace Nonemm.Session;

/// N1MM's statistics table: how many contacts fall under each pair of values of
/// the two fields chosen, with the running total down the right and the column
/// totals along the bottom.
public sealed class StatisticsPivot
{
    private readonly int[,] counts;

    private StatisticsPivot(
        StatisticsField row,
        StatisticsField column,
        IReadOnlyList<PivotKey> rows,
        IReadOnlyList<PivotKey> columns,
        int[,] counts)
    {
        Row = row;
        Column = column;
        Rows = rows;
        Columns = columns;
        this.counts = counts;

        int[] rowTotals = new int[rows.Count];
        int[] accumulated = new int[rows.Count];
        int[] columnTotals = new int[columns.Count];
        int running = 0;
        for (int down = 0; down < rows.Count; down++)
        {
            for (int across = 0; across < columns.Count; across++)
            {
                rowTotals[down] += counts[down, across];
                columnTotals[across] += counts[down, across];
            }
            running += rowTotals[down];
            accumulated[down] = running;
        }
        RowTotals = rowTotals;
        Accumulated = accumulated;
        ColumnTotals = columnTotals;
        Total = running;
    }

    /// `includeDupes` is N1MM's "Include Dupes & X-QSOs": with it clear, a
    /// contact left out of the claimed score and a contact marked as a dupe are
    /// both left out of the count.
    public static StatisticsPivot Of(
        IReadOnlyList<Qso> qsos,
        StatisticsField row,
        StatisticsField column,
        DateTime startUtc,
        bool includeDupes = false)
    {
        Dictionary<(PivotKey Down, PivotKey Across), int> cells = [];
        SortedSet<PivotKey> rows = [];
        SortedSet<PivotKey> columns = [];
        foreach (Qso qso in qsos)
        {
            if (!includeDupes && !qso.IsInScore)
            {
                continue;
            }
            PivotKey down = row.KeyOf(qso, startUtc);
            PivotKey across = column.KeyOf(qso, startUtc);
            rows.Add(down);
            columns.Add(across);
            cells[(down, across)] = cells.GetValueOrDefault((down, across)) + 1;
        }

        List<PivotKey> rowKeys = [.. rows];
        List<PivotKey> columnKeys = [.. columns];
        int[,] counts = new int[rowKeys.Count, columnKeys.Count];
        for (int down = 0; down < rowKeys.Count; down++)
        {
            for (int across = 0; across < columnKeys.Count; across++)
            {
                counts[down, across] = cells.GetValueOrDefault((rowKeys[down], columnKeys[across]));
            }
        }
        return new StatisticsPivot(row, column, rowKeys, columnKeys, counts);
    }

    public StatisticsField Row { get; }

    public StatisticsField Column { get; }

    public IReadOnlyList<PivotKey> Rows { get; }

    public IReadOnlyList<PivotKey> Columns { get; }

    /// The contacts under one row and one column.
    public int Count(int row, int column) => counts[row, column];

    public IReadOnlyList<int> RowTotals { get; }

    /// The row total plus every row above it, which is N1MM's `Accum` column.
    public IReadOnlyList<int> Accumulated { get; }

    public IReadOnlyList<int> ColumnTotals { get; }

    public int Total { get; }

    public bool IsEmpty => Rows.Count == 0;
}