using Schaad.Accounting;
using Schaad.Accounting.Datasets.Charts;

namespace Schaad.Accounting.UI.Components.Pages.Charts;

/// <summary>
/// Swiss (de-CH) formatting for chart labels/tooltips, plus the top-N + "Andere"
/// folding used to keep pies and stacked series legible. Plotly's own d3-format
/// tokens can't produce the apostrophe thousands separator, so values are
/// pre-formatted here in C# and passed to Plotly as literal text.
/// </summary>
public static class ChartFormatting
{
    private static readonly string[] MonthAbbreviations =
    [
        "Jan", "Feb", "Mrz", "Apr", "Mai", "Jun", "Jul", "Aug", "Sep", "Okt", "Nov", "Dez"
    ];

    public static string MonthLabel(DateOnly date) => $"{MonthAbbreviations[date.Month - 1]} {date.Year % 100:00}";

    public static string Chf(decimal value) => $"{value.ToFormattedString()} CHF";

    /// <summary>
    /// Sorts by magnitude descending and, past <see cref="ChartTheme.MaxCategories"/>,
    /// collapses the remainder into a single "Andere" entry so a pie/legend never
    /// has to carry more slices than the categorical palette can distinguish.
    /// </summary>
    public static IReadOnlyList<CategoryTotal> FoldTail(IReadOnlyList<CategoryTotal> items)
    {
        var sorted = items.OrderByDescending(i => Math.Abs(i.Value)).ToList();
        if (sorted.Count <= ChartTheme.MaxCategories)
        {
            return sorted;
        }

        var head = sorted.Take(ChartTheme.MaxCategories - 1).ToList();
        var tailTotal = sorted.Skip(ChartTheme.MaxCategories - 1).Sum(i => i.Value);
        head.Add(new CategoryTotal(ChartTheme.OtherLabel, tailTotal));
        return head;
    }

    /// <summary>
    /// Same idea as <see cref="FoldTail(IReadOnlyList{CategoryTotal})"/> for a set of
    /// monthly series (e.g. a stacked bar chart): series are ranked by total magnitude
    /// across all months, and everything past the cap is summed month-by-month into
    /// a single "Andere" series.
    /// </summary>
    public static IReadOnlyList<DataSerie> FoldTail(IReadOnlyList<DataSerie> series)
    {
        if (series.Count <= ChartTheme.MaxCategories)
        {
            return series;
        }

        var ranked = series.OrderByDescending(s => s.Y.Sum(Math.Abs)).ToList();
        var head = ranked.Take(ChartTheme.MaxCategories - 1).ToList();
        var tail = ranked.Skip(ChartTheme.MaxCategories - 1).ToList();

        var x = tail[0].X;
        var otherY = new decimal[x.Count];
        foreach (var serie in tail)
        {
            for (var i = 0; i < x.Count; i++)
            {
                otherY[i] += serie.Y[i];
            }
        }

        head.Add(new DataSerie(ChartTheme.OtherLabel, ChartTheme.OtherLabel, x, otherY));
        return head;
    }
}