using Nonemm.Core;

namespace Nonemm.Spotting;

/// Works out where each callsign goes. Two stations a hundred hertz apart would
/// have their text on top of each other, so a label that would cover the one
/// above is pushed below it and a leader line runs back to the real frequency.
/// This is what N1MM does.
public static class BandmapLayout
{
    /// N1MM leaves this much between two labels it had to separate.
    private const double Gap = 0.5;

    public static IReadOnlyList<BandmapLabel> Place(
        IEnumerable<Spot> spots,
        BandmapScale scale,
        double labelHeight)
    {
        List<BandmapLabel> placed = [];
        double? above = null;
        foreach (Spot spot in spots
            .Where(s => scale.Shows(s.Frequency))
            .OrderBy(s => s.Frequency.Hertz))
        {
            double markY = scale.YFor(spot.Frequency);
            double labelY = markY - (labelHeight / 2);
            if (above is { } previous && previous + labelHeight > labelY)
            {
                labelY = previous + labelHeight + Gap;
            }
            placed.Add(new BandmapLabel(spot, markY, labelY));
            above = labelY;
        }
        return placed;
    }

    /// The frequency ticks to draw, every `step` from the first round frequency
    /// at or below the top of the scale.
    public static IReadOnlyList<Frequency> Ticks(BandmapScale scale, Frequency step)
    {
        List<Frequency> ticks = [];
        long first = scale.Low.Hertz - (scale.Low.Hertz % step.Hertz);
        for (long at = first; at <= scale.High.Hertz; at += step.Hertz)
        {
            if (at >= scale.Low.Hertz)
            {
                ticks.Add(Frequency.FromHertz(at));
            }
        }
        return ticks;
    }
}