using SkiaSharp;

using System.Collections.Generic;

namespace Spectrogram;

static class Scale

{

public static SKBitmap Vertical(int width, Settings settings, int offsetHz = 0, int tickSize = 3, int reduction = 1)

{

double tickHz = 1;

int minSpacingPx = 50;

double[] multipliers = { 2, 2.5, 2 };

int multiplier = 0;

while (true)

{

tickHz *= multipliers[multiplier++ % multipliers.Length];

double tickCount = settings.FreqSpan / tickHz;

double pxBetweenTicks = settings.Height / tickCount;

if (pxBetweenTicks >= minSpacingPx * reduction)

break;

}

var imageInfo = new SKImageInfo(width, settings.Height / reduction, SKColorType.Rgba8888);

var bitmap = new SKBitmap(imageInfo);

using var canvas = new SKCanvas(bitmap);

canvas.Clear(SKColors.White);

var paint = new SKPaint

{

Color = SKColors.Black,

TextSize = 10,

IsAntialias = true,

Typeface = SKTypeface.FromFamilyName("Monospace")

};

List<double> freqs = new List<double>();

for (double f = settings.FreqMin; f <= settings.FreqMax; f += tickHz)

freqs.Add(f);

if (freqs.Count >= 2)

{

freqs.RemoveAt(0);

freqs.RemoveAt(freqs.Count - 1);

}

foreach (var freq in freqs)

{

int y = settings.PixelY(freq) / reduction;

canvas.DrawLine(0, y, tickSize, y, paint);

var text = $"{freq + offsetHz:N0} Hz";

canvas.DrawText(text, tickSize + 2, y + 5, paint);

}

return bitmap;

}

}