Data/src/main/java/de/ph87/data/series/graph/Graph.java

package de.ph87.data.series.graph;

import de.ph87.data.series.Aligned;
import de.ph87.data.series.SeriesDto;
import de.ph87.data.series.SeriesType;
import de.ph87.data.value.Autoscale;
import jakarta.annotation.Nullable;
import lombok.NonNull;

import java.awt.*;
import java.awt.geom.Line2D;
import java.awt.image.BufferedImage;
import java.util.List;
import java.util.function.Function;

import static java.lang.Math.max;

public class Graph {

  public static final Stroke NORMAL = new BasicStroke(1, BasicStroke.CAP_BUTT, BasicStroke.JOIN_MITER, 1);

  public static final Stroke DASHED = new BasicStroke(1, BasicStroke.CAP_BUTT, BasicStroke.JOIN_MITER, 1, new float[]{2, 2}, 0);

  @NonNull
  public final SeriesDto series;

  @NonNull
  public final Aligned begin;

  @NonNull
  public final Aligned end;

  public final int width;

  public final int height;

  public final int border;

  public final List<Point> points;

  public final long minuteMin;

  public final long minuteMax;

  public final long minuteRange;

  public final double minuteScale;

  public final double valueMin;

  public final double valueMax;

  public final double valueAvg;

  public final double valueRange;

  public final double valueScale;

  public final int heightInner;

  public final int widthInner;

  public final int maxLabelWidth;

  private final Autoscale autoscale;

  public Graph(@NonNull final SeriesDto series, @NonNull final List<GraphPoint> points, @NonNull final Aligned begin, @NonNull final Aligned end, final int width, final int height, final int border) {
    this.series = series;
    this.begin = begin;
    this.end = end;
    this.width = width;
    this.height = height;
    this.border = border;

    // find bounds
    double vSum = 0;
    double vMin = series.getYMin() == null || Double.isNaN(series.getYMin()) ? Double.MIN_VALUE : series.getYMin();
    double vMax = series.getYMax() == null || Double.isNaN(series.getYMax()) ? Double.MAX_VALUE : series.getYMax();
    for (final GraphPoint point : points) {
      vMin = Math.min(vMin, point.getValue());
      vMax = max(vMax, point.getValue());
      vSum += point.getValue();
    }

    // auto scale
    autoscale = new Autoscale(series, vMin, vMax);
    vMin *= autoscale.factor;
    vMax *= autoscale.factor;
    vSum *= autoscale.factor;

    // find max label width
    int __maxLabelWidth = 0;
    final FontMetrics fontMetrics = new BufferedImage(1, 1, BufferedImage.TYPE_INT_ARGB).getGraphics().getFontMetrics();
    for (final GraphPoint point : points) {
      __maxLabelWidth = max(__maxLabelWidth, fontMetrics.stringWidth(autoscale.format(point.getValue() * autoscale.factor)));
    }
    this.maxLabelWidth = __maxLabelWidth;

    widthInner = width - 3 * border - this.maxLabelWidth;
    heightInner = height - 2 * border;

    minuteMin = begin.date.toEpochSecond() / 60;
    minuteMax = end.date.toEpochSecond() / 60;
    minuteRange = minuteMax - minuteMin;
    minuteScale = (double) widthInner / (minuteRange + begin.alignment.maxDuration.toMinutes());

    valueMin = vMin;
    valueMax = vMax;
    valueAvg = vSum / points.size();
    valueRange = valueMax - valueMin;
    valueScale = heightInner / valueRange;

    this.points = points.stream().map(toPoint()).toList();
  }

  @NonNull
  public BufferedImage draw() {
    final BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
    final Graphics2D g = (Graphics2D) image.getGraphics();

    yLabel(g, valueMax, Color.red);
    yLabel(g, valueAvg, new Color(0, 255, 0));
    yLabel(g, valueMin, new Color(64, 128, 255));

    g.translate(border, height - border);
    g.scale(1, -1);

    // y-axis
    g.setStroke(NORMAL);
    g.setColor(Color.GRAY);
    g.drawLine(widthInner, 0, widthInner, heightInner);

    g.setColor(Color.WHITE);
    if (series.type == SeriesType.METER) {
      final int space = (int) (minuteScale * begin.alignment.maxDuration.toMinutes());
      final int width = (int) (space * 0.95);
      for (final Point point : points) {
        g.fillRect(point.x + (space - width), 0, width, point.y);
      }
    } else {
      Point last = null;
      for (final Point current : points) {
        if (last != null) {
          g.drawLine(last.x, last.y, current.x, current.y);
        }
        last = current;
      }
    }
    return image;
  }

  private void yLabel(@NonNull final Graphics2D g, final double value, @Nullable final Color color) {
    final String string = autoscale.format(value);
    final int offset = maxLabelWidth - g.getFontMetrics().stringWidth(string);
    final int y = height - ((int) Math.round((value - valueMin) * valueScale) + border);
    g.setColor(color);
    g.drawString(string, widthInner + 2 * border + offset, y + (int) Math.round(g.getFontMetrics().getHeight() * 0.25));
    if (color != null) {
      g.setStroke(Graph.DASHED);
      g.draw(new Line2D.Double(border, y, width - maxLabelWidth - border * 1.5, y));
    }
  }

  @NonNull
  private Function<GraphPoint, Point> toPoint() {
    return point -> {
      final long minuteEpoch = point.getDate().toEpochSecond() / 60;
      final long minuteRelative = minuteEpoch - minuteMin;
      final double minuteScaled = minuteRelative * minuteScale;
      final int x = (int) Math.round(minuteScaled);

      final double valueRelative = point.getValue() * autoscale.factor - valueMin;
      final double valueScaled = valueRelative * valueScale;
      final int y = (int) Math.round(valueScaled);

      return new Point(x, y);
    };
  }

}