[maps] show marker size in legend (elastic#132549)

* [Maps] size legend

* clean-up

* refine spacing

* clean up

* more cleanup

* use euiTheme for colors

* fix jest test

* do not show marker sizes for icons

* remove lodash

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

x-pack/plugins/maps/public/classes/styles/vector/components/legend/marker_size_legend.tsx

@@ -0,0 +1,164 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import React, { Component } from 'react';
+import { euiThemeVars } from '@kbn/ui-theme';
+import { EuiFlexGroup, EuiFlexItem, EuiText, EuiToolTip } from '@elastic/eui';
+import { DynamicSizeProperty } from '../../properties/dynamic_size_property';
+
+const FONT_SIZE = 10;
+const HALF_FONT_SIZE = FONT_SIZE / 2;
+const MIN_MARKER_DISTANCE = (FONT_SIZE + 2) / 2;
+
+const EMPTY_VALUE = '';
+
+interface Props {
+  style: DynamicSizeProperty;
+}
+
+interface State {
+  label: string;
+}
+
+export class MarkerSizeLegend extends Component<Props, State> {
+  private _isMounted: boolean = false;
+
+  state: State = {
+    label: EMPTY_VALUE,
+  };
+
+  componentDidMount() {
+    this._isMounted = true;
+    this._loadLabel();
+  }
+
+  componentDidUpdate() {
+    this._loadLabel();
+  }
+
+  componentWillUnmount() {
+    this._isMounted = false;
+  }
+
+  async _loadLabel() {
+    const field = this.props.style.getField();
+    if (!field) {
+      return;
+    }
+    const label = await field.getLabel();
+    if (this._isMounted && this.state.label !== label) {
+      this.setState({ label });
+    }
+  }
+
+  _formatValue(value: string | number) {
+    return value === EMPTY_VALUE ? value : this.props.style.formatField(value);
+  }
+
+  _renderMarkers() {
+    const fieldMeta = this.props.style.getRangeFieldMeta();
+    const options = this.props.style.getOptions();
+    if (!fieldMeta || !options) {
+      return null;
+    }
+
+    const circleStyle = {
+      fillOpacity: 0,
+      stroke: euiThemeVars.euiTextColor,
+      strokeWidth: 1,
+    };
+
+    const svgHeight = options.maxSize * 2 + HALF_FONT_SIZE + circleStyle.strokeWidth * 2;
+    const circleCenterX = options.maxSize + circleStyle.strokeWidth;
+    const circleBottomY = svgHeight - circleStyle.strokeWidth;
+
+    function makeMarker(radius: number, formattedValue: string | number) {
+      const circleCenterY = circleBottomY - radius;
+      const circleTopY = circleCenterY - radius;
+      return (
+        <g key={radius}>
+          <line
+            style={{ stroke: euiThemeVars.euiBorderColor }}
+            x1={circleCenterX}
+            y1={circleTopY}
+            x2={circleCenterX * 2.25}
+            y2={circleTopY}
+          />
+          <text
+            style={{ fontSize: FONT_SIZE, fill: euiThemeVars.euiTextColor }}
+            x={circleCenterX * 2.25 + HALF_FONT_SIZE}
+            y={circleTopY + HALF_FONT_SIZE}
+          >
+            {formattedValue}
+          </text>
+          <circle style={circleStyle} cx={circleCenterX} cy={circleCenterY} r={radius} />
+        </g>
+      );
+    }
+
+    function getMarkerRadius(percentage: number) {
+      const delta = options.maxSize - options.minSize;
+      return percentage * delta + options.minSize;
+    }
+
+    function getValue(percentage: number) {
+      // Markers interpolated by area instead of radius to be more consistent with how the human eye+brain perceive shapes
+      // and their visual relevance
+      // This function mirrors output of maplibre expression created from DynamicSizeProperty.getMbSizeExpression
+      const value = Math.pow(percentage * Math.sqrt(fieldMeta!.delta), 2) + fieldMeta!.min;
+      return fieldMeta!.delta > 3 ? Math.round(value) : value;
+    }
+
+    const markers = [];
+
+    if (fieldMeta.delta > 0) {
+      const smallestMarker = makeMarker(options.minSize, this._formatValue(fieldMeta.min));
+      markers.push(smallestMarker);
+
+      const markerDelta = options.maxSize - options.minSize;
+      if (markerDelta > MIN_MARKER_DISTANCE * 3) {
+        markers.push(makeMarker(getMarkerRadius(0.25), this._formatValue(getValue(0.25))));
+        markers.push(makeMarker(getMarkerRadius(0.5), this._formatValue(getValue(0.5))));
+        markers.push(makeMarker(getMarkerRadius(0.75), this._formatValue(getValue(0.75))));
+      } else if (markerDelta > MIN_MARKER_DISTANCE) {
+        markers.push(makeMarker(getMarkerRadius(0.5), this._formatValue(getValue(0.5))));
+      }
+    }
+
+    const largestMarker = makeMarker(options.maxSize, this._formatValue(fieldMeta.max));
+    markers.push(largestMarker);
+
+    return (
+      <svg height={svgHeight} xmlns="http://www.w3.org/2000/svg">
+        {markers}
+      </svg>
+    );
+  }
+
+  render() {
+    return (
+      <div>
+        <EuiFlexGroup gutterSize="xs" justifyContent="spaceBetween">
+          <EuiFlexItem grow={false}>
+            <EuiToolTip
+              position="top"
+              title={this.props.style.getDisplayStyleName()}
+              content={this.state.label}
+            >
+              <EuiText className="eui-textTruncate" size="xs" style={{ maxWidth: '180px' }}>
+                <small>
+                  <strong>{this.state.label}</strong>
+                </small>
+              </EuiText>
+            </EuiToolTip>
+          </EuiFlexItem>
+        </EuiFlexGroup>
+        {this._renderMarkers()}
+      </div>
+    );
+  }
+}