datahub/wherehows-web/app/components/visualization/charts/horizontal-bar-chart.ts

import Component from '@ember/component';
import { IChartDatum } from 'wherehows-web/typings/app/visualization/charts';
import { computed, get, set } from '@ember/object';
import ComputedProperty from '@ember/object/computed';

interface IBarSeriesDatum extends IChartDatum {
  yOffset: number;
  barLength: number;
  labelOffset: number;
}

/**
 * This custom component exists outside of highcharts as the library does not provide the amount
 * of capabilities we need to match up with our design vision for horizontal bar charts. As such,
 * there are similarities between this component and a highcharts component but it has been
 * tailor-fit to our needs
 */
export default class HorizontalBarChart extends Component {
  /**
   * Represents the series of data needed to power our chart. Format is
   * [ { name: string, value: number } ].
   * Since this chart is only meant to handle a single series of data where each bar is connected
   * to one value with one label, we don't have to worry about the idea of an "x axis * y axis"
   * @type {Array<IChartDatum>}
   */
  series: Array<IChartDatum>;

  /**
   * Helps to set the size of the svg element rendered by the component
   * @type {number}
   */
  size: number = 0;

  /**
   * Sets the tag for the rendered html elemenet for the component
   * @type {string}
   */
  tagName = 'figure';

  /**
   * Sets the classes for the rendered html element for the component
   * @type {Array<string>}
   */
  classNames = ['vz-chart', 'viz-bar-chart', 'single-series'];

  /**
   * Constant properties to be used in calculations for the size of the svg elements drawn
   */
  BAR_HEIGHT = 16;
  BAR_MARGIN_BOTTOM = 8;
  LABEL_HEIGHT = 15;
  LABEL_MARGIN_BOTTOM = 16;

  /**
   * Overall width of our chart. If we have a size, that means that the component and available space
   * has been measured.
   * @type {ComputedProperty<number>}
   */
  width: ComputedProperty<number> = computed('size', function(this: HorizontalBarChart) {
    return get(this, 'size') ? this.$(this.element).width() : 0;
  });

  /**
   * Overall height of our chart, calculated based on the amount of items we have in our series
   * @type {ComputedProperty<number>}
   */
  height: ComputedProperty<number> = computed('categories', function(this: HorizontalBarChart) {
    return (get(this, 'series') || []).length * this.heightModifier();
  });

  /**
   * Calculates information needed for the svg element to properly render each bar of our graph using the
   * correct dimensions relative to the data it's receiving
   * @type {ComputedProperty<IBarSeriesDatum[]}
   */
  seriesData: ComputedProperty<Array<IBarSeriesDatum>> = computed('series', 'size', function(this: HorizontalBarChart) {
    return (this.get('series') || []).map(this.bar.bind(this));
  });

  /**
   * Sets our highest value for the chart's Y axis, based on the highest value inside the series
   * @type {ComputedProperty<number>}
   */
  maxY: ComputedProperty<number> = computed('series', function(this: HorizontalBarChart) {
    return (get(this, 'series') || []).reduce((memo, dataPoint) => {
      if (dataPoint.value > memo) {
        return dataPoint.value;
      }
      return memo;
    }, Number.MIN_VALUE);
  });

  /**
   * Returns a "modifier" that is the height of a single bar and label in the chart, and can be multiplied
   * by the number of rows in the chart to get the total chart height
   * @param this - explicit this keyword declaration for typescript
   */
  heightModifier(this: HorizontalBarChart): number {
    return (
      get(this, 'BAR_HEIGHT') +
      get(this, 'BAR_MARGIN_BOTTOM') +
      get(this, 'LABEL_HEIGHT') +
      get(this, 'LABEL_MARGIN_BOTTOM')
    );
  }

  /**
   * Used as a predicate function in the mapping function for the series array to be mapped into the
   * seriesData array, this function adds values to each chart datum object so that the svg template
   * can render each bar with the correct dimensions and position
   * @param this - explicit this keyword declaration for typescript
   * @param data - single datum object in our series
   * @param index - current index in the series array
   */
  bar(this: HorizontalBarChart, data: IChartDatum, index: number) {
    const yOffset = 1 + index * this.heightModifier();

    return {
      ...data,
      yOffset,
      barLength: Math.max(1, Math.floor(data.value / get(this, 'maxY') * get(this, 'width'))),
      labelOffset: yOffset + get(this, 'BAR_HEIGHT') + get(this, 'BAR_MARGIN_BOTTOM') + get(this, 'LABEL_HEIGHT')
    };
  }

  /**
   * Once we have inserted our html element, we can determine the width (size) of our chart
   */
  didInsertElement() {
    this._super(...arguments);
    set(this, 'size', this.$(this.element).width() || 0);
  }
}