core.datasetController.js

import Animations from './core.animations';
import defaults from './core.defaults';
import {isObject, merge, _merger, isArray, valueOrDefault, mergeIf, resolveObjectKey, _capitalize} from '../helpers/helpers.core';
import {listenArrayEvents, unlistenArrayEvents} from '../helpers/helpers.collection';
import {resolve} from '../helpers/helpers.options';
import {getHoverColor} from '../helpers/helpers.color';
import {sign} from '../helpers/helpers.math';

/**
 * @typedef { import("./core.controller").default } Chart
 * @typedef { import("./core.scale").default } Scale
 */

function scaleClip(scale, allowedOverflow) {
	const opts = scale && scale.options || {};
	const reverse = opts.reverse;
	const min = opts.min === undefined ? allowedOverflow : 0;
	const max = opts.max === undefined ? allowedOverflow : 0;
	return {
		start: reverse ? max : min,
		end: reverse ? min : max
	};
}

function defaultClip(xScale, yScale, allowedOverflow) {
	if (allowedOverflow === false) {
		return false;
	}
	const x = scaleClip(xScale, allowedOverflow);
	const y = scaleClip(yScale, allowedOverflow);

	return {
		top: y.end,
		right: x.end,
		bottom: y.start,
		left: x.start
	};
}

function toClip(value) {
	let t, r, b, l;

	if (isObject(value)) {
		t = value.top;
		r = value.right;
		b = value.bottom;
		l = value.left;
	} else {
		t = r = b = l = value;
	}

	return {
		top: t,
		right: r,
		bottom: b,
		left: l
	};
}

function getSortedDatasetIndices(chart, filterVisible) {
	const keys = [];
	const metasets = chart._getSortedDatasetMetas(filterVisible);
	let i, ilen;

	for (i = 0, ilen = metasets.length; i < ilen; ++i) {
		keys.push(metasets[i].index);
	}
	return keys;
}

function applyStack(stack, value, dsIndex, allOther) {
	const keys = stack.keys;
	let i, ilen, datasetIndex, otherValue;

	for (i = 0, ilen = keys.length; i < ilen; ++i) {
		datasetIndex = +keys[i];
		if (datasetIndex === dsIndex) {
			if (allOther) {
				continue;
			}
			break;
		}
		otherValue = stack.values[datasetIndex];
		if (!isNaN(otherValue) && (value === 0 || sign(value) === sign(otherValue))) {
			value += otherValue;
		}
	}
	return value;
}

function convertObjectDataToArray(data) {
	const keys = Object.keys(data);
	const adata = new Array(keys.length);
	let i, ilen, key;
	for (i = 0, ilen = keys.length; i < ilen; ++i) {
		key = keys[i];
		adata[i] = {
			x: key,
			y: data[key]
		};
	}
	return adata;
}

function isStacked(scale, meta) {
	const stacked = scale && scale.options.stacked;
	return stacked || (stacked === undefined && meta.stack !== undefined);
}

function getStackKey(indexScale, valueScale, meta) {
	return indexScale.id + '.' + valueScale.id + '.' + meta.stack + '.' + meta.type;
}

function getUserBounds(scale) {
	const {min, max, minDefined, maxDefined} = scale.getUserBounds();
	return {
		min: minDefined ? min : Number.NEGATIVE_INFINITY,
		max: maxDefined ? max : Number.POSITIVE_INFINITY
	};
}

function getOrCreateStack(stacks, stackKey, indexValue) {
	const subStack = stacks[stackKey] || (stacks[stackKey] = {});
	return subStack[indexValue] || (subStack[indexValue] = {});
}

function updateStacks(controller, parsed) {
	const {chart, _cachedMeta: meta} = controller;
	const stacks = chart._stacks || (chart._stacks = {}); // map structure is {stackKey: {datasetIndex: value}}
	const {iScale, vScale, index: datasetIndex} = meta;
	const iAxis = iScale.axis;
	const vAxis = vScale.axis;
	const key = getStackKey(iScale, vScale, meta);
	const ilen = parsed.length;
	let stack;

	for (let i = 0; i < ilen; ++i) {
		const item = parsed[i];
		const {[iAxis]: index, [vAxis]: value} = item;
		const itemStacks = item._stacks || (item._stacks = {});
		stack = itemStacks[vAxis] = getOrCreateStack(stacks, key, index);
		stack[datasetIndex] = value;
	}
}

function getFirstScaleId(chart, axis) {
	const scales = chart.scales;
	return Object.keys(scales).filter(key => scales[key].axis === axis).shift();
}

function createDatasetContext(parent, index, dataset) {
	return Object.create(parent, {
		active: {
			writable: true,
			value: false
		},
		dataset: {
			value: dataset
		},
		datasetIndex: {
			value: index
		},
		index: {
			get() {
				return this.datasetIndex;
			}
		}
	});
}

function createDataContext(parent, index, point, element) {
	return Object.create(parent, {
		active: {
			writable: true,
			value: false
		},
		dataIndex: {
			value: index
		},
		dataPoint: {
			value: point
		},
		element: {
			value: element
		},
		index: {
			get() {
				return this.dataIndex;
			}
		}
	});
}

const optionKeys = (optionNames) => isArray(optionNames) ? optionNames : Object.keys(optionNames);
const optionKey = (key, active) => active ? 'hover' + _capitalize(key) : key;
const isDirectUpdateMode = (mode) => mode === 'reset' || mode === 'none';
const cloneIfNotShared = (cached, shared) => shared ? cached : Object.assign({}, cached);
const freezeIfShared = (values, shared) => shared ? Object.freeze(values) : values;

export default class DatasetController {

	/**
	 * @param {Chart} chart
	 * @param {number} datasetIndex
	 */
	constructor(chart, datasetIndex) {
		this.chart = chart;
		this._ctx = chart.ctx;
		this.index = datasetIndex;
		this._cachedAnimations = {};
		this._cachedDataOpts = {};
		this._cachedMeta = this.getMeta();
		this._type = this._cachedMeta.type;
		this._config = undefined;
		/** @type {boolean | object} */
		this._parsing = false;
		this._data = undefined;
		this._objectData = undefined;
		this._sharedOptions = undefined;
		this._drawStart = undefined;
		this._drawCount = undefined;
		this.enableOptionSharing = false;
		this.$context = undefined;

		this.initialize();
	}

	initialize() {
		const me = this;
		const meta = me._cachedMeta;
		me.configure();
		me.linkScales();
		meta._stacked = isStacked(meta.vScale, meta);
		me.addElements();
	}

	updateIndex(datasetIndex) {
		this.index = datasetIndex;
	}

	linkScales() {
		const me = this;
		const chart = me.chart;
		const meta = me._cachedMeta;
		const dataset = me.getDataset();

		const chooseId = (axis, x, y, r) => axis === 'x' ? x : axis === 'r' ? r : y;

		const xid = meta.xAxisID = valueOrDefault(dataset.xAxisID, getFirstScaleId(chart, 'x'));
		const yid = meta.yAxisID = valueOrDefault(dataset.yAxisID, getFirstScaleId(chart, 'y'));
		const rid = meta.rAxisID = valueOrDefault(dataset.rAxisID, getFirstScaleId(chart, 'r'));
		const indexAxis = meta.indexAxis;
		const iid = meta.iAxisID = chooseId(indexAxis, xid, yid, rid);
		const vid = meta.vAxisID = chooseId(indexAxis, yid, xid, rid);
		meta.xScale = me.getScaleForId(xid);
		meta.yScale = me.getScaleForId(yid);
		meta.rScale = me.getScaleForId(rid);
		meta.iScale = me.getScaleForId(iid);
		meta.vScale = me.getScaleForId(vid);
	}

	getDataset() {
		return this.chart.data.datasets[this.index];
	}

	getMeta() {
		return this.chart.getDatasetMeta(this.index);
	}

	/**
	 * @param {string} scaleID
	 * @return {Scale}
	 */
	getScaleForId(scaleID) {
		return this.chart.scales[scaleID];
	}

	/**
	 * @private
	 */
	_getOtherScale(scale) {
		const meta = this._cachedMeta;
		return scale === meta.iScale
			? meta.vScale
			: meta.iScale;
	}

	reset() {
		this._update('reset');
	}

	/**
	 * @private
	 */
	_destroy() {
		if (this._data) {
			unlistenArrayEvents(this._data, this);
		}
	}

	/**
	 * @private
	 */
	_dataCheck() {
		const me = this;
		const dataset = me.getDataset();
		const data = dataset.data || (dataset.data = []);

		// In order to correctly handle data addition/deletion animation (an thus simulate
		// real-time charts), we need to monitor these data modifications and synchronize
		// the internal meta data accordingly.

		if (isObject(data)) {
			me._data = convertObjectDataToArray(data);
		} else if (me._data !== data) {
			if (me._data) {
				// This case happens when the user replaced the data array instance.
				unlistenArrayEvents(me._data, me);
			}
			if (data && Object.isExtensible(data)) {
				listenArrayEvents(data, me);
			}
			me._data = data;
		}
	}

	addElements() {
		const me = this;
		const meta = me._cachedMeta;

		me._dataCheck();

		const data = me._data;
		const metaData = meta.data = new Array(data.length);

		for (let i = 0, ilen = data.length; i < ilen; ++i) {
			metaData[i] = new me.dataElementType();
		}

		if (me.datasetElementType) {
			meta.dataset = new me.datasetElementType();
		}
	}

	buildOrUpdateElements() {
		const me = this;
		const meta = me._cachedMeta;
		const dataset = me.getDataset();
		let stackChanged = false;

		me._dataCheck();

		// make sure cached _stacked status is current
		meta._stacked = isStacked(meta.vScale, meta);

		// detect change in stack option
		if (meta.stack !== dataset.stack) {
			stackChanged = true;
			// remove values from old stack
			meta._parsed.forEach((parsed) => {
				delete parsed._stacks[meta.vScale.id][meta.index];
			});
			meta.stack = dataset.stack;
		}

		// Re-sync meta data in case the user replaced the data array or if we missed
		// any updates and so make sure that we handle number of datapoints changing.
		me._resyncElements();

		// if stack changed, update stack values for the whole dataset
		if (stackChanged) {
			updateStacks(me, meta._parsed);
		}
	}

	/**
	 * Merges user-supplied and default dataset-level options
	 * @private
	 */
	configure() {
		const me = this;
		me._config = merge(Object.create(null), [
			defaults.controllers[me._type].datasets,
			me.chart.options[me._type]?.datasets,
			me.getDataset(),
		], {
			merger(key, target, source) {
				if (key !== 'data') {
					_merger(key, target, source);
				}
			}
		});
		me._parsing = resolve([me._config.parsing, me.chart.options.parsing, true]);
	}

	/**
	 * @param {number} start
	 * @param {number} count
	 */
	parse(start, count) {
		const me = this;
		const {_cachedMeta: meta, _data: data} = me;
		const {iScale, vScale, _stacked} = meta;
		const iAxis = iScale.axis;
		let sorted = true;
		let i, parsed, cur, prev;

		if (start > 0) {
			sorted = meta._sorted;
			prev = meta._parsed[start - 1];
		}

		if (me._parsing === false) {
			meta._parsed = data;
			meta._sorted = true;
		} else {
			if (isArray(data[start])) {
				parsed = me.parseArrayData(meta, data, start, count);
			} else if (isObject(data[start])) {
				parsed = me.parseObjectData(meta, data, start, count);
			} else {
				parsed = me.parsePrimitiveData(meta, data, start, count);
			}

			const isNotInOrderComparedToPrev = () => isNaN(cur[iAxis]) || (prev && cur[iAxis] < prev[iAxis]);
			for (i = 0; i < count; ++i) {
				meta._parsed[i + start] = cur = parsed[i];
				if (sorted) {
					if (isNotInOrderComparedToPrev()) {
						sorted = false;
					}
					prev = cur;
				}
			}
			meta._sorted = sorted;
		}

		if (_stacked) {
			updateStacks(me, parsed);
		}

		iScale.invalidateCaches();
		vScale.invalidateCaches();
	}

	/**
	 * Parse array of primitive values
	 * @param {object} meta - dataset meta
	 * @param {array} data - data array. Example [1,3,4]
	 * @param {number} start - start index
	 * @param {number} count - number of items to parse
	 * @returns {object} parsed item - item containing index and a parsed value
	 * for each scale id.
	 * Example: {xScale0: 0, yScale0: 1}
	 * @protected
	 */
	parsePrimitiveData(meta, data, start, count) {
		const {iScale, vScale} = meta;
		const iAxis = iScale.axis;
		const vAxis = vScale.axis;
		const labels = iScale.getLabels();
		const singleScale = iScale === vScale;
		const parsed = new Array(count);
		let i, ilen, index;

		for (i = 0, ilen = count; i < ilen; ++i) {
			index = i + start;
			parsed[i] = {
				[iAxis]: singleScale || iScale.parse(labels[index], index),
				[vAxis]: vScale.parse(data[index], index)
			};
		}
		return parsed;
	}

	/**
	 * Parse array of arrays
	 * @param {object} meta - dataset meta
	 * @param {array} data - data array. Example [[1,2],[3,4]]
	 * @param {number} start - start index
	 * @param {number} count - number of items to parse
	 * @returns {object} parsed item - item containing index and a parsed value
	 * for each scale id.
	 * Example: {x: 0, y: 1}
	 * @protected
	 */
	parseArrayData(meta, data, start, count) {
		const {xScale, yScale} = meta;
		const parsed = new Array(count);
		let i, ilen, index, item;

		for (i = 0, ilen = count; i < ilen; ++i) {
			index = i + start;
			item = data[index];
			parsed[i] = {
				x: xScale.parse(item[0], index),
				y: yScale.parse(item[1], index)
			};
		}
		return parsed;
	}

	/**
	 * Parse array of objects
	 * @param {object} meta - dataset meta
	 * @param {array} data - data array. Example [{x:1, y:5}, {x:2, y:10}]
	 * @param {number} start - start index
	 * @param {number} count - number of items to parse
	 * @returns {object} parsed item - item containing index and a parsed value
	 * for each scale id. _custom is optional
	 * Example: {xScale0: 0, yScale0: 1, _custom: {r: 10, foo: 'bar'}}
	 * @protected
	 */
	parseObjectData(meta, data, start, count) {
		const {xScale, yScale} = meta;
		const {xAxisKey = 'x', yAxisKey = 'y'} = this._parsing;
		const parsed = new Array(count);
		let i, ilen, index, item;

		for (i = 0, ilen = count; i < ilen; ++i) {
			index = i + start;
			item = data[index];
			parsed[i] = {
				x: xScale.parse(resolveObjectKey(item, xAxisKey), index),
				y: yScale.parse(resolveObjectKey(item, yAxisKey), index)
			};
		}
		return parsed;
	}

	/**
	 * @protected
	 */
	getParsed(index) {
		return this._cachedMeta._parsed[index];
	}

	/**
	 * @protected
	 */
	getDataElement(index) {
		return this._cachedMeta.data[index];
	}

	/**
	 * @protected
	 */
	applyStack(scale, parsed) {
		const chart = this.chart;
		const meta = this._cachedMeta;
		const value = parsed[scale.axis];
		const stack = {
			keys: getSortedDatasetIndices(chart, true),
			values: parsed._stacks[scale.axis]
		};
		return applyStack(stack, value, meta.index);
	}

	/**
	 * @protected
	 */
	updateRangeFromParsed(range, scale, parsed, stack) {
		let value = parsed[scale.axis];
		const values = stack && parsed._stacks[scale.axis];
		if (stack && values) {
			stack.values = values;
			// Need to consider individual stack values for data range,
			// in addition to the stacked value
			range.min = Math.min(range.min, value);
			range.max = Math.max(range.max, value);
			value = applyStack(stack, value, this._cachedMeta.index, true);
		}
		range.min = Math.min(range.min, value);
		range.max = Math.max(range.max, value);
	}

	/**
	 * @protected
	 */
	getMinMax(scale, canStack) {
		const me = this;
		const meta = me._cachedMeta;
		const _parsed = meta._parsed;
		const sorted = meta._sorted && scale === meta.iScale;
		const ilen = _parsed.length;
		const otherScale = me._getOtherScale(scale);
		const stack = canStack && meta._stacked && {keys: getSortedDatasetIndices(me.chart, true), values: null};
		const range = {min: Number.POSITIVE_INFINITY, max: Number.NEGATIVE_INFINITY};
		const {min: otherMin, max: otherMax} = getUserBounds(otherScale);
		let i, value, parsed, otherValue;

		function _skip() {
			parsed = _parsed[i];
			value = parsed[scale.axis];
			otherValue = parsed[otherScale.axis];
			return (isNaN(value) || isNaN(otherValue) || otherMin > otherValue || otherMax < otherValue);
		}

		for (i = 0; i < ilen; ++i) {
			if (_skip()) {
				continue;
			}
			me.updateRangeFromParsed(range, scale, parsed, stack);
			if (sorted) {
				// if the data is sorted, we don't need to check further from this end of array
				break;
			}
		}
		if (sorted) {
			// in the sorted case, find first non-skipped value from other end of array
			for (i = ilen - 1; i >= 0; --i) {
				if (_skip()) {
					continue;
				}
				me.updateRangeFromParsed(range, scale, parsed, stack);
				break;
			}
		}
		return range;
	}

	getAllParsedValues(scale) {
		const parsed = this._cachedMeta._parsed;
		const values = [];
		let i, ilen, value;

		for (i = 0, ilen = parsed.length; i < ilen; ++i) {
			value = parsed[i][scale.axis];
			if (!isNaN(value)) {
				values.push(value);
			}
		}
		return values;
	}

	/**
	 * @return {number|boolean}
	 * @protected
	 */
	getMaxOverflow() {
		return false;
	}

	/**
	 * @protected
	 */
	getLabelAndValue(index) {
		const me = this;
		const meta = me._cachedMeta;
		const iScale = meta.iScale;
		const vScale = meta.vScale;
		const parsed = me.getParsed(index);
		return {
			label: iScale ? '' + iScale.getLabelForValue(parsed[iScale.axis]) : '',
			value: vScale ? '' + vScale.getLabelForValue(parsed[vScale.axis]) : ''
		};
	}

	/**
	 * @private
	 */
	_update(mode) {
		const me = this;
		const meta = me._cachedMeta;
		me.configure();
		me._cachedAnimations = {};
		me._cachedDataOpts = {};
		me.update(mode || 'default');
		meta._clip = toClip(valueOrDefault(me._config.clip, defaultClip(meta.xScale, meta.yScale, me.getMaxOverflow())));
	}

	/**
	 * @param {string} mode
	 */
	update(mode) {} // eslint-disable-line no-unused-vars

	draw() {
		const me = this;
		const ctx = me._ctx;
		const chart = me.chart;
		const meta = me._cachedMeta;
		const elements = meta.data || [];
		const area = chart.chartArea;
		const active = [];
		const start = me._drawStart || 0;
		const count = me._drawCount || (elements.length - start);
		let i;

		if (meta.dataset) {
			meta.dataset.draw(ctx, area, start, count);
		}

		for (i = start; i < start + count; ++i) {
			const element = elements[i];
			if (element.active) {
				active.push(element);
			} else {
				element.draw(ctx, area);
			}
		}

		for (i = 0; i < active.length; ++i) {
			active[i].draw(ctx, area);
		}
	}

	/**
	 * @private
	 */
	_addAutomaticHoverColors(index, options) {
		const me = this;
		const normalOptions = me.getStyle(index);
		const missingColors = Object.keys(normalOptions).filter(key => key.indexOf('Color') !== -1 && !(key in options));
		let i = missingColors.length - 1;
		let color;
		for (; i >= 0; i--) {
			color = missingColors[i];
			options[color] = getHoverColor(normalOptions[color]);
		}
	}

	/**
	 * Returns a set of predefined style properties that should be used to represent the dataset
	 * or the data if the index is specified
	 * @param {number} index - data index
	 * @param {boolean} [active] - true if hover
	 * @return {object} style object
	 */
	getStyle(index, active) {
		const me = this;
		const meta = me._cachedMeta;
		const dataset = meta.dataset;

		if (!me._config) {
			me.configure();
		}

		const options = dataset && index === undefined
			? me.resolveDatasetElementOptions(active)
			: me.resolveDataElementOptions(index || 0, active && 'active');
		if (active) {
			me._addAutomaticHoverColors(index, options);
		}

		return options;
	}

	/**
	 * @protected
	 */
	getContext(index, active) {
		const me = this;
		let context;
		if (index >= 0 && index < me._cachedMeta.data.length) {
			const element = me._cachedMeta.data[index];
			context = element.$context ||
				(element.$context = createDataContext(me.getContext(), index, me.getParsed(index), element));
		} else {
			context = me.$context || (me.$context = createDatasetContext(me.chart.getContext(), me.index, me.getDataset()));
		}

		context.active = !!active;
		return context;
	}

	/**
	 * @param {boolean} [active]
	 * @protected
	 */
	resolveDatasetElementOptions(active) {
		return this._resolveOptions(this.datasetElementOptions, {
			active,
			type: this.datasetElementType.id
		});
	}

	/**
	 * @param {number} index
	 * @param {string} [mode]
	 * @protected
	 */
	resolveDataElementOptions(index, mode) {
		mode = mode || 'default';
		const me = this;
		const active = mode === 'active';
		const cache = me._cachedDataOpts;
		const cached = cache[mode];
		const sharing = me.enableOptionSharing;
		if (cached) {
			return cloneIfNotShared(cached, sharing);
		}
		const info = {cacheable: !active};

		const values = me._resolveOptions(me.dataElementOptions, {
			index,
			active,
			info,
			type: me.dataElementType.id
		});

		if (info.cacheable) {
			// `$shared` indicates this set of options can be shared between multiple elements.
			// Sharing is used to reduce number of properties to change during animation.
			values.$shared = sharing;

			// We cache options by `mode`, which can be 'active' for example. This enables us
			// to have the 'active' element options and 'default' options to switch between
			// when interacting.
			cache[mode] = freezeIfShared(values, sharing);
		}

		return values;
	}

	/**
	 * @private
	 */
	_resolveOptions(optionNames, args) {
		const me = this;
		const {index, active, type, info} = args;
		const datasetOpts = me._config;
		const options = me.chart.options.elements[type] || {};
		const values = {};
		const context = me.getContext(index, active);
		const keys = optionKeys(optionNames);

		for (let i = 0, ilen = keys.length; i < ilen; ++i) {
			const key = keys[i];
			const readKey = optionKey(key, active);
			const value = resolve([
				datasetOpts[optionNames[readKey]],
				datasetOpts[readKey],
				options[readKey]
			], context, index, info);

			if (value !== undefined) {
				values[key] = value;
			}
		}

		return values;
	}

	/**
	 * @private
	 */
	_resolveAnimations(index, mode, active) {
		const me = this;
		const chart = me.chart;
		const cached = me._cachedAnimations;
		mode = mode || 'default';

		if (cached[mode]) {
			return cached[mode];
		}

		const info = {cacheable: true};
		const context = me.getContext(index, active);
		const chartAnim = resolve([chart.options.animation], context, index, info);
		const datasetAnim = resolve([me._config.animation], context, index, info);
		let config = chartAnim && mergeIf({}, [datasetAnim, chartAnim]);

		if (config[mode]) {
			config = Object.assign({}, config, config[mode]);
		}

		const animations = new Animations(chart, config);

		if (info.cacheable) {
			cached[mode] = animations && Object.freeze(animations);
		}

		return animations;
	}

	/**
	 * Utility for getting the options object shared between elements
	 * @protected
	 */
	getSharedOptions(options) {
		if (!options.$shared) {
			return;
		}
		return this._sharedOptions || (this._sharedOptions = Object.assign({}, options));
	}

	/**
	 * Utility for determining if `options` should be included in the updated properties
	 * @protected
	 */
	includeOptions(mode, sharedOptions) {
		return !sharedOptions || isDirectUpdateMode(mode);
	}

	/**
	 * Utility for updating an element with new properties, using animations when appropriate.
	 * @protected
	 */
	updateElement(element, index, properties, mode) {
		if (isDirectUpdateMode(mode)) {
			Object.assign(element, properties);
		} else {
			this._resolveAnimations(index, mode).update(element, properties);
		}
	}

	/**
	 * Utility to animate the shared options, that are potentially affecting multiple elements.
	 * @protected
	 */
	updateSharedOptions(sharedOptions, mode, newOptions) {
		if (sharedOptions) {
			this._resolveAnimations(undefined, mode).update({options: sharedOptions}, {options: newOptions});
		}
	}

	/**
	 * @private
	 */
	_setStyle(element, index, mode, active) {
		element.active = active;
		const options = this.getStyle(index, active);
		this._resolveAnimations(index, mode, active).update(element, {options: this.getSharedOptions(options) || options});
	}

	removeHoverStyle(element, datasetIndex, index) {
		this._setStyle(element, index, 'active', false);
	}

	setHoverStyle(element, datasetIndex, index) {
		this._setStyle(element, index, 'active', true);
	}

	/**
	 * @private
	 */
	_removeDatasetHoverStyle() {
		const element = this._cachedMeta.dataset;

		if (element) {
			this._setStyle(element, undefined, 'active', false);
		}
	}

	/**
	 * @private
	 */
	_setDatasetHoverStyle() {
		const element = this._cachedMeta.dataset;

		if (element) {
			this._setStyle(element, undefined, 'active', true);
		}
	}

	/**
	 * @private
	 */
	_resyncElements() {
		const me = this;
		const meta = me._cachedMeta;
		const numMeta = meta.data.length;
		const numData = me._data.length;

		if (numData > numMeta) {
			me._insertElements(numMeta, numData - numMeta);
		} else if (numData < numMeta) {
			meta.data.splice(numData, numMeta - numData);
			meta._parsed.splice(numData, numMeta - numData);
		}
		// Re-parse the old elements (new elements are parsed in _insertElements)
		me.parse(0, Math.min(numData, numMeta));
	}

	/**
	 * @private
	 */
	_insertElements(start, count) {
		const me = this;
		const elements = new Array(count);
		const meta = me._cachedMeta;
		const data = meta.data;
		let i;

		for (i = 0; i < count; ++i) {
			elements[i] = new me.dataElementType();
		}
		data.splice(start, 0, ...elements);

		if (me._parsing) {
			meta._parsed.splice(start, 0, ...new Array(count));
		}
		me.parse(start, count);

		me.updateElements(data, start, count, 'reset');
	}

	updateElements(element, start, count, mode) {} // eslint-disable-line no-unused-vars

	/**
	 * @private
	 */
	_removeElements(start, count) {
		const me = this;
		if (me._parsing) {
			me._cachedMeta._parsed.splice(start, count);
		}
		me._cachedMeta.data.splice(start, count);
	}


	/**
	 * @private
	 */
	_onDataPush() {
		const count = arguments.length;
		this._insertElements(this.getDataset().data.length - count, count);
	}

	/**
	 * @private
	 */
	_onDataPop() {
		this._removeElements(this._cachedMeta.data.length - 1, 1);
	}

	/**
	 * @private
	 */
	_onDataShift() {
		this._removeElements(0, 1);
	}

	/**
	 * @private
	 */
	_onDataSplice(start, count) {
		this._removeElements(start, count);
		this._insertElements(start, arguments.length - 2);
	}

	/**
	 * @private
	 */
	_onDataUnshift() {
		this._insertElements(0, arguments.length);
	}
}

/**
 * @type {any}
 */
DatasetController.defaults = {};

/**
 * Element type used to generate a meta dataset (e.g. Chart.element.LineElement).
 */
DatasetController.prototype.datasetElementType = null;

/**
 * Element type used to generate a meta data (e.g. Chart.element.PointElement).
 */
DatasetController.prototype.dataElementType = null;

/**
 * Dataset element option keys to be resolved in resolveDatasetElementOptions.
 * A derived controller may override this to resolve controller-specific options.
 * The keys defined here are for backward compatibility for legend styles.
 * @type {string[]}
 */
DatasetController.prototype.datasetElementOptions = [
	'backgroundColor',
	'borderCapStyle',
	'borderColor',
	'borderDash',
	'borderDashOffset',
	'borderJoinStyle',
	'borderWidth'
];

/**
 * Data element option keys to be resolved in resolveDataElementOptions.
 * A derived controller may override this to resolve controller-specific options.
 * The keys defined here are for backward compatibility for legend styles.
 * @type {string[]|object}
 */
DatasetController.prototype.dataElementOptions = [
	'backgroundColor',
	'borderColor',
	'borderWidth',
	'pointStyle'
];