plugin.legend.js

'use strict';

var defaults = require('../core/core.defaults');
var Element = require('../core/core.element');
var helpers = require('../helpers/index');
var layouts = require('../core/core.layouts');

var noop = helpers.noop;

defaults._set('global', {
	legend: {
		display: true,
		position: 'top',
		fullWidth: true,
		reverse: false,
		weight: 1000,

		// a callback that will handle
		onClick: function(e, legendItem) {
			var index = legendItem.datasetIndex;
			var ci = this.chart;
			var meta = ci.getDatasetMeta(index);

			// See controller.isDatasetVisible comment
			meta.hidden = meta.hidden === null ? !ci.data.datasets[index].hidden : null;

			// We hid a dataset ... rerender the chart
			ci.update();
		},

		onHover: null,

		labels: {
			boxWidth: 40,
			padding: 10,
			// Generates labels shown in the legend
			// Valid properties to return:
			// text : text to display
			// fillStyle : fill of coloured box
			// strokeStyle: stroke of coloured box
			// hidden : if this legend item refers to a hidden item
			// lineCap : cap style for line
			// lineDash
			// lineDashOffset :
			// lineJoin :
			// lineWidth :
			generateLabels: function(chart) {
				var data = chart.data;
				return helpers.isArray(data.datasets) ? data.datasets.map(function(dataset, i) {
					return {
						text: dataset.label,
						fillStyle: (!helpers.isArray(dataset.backgroundColor) ? dataset.backgroundColor : dataset.backgroundColor[0]),
						hidden: !chart.isDatasetVisible(i),
						lineCap: dataset.borderCapStyle,
						lineDash: dataset.borderDash,
						lineDashOffset: dataset.borderDashOffset,
						lineJoin: dataset.borderJoinStyle,
						lineWidth: dataset.borderWidth,
						strokeStyle: dataset.borderColor,
						pointStyle: dataset.pointStyle,

						// Below is extra data used for toggling the datasets
						datasetIndex: i
					};
				}, this) : [];
			}
		}
	},

	legendCallback: function(chart) {
		var text = [];
		text.push('<ul class="' + chart.id + '-legend">');
		for (var i = 0; i < chart.data.datasets.length; i++) {
			text.push('<li><span style="background-color:' + chart.data.datasets[i].backgroundColor + '"></span>');
			if (chart.data.datasets[i].label) {
				text.push(chart.data.datasets[i].label);
			}
			text.push('</li>');
		}
		text.push('</ul>');
		return text.join('');
	}
});

/**
 * Helper function to get the box width based on the usePointStyle option
 * @param labelopts {Object} the label options on the legend
 * @param fontSize {Number} the label font size
 * @return {Number} width of the color box area
 */
function getBoxWidth(labelOpts, fontSize) {
	return labelOpts.usePointStyle ?
		fontSize * Math.SQRT2 :
		labelOpts.boxWidth;
}

/**
 * IMPORTANT: this class is exposed publicly as Chart.Legend, backward compatibility required!
 */
var Legend = Element.extend({

	initialize: function(config) {
		helpers.extend(this, config);

		// Contains hit boxes for each dataset (in dataset order)
		this.legendHitBoxes = [];

		// Are we in doughnut mode which has a different data type
		this.doughnutMode = false;
	},

	// These methods are ordered by lifecycle. Utilities then follow.
	// Any function defined here is inherited by all legend types.
	// Any function can be extended by the legend type

	beforeUpdate: noop,
	update: function(maxWidth, maxHeight, margins) {
		var me = this;

		// Update Lifecycle - Probably don't want to ever extend or overwrite this function ;)
		me.beforeUpdate();

		// Absorb the master measurements
		me.maxWidth = maxWidth;
		me.maxHeight = maxHeight;
		me.margins = margins;

		// Dimensions
		me.beforeSetDimensions();
		me.setDimensions();
		me.afterSetDimensions();
		// Labels
		me.beforeBuildLabels();
		me.buildLabels();
		me.afterBuildLabels();

		// Fit
		me.beforeFit();
		me.fit();
		me.afterFit();
		//
		me.afterUpdate();

		return me.minSize;
	},
	afterUpdate: noop,

	//

	beforeSetDimensions: noop,
	setDimensions: function() {
		var me = this;
		// Set the unconstrained dimension before label rotation
		if (me.isHorizontal()) {
			// Reset position before calculating rotation
			me.width = me.maxWidth;
			me.left = 0;
			me.right = me.width;
		} else {
			me.height = me.maxHeight;

			// Reset position before calculating rotation
			me.top = 0;
			me.bottom = me.height;
		}

		// Reset padding
		me.paddingLeft = 0;
		me.paddingTop = 0;
		me.paddingRight = 0;
		me.paddingBottom = 0;

		// Reset minSize
		me.minSize = {
			width: 0,
			height: 0
		};
	},
	afterSetDimensions: noop,

	//

	beforeBuildLabels: noop,
	buildLabels: function() {
		var me = this;
		var labelOpts = me.options.labels || {};
		var legendItems = helpers.callback(labelOpts.generateLabels, [me.chart], me) || [];

		if (labelOpts.filter) {
			legendItems = legendItems.filter(function(item) {
				return labelOpts.filter(item, me.chart.data);
			});
		}

		if (me.options.reverse) {
			legendItems.reverse();
		}

		me.legendItems = legendItems;
	},
	afterBuildLabels: noop,

	//

	beforeFit: noop,
	fit: function() {
		var me = this;
		var opts = me.options;
		var labelOpts = opts.labels;
		var display = opts.display;

		var ctx = me.ctx;

		var globalDefault = defaults.global;
		var valueOrDefault = helpers.valueOrDefault;
		var fontSize = valueOrDefault(labelOpts.fontSize, globalDefault.defaultFontSize);
		var fontStyle = valueOrDefault(labelOpts.fontStyle, globalDefault.defaultFontStyle);
		var fontFamily = valueOrDefault(labelOpts.fontFamily, globalDefault.defaultFontFamily);
		var labelFont = helpers.fontString(fontSize, fontStyle, fontFamily);

		// Reset hit boxes
		var hitboxes = me.legendHitBoxes = [];

		var minSize = me.minSize;
		var isHorizontal = me.isHorizontal();

		if (isHorizontal) {
			minSize.width = me.maxWidth; // fill all the width
			minSize.height = display ? 10 : 0;
		} else {
			minSize.width = display ? 10 : 0;
			minSize.height = me.maxHeight; // fill all the height
		}

		// Increase sizes here
		if (display) {
			ctx.font = labelFont;

			if (isHorizontal) {
				// Labels

				// Width of each line of legend boxes. Labels wrap onto multiple lines when there are too many to fit on one
				var lineWidths = me.lineWidths = [0];
				var totalHeight = me.legendItems.length ? fontSize + (labelOpts.padding) : 0;

				ctx.textAlign = 'left';
				ctx.textBaseline = 'top';

				helpers.each(me.legendItems, function(legendItem, i) {
					var boxWidth = getBoxWidth(labelOpts, fontSize);
					var width = boxWidth + (fontSize / 2) + ctx.measureText(legendItem.text).width;

					if (lineWidths[lineWidths.length - 1] + width + labelOpts.padding >= me.width) {
						totalHeight += fontSize + (labelOpts.padding);
						lineWidths[lineWidths.length] = me.left;
					}

					// Store the hitbox width and height here. Final position will be updated in `draw`
					hitboxes[i] = {
						left: 0,
						top: 0,
						width: width,
						height: fontSize
					};

					lineWidths[lineWidths.length - 1] += width + labelOpts.padding;
				});

				minSize.height += totalHeight;

			} else {
				var vPadding = labelOpts.padding;
				var columnWidths = me.columnWidths = [];
				var totalWidth = labelOpts.padding;
				var currentColWidth = 0;
				var currentColHeight = 0;
				var itemHeight = fontSize + vPadding;

				helpers.each(me.legendItems, function(legendItem, i) {
					var boxWidth = getBoxWidth(labelOpts, fontSize);
					var itemWidth = boxWidth + (fontSize / 2) + ctx.measureText(legendItem.text).width;

					// If too tall, go to new column
					if (currentColHeight + itemHeight > minSize.height) {
						totalWidth += currentColWidth + labelOpts.padding;
						columnWidths.push(currentColWidth); // previous column width

						currentColWidth = 0;
						currentColHeight = 0;
					}

					// Get max width
					currentColWidth = Math.max(currentColWidth, itemWidth);
					currentColHeight += itemHeight;

					// Store the hitbox width and height here. Final position will be updated in `draw`
					hitboxes[i] = {
						left: 0,
						top: 0,
						width: itemWidth,
						height: fontSize
					};
				});

				totalWidth += currentColWidth;
				columnWidths.push(currentColWidth);
				minSize.width += totalWidth;
			}
		}

		me.width = minSize.width;
		me.height = minSize.height;
	},
	afterFit: noop,

	// Shared Methods
	isHorizontal: function() {
		return this.options.position === 'top' || this.options.position === 'bottom';
	},

	// Actually draw the legend on the canvas
	draw: function() {
		var me = this;
		var opts = me.options;
		var labelOpts = opts.labels;
		var globalDefault = defaults.global;
		var lineDefault = globalDefault.elements.line;
		var legendWidth = me.width;
		var lineWidths = me.lineWidths;

		if (opts.display) {
			var ctx = me.ctx;
			var valueOrDefault = helpers.valueOrDefault;
			var fontColor = valueOrDefault(labelOpts.fontColor, globalDefault.defaultFontColor);
			var fontSize = valueOrDefault(labelOpts.fontSize, globalDefault.defaultFontSize);
			var fontStyle = valueOrDefault(labelOpts.fontStyle, globalDefault.defaultFontStyle);
			var fontFamily = valueOrDefault(labelOpts.fontFamily, globalDefault.defaultFontFamily);
			var labelFont = helpers.fontString(fontSize, fontStyle, fontFamily);
			var cursor;

			// Canvas setup
			ctx.textAlign = 'left';
			ctx.textBaseline = 'middle';
			ctx.lineWidth = 0.5;
			ctx.strokeStyle = fontColor; // for strikethrough effect
			ctx.fillStyle = fontColor; // render in correct colour
			ctx.font = labelFont;

			var boxWidth = getBoxWidth(labelOpts, fontSize);
			var hitboxes = me.legendHitBoxes;

			// current position
			var drawLegendBox = function(x, y, legendItem) {
				if (isNaN(boxWidth) || boxWidth <= 0) {
					return;
				}

				// Set the ctx for the box
				ctx.save();

				ctx.fillStyle = valueOrDefault(legendItem.fillStyle, globalDefault.defaultColor);
				ctx.lineCap = valueOrDefault(legendItem.lineCap, lineDefault.borderCapStyle);
				ctx.lineDashOffset = valueOrDefault(legendItem.lineDashOffset, lineDefault.borderDashOffset);
				ctx.lineJoin = valueOrDefault(legendItem.lineJoin, lineDefault.borderJoinStyle);
				ctx.lineWidth = valueOrDefault(legendItem.lineWidth, lineDefault.borderWidth);
				ctx.strokeStyle = valueOrDefault(legendItem.strokeStyle, globalDefault.defaultColor);
				var isLineWidthZero = (valueOrDefault(legendItem.lineWidth, lineDefault.borderWidth) === 0);

				if (ctx.setLineDash) {
					// IE 9 and 10 do not support line dash
					ctx.setLineDash(valueOrDefault(legendItem.lineDash, lineDefault.borderDash));
				}

				if (opts.labels && opts.labels.usePointStyle) {
					// Recalculate x and y for drawPoint() because its expecting
					// x and y to be center of figure (instead of top left)
					var radius = fontSize * Math.SQRT2 / 2;
					var offSet = radius / Math.SQRT2;
					var centerX = x + offSet;
					var centerY = y + offSet;

					// Draw pointStyle as legend symbol
					helpers.canvas.drawPoint(ctx, legendItem.pointStyle, radius, centerX, centerY);
				} else {
					// Draw box as legend symbol
					if (!isLineWidthZero) {
						ctx.strokeRect(x, y, boxWidth, fontSize);
					}
					ctx.fillRect(x, y, boxWidth, fontSize);
				}

				ctx.restore();
			};
			var fillText = function(x, y, legendItem, textWidth) {
				var halfFontSize = fontSize / 2;
				var xLeft = boxWidth + halfFontSize + x;
				var yMiddle = y + halfFontSize;

				ctx.fillText(legendItem.text, xLeft, yMiddle);

				if (legendItem.hidden) {
					// Strikethrough the text if hidden
					ctx.beginPath();
					ctx.lineWidth = 2;
					ctx.moveTo(xLeft, yMiddle);
					ctx.lineTo(xLeft + textWidth, yMiddle);
					ctx.stroke();
				}
			};

			// Horizontal
			var isHorizontal = me.isHorizontal();
			if (isHorizontal) {
				cursor = {
					x: me.left + ((legendWidth - lineWidths[0]) / 2),
					y: me.top + labelOpts.padding,
					line: 0
				};
			} else {
				cursor = {
					x: me.left + labelOpts.padding,
					y: me.top + labelOpts.padding,
					line: 0
				};
			}

			var itemHeight = fontSize + labelOpts.padding;
			helpers.each(me.legendItems, function(legendItem, i) {
				var textWidth = ctx.measureText(legendItem.text).width;
				var width = boxWidth + (fontSize / 2) + textWidth;
				var x = cursor.x;
				var y = cursor.y;

				if (isHorizontal) {
					if (x + width >= legendWidth) {
						y = cursor.y += itemHeight;
						cursor.line++;
						x = cursor.x = me.left + ((legendWidth - lineWidths[cursor.line]) / 2);
					}
				} else if (y + itemHeight > me.bottom) {
					x = cursor.x = x + me.columnWidths[cursor.line] + labelOpts.padding;
					y = cursor.y = me.top + labelOpts.padding;
					cursor.line++;
				}

				drawLegendBox(x, y, legendItem);

				hitboxes[i].left = x;
				hitboxes[i].top = y;

				// Fill the actual label
				fillText(x, y, legendItem, textWidth);

				if (isHorizontal) {
					cursor.x += width + (labelOpts.padding);
				} else {
					cursor.y += itemHeight;
				}

			});
		}
	},

	/**
	 * Handle an event
	 * @private
	 * @param {IEvent} event - The event to handle
	 * @return {Boolean} true if a change occured
	 */
	handleEvent: function(e) {
		var me = this;
		var opts = me.options;
		var type = e.type === 'mouseup' ? 'click' : e.type;
		var changed = false;

		if (type === 'mousemove') {
			if (!opts.onHover) {
				return;
			}
		} else if (type === 'click') {
			if (!opts.onClick) {
				return;
			}
		} else {
			return;
		}

		// Chart event already has relative position in it
		var x = e.x;
		var y = e.y;

		if (x >= me.left && x <= me.right && y >= me.top && y <= me.bottom) {
			// See if we are touching one of the dataset boxes
			var lh = me.legendHitBoxes;
			for (var i = 0; i < lh.length; ++i) {
				var hitBox = lh[i];

				if (x >= hitBox.left && x <= hitBox.left + hitBox.width && y >= hitBox.top && y <= hitBox.top + hitBox.height) {
					// Touching an element
					if (type === 'click') {
						// use e.native for backwards compatibility
						opts.onClick.call(me, e.native, me.legendItems[i]);
						changed = true;
						break;
					} else if (type === 'mousemove') {
						// use e.native for backwards compatibility
						opts.onHover.call(me, e.native, me.legendItems[i]);
						changed = true;
						break;
					}
				}
			}
		}

		return changed;
	}
});

function createNewLegendAndAttach(chart, legendOpts) {
	var legend = new Legend({
		ctx: chart.ctx,
		options: legendOpts,
		chart: chart
	});

	layouts.configure(chart, legend, legendOpts);
	layouts.addBox(chart, legend);
	chart.legend = legend;
}

module.exports = {
	id: 'legend',

	/**
	 * Backward compatibility: since 2.1.5, the legend is registered as a plugin, making
	 * Chart.Legend obsolete. To avoid a breaking change, we export the Legend as part of
	 * the plugin, which one will be re-exposed in the chart.js file.
	 * https://github.com/chartjs/Chart.js/pull/2640
	 * @private
	 */
	_element: Legend,

	beforeInit: function(chart) {
		var legendOpts = chart.options.legend;

		if (legendOpts) {
			createNewLegendAndAttach(chart, legendOpts);
		}
	},

	beforeUpdate: function(chart) {
		var legendOpts = chart.options.legend;
		var legend = chart.legend;

		if (legendOpts) {
			helpers.mergeIf(legendOpts, defaults.global.legend);

			if (legend) {
				layouts.configure(chart, legend, legendOpts);
				legend.options = legendOpts;
			} else {
				createNewLegendAndAttach(chart, legendOpts);
			}
		} else if (legend) {
			layouts.removeBox(chart, legend);
			delete chart.legend;
		}
	},

	afterEvent: function(chart, e) {
		var legend = chart.legend;
		if (legend) {
			legend.handleEvent(e);
		}
	}
};