'use strict';

module.exports = function(Chart) {

	// Default config for a category scale
	var defaultConfig = {
		position: 'bottom'
	};

	var DatasetScale = Chart.Scale.extend({
		/**
		* Internal function to get the correct labels. If data.xLabels or data.yLabels are defined, use those
		* else fall back to data.labels
		* @private
		*/
		getLabels: function() {
			var data = this.chart.data;
			return this.options.labels || (this.isHorizontal() ? data.xLabels : data.yLabels) || data.labels;
		},

		determineDataLimits: function() {
			var me = this;
			var labels = me.getLabels();
			me.minIndex = 0;
			me.maxIndex = labels.length - 1;
			var findIndex;

			if (me.options.ticks.min !== undefined) {
				// user specified min value
				findIndex = labels.indexOf(me.options.ticks.min);
				me.minIndex = findIndex !== -1 ? findIndex : me.minIndex;
			}

			if (me.options.ticks.max !== undefined) {
				// user specified max value
				findIndex = labels.indexOf(me.options.ticks.max);
				me.maxIndex = findIndex !== -1 ? findIndex : me.maxIndex;
			}

			me.min = labels[me.minIndex];
			me.max = labels[me.maxIndex];
		},

		buildTicks: function() {
			var me = this;
			var labels = me.getLabels();
			// If we are viewing some subset of labels, slice the original array
			me.ticks = (me.minIndex === 0 && me.maxIndex === labels.length - 1) ? labels : labels.slice(me.minIndex, me.maxIndex + 1);
		},

		getLabelForIndex: function(index, datasetIndex) {
			var me = this;
			var data = me.chart.data;
			var isHorizontal = me.isHorizontal();

			if (data.yLabels && !isHorizontal) {
				return me.getRightValue(data.datasets[datasetIndex].data[index]);
			}
			return me.ticks[index - me.minIndex];
		},

		// Used to get data value locations.  Value can either be an index or a numerical value
		getPixelForValue: function(value, index, datasetIndex, includeOffset) {
			var me = this;
			// 1 is added because we need the length but we have the indexes
			var offsetAmt = Math.max((me.maxIndex + 1 - me.minIndex - ((me.options.gridLines.offsetGridLines) ? 0 : 1)), 1);

			// If value is a data object, then index is the index in the data array,
			// not the index of the scale. We need to change that.
			var valueCategory;
			if (value !== undefined && value !== null) {
				valueCategory = me.isHorizontal() ? value.x : value.y;
			}
			if (valueCategory !== undefined || (value !== undefined && isNaN(index))) {
				var labels = me.getLabels();
				value = valueCategory || value;
				var idx = labels.indexOf(value);
				index = idx !== -1 ? idx : index;
			}

			if (me.isHorizontal()) {
				var valueWidth = me.width / offsetAmt;
				var widthOffset = (valueWidth * (index - me.minIndex));

				if (me.options.gridLines.offsetGridLines && includeOffset || me.maxIndex === me.minIndex && includeOffset) {
					widthOffset += (valueWidth / 2);
				}

				return me.left + Math.round(widthOffset);
			}
			var valueHeight = me.height / offsetAmt;
			var heightOffset = (valueHeight * (index - me.minIndex));

			if (me.options.gridLines.offsetGridLines && includeOffset) {
				heightOffset += (valueHeight / 2);
			}

			return me.top + Math.round(heightOffset);
		},
		getPixelForTick: function(index, includeOffset) {
			return this.getPixelForValue(this.ticks[index], index + this.minIndex, null, includeOffset);
		},
		getValueForPixel: function(pixel) {
			var me = this;
			var value;
			var offsetAmt = Math.max((me.ticks.length - ((me.options.gridLines.offsetGridLines) ? 0 : 1)), 1);
			var horz = me.isHorizontal();
			var valueDimension = (horz ? me.width : me.height) / offsetAmt;

			pixel -= horz ? me.left : me.top;

			if (me.options.gridLines.offsetGridLines) {
				pixel -= (valueDimension / 2);
			}

			if (pixel <= 0) {
				value = 0;
			} else {
				value = Math.round(pixel / valueDimension);
			}

			return value;
		},
		getBasePixel: function() {
			return this.bottom;
		}
	});

	Chart.scaleService.registerScaleType('category', DatasetScale, defaultConfig);

};