'use strict';

module.exports = function(Chart) {
	/**
	 * Plugin based on discussion from the following Chart.js issues:
	 * @see https://github.com/chartjs/Chart.js/issues/2380#issuecomment-279961569
	 * @see https://github.com/chartjs/Chart.js/issues/2440#issuecomment-256461897
	 */
	Chart.defaults.global.plugins.filler = {
		propagate: true
	};

	var defaults = Chart.defaults;
	var helpers = Chart.helpers;
	var mappers = {
		dataset: function(source) {
			var index = source.fill;
			var chart = source.chart;
			var meta = chart.getDatasetMeta(index);
			var visible = meta && chart.isDatasetVisible(index);
			var points = (visible && meta.dataset._children) || [];

			return !points.length? null : function(point, i) {
				return points[i]._view || null;
			};
		},

		boundary: function(source) {
			var boundary = source.boundary;
			var x = boundary? boundary.x : null;
			var y = boundary? boundary.y : null;

			return function(point) {
				return {
					x: x === null? point.x : x,
					y: y === null? point.y : y,
				};
			};
		}
	};

	// @todo if (fill[0] === '#')
	function decodeFill(el, index, count) {
		var model = el._model || {};
		var fill = model.fill;
		var target;

		if (fill === undefined) {
			fill = !!model.backgroundColor;
		}

		if (fill === false || fill === null) {
			return false;
		}

		if (fill === true) {
			return 'origin';
		}

		target = parseFloat(fill, 10);
		if (isFinite(target) && Math.floor(target) === target) {
			if (fill[0] === '-' || fill[0] === '+') {
				target = index + target;
			}

			if (target === index || target < 0 || target >= count) {
				return false;
			}

			return target;
		}

		switch (fill) {
		// compatibility
		case 'bottom':
			return 'start';
		case 'top':
			return 'end';
		case 'zero':
			return 'origin';
		// supported boundaries
		case 'origin':
		case 'start':
		case 'end':
			return fill;
		// invalid fill values
		default:
			return false;
		}
	}

	function computeBoundary(source) {
		var model = source.el._model || {};
		var scale = source.el._scale || {};
		var fill = source.fill;
		var target = null;
		var horizontal;

		if (isFinite(fill)) {
			return null;
		}

		// Backward compatibility: until v3, we still need to support boundary values set on
		// the model (scaleTop, scaleBottom and scaleZero) because some external plugins and
		// controllers might still use it (e.g. the Smith chart).

		if (fill === 'start') {
			target = model.scaleBottom === undefined? scale.bottom : model.scaleBottom;
		} else if (fill === 'end') {
			target = model.scaleTop === undefined? scale.top : model.scaleTop;
		} else if (model.scaleZero !== undefined) {
			target = model.scaleZero;
		} else if (scale.getBasePosition) {
			target = scale.getBasePosition();
		} else if (scale.getBasePixel) {
			target = scale.getBasePixel();
		}

		if (target !== undefined && target !== null) {
			if (target.x !== undefined && target.y !== undefined) {
				return target;
			}

			if (typeof target === 'number' && isFinite(target)) {
				horizontal = scale.isHorizontal();
				return {
					x: horizontal? target : null,
					y: horizontal? null : target
				};
			}
		}

		return null;
	}

	function resolveTarget(sources, index, propagate) {
		var source = sources[index];
		var fill = source.fill;
		var visited = [index];
		var target;

		if (!propagate) {
			return fill;
		}

		while (fill !== false && visited.indexOf(fill) === -1) {
			if (!isFinite(fill)) {
				return fill;
			}

			target = sources[fill];
			if (!target) {
				return false;
			}

			if (target.visible) {
				return fill;
			}

			visited.push(fill);
			fill = target.fill;
		}

		return false;
	}

	function createMapper(source) {
		var fill = source.fill;
		var type = 'dataset';

		if (fill === false) {
			return null;
		}

		if (!isFinite(fill)) {
			type = 'boundary';
		}

		return mappers[type](source);
	}

	function isDrawable(point) {
		return point && !point.skip;
	}

	function drawArea(ctx, curve0, curve1, len0, len1) {
		var i;

		if (!len0 || !len1) {
			return;
		}

		// building first area curve (normal)
		ctx.moveTo(curve0[0].x, curve0[0].y);
		for (i=1; i<len0; ++i) {
			helpers.canvas.lineTo(ctx, curve0[i-1], curve0[i]);
		}

		// joining the two area curves
		ctx.lineTo(curve1[len1-1].x, curve1[len1-1].y);

		// building opposite area curve (reverse)
		for (i=len1-1; i>0; --i) {
			helpers.canvas.lineTo(ctx, curve1[i], curve1[i-1], true);
		}
	}

	function doFill(ctx, points, mapper, view, color, loop) {
		var count = points.length;
		var span = view.spanGaps;
		var curve0 = [];
		var curve1 = [];
		var len0 = 0;
		var len1 = 0;
		var i, ilen, index, p0, p1, d0, d1;

		ctx.beginPath();

		for (i = 0, ilen = (count + !!loop); i < ilen; ++i) {
			index = i%count;
			p0 = points[index]._view;
			p1 = mapper(p0, index, view);
			d0 = isDrawable(p0);
			d1 = isDrawable(p1);

			if (d0 && d1) {
				len0 = curve0.push(p0);
				len1 = curve1.push(p1);
			} else if (len0 && len1) {
				if (!span) {
					drawArea(ctx, curve0, curve1, len0, len1);
					len0 = len1 = 0;
					curve0 = [];
					curve1 = [];
				} else {
					if (d0) {
						curve0.push(p0);
					}
					if (d1) {
						curve1.push(p1);
					}
				}
			}
		}

		drawArea(ctx, curve0, curve1, len0, len1);

		ctx.closePath();
		ctx.fillStyle = color;
		ctx.fill();
	}

	return {
		id: 'filler',

		afterDatasetsUpdate: function(chart, options) {
			var count = (chart.data.datasets || []).length;
			var propagate = options.propagate;
			var sources = [];
			var meta, i, el, source;

			for (i = 0; i < count; ++i) {
				meta = chart.getDatasetMeta(i);
				el = meta.dataset;
				source = null;

				if (el && el._model && el instanceof Chart.elements.Line) {
					source = {
						visible: chart.isDatasetVisible(i),
						fill: decodeFill(el, i, count),
						chart: chart,
						el: el
					};
				}

				meta.$filler = source;
				sources.push(source);
			}

			for (i=0; i<count; ++i) {
				source = sources[i];
				if (!source) {
					continue;
				}

				source.fill = resolveTarget(sources, i, propagate);
				source.boundary = computeBoundary(source);
				source.mapper = createMapper(source);
			}
		},

		beforeDatasetDraw: function(chart, args) {
			var meta = args.meta.$filler;
			if (!meta) {
				return;
			}

			var el = meta.el;
			var view = el._view;
			var points = el._children || [];
			var mapper = meta.mapper;
			var color = view.backgroundColor || defaults.global.defaultColor;

			if (mapper && color && points.length) {
				doFill(chart.ctx, points, mapper, view, color, el._loop);
			}
		}
	};
};
