import { createElement } from './dom.js';

export function linear(t) {
	return t;
}

export function generateRule(
	a,
	b,
	delta,
	duration,
	ease,
	fn
) {
	var keyframes = '{\n';

	for (var p = 0; p <= 1; p += 16.666 / duration) {
		var t = a + delta * ease(p);
		keyframes += p * 100 + '%{' + fn(t) + '}\n';
	}

	return keyframes + '100% {' + fn(b) + '}\n}';
}

// https://github.com/darkskyapp/string-hash/blob/master/index.js
export function hash(str) {
	var hash = 5381;
	var i = str.length;

	while (i--) hash = ((hash << 5) - hash) ^ str.charCodeAt(i);
	return hash >>> 0;
}

export function wrapTransition(component, node, fn, params, intro, outgroup) {
	var obj = fn(node, params);
	var duration = obj.duration || 300;
	var ease = obj.easing || linear;
	var cssText;

	// TODO share <style> tag between all transitions?
	if (obj.css && !transitionManager.stylesheet) {
		var style = createElement('style');
		document.head.appendChild(style);
		transitionManager.stylesheet = style.sheet;
	}

	if (intro) {
		if (obj.css && obj.delay) {
			cssText = node.style.cssText;
			node.style.cssText += obj.css(0);
		}

		if (obj.tick) obj.tick(0);
	}

	return {
		t: intro ? 0 : 1,
		running: false,
		program: null,
		pending: null,
		run: function(intro, callback) {
			var program = {
				start: window.performance.now() + (obj.delay || 0),
				intro: intro,
				callback: callback
			};

			if (obj.delay) {
				this.pending = program;
			} else {
				this.start(program);
			}

			if (!this.running) {
				this.running = true;
				transitionManager.add(this);
			}
		},
		start: function(program) {
			component.fire(program.intro ? 'intro.start' : 'outro.start', { node: node });

			program.a = this.t;
			program.b = program.intro ? 1 : 0;
			program.delta = program.b - program.a;
			program.duration = duration * Math.abs(program.b - program.a);
			program.end = program.start + program.duration;

			if (obj.css) {
				if (obj.delay) node.style.cssText = cssText;

				program.rule = generateRule(
					program.a,
					program.b,
					program.delta,
					program.duration,
					ease,
					obj.css
				);

				transitionManager.addRule(program.rule, program.name = '__svelte_' + hash(program.rule));

				node.style.animation = (node.style.animation || '')
					.split(', ')
					.filter(function(anim) {
						// when introing, discard old animations if there are any
						return anim && (program.delta < 0 || !/__svelte/.test(anim));
					})
					.concat(program.name + ' ' + program.duration + 'ms linear 1 forwards')
					.join(', ');
			}

			this.program = program;
			this.pending = null;
		},
		update: function(now) {
			var program = this.program;
			if (!program) return;

			var p = now - program.start;
			this.t = program.a + program.delta * ease(p / program.duration);
			if (obj.tick) obj.tick(this.t);
		},
		done: function() {
			var program = this.program;
			this.t = program.b;
			if (obj.tick) obj.tick(this.t);
			if (obj.css) transitionManager.deleteRule(node, program.name);
			program.callback();
			program = null;
			this.running = !!this.pending;
		},
		abort: function() {
			if (obj.tick) obj.tick(1);
			if (obj.css) transitionManager.deleteRule(node, this.program.name);
			this.program = this.pending = null;
			this.running = false;
		}
	};
}

export var transitionManager = {
	running: false,
	transitions: [],
	bound: null,
	stylesheet: null,
	activeRules: {},

	add: function(transition) {
		this.transitions.push(transition);

		if (!this.running) {
			this.running = true;
			requestAnimationFrame(this.bound || (this.bound = this.next.bind(this)));
		}
	},

	addRule: function(rule, name) {
		if (!this.activeRules[name]) {
			this.activeRules[name] = true;
			this.stylesheet.insertRule('@keyframes ' + name + ' ' + rule, this.stylesheet.cssRules.length);
		}
	},

	next: function() {
		this.running = false;

		var now = window.performance.now();
		var i = this.transitions.length;

		while (i--) {
			var transition = this.transitions[i];

			if (transition.program && now >= transition.program.end) {
				transition.done();
			}

			if (transition.pending && now >= transition.pending.start) {
				transition.start(transition.pending);
			}

			if (transition.running) {
				transition.update(now);
				this.running = true;
			} else if (!transition.pending) {
				this.transitions.splice(i, 1);
			}
		}

		if (this.running) {
			requestAnimationFrame(this.bound);
		} else if (this.stylesheet) {
			var i = this.stylesheet.cssRules.length;
			while (i--) this.stylesheet.deleteRule(i);
			this.activeRules = {};
		}
	},

	deleteRule: function(node, name) {
		node.style.animation = node.style.animation
			.split(', ')
			.filter(function(anim) {
				return anim.indexOf(name) === -1;
			})
			.join(', ');
	}
};