(function (factory) {

	if (typeof module === 'object' && module.export) {
		module.export = factory()
	} else if (typeof define === 'function' && (define.amd || define.cmd)) {
		define([], factory)
	} else if (typeof window !== 'undefined') {
		window.IndexSidebar = factory()
	}

})(function () {

var defaultOptions = {
	chars: '*ABCDEFGHIJKLMNOPQRSTUVWXYZ#',
	isAdjust: true,
	offsetTop: 70,
	offsetBottom: 10,
	lineScale: 0.7,
	charOffsetX: 80,
	charOffsetY: 20
}

function IndexSidebar(options) {
	options = options || {}

	for (var k in defaultOptions) {
		if (defaultOptions.hasOwnProperty(k)) {
			options[k] = options[k] || defaultOptions[k]
		}
	}

	this.options = options
	this.initialize(options)
}

IndexSidebar.prototype.initialize = function (options) {

	var chars = options.chars
	var el =  document.createElement('div')
	el.className = 'index-sidebar-container'
	el.innerHTML = this.render(chars)
	document.body.appendChild(el)

	this.el = el
	this.elChar = el.querySelector('.current-char')
	this.chars = chars
	if (options.isAdjust) {
		this.adjust(options)
	}
	this.initEvents(options)
}

IndexSidebar.prototype.render = function (chars) {
	return (
		'<span class="current-char"></span>' +
		'<ul>' +
			[].map.call(chars, function (ch) {
				return '<li>' + ch + '</li>'
			}).join('') +
		'</ul>'
	)
}

IndexSidebar.prototype.initEvents = function (options) {
	var view = this
	var el = this.el
	var elChar = this.elChar
	var chars = this.chars

	var boxRect = el.getBoundingClientRect()
	var boxHeight = boxRect.height
	var boxClientTop = boxRect.top

	var charOffsetX = options.charOffsetX
	var charOffsetY = options.charOffsetY

	var touching = false
	var lastChar

	// touch events
	if ('ontouchstart' in document) {
		el.addEventListener('touchstart', function (e) {
			if (!touching) {
				e.preventDefault()
				var t = e.touches[0]
				start(t.clientX, t.clientY)
			}
		}, false)
		document.addEventListener('touchmove', function handler(e) {
			if (touching) {
				if (e.cancelable) {
			        // 判断默认行为是否已经被禁用
			        if (!e.defaultPrevented) {
			            e.preventDefault();
			        }
			    }
				var t = e.touches[0]
				move(t.clientX, t.clientY)
			}
		}, false)
		document.addEventListener('touchend', function (e) {
			if (touching) {
				e.preventDefault()
				end()
			}
		}, false)
	}
	// mouse events
	else {
		el.addEventListener('mousedown', function (e) {
			if (!touching) {
				e.preventDefault()
				start(e.clientX, e.clientY)
			}
		})
		document.addEventListener('mousemove', function (e) {
			if (touching) {
				e.preventDefault()
				move(e.clientX, e.clientY)
			}
		})
		document.addEventListener('mouseup', function (e) {
			if (touching) {
				e.preventDefault()
				end()
			}
		})
	}

	function start(clientX, clientY) {
		touching = true
		elChar.style.display = 'block'
		move(clientX, clientY)
	}

	function move(clientX, clientY) {
		var offset = calcRelativePosition(clientY)
		var percent = offset / boxHeight
		var ch = getPositionChar(percent)

		updateChar(clientX, clientY, ch)
	}

	function end() {
		touching = false
		elChar.style.display = 'none'
	}

	function updateChar(clientX, clientY, ch) {
		var x = Math.max(clientX, charOffsetX)
		var yMin = boxClientTop
		var yMax = window.innerHeight - charOffsetY
		var y = Math.min(Math.max(clientY, yMin), yMax)

		elChar.textContent = ch
		elChar.style.left = x + 'px'
		elChar.style.top = y + 'px'

		if (ch && lastChar !== ch) {
			lastChar = ch
			view.trigger('charChange', ch)
		}
	}

	function calcRelativePosition(clientY) {
		var y = clientY - boxClientTop
		if (y < 0) {
			y = 0
		} else if (y > boxHeight) {
			y = boxHeight
		}
		return y
	}

	// yPercent {Number} in range of [0, 1]
	function getPositionChar(yPercent) {
		var min = 1
		var max = chars.length
		var index = Math.ceil(yPercent * max)
		if (index < min) {
			index = min
		} else if (index > max) {
			index = max
		}
		return chars[index - 1]
	}
}

IndexSidebar.prototype.adjust = function (options) {
	var charCount = options.chars.length

	var expectHeight = window.innerHeight - options.offsetTop - options.offsetBottom
	var expectLineHeight = expectHeight / charCount
	var expectFontSize = expectLineHeight * options.lineScale

	var style = this.el.querySelector('ul').style
	style.lineHeight = expectLineHeight + 'px'
	style.fontSize = expectFontSize + 'px'
}

/* Event Emitter API */

IndexSidebar.prototype.trigger = function (event, data) {
	var listeners = this._listeners && this._listeners[event]
	if (listeners) {
		listeners.forEach(function (listener) {
			listener(data)
		})
	}
}

IndexSidebar.prototype.on = function (event, callback) {
	this._listeners = this._listeners || {}
	var listeners = this._listeners[event] || (this._listeners[event] = [])
	listeners.push(callback)
}

IndexSidebar.prototype.off = function (event, callback) {
	var listeners = this._listeners && this._listeners[event]
	if (listeners) {
		var i = listeners.indexOf(callback)
		if (i > -1) {
			listeners.splice(i, 1)
			if (listeners.length === 0) {
				this._listeners[event] = null
			}
		}
	}
}

return IndexSidebar

})