###########################################################
# RapydScript Standard Library
# Author: Alexander Tsepkov
# Copyright 2013 Pyjeon Software LLC
# License: Apache License	2.0
# This library is covered under Apache license, so that
# you can distribute it with your RapydScript applications.
###########################################################

# This class implements a lightweight YQL API for RapydScript
# this query class is based on the logic from the following website:
# http://james.padolsey.com/javascript/using-yql-with-jsonp/
# YQL serves JSONP (with a callback) so all we have to do
# is create a script element with the right 'src':
class YQLError(Error):
	def __init__(self, message):
		self.name = 'YQLError'
		self.message = message

class YQL:
	"""
	This class asynchronously performs passed in YQL query, and triggers a callback function
	upon completion. It's designed to handle multiple simultaneous queries without breaking.

	Usage Example:
		query = YQL('select * from geo.places where text="san francisco, ca"', showMePlaces)
		query.fetch()

	If you only need the query result once, you can retrieve it immediatelly:
		result = YQL('select * from weather.forecast where location=90210').fetch()

	If you're trying to debug your query, you can turn diagnostics on to retrieve more info:
		query = YQL(statement, callback, True)

	You may also set all 3 of these qttributes manually after YQL() constructor fires:
		query = YQL()
		query.query = statement
		query.callback = callback
		query.diagnostics = True

	"""
	def __init__(self, query, callback, diagnostics=False):
		self.query = query
		doNothing = def(): pass
		self.callback = callback or doNothing
		self.diagnostics = diagnostics

	def fetch(self):
		if not self.query:
			raise YQLError('YQL.query attribute must be defined before invoking YQL.fetch()')
		elif not self.callback:
			raise YQLError('YQL.callback attribute must be defined before invoking YQL.fetch()')

		scriptEl = document.createElement('script')

		# uid needs to be unique, to ensure that collision doesn't happen, we convert
		# the timestamp to milliseconds and append a random integer at the end, zero-padding
		# it to avoid two unrelated times from possibility of clashing
		uid = 'yql' + Date().getTime() + str(Math.floor(Math.random()*1000)).zfill(3)
		encodedQuery =	encodeURIComponent(self.query.toLowerCase())

		window[uid] = def(json):
			self.callback(json['query'])
			del window[uid]
			document.body.removeChild(scriptEl)

		url = 'http://query.yahooapis.com/v1/public/yql?q=' + encodedQuery
		if self.diagnostics:
			url += '&diagnostics=true'
		scriptEl.src = url + '&format=json&callback=' + uid
		document.body.appendChild(scriptEl)