# This code comes from youtube-dl: https://github.com/rg3/youtube-dl/blob/master/youtube_dl/jsinterp.py

from __future__ import unicode_literals
from __future__ import print_function

import json
import operator
import re


_OPERATORS = [
	('|', operator.or_),
	('^', operator.xor),
	('&', operator.and_),
	('>>', operator.rshift),
	('<<', operator.lshift),
	('-', operator.sub),
	('+', operator.add),
	('%', operator.mod),
	('/', operator.truediv),
	('*', operator.mul),
]
_ASSIGN_OPERATORS = [(op + '=', opfunc) for op, opfunc in _OPERATORS]
_ASSIGN_OPERATORS.append(('=', lambda cur, right: right))

_NAME_RE = r'[a-zA-Z_$][a-zA-Z_$0-9]*'


def remove_quotes(s):
	if s is None or len(s) < 2:
		return s
	for quote in ('"', "'", ):
		if s[0] == quote and s[-1] == quote:
			return s[1:-1]
	return s


class JSInterpreter(object):
	def __init__(self, code):
		self.code = code
		self._functions = {}
		self._objects = {}

	def interpret_statement(self, stmt, local_vars, allow_recursion=100):
		if allow_recursion < 0:
			print('[JSInterpreter] Recursion limit reached')
			return None

		should_abort = False
		stmt = stmt.lstrip()
		stmt_m = re.match(r'var\s', stmt)
		if stmt_m:
			expr = stmt[len(stmt_m.group(0)):]
		else:
			return_m = re.match(r'return(?:\s+|$)', stmt)
			if return_m:
				expr = stmt[len(return_m.group(0)):]
				should_abort = True
			else:
				# Try interpreting it as an expression
				expr = stmt

		v = self.interpret_expression(expr, local_vars, allow_recursion)
		return v, should_abort

	def interpret_expression(self, expr, local_vars, allow_recursion):
		expr = expr.strip()
		if expr == '':  # Empty expression
			return None

		if expr.startswith('('):
			parens_count = 0
			for m in re.finditer(r'[()]', expr):
				if m.group(0) == '(':
					parens_count += 1
				else:
					parens_count -= 1
					if parens_count == 0:
						sub_expr = expr[1:m.start()]
						sub_result = self.interpret_expression(
							sub_expr, local_vars, allow_recursion)
						remaining_expr = expr[m.end():].strip()
						if not remaining_expr:
							return sub_result
						else:
							expr = json.dumps(sub_result) + remaining_expr
						break
			else:
				print('[JSInterpreter] Premature end of parens in %r' % expr)
				return None

		for op, opfunc in _ASSIGN_OPERATORS:
			m = re.match(r'''(?x)
				(?P<out>%s)(?:\[(?P<index>[^\]]+?)\])?
				\s*%s
				(?P<expr>.*)$''' % (_NAME_RE, re.escape(op)), expr)
			if not m:
				continue
			right_val = self.interpret_expression(
				m.group('expr'), local_vars, allow_recursion - 1)

			if m.groupdict().get('index'):
				lvar = local_vars[m.group('out')]
				idx = self.interpret_expression(
					m.group('index'), local_vars, allow_recursion)
				assert isinstance(idx, int)
				cur = lvar[idx]
				val = opfunc(cur, right_val)
				lvar[idx] = val
				return val
			else:
				cur = local_vars.get(m.group('out'))
				val = opfunc(cur, right_val)
				local_vars[m.group('out')] = val
				return val

		if expr.isdigit():
			return int(expr)

		var_m = re.match(
			r'(?!if|return|true|false)(?P<name>%s)$' % _NAME_RE,
			expr)
		if var_m:
			return local_vars[var_m.group('name')]

		try:
			return json.loads(expr)
		except ValueError:
			pass

		m = re.match(
			r'(?P<in>%s)\[(?P<idx>.+)\]$' % _NAME_RE, expr)
		if m:
			val = local_vars[m.group('in')]
			idx = self.interpret_expression(
				m.group('idx'), local_vars, allow_recursion - 1)
			return val[idx]

		m = re.match(
			r'(?P<var>%s)(?:\.(?P<member>[^(]+)|\[(?P<member2>[^]]+)\])\s*(?:\(+(?P<args>[^()]*)\))?$' % _NAME_RE,
			expr)
		if m:
			variable = m.group('var')
			member = remove_quotes(m.group('member') or m.group('member2'))
			arg_str = m.group('args')

			if variable in local_vars:
				obj = local_vars[variable]
			else:
				if variable not in self._objects:
					self._objects[variable] = self.extract_object(variable)
				obj = self._objects[variable]

			if arg_str is None:
				# Member access
				if member == 'length':
					return len(obj)
				return obj[member]

			assert expr.endswith(')')
			# Function call
			if arg_str == '':
				argvals = tuple()
			else:
				argvals = tuple([
					self.interpret_expression(v, local_vars, allow_recursion)
					for v in arg_str.split(',')])

			if member == 'split':
				assert argvals == ('',)
				return list(obj)
			if member == 'join':
				assert len(argvals) == 1
				return argvals[0].join(obj)
			if member == 'reverse':
				assert len(argvals) == 0
				obj.reverse()
				return obj
			if member == 'slice':
				assert len(argvals) == 1
				return obj[argvals[0]:]
			if member == 'splice':
				assert isinstance(obj, list)
				index, howMany = argvals
				res = []
				for i in range(index, min(index + howMany, len(obj))):
					res.append(obj.pop(index))
				return res

			return obj[member](argvals)

		for op, opfunc in _OPERATORS:
			m = re.match(r'(?P<x>.+?)%s(?P<y>.+)' % re.escape(op), expr)
			if not m:
				continue
			x, abort = self.interpret_statement(
				m.group('x'), local_vars, allow_recursion - 1)
			if abort:
				print('[JSInterpreter] Premature left-side return of %s in %r' % (op, expr))
				return None
			y, abort = self.interpret_statement(
				m.group('y'), local_vars, allow_recursion - 1)
			if abort:
				print('[JSInterpreter] Premature right-side return of %s in %r' % (op, expr))
				return None
			return opfunc(x, y)

		m = re.match(
			r'^(?P<func>%s)\((?P<args>[a-zA-Z0-9_$,]*)\)$' % _NAME_RE, expr)
		if m:
			fname = m.group('func')
			argvals = tuple([
				int(v) if v.isdigit() else local_vars[v]
				for v in m.group('args').split(',')]) if len(m.group('args')) > 0 else tuple()
			if fname not in self._functions:
				self._functions[fname] = self.extract_function(fname)
			return self._functions[fname](argvals)

		print('[JSInterpreter] Unsupported JS expression %r' % expr)
		return None

	def extract_object(self, objname):
		_FUNC_NAME_RE = r'''(?:[a-zA-Z$0-9]+|"[a-zA-Z$0-9]+"|'[a-zA-Z$0-9]+')'''
		obj = {}
		obj_m = re.search(
			r'''(?x)
				(?<!this\.)%s\s*=\s*{\s*
					(?P<fields>(%s\s*:\s*function\s*\(.*?\)\s*{.*?}(?:,\s*)?)*)
				}\s*;
			''' % (re.escape(objname), _FUNC_NAME_RE),
			self.code)
		fields = obj_m.group('fields')
		# Currently, it only supports function definitions
		fields_m = re.finditer(
			r'''(?x)
				(?P<key>%s)\s*:\s*function\s*\((?P<args>[a-z,]+)\){(?P<code>[^}]+)}
			''' % _FUNC_NAME_RE,
			fields)
		for f in fields_m:
			argnames = f.group('args').split(',')
			obj[remove_quotes(f.group('key'))] = self.build_function(argnames, f.group('code'))

		return obj

	def extract_function(self, funcname):
		func_m = re.search(
			r'''(?x)
				(?:function\s+%s|[{;,]\s*%s\s*=\s*function|var\s+%s\s*=\s*function)\s*
				\((?P<args>[^)]*)\)\s*
				\{(?P<code>[^}]+)\}''' % (
				re.escape(funcname), re.escape(funcname), re.escape(funcname)),
			self.code)
		if func_m is None:
			print('[JSInterpreter] Could not find JS function %r' % funcname)
			return None
		argnames = func_m.group('args').split(',')

		return self.build_function(argnames, func_m.group('code'))

	def build_function(self, argnames, code):
		def resf(args):
			local_vars = dict(list(zip(argnames, args)))
			for stmt in code.split(';'):
				res, abort = self.interpret_statement(stmt, local_vars)
				if abort:
					break
			return res
		return resf
