#   pyRCV2: Preferential vote counting
#   Copyright © 2020–2021  Lee Yingtong Li (RunasSudo)
#
#   This program is free software: you can redistribute it and/or modify
#   it under the terms of the GNU Affero General Public License as published by
#   the Free Software Foundation, either version 3 of the License, or
#   (at your option) any later version.
#
#   This program is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#   GNU Affero General Public License for more details.
#
#   You should have received a copy of the GNU Affero General Public License
#   along with this program.  If not, see <https://www.gnu.org/licenses/>.

from pyRCV2.numbers.base import BasePyNum, compatible_types

import decimal

_quantize_exp = decimal.Decimal('10') ** -12
_pos_epsilon = decimal.Decimal('10') ** -6 / decimal.Decimal('2')
_neg_epsilon = -_pos_epsilon

def _gfixed_set_dps(dps):
	global _quantize_exp
	_quantize_exp = decimal.Decimal('10') ** -(2 * dps)
	_pos_epsilon = decimal.Decimal('10') ** -dps / decimal.Decimal('2')
	_neg_epsilon = -_pos_epsilon

class FixedGuarded(BasePyNum):
	"""
	Wrapper for Python Decimal (for fixed-point arithmetic)
	Implements guarded (quasi-exact) fixed-point
	"""
	
	_py_class = decimal.Decimal # For BasePyNum
	
	ROUND_DOWN = decimal.ROUND_DOWN
	ROUND_HALF_UP = decimal.ROUND_HALF_UP
	ROUND_HALF_EVEN = decimal.ROUND_HALF_EVEN
	ROUND_UP = decimal.ROUND_UP
	
	@classmethod
	def _to_impl(cls, value):
		"""Overrides BasePyNum._to_impl"""
		return decimal.Decimal(value).quantize(_quantize_exp)
	
	@classmethod
	def _truediv_impl(cls, i1, i2):
		"""Overrides BasePyNum._truediv_impl"""
		return (i1 / i2).quantize(_quantize_exp)
	
	@compatible_types
	def __eq__(self, other):
		"""Overrides BasePyNum.__eq__"""
		diff = self.impl - other.impl
		return diff < _pos_epsilon and diff > _neg_epsilon
	@compatible_types
	def __ne__(self, other):
		"""Overrides BasePyNum.__ne__"""
		return not self.__eq__(other)
	@compatible_types
	def __gt__(self, other):
		"""Overrides BasePyNum.__gt__"""
		diff = self.impl - other.impl
		return diff > _pos_epsilon
	@compatible_types
	def __ge__(self, other):
		"""Overrides BasePyNum.__ge__"""
		diff = self.impl - other.impl
		return diff > _neg_epsilon
	@compatible_types
	def __lt__(self, other):
		"""Overrides BasePyNum.__lt__"""
		diff = self.impl - other.impl
		return diff < _neg_epsilon
	@compatible_types
	def __le__(self, other):
		"""Overrides BasePyNum.__le__"""
		diff = self.impl - other.impl
		return diff < _pos_epsilon
	
	@compatible_types
	def __itruediv__(self, other):
		"""Overrides BasePyNum.__itruediv__"""
		self.impl = (self.impl / other.impl).quantize(_quantize_exp)
		return self
	
	def round(self, dps, mode):
		"""Implements BaseNum.round"""
		return FixedGuarded._from_impl(self.impl.quantize(decimal.Decimal('10') ** -dps, mode))