# Lint as: python3
# Copyright 2019 DeepMind Technologies Limited. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Basic data on chemical elements."""

import collections
from typing import Optional
import attr


@attr.s
class Element(object):
  """Chemical element.

  Attributes:
    symbol: official symbol of element.
    atomic_number: atomic number of element.
    period: period to which the element belongs.
    spin: overrides default ground-state spin-configuration based on the
      element's group (main groups only).
  """
  symbol: str = attr.ib()
  atomic_number: int = attr.ib()
  period: int = attr.ib()
  _spin: Optional[int] = attr.ib(default=None, repr=False)

  @property
  def group(self) -> int:
    """Group to which element belongs. Set to -1 for actines and lanthanides."""
    is_lanthanide = (58 <= self.atomic_number <= 71)
    is_actinide = (90 <= self.atomic_number <= 103)
    if is_lanthanide or is_actinide:
      return -1
    if self.symbol == 'He':
      # n=1 shell only has s orbital -> He is a noble gas.
      return 18
    period_starts = (1, 3, 11, 19, 37, 55, 87)
    period_start = period_starts[self.period - 1]
    group_ = self.atomic_number - period_start + 1
    # Adjust for absence of d block in periods 2 and 3.
    if self.period < 4 and group_ > 2:
      group_ += 10
    # Adjust for Lanthanides and Actinides in periods 6 and 7.
    if self.period >= 6 and group_ > 3:
      group_ -= 14
    return group_

  @property
  def spin_config(self) -> int:
    """Canonical spin configuration (via Hund's rules) of neutral atom.

    Returns:
      Number of unpaired electrons (as required by PySCF) in the neutral atom's
      ground state.

    Raises:
      NotImplementedError: if element is a transition metal and the spin
      configuration is not set at initialization.
    """
    if self._spin is not None:
      return self._spin
    unpaired = {1: 1, 2: 0, 13: 1, 14: 2, 15: 3, 16: 2, 17: 1, 18: 0}
    if self.group in unpaired:
      return unpaired[self.group]
    else:
      raise NotImplementedError(
          'Spin configuration for transition metals not set.')

  @property
  def nalpha(self) -> int:
    """Returns the number of alpha electrons of the ground state neutral atom.

    Without loss of generality, the number of alpha electrons is taken to be
    equal to or greater than the number of beta electrons.
    """
    electrons = self.atomic_number
    unpaired = self.spin_config
    return (electrons + unpaired) // 2

  @property
  def nbeta(self) -> int:
    """Returns the number of beta electrons of the ground state neutral atom.

    Without loss of generality, the number of alpha electrons is taken to be
    equal to or greater than the number of beta electrons.
    """
    electrons = self.atomic_number
    unpaired = self.spin_config
    return (electrons - unpaired) // 2


# Atomic symbols for all known elements
# Generated using
#   def _element(symbol, atomic_number):
#     # period_start[n] = atomic number of group 1 element in (n+1)-th period.
#     period_start = (1, 3, 11, 19, 37, 55, 87)
#     for p, group1_no in enumerate(period_start):
#       if atomic_number < group1_no:
#         # In previous period but n is 0-based.
#         period = p
#         break
#     else:
#       period = p + 1
#     return Element(symbol=symbol, atomic_number=atomic_number, period=period)
#   [_element(s, n+1) for n, s in enumerate(symbols)]
# where symbols is the list of chemical symbols of all elements.
_ELEMENTS = (
    Element(symbol='H', atomic_number=1, period=1),
    Element(symbol='He', atomic_number=2, period=1),
    Element(symbol='Li', atomic_number=3, period=2),
    Element(symbol='Be', atomic_number=4, period=2),
    Element(symbol='B', atomic_number=5, period=2),
    Element(symbol='C', atomic_number=6, period=2),
    Element(symbol='N', atomic_number=7, period=2),
    Element(symbol='O', atomic_number=8, period=2),
    Element(symbol='F', atomic_number=9, period=2),
    Element(symbol='Ne', atomic_number=10, period=2),
    Element(symbol='Na', atomic_number=11, period=3),
    Element(symbol='Mg', atomic_number=12, period=3),
    Element(symbol='Al', atomic_number=13, period=3),
    Element(symbol='Si', atomic_number=14, period=3),
    Element(symbol='P', atomic_number=15, period=3),
    Element(symbol='S', atomic_number=16, period=3),
    Element(symbol='Cl', atomic_number=17, period=3),
    Element(symbol='Ar', atomic_number=18, period=3),
    Element(symbol='K', atomic_number=19, period=4),
    Element(symbol='Ca', atomic_number=20, period=4),
    Element(symbol='Sc', atomic_number=21, period=4, spin=1),
    Element(symbol='Ti', atomic_number=22, period=4, spin=2),
    Element(symbol='V', atomic_number=23, period=4, spin=3),
    Element(symbol='Cr', atomic_number=24, period=4, spin=6),
    Element(symbol='Mn', atomic_number=25, period=4, spin=5),
    Element(symbol='Fe', atomic_number=26, period=4, spin=4),
    Element(symbol='Co', atomic_number=27, period=4, spin=3),
    Element(symbol='Ni', atomic_number=28, period=4, spin=2),
    Element(symbol='Cu', atomic_number=29, period=4, spin=1),
    Element(symbol='Zn', atomic_number=30, period=4, spin=0),
    Element(symbol='Ga', atomic_number=31, period=4),
    Element(symbol='Ge', atomic_number=32, period=4),
    Element(symbol='As', atomic_number=33, period=4),
    Element(symbol='Se', atomic_number=34, period=4),
    Element(symbol='Br', atomic_number=35, period=4),
    Element(symbol='Kr', atomic_number=36, period=4),
    Element(symbol='Rb', atomic_number=37, period=5),
    Element(symbol='Sr', atomic_number=38, period=5),
    Element(symbol='Y', atomic_number=39, period=5, spin=1),
    Element(symbol='Zr', atomic_number=40, period=5, spin=2),
    Element(symbol='Nb', atomic_number=41, period=5, spin=5),
    Element(symbol='Mo', atomic_number=42, period=5, spin=6),
    Element(symbol='Tc', atomic_number=43, period=5, spin=5),
    Element(symbol='Ru', atomic_number=44, period=5, spin=4),
    Element(symbol='Rh', atomic_number=45, period=5, spin=3),
    Element(symbol='Pd', atomic_number=46, period=5, spin=0),
    Element(symbol='Ag', atomic_number=47, period=5, spin=1),
    Element(symbol='Cd', atomic_number=48, period=5, spin=0),
    Element(symbol='In', atomic_number=49, period=5),
    Element(symbol='Sn', atomic_number=50, period=5),
    Element(symbol='Sb', atomic_number=51, period=5),
    Element(symbol='Te', atomic_number=52, period=5),
    Element(symbol='I', atomic_number=53, period=5),
    Element(symbol='Xe', atomic_number=54, period=5),
    Element(symbol='Cs', atomic_number=55, period=6),
    Element(symbol='Ba', atomic_number=56, period=6),
    Element(symbol='La', atomic_number=57, period=6),
    Element(symbol='Ce', atomic_number=58, period=6),
    Element(symbol='Pr', atomic_number=59, period=6),
    Element(symbol='Nd', atomic_number=60, period=6),
    Element(symbol='Pm', atomic_number=61, period=6),
    Element(symbol='Sm', atomic_number=62, period=6),
    Element(symbol='Eu', atomic_number=63, period=6),
    Element(symbol='Gd', atomic_number=64, period=6),
    Element(symbol='Tb', atomic_number=65, period=6),
    Element(symbol='Dy', atomic_number=66, period=6),
    Element(symbol='Ho', atomic_number=67, period=6),
    Element(symbol='Er', atomic_number=68, period=6),
    Element(symbol='Tm', atomic_number=69, period=6),
    Element(symbol='Yb', atomic_number=70, period=6),
    Element(symbol='Lu', atomic_number=71, period=6),
    Element(symbol='Hf', atomic_number=72, period=6),
    Element(symbol='Ta', atomic_number=73, period=6),
    Element(symbol='W', atomic_number=74, period=6),
    Element(symbol='Re', atomic_number=75, period=6),
    Element(symbol='Os', atomic_number=76, period=6),
    Element(symbol='Ir', atomic_number=77, period=6),
    Element(symbol='Pt', atomic_number=78, period=6),
    Element(symbol='Au', atomic_number=79, period=6),
    Element(symbol='Hg', atomic_number=80, period=6),
    Element(symbol='Tl', atomic_number=81, period=6),
    Element(symbol='Pb', atomic_number=82, period=6),
    Element(symbol='Bi', atomic_number=83, period=6),
    Element(symbol='Po', atomic_number=84, period=6),
    Element(symbol='At', atomic_number=85, period=6),
    Element(symbol='Rn', atomic_number=86, period=6),
    Element(symbol='Fr', atomic_number=87, period=7),
    Element(symbol='Ra', atomic_number=88, period=7),
    Element(symbol='Ac', atomic_number=89, period=7),
    Element(symbol='Th', atomic_number=90, period=7),
    Element(symbol='Pa', atomic_number=91, period=7),
    Element(symbol='U', atomic_number=92, period=7),
    Element(symbol='Np', atomic_number=93, period=7),
    Element(symbol='Pu', atomic_number=94, period=7),
    Element(symbol='Am', atomic_number=95, period=7),
    Element(symbol='Cm', atomic_number=96, period=7),
    Element(symbol='Bk', atomic_number=97, period=7),
    Element(symbol='Cf', atomic_number=98, period=7),
    Element(symbol='Es', atomic_number=99, period=7),
    Element(symbol='Fm', atomic_number=100, period=7),
    Element(symbol='Md', atomic_number=101, period=7),
    Element(symbol='No', atomic_number=102, period=7),
    Element(symbol='Lr', atomic_number=103, period=7),
    Element(symbol='Rf', atomic_number=104, period=7),
    Element(symbol='Db', atomic_number=105, period=7),
    Element(symbol='Sg', atomic_number=106, period=7),
    Element(symbol='Bh', atomic_number=107, period=7),
    Element(symbol='Hs', atomic_number=108, period=7),
    Element(symbol='Mt', atomic_number=109, period=7),
    Element(symbol='Ds', atomic_number=110, period=7),
    Element(symbol='Rg', atomic_number=111, period=7),
    Element(symbol='Cn', atomic_number=112, period=7),
    Element(symbol='Nh', atomic_number=113, period=7),
    Element(symbol='Fl', atomic_number=114, period=7),
    Element(symbol='Mc', atomic_number=115, period=7),
    Element(symbol='Lv', atomic_number=116, period=7),
    Element(symbol='Ts', atomic_number=117, period=7),
    Element(symbol='Og', atomic_number=118, period=7),
)


ATOMIC_NUMS = {element.atomic_number: element for element in _ELEMENTS}


# Lookup by symbol instead of atomic number.
SYMBOLS = {element.symbol: element for element in _ELEMENTS}


# Lookup by period.
PERIODS = collections.defaultdict(list)
for element in _ELEMENTS:
  PERIODS[element.period].append(element)
PERIODS = {period: tuple(elements) for period, elements in PERIODS.items()}
