"""
List of all pointers and constants used in the Amber topology file.

Can be used like:
   from parmed.constants import *
"""
from __future__ import division
from math import pi as _pi, sqrt as _sqrt, log10 as _log10, acos as _acos

__all__ = ['AMBER_ELECTROSTATIC', 'AMBER_POINTERS', 'NATOM', 'NTYPES', 'NBONH', 'MBONA', 'NTHETH',
           'MTHETA', 'NPHIH', 'MPHIA', 'NHPARM', 'NPARM', 'NEXT', 'NRES', 'NBONA', 'NTHETA',
           'NPHIA', 'NUMBND', 'NUMANG', 'NPTRA', 'NATYP', 'NPHB', 'IFPERT', 'NBPER', 'NGPER',
           'NDPER', 'MBPER', 'MGPER', 'MDPER', 'IFBOX', 'NMXRS', 'IFCAP', 'NUMEXTRA', 'NCOPY',
           'NNB', 'RAD_TO_DEG', 'DEG_TO_RAD', 'TRUNCATED_OCTAHEDRON_ANGLE']

AMBER_ELECTROSTATIC = 18.2223
CHARMM_ELECTROSTATIC = _sqrt(332.0716)

AMBER_POINTERS = """
NATOM  : total number of atoms
NTYPES : total number of distinct atom types
NBONH  : number of bonds containing hydrogen
MBONA  : number of bonds not containing hydrogen
NTHETH : number of angles containing hydrogen
MTHETA : number of angles not containing hydrogen
NPHIH  : number of dihedrals containing hydrogen
MPHIA  : number of dihedrals not containing hydrogen
NHPARM : currently not used
NPARM  : currently not used
NEXT   : number of excluded atoms
NRES   : number of residues
NBONA  : MBONA + number of constraint bonds
NTHETA : MTHETA + number of constraint angles
NPHIA  : MPHIA + number of constraint dihedrals
NUMBND : number of unique bond types
NUMANG : number of unique angle types
NPTRA  : number of unique dihedral types
NATYP  : number of atom types in parameter file, see SOLTY below
NPHB   : number of distinct 10-12 hydrogen bond pair types
IFPERT : set to 1 if perturbation info is to be read in
NBPER  : number of bonds to be perturbed
NGPER  : number of angles to be perturbed
NDPER  : number of dihedrals to be perturbed
MBPER  : number of bonds with atoms completely in perturbed group
MGPER  : number of angles with atoms completely in perturbed group
MDPER  : number of dihedrals with atoms completely in perturbed groups
IFBOX  : set to 1 if standard periodic box, 2 when truncated octahedral
NMXRS  : number of atoms in the largest residue
IFCAP  : set to 1 if the CAP option from edit was specified
NUMEXTRA: number of extra points
NCOPY  : Number of copies for advanded simulations
"""
# These global variables provide a more natural way of accessing
# the various pointers.  Most useful if they're loaded into the
# top-level namespace.
NATOM  = 0; NTYPES = 1; NBONH  = 2; MBONA  = 3; NTHETH = 4
MTHETA = 5; NPHIH  = 6; MPHIA  = 7; NHPARM = 8; NPARM  = 9
NEXT   = 10; NRES   = 11; NBONA  = 12; NTHETA = 13; NPHIA  = 14
NUMBND = 15; NUMANG = 16; NPTRA  = 17; NATYP  = 18; NPHB   = 19
IFPERT = 20; NBPER  = 21; NGPER  = 22; NDPER  = 23; MBPER  = 24
MGPER  = 25; MDPER  = 26; IFBOX  = 27; NMXRS  = 28; IFCAP  = 29
NUMEXTRA= 30; NCOPY  = 31

# An alias
NNB = NEXT

RAD_TO_DEG = 180.0 / _pi
DEG_TO_RAD = _pi / 180.0
TRUNCATED_OCTAHEDRON_ANGLE = _acos(-1/3) * 180 / _pi

# For use in floating point comparisons
TINY = 1.0e-8
SMALL = 1.0e-4
TINY_DIGITS = int(_log10(TINY) + 0.5)
SMALL_DIGITS = int(_log10(SMALL) + 0.5)

# For I/O
DEFAULT_ENCODING = 'UTF-8'