# Source code for sympy.physics.units.util

# -*- coding: utf-8 -*-

"""
Several methods to simplify expressions involving unit objects.
"""

from __future__ import division

import collections

from sympy.physics.units.quantities import Quantity
from sympy import Add, Mul, Pow, Function, Rational, Tuple, sympify
from sympy.core.compatibility import reduce
from sympy.physics.units.dimensions import Dimension

def dim_simplify(expr):
"""
NOTE: this function could be deprecated in the future.

Simplify expression by recursively evaluating the dimension arguments.

This function proceeds to a very rough dimensional analysis. It tries to
simplify expression with dimensions, and it deletes all what multiplies a
dimension without being a dimension. This is necessary to avoid strange
behavior when Add(L, L) be transformed into Mul(2, L).
"""

if isinstance(expr, Dimension):
return expr

if isinstance(expr, Pow):
return dim_simplify(expr.base)**dim_simplify(expr.exp)
elif isinstance(expr, Function):
return dim_simplify(expr.args[0])
if (all(isinstance(arg, Dimension) for arg in expr.args) or
all(arg.is_dimensionless for arg in expr.args if isinstance(arg, Dimension))):
return reduce(lambda x, y: x.add(y), expr.args)
else:
raise ValueError("Dimensions cannot be added: %s" % expr)
elif isinstance(expr, Mul):
return Dimension(Mul(*[dim_simplify(i).name for i in expr.args if isinstance(i, Dimension)]))

raise ValueError("Cannot be simplifed: %s", expr)

def _get_conversion_matrix_for_expr(expr, target_units):
from sympy import Matrix

expr_dim = Dimension(Quantity.get_dimensional_expr(expr))
dim_dependencies = expr_dim.get_dimensional_dependencies(mark_dimensionless=True)
target_dims = [Dimension(Quantity.get_dimensional_expr(x)) for x in target_units]
canon_dim_units = {i for x in target_dims for i in x.get_dimensional_dependencies(mark_dimensionless=True)}
canon_expr_units = {i for i in dim_dependencies}

if not canon_expr_units.issubset(canon_dim_units):
return None

canon_dim_units = sorted(canon_dim_units)

camat = Matrix([[i.get_dimensional_dependencies(mark_dimensionless=True).get(j, 0)  for i in target_dims] for j in canon_dim_units])
exprmat = Matrix([dim_dependencies.get(k, 0) for k in canon_dim_units])

res_exponents = camat.solve_least_squares(exprmat, method=None)
return res_exponents

[docs]def convert_to(expr, target_units):
"""
Convert expr to the same expression with all of its units and quantities
represented as factors of target_units, whenever the dimension is compatible.

target_units may be a single unit/quantity, or a collection of
units/quantities.

Examples
========

>>> from sympy.physics.units import speed_of_light, meter, gram, second, day
>>> from sympy.physics.units import mile, newton, kilogram, atomic_mass_constant
>>> from sympy.physics.units import kilometer, centimeter
>>> from sympy.physics.units import convert_to
>>> convert_to(mile, kilometer)
25146*kilometer/15625
>>> convert_to(mile, kilometer).n()
1.609344*kilometer
>>> convert_to(speed_of_light, meter/second)
299792458*meter/second
>>> convert_to(day, second)
86400*second
>>> 3*newton
3*newton
>>> convert_to(3*newton, kilogram*meter/second**2)
3*kilogram*meter/second**2
>>> convert_to(atomic_mass_constant, gram)
1.66053904e-24*gram

Conversion to multiple units:

>>> convert_to(speed_of_light, [meter, second])
299792458*meter/second
>>> convert_to(3*newton, [centimeter, gram, second])
300000*centimeter*gram/second**2

Conversion to Planck units:

>>> from sympy.physics.units import gravitational_constant, hbar
>>> convert_to(atomic_mass_constant, [gravitational_constant, speed_of_light, hbar]).n()
7.62950196312651e-20*gravitational_constant**(-0.5)*hbar**0.5*speed_of_light**0.5

"""
if not isinstance(target_units, (collections.Iterable, Tuple)):
target_units = [target_units]

return Add.fromiter(convert_to(i, target_units) for i in expr.args)

expr = sympify(expr)

if not isinstance(expr, Quantity) and expr.has(Quantity):
expr = expr.replace(lambda x: isinstance(x, Quantity), lambda x: x.convert_to(target_units))

def get_total_scale_factor(expr):
if isinstance(expr, Mul):
return reduce(lambda x, y: x * y, [get_total_scale_factor(i) for i in expr.args])
elif isinstance(expr, Pow):
return get_total_scale_factor(expr.base) ** expr.exp
elif isinstance(expr, Quantity):
return expr.scale_factor
return expr

depmat = _get_conversion_matrix_for_expr(expr, target_units)
if depmat is None:
return expr

expr_scale_factor = get_total_scale_factor(expr)
return expr_scale_factor * Mul.fromiter((1/get_total_scale_factor(u) * u) ** p for u, p in zip(target_units, depmat))