# IfcOpenShell - IFC toolkit and geometry engine
# Copyright (C) 2021 Dion Moult <dion@thinkmoult.com>
#
# This file is part of IfcOpenShell.
#
# IfcOpenShell is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# IfcOpenShell 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 Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.

import ifcopenshell
import ifcopenshell.util.unit
from typing import Optional


def add_conversion_based_unit(
    file: ifcopenshell.file, name: str = "foot", conversion_offset: Optional[float] = None
) -> ifcopenshell.entity_instance:
    """Add a conversion based unit

    If you're in one of those countries who don't use SI units, you're
    probably simply using SI units converted into another unit. If you want
    to use _those_ units, you can create a conversion based unit with this
    function. You can choose from one of: inch, foot, yard, mile, square
    inch, square foot, square yard, acre, square mile, cubic inch, cubic
    foot, cubic yard, litre, fluid ounce UK, fluid ounce US, pint UK, pint
    US, gallon UK, gallon US, degree, ounce, pound, ton UK, ton US, lbf,
    kip, psi, ksi, minute, hour, day, btu, and fahrenheit.

    :param name: A converted name chosen from the list above.
    :param conversion_offset: If you want to offset the conversion further
        by a set number, you may specify it here. For example, fahrenheit is
        1.8 * kelvin - 459.67. The -459.67 is the conversion offset. Note
        that this is just an example and you don't actually need to specify
        that for fahrenheit as it's built into this API function. For
        advanced users only.
    :return: The new IfcConversionBasedUnit or
        IfcConversionBasedUnitWithOffset

    Example:

    .. code:: python

        # Some common imperial measurements
        length = ifcopenshell.api.unit.add_conversion_based_unit(model, name="inch")
        area = ifcopenshell.api.unit.add_conversion_based_unit(model, name="square foot")

        # Make it our default units, if we are doing an imperial building
        ifcopenshell.api.unit.assign_unit(model, units=[length, area])
    """

    unit_type = ifcopenshell.util.unit.imperial_types.get(name, "USERDEFINED")
    dimensions = ifcopenshell.util.unit.named_dimensions[unit_type]
    exponents = file.createIfcDimensionalExponents(*dimensions)
    si_name = ifcopenshell.util.unit.si_type_names[unit_type]

    if unit_type == "MASSUNIT":
        si_unit = file.createIfcSIUnit(UnitType=unit_type, Name=si_name, Prefix="KILO")
    else:
        si_unit = file.createIfcSIUnit(UnitType=unit_type, Name=si_name)

    conversion_real = ifcopenshell.util.unit.si_conversions.get(name, 1)
    value_component = file.create_entity("IfcReal", **{"wrappedValue": conversion_real})
    conversion_factor = file.createIfcMeasureWithUnit(value_component, si_unit)

    if not conversion_offset:
        conversion_offset = ifcopenshell.util.unit.si_offsets.get(name, 0)

    if conversion_offset:
        return file.createIfcConversionBasedUnitWithOffset(
            exponents,
            unit_type,
            name,
            conversion_factor,
            conversion_offset,
        )
    return file.createIfcConversionBasedUnit(exponents, unit_type, name, conversion_factor)