# Source code for pymunk.arbiter

    __version__ = "$Id$"
    __docformat__ = "reStructuredText"

    from .vec2d import Vec2d

    from . import _chipmunk_cffi
    cp = _chipmunk_cffi.lib
    ffi = _chipmunk_cffi.ffi

    from .contact_point_set import ContactPointSet

    class Arbiter(object):
        """The Arbiter object encapsulates a pair of colliding shapes and all of
            the data about their collision.

            They are created when a collision starts, and persist until those
            shapes are no longer colliding.

        .. Warning::
            Because arbiters are handled by the space you should never
            hold onto a reference to an arbiter as you don't know when it will be
            destroyed! Use them within the callback where they are given to you
            and then forget about them or copy out the information you need from
            them.
        """
        def __init__(self, _arbiter, space):
            """Initialize an Arbiter object from the Chipmunk equivalent struct
            and the Space.

            .. note::
                You should never need to create an instance of this class directly.
            """

            self._arbiter = _arbiter
            self._space = space

        def _get_contact_point_set(self):
            _set = cp.cpArbiterGetContactPointSet(self._arbiter)
            return ContactPointSet._from_cp(_set)

        def _set_contact_point_set(self, point_set):
            # This has to be done by fetching a new chipmuk point set, update it
            # according to whats passed in and the pass that back to chipmunk due
            # to the fact that ContactPointSet doesnt contain a reference to the
            # corresponding c struct.

            _set = cp.cpArbiterGetContactPointSet(self._arbiter)
            _set.normal = point_set.normal

            if len(point_set.points) == _set.count:
                for i in range(_set.count):
                    _set.points[i].pointA = point_set.points[0].point_a
                    _set.points[i].pointB = point_set.points[0].point_b
                    _set.points[i].distance = point_set.points[0].distance
            else:
                msg = 'Expected {} points, got {} points in point_set'.format(
                    _set.count,  len(point_set.points))
                raise Exception(msg)

            cp.cpArbiterSetContactPointSet(self._arbiter, ffi.addressof(_set))

        contact_point_set = property(_get_contact_point_set, _set_contact_point_set,
            doc="""Contact point sets make getting contact information from the
            Arbiter simpler.

            Return `ContactPointSet`""")

        def _get_shapes(self):
            shapeA_p = ffi.new("cpShape *[1]")
            shapeB_p = ffi.new("cpShape *[1]")

            cp.cpArbiterGetShapes(self._arbiter, shapeA_p, shapeB_p)

            a, b = self._space._get_shape(shapeA_p[0]), self._space._get_shape(shapeB_p[0])
            return a, b

        shapes = property(_get_shapes,
            doc="""Get the shapes in the order that they were defined in the
            collision handler associated with this arbiter""")

        def _get_restitution(self):
            return cp.cpArbiterGetRestitution(self._arbiter)
        def _set_restitution(self, restitution):
            cp.cpArbiterSetRestitution(self._arbiter, restitution)
        restitution = property(_get_restitution, _set_restitution,
            doc="""The calculated restitution (elasticity) for this collision
            pair.

            Setting the value in a pre_solve() callback will override the value
            calculated by the space. The default calculation multiplies the
            elasticity of the two shapes together.
            """)

        def _get_friction(self):
            return cp.cpArbiterGetFriction(self._arbiter)
        def _set_friction(self, friction):
            cp.cpArbiterSetFriction(self._arbiter, friction)
        friction = property(_get_friction, _set_friction,
            doc="""The calculated friction for this collision pair.

            Setting the value in a pre_solve() callback will override the value
            calculated by the space. The default calculation multiplies the
            friction of the two shapes together.
            """)

        def _get_surface_velocity(self):
            return Vec2d._fromcffi(cp.cpArbiterGetSurfaceVelocity(self._arbiter))
        def _set_surface_velocity(self, velocity):
            cp.cpArbiterSetSurfaceVelocity(self._arbiter, velocity)
        surface_velocity = property(_get_surface_velocity, _set_surface_velocity,
            doc="""The calculated surface velocity for this collision pair.

            Setting the value in a pre_solve() callback will override the value
            calculated by the space. the default calculation subtracts the
            surface velocity of the second shape from the first and then projects
            that onto the tangent of the collision. This is so that only
            friction is affected by default calculation. Using a custom
            calculation, you can make something that responds like a pinball
            bumper, or where the surface velocity is dependent on the location
            of the contact point.
            """)

        def _get_total_impulse(self):
            return Vec2d._fromcffi(cp.cpArbiterTotalImpulse(self._arbiter))
        total_impulse = property(_get_total_impulse,
            doc="""Returns the impulse that was applied this step to resolve the
            collision.

            This property should only be called from a post-solve, post-step""")

        def _get_total_ke(self):
            return cp.cpArbiterTotalKE(self._arbiter)
        total_ke = property(_get_total_ke,
            doc="""The amount of energy lost in a collision including static, but
            not dynamic friction.

            This property should only be called from a post-solve, post-step""")

        def _get_is_first_contact(self):
            return bool(cp.cpArbiterIsFirstContact(self._arbiter))
        is_first_contact = property(_get_is_first_contact,
            doc="""Returns true if this is the first step the two shapes started
            touching.

            This can be useful for sound effects for instance. If its the first
            frame for a certain collision, check the energy of the collision in a
            post_step() callback and use that to determine the volume of a sound
            effect to play.
            """)

        def _get_is_removal(self):
            return bool(cp.cpArbiterIsRemoval(self._arbiter))
        is_removal = property(_get_is_removal,
            doc="""Returns True during a separate() callback if the callback was
            invoked due to an object removal.
            """)