# Copyright 2019 The dm_control Authors.
#
# 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
#
#    http://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.
# ============================================================================

"""A soccer pitch with home/away goals and one field with position detection."""

import colorsys
import os

from absl import logging
from dm_control import composer
from dm_control import mjcf
from dm_control.composer.variation import distributions
from dm_control.entities import props
from dm_control.locomotion.soccer import team
import numpy as np

from dm_control.utils import io as resources

_ASSETS_PATH = os.path.join(os.path.dirname(__file__), 'assets', 'pitch')


def _get_texture(name):
  contents = resources.GetResource(
      os.path.join(_ASSETS_PATH, '{}.png'.format(name)))
  return mjcf.Asset(contents, '.png')


_TOP_CAMERA_Y_PADDING_FACTOR = 1.1
_TOP_CAMERA_DISTANCE = 95.
_WALL_HEIGHT = 10.
_WALL_THICKNESS = .5
_SIDE_WIDTH = 32. / 6.
_GROUND_GEOM_GRID_RATIO = 1. / 100  # Grid size for lighting.
_FIELD_BOX_CONTACT_BIT = 1 << 7  # Use a higher bit to prevent potential clash.

_DEFAULT_PITCH_SIZE = (12, 9)
_DEFAULT_GOAL_LENGTH_RATIO = 0.33  # Goal length / pitch width.

_GOALPOST_RELATIVE_SIZE = 0.07  # Ratio of the goalpost radius to goal size.
_NET_RELATIVE_SIZE = 0.01  # Ratio of the net thickness to goal size.
_SUPPORT_POST_RATIO = 0.75  # Ratio of support post to goalpost radius.
# Goalposts defined in the unit box [-1, 1]**3 facing to the positive X.
_GOALPOSTS = {'right_post': (1, -1, -1, 1, -1, 1),
              'left_post': (1, 1, -1, 1, 1, 1),
              'top_post': (1, -1, 1, 1, 1, 1),
              'right_base': (1, -1, -1, -1, -1, -1),
              'left_base': (1, 1, -1, -1, 1, -1),
              'back_base': (-1, -1, -1, -1, 1, -1),
              'right_support': (-1, -1, -1, .2, -1, 1),
              'right_top_support': (.2, -1, 1, 1, -1, 1),
              'left_support': (-1, 1, -1, .2, 1, 1),
              'left_top_support': (.2, 1, 1, 1, 1, 1)}
# Vertices of net polygons, reshaped to 4x3 arrays.
_NET = {'top': _GOALPOSTS['right_top_support'] + _GOALPOSTS['left_top_support'],
        'back': _GOALPOSTS['right_support'] + _GOALPOSTS['left_support'],
        'left': _GOALPOSTS['left_base'] + _GOALPOSTS['left_top_support'],
        'right': _GOALPOSTS['right_base'] + _GOALPOSTS['right_top_support']}
_NET = {key: np.array(value).reshape(4, 3) for key, value in _NET.items()}

# Number of visual hoarding boxes per side of the pitch.
_NUM_HOARDING = 30


def _top_down_cam_fovy(size, top_camera_distance):
  return (360 / np.pi) * np.arctan2(_TOP_CAMERA_Y_PADDING_FACTOR * max(size),
                                    top_camera_distance)


def _wall_pos_xyaxes(size):
  """Infers position and size of bounding walls given pitch size.

  Walls are placed around `ground_geom` that represents the pitch. Note that
  the ball cannot travel beyond `field` but walkers can walk outside of the
  `field` but not the surrounding walls.

  Args:
    size: a tuple of (length, width) of the pitch.

  Returns:
    a list of 4 tuples, each representing the position and xyaxes of a wall
    plane. In order, walls are placed along x-negative, x-positive, y-negative,
    y-positive relative the center of the pitch.
  """
  return [
      ((0., -size[1], 0.), (-1, 0, 0, 0, 0, 1)),
      ((0., size[1], 0.), (1, 0, 0, 0, 0, 1)),
      ((-size[0], 0., 0.), (0, 1, 0, 0, 0, 1)),
      ((size[0], 0., 0.), (0, -1, 0, 0, 0, 1)),
  ]


def _fieldbox_pos_size(field_size, goal_size):
  """Infers position and size of fieldbox given pitch size.

  Walls are placed around the field so that the ball cannot travel beyond
  `field` but walkers can walk outside of the `field` but not the surrounding
  pitch. Holes are left in the fieldbox at the goal positions to enable scoring.

  Args:
    field_size: a tuple of (length, width) of the field.
    goal_size: a tuple of (unused_depth, width, height) of the goal.

  Returns:
    a list of 8 tuples, each representing the position and size of a wall box.
  """

  box_half_height = 20.
  corner_pos_y = 0.5 * (field_size[1] + goal_size[1])
  corner_size_y = 0.5 * (field_size[1] - goal_size[1])
  thickness = 1.0
  top_pos_z = box_half_height + goal_size[2]
  top_size_z = box_half_height - goal_size[2]
  wall_offset_x = field_size[0] + thickness
  wall_offset_y = field_size[1] + thickness
  return [
      ((0., -wall_offset_y, box_half_height),
       (field_size[0], thickness, box_half_height)),  # near side
      ((0., wall_offset_y, box_half_height),
       (field_size[0], thickness, box_half_height)),  # far side
      ((-wall_offset_x, -corner_pos_y, box_half_height),
       (thickness, corner_size_y, box_half_height)),  # left near corner
      ((-wall_offset_x, 0., top_pos_z),
       (thickness, goal_size[1], top_size_z)),  # left top corner
      ((-wall_offset_x, corner_pos_y, box_half_height),
       (thickness, corner_size_y, box_half_height)),  # left far corner
      ((wall_offset_x, -corner_pos_y, box_half_height),
       (thickness, corner_size_y, box_half_height)),  # right near corner
      ((wall_offset_x, 0., top_pos_z),
       (thickness, goal_size[1], top_size_z)),  # right top corner
      ((wall_offset_x, corner_pos_y, box_half_height),
       (thickness, corner_size_y, box_half_height)),  # right far corner
  ]


def _roof_size(size):
  return (size[0], size[1], _WALL_THICKNESS)


def _reposition_corner_lights(lights, size):
  """Place four lights at the corner of the pitch."""
  mean_size = 0.5 * sum(size)
  height = mean_size * 2/3
  counter = 0
  for x in [-size[0], size[0]]:
    for y in [-size[1], size[1]]:
      position = np.array((x, y, height))
      direction = -np.array((x, y, height*2))
      lights[counter].pos = position
      lights[counter].dir = direction
      counter += 1


def _goalpost_radius(size):
  """Compute goal post radius as scaled average goal size."""
  return _GOALPOST_RELATIVE_SIZE * sum(size) / 3.


def _post_radius(goalpost_name, goalpost_radius):
  """Compute the radius of a specific goalpost."""
  radius = goalpost_radius
  if 'top' in goalpost_name:
    radius *= 1.01  # Prevent z-fighting at the corners.
  if 'support' in goalpost_name:
    radius *= _SUPPORT_POST_RATIO  # Suport posts are a bit narrower.
  return radius


def _goalpost_fromto(unit_fromto, size, pos, direction):
  """Rotate, scale and translate the `fromto` attribute of a goalpost.

  The goalposts are defined in the unit cube [-1, 1]**3 using MuJoCo fromto
  specifier for capsules, they are then flipped according to whether they face
  in the +x or -x, scaled and moved.

  Args:
    unit_fromto: two concatenated 3-vectors in the unit cube in xyzxyz order.
    size: a 3-vector, scaling of the goal.
    pos: a 3-vector, goal position.
    direction: a 3-vector, either (1,1,1) or (-1,-1,1), direction of the goal
      along the x-axis.

  Returns:
    two concatenated 3-vectors, the `fromto` of a goal geom.
  """
  fromto = np.array(unit_fromto) * np.hstack((direction, direction))
  return fromto*np.array(size+size) + np.array(pos+pos)


class Goal(props.PositionDetector):
  """Goal for soccer-like games: A PositionDetector with goalposts."""

  def _make_net_vertices(self, size=(1, 1, 1)):
    """Make vertices for the four net meshes by offsetting net polygons."""
    thickness = _NET_RELATIVE_SIZE * sum(size) / 3
    # Get mesh offsets, compensate for mesh.scale deformation.
    dx = np.array((thickness / size[0], 0, 0))
    dy = np.array((0, thickness / size[1], 0))
    dz = np.array((0, 0, thickness / size[2]))
    # Make mesh vertices with specified thickness.
    top = [v+dz for v in _NET['top']] + [v-dz for v in _NET['top']]
    right = [v+dy for v in _NET['right']] + [v-dy for v in _NET['right']]
    left = [v+dy for v in _NET['left']] + [v-dy for v in _NET['left']]
    back = ([v+dz for v in _NET['back'] if v[2] == 1] +
            [v-dz for v in _NET['back'] if v[2] == 1] +
            [v+dx for v in _NET['back'] if v[2] == -1] +
            [v-dx for v in _NET['back'] if v[2] == -1])
    vertices = {'top': top, 'back': back, 'left': left, 'right': right}
    return  {key: (val*self._direction).flatten()
             for key, val in vertices.items()}

  def _move_goal(self, pos, size):
    """Translate and scale the goal."""
    for geom in self._goal_geoms:
      unit_fromto = _GOALPOSTS[geom.name]
      geom.fromto = _goalpost_fromto(unit_fromto, size, pos, self._direction)
      geom.size = (_post_radius(geom.name, self._goalpost_radius),)
    if self._make_net:
      net_vertices = self._make_net_vertices(size)
      for geom in self._net_geoms:
        geom.pos = pos
        geom.mesh.vertex = net_vertices[geom.mesh.name]
        geom.mesh.scale = size

  def _build(self, direction, net_rgba=(1, 1, 1, .15), make_net=True, **kwargs):
    """Builds the goalposts and net.

    Args:
      direction: Is the goal oriented towards positive or negative x-axis.
      net_rgba: rgba value of the net geoms.
      make_net: Where to add net geoms.
      **kwargs: arguments of PositionDetector superclass, see therein.

    Raises:
      ValueError: If either `pos` or `size` arrays are not of length 3.
      ValueError: If direction in not 1 or -1.
    """
    if len(kwargs['size']) != 3 or len(kwargs['pos']) != 3:
      raise ValueError('Only 3D Goals are supported.')
    if direction not in [1, -1]:
      raise ValueError('direction must be either 1 or -1.')
    # Flip both x and y, to maintain left / right name correctness.
    self._direction = np.array((direction, direction, 1))
    self._make_net = make_net

    # Force the underlying PositionDetector to a non visible site group.
    kwargs['visible'] = False
    # Make a Position_Detector.
    super()._build(retain_substep_detections=True, **kwargs)

    # Add goalpost geoms.
    size = kwargs['size']
    pos = kwargs['pos']
    self._goalpost_radius = _goalpost_radius(size)
    self._goal_geoms = []
    for geom_name, unit_fromto in _GOALPOSTS.items():
      geom_fromto = _goalpost_fromto(unit_fromto, size, pos, self._direction)
      geom_size = (_post_radius(geom_name, self._goalpost_radius),)
      self._goal_geoms.append(
          self._mjcf_root.worldbody.add(
              'geom',
              type='capsule',
              name=geom_name,
              size=geom_size,
              fromto=geom_fromto,
              rgba=self.goalpost_rgba))

    # Add net meshes and geoms.
    if self._make_net:
      net_vertices = self._make_net_vertices()
      self._net_geoms = []
      for name, vertex in net_vertices.items():
        mesh = self._mjcf_root.asset.add('mesh', name=name, vertex=vertex)
        geom = self._mjcf_root.worldbody.add('geom', type='mesh', mesh=mesh,
                                             name=name, rgba=net_rgba,
                                             contype=0, conaffinity=0)
        self._net_geoms.append(geom)

  def resize(self, pos, size):
    """Call PositionDetector.resize(), move the goal."""
    super().resize(pos, size)
    self._goalpost_radius = _goalpost_radius(size)
    self._move_goal(pos, size)

  def set_position(self, physics, pos):
    """Call PositionDetector.set_position(), move the goal."""
    super().set_position(pos)
    size = 0.5*(self.upper - self.lower)
    self._move_goal(pos, size)

  def _update_detection(self, physics):
    """Call PositionDetector._update_detection(), then recolor the goalposts."""
    super()._update_detection(physics)
    if self._detected and not self._previously_detected:
      physics.bind(self._goal_geoms).rgba = self.goalpost_detected_rgba
    elif self._previously_detected and not self._detected:
      physics.bind(self._goal_geoms).rgba = self.goalpost_rgba

  @property
  def goalpost_rgba(self):
    """Goalposts are always opaque."""
    rgba = self._rgba.copy()
    rgba[3] = 1
    return rgba

  @property
  def goalpost_detected_rgba(self):
    """Goalposts are always opaque."""
    detected_rgba = self._detected_rgba.copy()
    detected_rgba[3] = 1
    return detected_rgba


class Pitch(composer.Arena):
  """A pitch with a plane, two goals and a field with position detection."""

  def _build(self,
             size=_DEFAULT_PITCH_SIZE,
             goal_size=None,
             top_camera_distance=_TOP_CAMERA_DISTANCE,
             field_box=False,
             field_box_offset=0.0,
             hoarding_color_scheme_id=0,
             name='pitch'):
    """Construct a pitch with walls and position detectors.

    Args:
      size: a tuple of (length, width) of the pitch.
      goal_size: optional (depth, width, height) indicating the goal size.
        If not specified, the goal size is inferred from pitch size with a fixed
        default ratio.
      top_camera_distance: the distance of the top-down camera to the pitch.
      field_box: adds a "field box" that collides with the ball but not the
        walkers.
      field_box_offset: offset for the fieldbox if used.
      hoarding_color_scheme_id: An integer with value 0, 1, 2, or 3, specifying
        a preset scheme for the hoarding colors.
      name: the name of this arena.
    """
    super()._build(name=name)
    self._size = size
    self._goal_size = goal_size
    self._top_camera_distance = top_camera_distance
    self._hoarding_color_scheme_id = hoarding_color_scheme_id

    self._top_camera = self._mjcf_root.worldbody.add(
        'camera',
        name='top_down',
        pos=[0, 0, top_camera_distance],
        zaxis=[0, 0, 1],
        fovy=_top_down_cam_fovy(self._size, top_camera_distance))

    # Set the `extent`, an "average distance" to 0.1 * pitch length.
    extent = 0.1 * max(self._size)
    self._mjcf_root.statistic.extent = extent
    self._mjcf_root.statistic.center = (0, 0, extent)
    # The near and far clipping planes are scaled by `extent`.
    self._mjcf_root.visual.map.zfar = 50             # 5 pitch lengths
    self._mjcf_root.visual.map.znear = 0.1 / extent  # 10 centimeters

    # Add skybox.
    self._mjcf_root.asset.add(
        'texture',
        name='skybox',
        type='skybox',
        builtin='gradient',
        rgb1=(.7, .9, .9),
        rgb2=(.03, .09, .27),
        width=400,
        height=400)

    # Add and position corner lights.
    self._corner_lights = [self._mjcf_root.worldbody.add('light', cutoff=60)
                           for _ in range(4)]
    _reposition_corner_lights(self._corner_lights, size)

    # Increase shadow resolution, (default is 1024).
    self._mjcf_root.visual.quality.shadowsize = 8192

    # Build groundplane.
    if len(self._size) != 2:
      raise ValueError('`size` should be a sequence of length 2: got {!r}'
                       .format(self._size))
    self._field_texture = self._mjcf_root.asset.add(
        'texture',
        type='2d',
        file=_get_texture('pitch_nologo_l'),
        name='fieldplane')
    self._field_material = self._mjcf_root.asset.add(
        'material', name='fieldplane', texture=self._field_texture)

    self._ground_geom = self._mjcf_root.worldbody.add(
        'geom',
        name='ground',
        type='plane',
        material=self._field_material,
        size=list(self._size) + [max(self._size) * _GROUND_GEOM_GRID_RATIO])

    # Build walls.
    self._walls = []
    for wall_pos, wall_xyaxes in _wall_pos_xyaxes(self._size):
      self._walls.append(
          self._mjcf_root.worldbody.add(
              'geom',
              type='plane',
              rgba=[.1, .1, .1, .8],
              pos=wall_pos,
              size=[1e-7, 1e-7, 1e-7],
              xyaxes=wall_xyaxes))

    # Build goal position detectors.
    # If field_box is enabled, offset goal by 1.0 such that ball reaches the
    # goal position detector before bouncing off the field_box.
    self._fb_offset = field_box_offset if field_box else 0.0
    goal_size = self._get_goal_size()
    self._home_goal = Goal(
        direction=1,
        make_net=False,
        pos=(-self._size[0] + goal_size[0] + self._fb_offset, 0,
             goal_size[2]),
        size=goal_size,
        rgba=(.2, .2, 1, 0.5),
        visible=True,
        name='home_goal')
    self.attach(self._home_goal)

    self._away_goal = Goal(
        direction=-1,
        make_net=False,
        pos=(self._size[0] - goal_size[0] - self._fb_offset, 0, goal_size[2]),
        size=goal_size,
        rgba=(1, .2, .2, 0.5),
        visible=True,
        name='away_goal')
    self.attach(self._away_goal)

    # Build inverted field position detectors.
    self._field = props.PositionDetector(
        pos=(0, 0),
        size=(self._size[0] - 2 * goal_size[0],
              self._size[1] - 2 * goal_size[0]),
        inverted=True,
        visible=False,
        name='field')
    self.attach(self._field)

    # Build field perimeter.
    def _visual_plane():
      return self._mjcf_root.worldbody.add(
          'geom',
          type='plane',
          size=(1, 1, 1),
          rgba=(0.306, 0.682, 0.223, 1),
          contype=0,
          conaffinity=0)

    self._perimeter = [_visual_plane() for _ in range(8)]
    self._update_perimeter()

    # Build field box.
    self._field_box = []
    if field_box:
      for box_pos, box_size in _fieldbox_pos_size(
          (self._field.upper - self._field.lower) / 2.0, goal_size):
        self._field_box.append(
            self._mjcf_root.worldbody.add(
                'geom',
                type='box',
                rgba=[.3, .3, .3, .0],
                pos=box_pos,
                size=box_size))

    # Build hoarding sites.
    def _box_site():
      return self._mjcf_root.worldbody.add('site', type='box', size=(1, 1, 1))
    self._hoarding = [_box_site() for _ in range(4 * _NUM_HOARDING)]
    self._update_hoarding()

  def _update_hoarding(self):
    # Resize, reposition and re-color visual perimeter box geoms.
    num_boxes = _NUM_HOARDING
    counter = 0
    for dim in [0, 1]:  # Semantics are [x, y]
      width = self._get_goal_size()[2] / 8  # Eighth of the goal height.
      height = self._get_goal_size()[2] / 2  # Half of the goal height.
      length = self._size[dim]
      if dim == 1:  # Stretch the y-dim length in order to cover the corners.
        length += 2 * width
      box_size = height * np.ones(3)
      box_size[dim] = length / num_boxes
      box_size[1-dim] = width
      dim_pos = np.linspace(-length, length, num_boxes, endpoint=False)
      dim_pos += length / num_boxes  # Offset to center.
      for sign in [-1, 1]:
        alt_pos = sign * (self._size[1-dim] * np.ones(num_boxes) + width)
        dim_alt = (dim_pos, alt_pos)
        for box in range(num_boxes):
          box_pos = np.array((dim_alt[dim][box], dim_alt[1-dim][box], width))
          if self._hoarding_color_scheme_id == 0:
            # Red to blue through green + blue hoarding behind blue goal
            angle = np.pi + np.arctan2(box_pos[0], -np.abs(box_pos[1]))
          elif self._hoarding_color_scheme_id == 1:
            # Red to blue through green + blue hoarding behind red goal
            angle = np.arctan2(box_pos[0], np.abs(box_pos[1]))
          elif self._hoarding_color_scheme_id == 2:
            # Red to blue through purple + blue hoarding behind red goal
            angle = np.arctan2(box_pos[0], -np.abs(box_pos[1]))
          elif self._hoarding_color_scheme_id == 3:
            # Red to blue through purple + blue hoarding behind blue goal
            angle = np.pi + np.arctan2(box_pos[0], np.abs(box_pos[1]))
          hue = 0.5 + angle / (2*np.pi)  # In [0, 1]
          hue_offset = .25
          hue = (hue - hue_offset) % 1.0  # Apply offset and wrap back to [0, 1]
          saturation = .7
          value = 1.0
          col_r, col_g, col_b = colorsys.hsv_to_rgb(hue, saturation, value)
          self._hoarding[counter].pos = box_pos
          self._hoarding[counter].size = box_size
          self._hoarding[counter].rgba = (col_r, col_g, col_b, 1.)
          counter += 1

  def _update_perimeter(self):
    # Resize and reposition visual perimeter plane geoms.
    width = self._get_goal_size()[0]
    counter = 0
    for x in [-1, 0, 1]:
      for y in [-1, 0, 1]:
        if x == 0 and y == 0:
          continue
        size_0 = self._size[0]-2*width if x == 0 else width
        size_1 = self._size[1]-2*width if y == 0 else width
        size = [size_0, size_1, max(self._size) * _GROUND_GEOM_GRID_RATIO]
        pos = (x*(self._size[0]-width), y*(self._size[1]-width), 0)
        self._perimeter[counter].size = size
        self._perimeter[counter].pos = pos
        counter += 1

  def _get_goal_size(self):
    goal_size = self._goal_size
    if goal_size is None:
      goal_size = (
          _SIDE_WIDTH / 2,
          self._size[1] * _DEFAULT_GOAL_LENGTH_RATIO,
          _SIDE_WIDTH / 2,
      )
    return goal_size

  def register_ball(self, ball):
    self._home_goal.register_entities(ball)
    self._away_goal.register_entities(ball)

    if self._field_box:
      # Geoms a and b collides if:
      #   (a.contype & b.conaffinity) || (b.contype & a.conaffinity) != 0.
      #   See: http://www.mujoco.org/book/computation.html#Collision
      ball.geom.contype = (ball.geom.contype or 1) | _FIELD_BOX_CONTACT_BIT
      for wall in self._field_box:
        wall.conaffinity = _FIELD_BOX_CONTACT_BIT
        wall.contype = _FIELD_BOX_CONTACT_BIT
    else:
      self._field.register_entities(ball)

  def detected_goal(self):
    """Returning the team that scored a goal."""
    if self._home_goal.detected_entities:
      return team.Team.AWAY
    if self._away_goal.detected_entities:
      return team.Team.HOME
    return None

  def detected_off_court(self):
    return self._field.detected_entities

  @property
  def size(self):
    return self._size

  @property
  def home_goal(self):
    return self._home_goal

  @property
  def away_goal(self):
    return self._away_goal

  @property
  def field(self):
    return self._field

  @property
  def ground_geom(self):
    return self._ground_geom


class RandomizedPitch(Pitch):
  """RandomizedPitch that randomizes its size between (min_size, max_size)."""

  def __init__(self,
               min_size,
               max_size,
               randomizer=None,
               keep_aspect_ratio=False,
               goal_size=None,
               field_box=False,
               field_box_offset=0.0,
               top_camera_distance=_TOP_CAMERA_DISTANCE,
               name='randomized_pitch'):
    """Construct a randomized pitch.

    Args:
      min_size: a tuple of minimum (length, width) of the pitch.
      max_size: a tuple of maximum (length, width) of the pitch.
      randomizer: a callable that returns ratio between [0., 1.] that scales
        between min_size, max_size.
      keep_aspect_ratio: if `True`, keep the aspect ratio constant during
        randomization.
      goal_size: optional (depth, width, height) indicating the goal size.
        If not specified, the goal size is inferred from pitch size with a fixed
        default ratio.
      field_box: optional indicating if we should construct field box containing
        the ball (but not the walkers).
      field_box_offset: offset for the fieldbox if used.
      top_camera_distance: the distance of the top-down camera to the pitch.
      name: the name of this arena.
    """
    super().__init__(
        size=max_size,
        goal_size=goal_size,
        top_camera_distance=top_camera_distance,
        field_box=field_box,
        field_box_offset=field_box_offset,
        name=name)

    self._min_size = min_size
    self._max_size = max_size

    self._randomizer = randomizer or distributions.Uniform()
    self._keep_aspect_ratio = keep_aspect_ratio

    # Sample a new size and regenerate the soccer pitch.
    logging.info('%s between (%s, %s) with %s', self.__class__.__name__,
                 min_size, max_size, self._randomizer)

  def _resize_goals(self, goal_size):
    self._home_goal.resize(
        pos=(-self._size[0] + goal_size[0] + self._fb_offset, 0, goal_size[2]),
        size=goal_size)
    self._away_goal.resize(
        pos=(self._size[0] - goal_size[0] - self._fb_offset, 0, goal_size[2]),
        size=goal_size)

  def initialize_episode_mjcf(self, random_state):
    super().initialize_episode_mjcf(random_state)
    min_len, min_wid = self._min_size
    max_len, max_wid = self._max_size

    if self._keep_aspect_ratio:
      len_ratio = self._randomizer(random_state=random_state)
      wid_ratio = len_ratio
    else:
      len_ratio = self._randomizer(random_state=random_state)
      wid_ratio = self._randomizer(random_state=random_state)

    self._size = (min_len + len_ratio * (max_len - min_len),
                  min_wid + wid_ratio * (max_wid - min_wid))

    # Reset top_down camera field of view.
    self._top_camera.fovy = _top_down_cam_fovy(self._size,
                                               self._top_camera_distance)

    # Resize ground perimeter.
    self._update_perimeter()

    # Resize and reposition walls and roof geoms.
    for i, (wall_pos, _) in enumerate(_wall_pos_xyaxes(self._size)):
      self._walls[i].pos = wall_pos

    goal_size = self._get_goal_size()
    self._resize_goals(goal_size)

    # Resize inverted field position detectors.
    field_size = (self._size[0] -2*goal_size[0], self._size[1] -2*goal_size[0])
    self._field.resize(pos=(0, 0), size=field_size)

    # Resize ground geom size.
    self._ground_geom.size = list(
        field_size) + [max(self._size) * _GROUND_GEOM_GRID_RATIO]

    # Resize and reposition field box geoms.
    if self._field_box:
      for i, (pos, size) in enumerate(
          _fieldbox_pos_size((self._field.upper - self._field.lower) / 2.0,
                             goal_size)):
        self._field_box[i].pos = pos
        self._field_box[i].size = size

    # Reposition corner lights.
    _reposition_corner_lights(
        self._corner_lights,
        size=(self._size[0] - 2 * goal_size[0],
              self._size[1] - 2 * goal_size[0]))

    # Resize, reposition and recolor hoarding geoms.
    self._update_hoarding()


# Mini-football (5v5) dimensions.
_GOAL_LENGTH = 3.66
_GOAL_SIDE = 1.22

MINI_FOOTBALL_MIN_AREA_PER_HUMANOID = 100.0
MINI_FOOTBALL_MAX_AREA_PER_HUMANOID = 350.0
MINI_FOOTBALL_GOAL_SIZE = (_GOAL_SIDE / 2, _GOAL_LENGTH / 2, _GOAL_SIDE / 2)
