Mujoco_WASM/python/mujoco/codegen/generate_spec_bindings.py

# Copyright 2024 DeepMind Technologies Limited
#
# 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.
# ==============================================================================
"""Generates the bindings for the MuJoCo specs."""

from collections.abc import Sequence

from absl import app

from introspect import ast_nodes
from introspect import structs


def _scalar_binding_code(
    field: ast_nodes.ValueType, classname: str = '', varname: str = ''
) -> str:
  """Creates a string that defines Python bindings for a scalar type."""
  fulltype = field.name + '&'  # default return type is by reference
  fullvarname = varname
  rawclassname = classname.replace('mjs', 'raw::Mjs')
  if classname == 'mjSpec':  # raw mjSpec has a wrapper
    rawclassname = classname.replace('mjS', 'MjS')
    fullvarname = 'ptr->' + varname
  if field.name.startswith('mjs'):  # all other mjs are raw structs
    fulltype = field.name.replace('mjs', 'raw::Mjs')
    if field.name != 'mjsPlugin' and field.name != 'mjsOrientation':
      fulltype = fulltype + '*'  # plugin and orientation are pointers
  return f"""\
  {classname}.def_property(
      "{varname}",
      []({rawclassname}& self) -> {fulltype} {{
        return self.{fullvarname};
    }},
      []({rawclassname}& self, {fulltype} {varname}) {{
        (self.{fullvarname}) = {varname};
    }}, py::return_value_policy::reference_internal);"""


def _array_binding_code(
    field: ast_nodes.ArrayType, classname: str = '', varname: str = ''
) -> str:
  """Creates a string that declares Python bindings for an array type."""
  if len(field.extents) > 1:
    raise NotImplementedError()
  innertype = field.inner_type.decl()
  rawclassname = classname.replace('mjs', 'raw::Mjs')
  fullvarname = varname
  if classname == 'mjSpec':  # raw mjSpec has a wrapper
    rawclassname = classname.replace('mjS', 'MjS')
    fullvarname = 'ptr->' + varname
  if innertype == 'double' or innertype == 'mjtNum':
    innertype = 'MjDouble'  # custom Eigen type
  elif innertype == 'float':
    innertype = 'MjFloat'  # custom Eigen type
  elif innertype == 'int':
    innertype = 'MjInt'  # custom Eigen type
  elif innertype == 'char':
    # char array special case
    return f"""\
  {classname}.def_property(
    "{varname}",
    []({rawclassname}& self) -> py::array_t<char> {{
      return py::array_t<char>({field.extents[0]}, self.{fullvarname});
    }},
    []({rawclassname}& self, py::object rhs) {{
      int i = 0;
      for (auto val : rhs) {{
        self.{fullvarname}[i++] = (py::cast<char>(val));
      }}
    }}, py::return_value_policy::reference_internal);"""
  # all other array types
  return f"""\
  {classname}.def_property(
      "{varname}",
      []({rawclassname}& self) -> {innertype}{field.extents[0]} {{
        return {innertype}{field.extents[0]}(self.{fullvarname});
    }},
      []({rawclassname}& self, {innertype}Ref{field.extents[0]} {varname}) {{
        {innertype}{field.extents[0]}(self.{fullvarname}) = {varname};
    }}, py::return_value_policy::reference_internal);"""


def _ptr_binding_code(
    field: ast_nodes.PointerType, classname: str = '', varname: str = ''
) -> str:
  """Creates a string that declares Python bindings for a pointer type."""
  vartype = field.inner_type.decl()
  rawclassname = classname.replace('mjs', 'raw::Mjs')
  fullvarname = varname
  if classname == 'mjSpec':  # raw mjSpec has a wrapper
    rawclassname = classname.replace('mjS', 'MjS')
    fullvarname = 'ptr->' + varname
  if vartype == 'mjsElement':  # this is ignored by the caller
    return 'mjsElement'
  if vartype.startswith('mjs'):  # for structs, use the scalar case
    return _scalar_binding_code(field.inner_type, classname, varname)
  elif vartype == 'mjString':  # C++ string -> Python string
    return f"""\
  {classname}.def_property(
      "{varname}",
      []({rawclassname}& self) -> std::string_view {{
        return *self.{fullvarname};
      }},
      []({rawclassname}& self, std::string_view {varname}) {{
        *(self.{fullvarname}) = {varname};
    }}, py::return_value_policy::reference_internal);"""
  elif (  # C++ vectors of scalars -> Python array
      vartype == 'mjDoubleVec'
      or vartype == 'mjFloatVec'
      or vartype == 'mjIntVec'
    ):
    vartype = vartype.replace('mj', '').replace('Vec', '').lower()
    return f"""\
  {classname}.def_property(
    "{varname}",
    []({rawclassname}& self) -> py::array_t<{vartype}> {{
        return py::array_t<{vartype}>(self.{fullvarname}->size(),
                                      self.{fullvarname}->data());
      }},
    []({rawclassname}& self, py::object rhs) {{
        self.{fullvarname}->clear();
        self.{fullvarname}->reserve(py::len(rhs));
        for (auto val : rhs) {{
          self.{fullvarname}->push_back(py::cast<{vartype}>(val));
      }}
    }}, py::return_value_policy::reference_internal);"""
  elif vartype == 'mjStringVec':  # C++ vector of strings -> Python list
    return f"""\
  {classname}.def_property(
    "{varname}",
    []({rawclassname}& self) -> py::list {{
        py::list list;
        for (auto val : *self.{fullvarname}) {{
          list.append(val);
        }}
        return list;
      }},
    []({rawclassname}& self, py::object rhs) {{
        self.{fullvarname}->clear();
        self.{fullvarname}->reserve(py::len(rhs));
        for (auto val : rhs) {{
          self.{fullvarname}->push_back(py::cast<std::string>(val));
      }}
    }}, py::return_value_policy::reference_internal);"""
  elif 'VecVec' in vartype:  # C++ vector of vectors -> Python list of lists
    vartype = vartype.replace('mj', '').replace('VecVec', '').lower()
    return f"""\
  {classname}.def_property(
    "{varname}",
    []({rawclassname}& self) -> py::list {{
        py::list list;
        for (auto inner_vec : *self.{fullvarname}) {{
          py::list inner_list;
          for (auto val : inner_vec) {{
            inner_list.append(val);
          }}
          list.append(inner_list);
        }}
        return list;
      }},
    []({rawclassname}& self, py::object rhs) {{
        self.{fullvarname}->clear();
        self.{fullvarname}->reserve(py::len(rhs));
        for (auto inner_list : rhs) {{
          auto inner_vec = py::cast<std::vector<{vartype}>>(inner_list);
          self.{fullvarname}->push_back(inner_vec);
        }}
    }}, py::return_value_policy::reference_internal);"""

  raise NotImplementedError()


def _binding_code(field: ast_nodes.StructFieldDecl, key: str) -> str:
  if isinstance(field.type, ast_nodes.ValueType):
    return _scalar_binding_code(field.type, key, field.name)
  elif isinstance(field.type, ast_nodes.PointerType):
    return _ptr_binding_code(field.type, key, field.name)
  elif isinstance(field.type, ast_nodes.ArrayType):
    return _array_binding_code(field.type, key, field.name)
  return ''


def generate() -> None:
  for key in structs.STRUCTS.keys():
    if (key.startswith('mjs') or key == 'mjSpec') and key != 'mjsElement':
      print('\n  // ' + key)
      for field in structs.STRUCTS[key].fields:
        code = _binding_code(field, key)
        if code != 'mjsElement':
          print(code)


def main(argv: Sequence[str]) -> None:
  if len(argv) > 1:
    raise app.UsageError('Too many command-line arguments.')
  generate()

if __name__ == '__main__':
  app.run(main)