text: # Copyright 2018-2021 Streamlit Inc.
  #
  # 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.
  
  import textwrap
  from typing import cast, Optional, NamedTuple
  
  import streamlit
  from streamlit.errors import StreamlitAPIException
  from streamlit.proto import Block_pb2
  from streamlit.report_thread import get_report_ctx
  
  
  class FormData(NamedTuple):
      """Form data stored on a DeltaGenerator."""
  
      # The form's unique ID.
      form_id: str
  
  
  def _current_form(
      this_dg: "streamlit.delta_generator.DeltaGenerator",
  ) -> Optional[FormData]:
      """Find the FormData for the given DeltaGenerator.
  
      Forms are blocks, and can have other blocks nested inside them.
      To find the current form, we walk up the dg_stack until we find
      a DeltaGenerator that has FormData.
      """
      if not streamlit._is_running_with_streamlit:
          return None
  
      if this_dg._form_data is not None:
          return this_dg._form_data
  
      if this_dg == this_dg._main_dg:
          # We were created via an `st.foo` call.
          # Walk up the dg_stack to see if we're nested inside a `with st.form` statement.
          ctx = get_report_ctx()
          if ctx is None or len(ctx.dg_stack) == 0:
              return None
  
          for dg in reversed(ctx.dg_stack):
              if dg._form_data is not None:
                  return dg._form_data
      else:
          # We were created via an `dg.foo` call.
          # Take a look at our parent's form data to see if we're nested inside a form.
          parent = this_dg._parent
          if parent is not None and parent._form_data is not None:
              return parent._form_data
  
      return None
  
  
  def current_form_id(dg: "streamlit.delta_generator.DeltaGenerator") -> str:
      """Return the form_id for the current form, or the empty string if we're
      not inside an `st.form` block.
  
      (We return the empty string, instead of None, because this value is
      assigned to protobuf message fields, and None is not valid.)
      """
      form_data = _current_form(dg)
      if form_data is None:
          return ""
      return form_data.form_id
  
  
  def is_in_form(dg: "streamlit.delta_generator.DeltaGenerator") -> bool:
      """True if the DeltaGenerator is inside an st.form block."""
      return current_form_id(dg) != ""
  
  
  def _build_duplicate_form_message(user_key: Optional[str] = None) -> str:
      if user_key is not None:
          message = textwrap.dedent(
              f"""
              There are multiple identical forms with `key='{user_key}'`.
  
              To fix this, please make sure that the `key` argument is unique for
              each `st.form` you create.
              """
          )
      else:
          message = textwrap.dedent(
              """
              There are multiple identical forms with the same generated key.
  
              When a form is created, it's assigned an internal key based on
              its structure. Multiple forms with an identical structure will
              result in the same internal key, which causes this error.
  
              To fix this error, please pass a unique `key` argument to
              `st.form`.
              """
          )
  
      return message.strip("\n")
  
  
  class FormMixin:
      def form(self, key: str):
          """Create a form that batches elements together with a "Submit" button.
  
          A form is a container that visually groups other elements and
          widgets together, and contains a Submit button. When the form's
          Submit button is pressed, all widget values inside the form will be
          sent to Streamlit in a batch.
  
          To add elements to the returned form object, you can use "with" notation
          (preferred) or just call methods directly on the returned object. See
          examples below.
  
          Forms have a few constraints:
          - Every form must contain a `st.form_submit_button`.
          - You cannot add a normal `st.button` to a form.
          - Forms can appear anywhere in your app (sidebar, columns, etc),
            but they cannot be embedded inside other forms.
  
          Parameters
          ----------
          key : str
              A string that identifies the form. Each form must have its own
              key. (This key is not displayed to the user in the interface.)
  
          Examples
          --------
  
          Inserting elements using "with" notation:
  
          >>> with st.form("my_form"):
          ...    st.write("Inside the form")
          ...    slider_val = st.slider("Form slider")
          ...    checkbox_val = st.checkbox("Form checkbox")
          ...
          ...    # Every form must have a submit button.
          ...    submitted = st.form_submit_button("Submit")
          ...    if submitted:
          ...        st.write("slider", slider_val, "checkbox", checkbox_val)
          ...
          >>> st.write("Outside the form")
  
          .. output ::
              https://static.streamlit.io/0.80.0-xWVf/index.html?id=JMUHDxSEHmT9yRPNDDWAb5
  
          Inserting elements out of order:
  
          >>> form = st.form("my_form")
          >>> form.slider("Inside the form")
          >>> st.slider("Outside the form")
          >>>
          >>> # Now add a submit button to the form:
          >>> form.form_submit_button("Submit")
  
          .. output ::
              https://static.streamlit.io/0.80.0-xWVf/index.html?id=9DmSCcbDAfyC6dPxaKmJK4
          """
  
          if is_in_form(self.dg):
              raise StreamlitAPIException("Forms cannot be nested in other forms.")
  
          # A form is uniquely identified by its key.
          form_id = key
  
          ctx = get_report_ctx()
          if ctx is not None:
              added_form_id = ctx.form_ids_this_run.add(form_id)
              if not added_form_id:
                  raise StreamlitAPIException(_build_duplicate_form_message(key))
  
          block_proto = Block_pb2.Block()
          block_proto.form_id = form_id
          block_dg = self.dg._block(block_proto)
  
          # Attach the form's button info to the newly-created block's
          # DeltaGenerator.
          block_dg._form_data = FormData(form_id)
          return block_dg
  
      def form_submit_button(self, label="Submit"):
          """Display a form submit button.
  
          When this button is clicked, all widget values inside the form will be
          sent to Streamlit in a batch.
  
          Every form must have a form_submit_button. A form_submit_button
          cannot exist outside a form.
  
          Parameters
          ----------
          label : str
              A short label explaining to the user what this button is for.
              Defaults to "Submit".
  
          Returns
          -------
          bool
              True if the submit button was clicked.
          """
          return self.dg._button(
              label=label,
              key=f"FormSubmitter:{current_form_id(self.dg)}",
              help=None,
              is_form_submitter=True,
          )
  
      @property
      def dg(self) -> "streamlit.delta_generator.DeltaGenerator":
          """Get our DeltaGenerator."""
          return cast("streamlit.delta_generator.DeltaGenerator", self)
  