fancy_chat.py

import random
import time
from dataclasses import asdict, dataclass
from typing import Callable, Literal

import mesop as me

Role = Literal["user", "bot"]


_APP_TITLE = "Fancy Mesop Chat"
_BOT_AVATAR_LETTER = "M"
_EMPTY_CHAT_MESSAGE = "Get started with an example"
_EXAMPLE_USER_QUERIES = (
  "What is Mesop?",
  "Make me a chat app.",
  "How do I make a web component?",
)
_CHAT_MAX_WIDTH = "800px"
_MOBILE_BREAKPOINT = 640


@dataclass(kw_only=True)
class ChatMessage:
  """Chat message metadata."""

  role: Role = "user"
  content: str = ""
  edited: bool = False
  # 1 is positive
  # -1 is negative
  # 0 is no rating
  rating: int = 0


@me.stateclass
class State:
  input: str
  output: list[ChatMessage]
  in_progress: bool
  sidebar_expanded: bool = False
  # Need to use dict instead of ChatMessage due to serialization bug.
  # See: https://github.com/google/mesop/issues/659
  history: list[list[dict]]


def respond_to_chat(input: str, history: list[ChatMessage]):
  """Displays random canned text.

  Edit this function to process messages with a real chatbot/LLM.
  """
  lines = [
    "Mesop is a Python-based UI framework designed to simplify web UI development for engineers without frontend experience.",
    "It leverages the power of the Angular web framework and Angular Material components, allowing rapid construction of web demos and internal tools.",
    "With Mesop, developers can enjoy a fast build-edit-refresh loop thanks to its hot reload feature, making UI tweaks and component integration seamless.",
    "Deployment is straightforward, utilizing standard HTTP technologies.",
    "Mesop's component library aims for comprehensive Angular Material component coverage, enhancing UI flexibility and composability.",
    "It supports custom components for specific use cases, ensuring developers can extend its capabilities to fit their unique requirements.",
    "Mesop's roadmap includes expanding its component library and simplifying the onboarding processs.",
  ]

  for line in random.sample(lines, random.randint(3, len(lines) - 1)):
    time.sleep(0.3)
    yield line + " "


def on_load(e: me.LoadEvent):
  me.set_theme_mode("system")


@me.page(
  security_policy=me.SecurityPolicy(
    allowed_iframe_parents=["https://google.github.io", "https://huggingface.co."]
  ),
  title="Fancy Mesop Demo Chat",
  path="/fancy_chat",
  on_load=on_load,
)
def page():
  state = me.state(State)

  with me.box(
    style=me.Style(
      background=me.theme_var("surface-container-lowest"),
      display="flex",
      flex_direction="column",
      height="100%",
    )
  ):
    with me.box(
      style=me.Style(
        display="flex", flex_direction="row", flex_grow=1, overflow="hidden"
      )
    ):
      with me.box(
        style=me.Style(
          background=me.theme_var("surface-container-low"),
          display="flex",
          flex_direction="column",
          flex_shrink=0,
          position="absolute"
          if state.sidebar_expanded and _is_mobile()
          else None,
          height="100%" if state.sidebar_expanded and _is_mobile() else None,
          width=300 if state.sidebar_expanded else None,
          z_index=2000,
        )
      ):
        sidebar()

      with me.box(
        style=me.Style(
          display="flex",
          flex_direction="column",
          flex_grow=1,
          padding=me.Padding(left=60)
          if state.sidebar_expanded and _is_mobile()
          else None,
        )
      ):
        header()
        with me.box(style=me.Style(flex_grow=1, overflow_y="scroll")):
          if state.output:
            chat_pane()
          else:
            examples_pane()
        chat_input()


def sidebar():
  state = me.state(State)
  with me.box(
    style=me.Style(
      display="flex",
      flex_direction="column",
      flex_grow=1,
    )
  ):
    with me.box(style=me.Style(display="flex", gap=20)):
      menu_icon(icon="menu", tooltip="Menu", on_click=on_click_menu_icon)
      if state.sidebar_expanded:
        me.text(
          _APP_TITLE,
          style=me.Style(margin=me.Margin(bottom=0, top=14)),
          type="headline-6",
        )

    if state.sidebar_expanded:
      menu_item(icon="add", label="New chat", on_click=on_click_new_chat)
    else:
      menu_icon(icon="add", tooltip="New chat", on_click=on_click_new_chat)

    if state.sidebar_expanded:
      history_pane()


def history_pane():
  state = me.state(State)
  for index, chat in enumerate(state.history):
    with me.box(
      key=f"chat-{index}",
      on_click=on_click_history,
      style=me.Style(
        background=me.theme_var("surface-container"),
        border=me.Border.all(
          me.BorderSide(
            width=1, color=me.theme_var("outline-variant"), style="solid"
          )
        ),
        border_radius=5,
        cursor="pointer",
        margin=me.Margin.symmetric(horizontal=10, vertical=10),
        padding=me.Padding.all(10),
        text_overflow="ellipsis",
      ),
    ):
      me.text(_truncate_text(chat[0]["content"]))


def header():
  state = me.state(State)
  with me.box(
    style=me.Style(
      align_items="center",
      background=me.theme_var("surface-container-lowest"),
      display="flex",
      gap=5,
      justify_content="space-between",
      padding=me.Padding.symmetric(horizontal=20, vertical=10),
    )
  ):
    with me.box(style=me.Style(display="flex", gap=5)):
      if not state.sidebar_expanded:
        me.text(
          _APP_TITLE,
          style=me.Style(margin=me.Margin(bottom=0)),
          type="headline-6",
        )

    with me.box(style=me.Style(display="flex", gap=5)):
      icon_button(
        key="",
        icon="dark_mode" if me.theme_brightness() == "light" else "light_mode",
        tooltip="Dark mode"
        if me.theme_brightness() == "light"
        else "Light mode",
        on_click=on_click_theme_brightness,
      )


def examples_pane():
  with me.box(
    style=me.Style(
      margin=me.Margin.symmetric(horizontal="auto"),
      padding=me.Padding.all(15),
      width=f"min({_CHAT_MAX_WIDTH}, 100%)",
    )
  ):
    with me.box(style=me.Style(margin=me.Margin(top=25), font_size=24)):
      me.text(_EMPTY_CHAT_MESSAGE)

    with me.box(
      style=me.Style(
        display="flex",
        flex_direction="column" if _is_mobile() else "row",
        gap=20,
        margin=me.Margin(top=25),
      )
    ):
      for index, query in enumerate(_EXAMPLE_USER_QUERIES):
        with me.box(
          key=f"query-{index}",
          on_click=on_click_example_user_query,
          style=me.Style(
            background=me.theme_var("surface-container-highest"),
            border_radius=15,
            padding=me.Padding.all(20),
            cursor="pointer",
          ),
        ):
          me.text(query)


def chat_pane():
  state = me.state(State)
  with me.box(
    style=me.Style(
      background=me.theme_var("surface-container-lowest"),
      color=me.theme_var("on-surface"),
      display="flex",
      flex_direction="column",
      margin=me.Margin.symmetric(horizontal="auto"),
      padding=me.Padding.all(15),
      width=f"min({_CHAT_MAX_WIDTH}, 100%)",
    )
  ):
    for index, msg in enumerate(state.output):
      if msg.role == "user":
        user_message(message=msg)
      else:
        bot_message(message_index=index, message=msg)

    if state.in_progress:
      with me.box(key="scroll-to", style=me.Style(height=250)):
        pass


def user_message(*, message: ChatMessage):
  with me.box(
    style=me.Style(
      display="flex",
      gap=15,
      justify_content="end",
      margin=me.Margin.all(20),
    )
  ):
    with me.box(
      style=me.Style(
        background=me.theme_var("surface-container-low"),
        border_radius=10,
        color=me.theme_var("on-surface-variant"),
        padding=me.Padding.symmetric(vertical=0, horizontal=10),
        width="66%",
      )
    ):
      me.markdown(message.content)


def bot_message(*, message_index: int, message: ChatMessage):
  with me.box(style=me.Style(display="flex", gap=15, margin=me.Margin.all(20))):
    text_avatar(
      background=me.theme_var("primary"),
      color=me.theme_var("on-primary"),
      label=_BOT_AVATAR_LETTER,
    )

    # Bot message response
    with me.box(style=me.Style(display="flex", flex_direction="column")):
      me.markdown(
        message.content,
        style=me.Style(color=me.theme_var("on-surface")),
      )

      # Actions panel
      with me.box():
        icon_button(
          key=f"thumb_up-{message_index}",
          icon="thumb_up",
          is_selected=message.rating == 1,
          tooltip="Good response",
          on_click=on_click_thumb_up,
        )
        icon_button(
          key=f"thumb_down-{message_index}",
          icon="thumb_down",
          is_selected=message.rating == -1,
          tooltip="Bad response",
          on_click=on_click_thumb_down,
        )
        icon_button(
          key=f"restart-{message_index}",
          icon="restart_alt",
          tooltip="Regenerate answer",
          on_click=on_click_regenerate,
        )


def chat_input():
  state = me.state(State)
  with me.box(
    style=me.Style(
      background=me.theme_var("surface-container")
      if _is_mobile()
      else me.theme_var("surface-container"),
      border_radius=16,
      display="flex",
      margin=me.Margin.symmetric(horizontal="auto", vertical=15),
      padding=me.Padding.all(8),
      width=f"min({_CHAT_MAX_WIDTH}, 90%)",
    )
  ):
    with me.box(
      style=me.Style(
        flex_grow=1,
      )
    ):
      me.native_textarea(
        autosize=True,
        key="chat_input",
        min_rows=4,
        on_blur=on_chat_input,
        shortcuts={
          me.Shortcut(shift=True, key="Enter"): on_submit_chat_msg,
        },
        placeholder="Enter your prompt",
        style=me.Style(
          background=me.theme_var("surface-container")
          if _is_mobile()
          else me.theme_var("surface-container"),
          border=me.Border.all(
            me.BorderSide(style="none"),
          ),
          color=me.theme_var("on-surface-variant"),
          outline="none",
          overflow_y="auto",
          padding=me.Padding(top=16, left=16),
          width="100%",
        ),
        value=state.input,
      )
    with me.content_button(
      disabled=state.in_progress,
      on_click=on_click_submit_chat_msg,
      type="icon",
    ):
      me.icon("send")


@me.component
def text_avatar(*, label: str, background: str, color: str):
  me.text(
    label,
    style=me.Style(
      background=background,
      border_radius="50%",
      color=color,
      font_size=20,
      height=40,
      line_height="1",
      margin=me.Margin(top=16),
      padding=me.Padding(top=10),
      text_align="center",
      width="40px",
    ),
  )


@me.component
def icon_button(
  *,
  icon: str,
  tooltip: str,
  key: str = "",
  is_selected: bool = False,
  on_click: Callable | None = None,
):
  selected_style = me.Style(
    background=me.theme_var("surface-container-low"),
    color=me.theme_var("on-surface-variant"),
  )
  with me.tooltip(message=tooltip):
    with me.content_button(
      type="icon",
      key=key,
      on_click=on_click,
      style=selected_style if is_selected else None,
    ):
      me.icon(icon)


@me.component
def menu_icon(
  *, icon: str, tooltip: str, key: str = "", on_click: Callable | None = None
):
  with me.tooltip(message=tooltip):
    with me.content_button(
      key=key,
      on_click=on_click,
      style=me.Style(margin=me.Margin.all(10)),
      type="icon",
    ):
      me.icon(icon)


@me.component
def menu_item(
  *, icon: str, label: str, key: str = "", on_click: Callable | None = None
):
  with me.box(on_click=on_click):
    with me.box(
      style=me.Style(
        background=me.theme_var("surface-container-high"),
        border_radius=20,
        cursor="pointer",
        display="inline-flex",
        gap=10,
        line_height=1,
        margin=me.Margin.all(10),
        padding=me.Padding(top=10, left=10, right=20, bottom=10),
      ),
    ):
      me.icon(icon)
      me.text(label, style=me.Style(height=24, line_height="24px"))


# Event Handlers


def on_click_example_user_query(e: me.ClickEvent):
  """Populates the user input with the example query"""
  state = me.state(State)
  _, example_index = e.key.split("-")
  state.input = _EXAMPLE_USER_QUERIES[int(example_index)]
  me.focus_component(key="chat_input")


def on_click_thumb_up(e: me.ClickEvent):
  """Gives the message a positive rating"""
  state = me.state(State)
  _, msg_index = e.key.split("-")
  msg_index = int(msg_index)
  state.output[msg_index].rating = 1


def on_click_thumb_down(e: me.ClickEvent):
  """Gives the message a negative rating"""
  state = me.state(State)
  _, msg_index = e.key.split("-")
  msg_index = int(msg_index)
  state.output[msg_index].rating = -1


def on_click_new_chat(e: me.ClickEvent):
  """Resets messages."""
  state = me.state(State)
  if state.output:
    state.history.insert(0, [asdict(messages) for messages in state.output])
  state.output = []
  me.focus_component(key="chat_input")


def on_click_history(e: me.ClickEvent):
  """Loads existing chat from history and saves current chat"""
  state = me.state(State)
  _, chat_index = e.key.split("-")
  chat_messages = [
    ChatMessage(**chat) for chat in state.history.pop(int(chat_index))
  ]
  if state.output:
    state.history.insert(0, [asdict(messages) for messages in state.output])
  state.output = chat_messages
  me.focus_component(key="chat_input")


def on_click_theme_brightness(e: me.ClickEvent):
  """Toggles dark mode."""
  if me.theme_brightness() == "light":
    me.set_theme_mode("dark")
  else:
    me.set_theme_mode("light")


def on_click_menu_icon(e: me.ClickEvent):
  """Expands and collapses sidebar menu."""
  state = me.state(State)
  state.sidebar_expanded = not state.sidebar_expanded


def on_chat_input(e: me.InputBlurEvent):
  """Capture chat text input on blur."""
  state = me.state(State)
  state.input = e.value


def on_click_regenerate(e: me.ClickEvent):
  """Regenerates response from an existing message"""
  state = me.state(State)
  _, msg_index = e.key.split("-")
  msg_index = int(msg_index)

  # Get the user message which is the previous message
  user_message = state.output[msg_index - 1]
  # Get bot message to be regenerated
  assistant_message = state.output[msg_index]
  assistant_message.content = ""
  state.in_progress = True
  yield

  start_time = time.time()
  # Send in the old user input and chat history to get the bot response.
  # We make sure to only pass in the chat history up to this message.
  output_message = respond_to_chat(
    user_message.content, state.output[:msg_index]
  )
  for content in output_message:
    assistant_message.content += content
    # TODO: 0.25 is an abitrary choice. In the future, consider making this adjustable.
    if (time.time() - start_time) >= 0.25:
      start_time = time.time()
      yield

  state.in_progress = False
  me.focus_component(key="chat_input")
  yield


def on_submit_chat_msg(e: me.TextareaShortcutEvent):
  state = me.state(State)
  state.input = e.value
  yield
  yield from _submit_chat_msg()


def on_click_submit_chat_msg(e: me.ClickEvent):
  yield from _submit_chat_msg()


def _submit_chat_msg():
  """Handles submitting a chat message."""
  state = me.state(State)
  if state.in_progress or not state.input:
    return
  input = state.input
  # Clear the text input.
  state.input = ""
  yield

  output = state.output
  if output is None:
    output = []
  output.append(ChatMessage(role="user", content=input))
  state.in_progress = True
  me.scroll_into_view(key="scroll-to")
  yield

  start_time = time.time()
  # Send user input and chat history to get the bot response.
  output_message = respond_to_chat(input, state.output)
  assistant_message = ChatMessage(role="bot")
  output.append(assistant_message)
  state.output = output
  for content in output_message:
    assistant_message.content += content
    # TODO: 0.25 is an abitrary choice. In the future, consider making this adjustable.
    if (time.time() - start_time) >= 0.25:
      start_time = time.time()
      yield

  state.in_progress = False
  me.focus_component(key="chat_input")
  yield


# Helpers


def _is_mobile():
  return me.viewport_size().width < _MOBILE_BREAKPOINT


def _truncate_text(text, char_limit=100):
  """Truncates text that is too long."""
  if len(text) <= char_limit:
    return text
  truncated_text = text[:char_limit].rsplit(" ", 1)[0]
  return truncated_text.rstrip(".,!?;:") + "..."