src/streamlit_app.py

import ast
import operator as op
import random
from datetime import datetime
import json
import re
import streamlit as st

# -----------------------------
# Utilities
# -----------------------------
def safe_eval(expr: str):
    """
    Safely evaluate a simple arithmetic expression using Python's AST.
    Supports: +, -, *, /, %, //, **, parentheses, unary +/-, ints/floats.
    """
    # Map AST operator nodes to actual Python operators
    operators = {
        ast.Add: op.add,
        ast.Sub: op.sub,
        ast.Mult: op.mul,
        ast.Div: op.truediv,
        ast.Mod: op.mod,
        ast.FloorDiv: op.floordiv,
        ast.Pow: op.pow,
        ast.UAdd: op.pos,
        ast.USub: op.neg,
    }

    def _eval(node):
        if isinstance(node, ast.Expression):
            return _eval(node.body)
        if isinstance(node, ast.Constant) and isinstance(node.value, (int, float)):
            return node.value
        if isinstance(node, ast.BinOp):
            if type(node.op) not in operators:
                raise ValueError("Unsupported operator.")
            return operators[type(node.op)](_eval(node.left), _eval(node.right))
        if isinstance(node, ast.UnaryOp) and type(node.op) in (ast.UAdd, ast.USub):
            return operators[type(node.op)](_eval(node.operand))
        if isinstance(node, ast.Paren):
            return _eval(node.value)
        raise ValueError("Unsupported expression.")

    # Allow only a strict subset of characters
    if not re.fullmatch(r"[0-9\.\+\-\*\/%\(\)\s]+", expr):
        raise ValueError("Expression contains invalid characters.")
    try:
        parsed = ast.parse(expr, mode="eval")
        return _eval(parsed)
    except Exception as e:
        raise ValueError(str(e)) from e


def small_talk_response(text: str) -> str:
    """Very simple keyword-based small talk."""
    low = text.lower()

    if any(w in low for w in ["hi", "hello", "hey"]):
        return "Hello! How can I help you today?"

    if "time" in low:
        return f"The current time is {datetime.now().strftime('%H:%M:%S')}."

    if "date" in low or "day" in low:
        return f"Today is {datetime.now().strftime('%A, %B %d, %Y')}."

    if "joke" in low:
        jokes = [
            "Why do programmers prefer dark mode? Because light attracts bugs.",
            "I told my computer I needed a break, and it said 'No problem, I'll go to sleep.'",
            "There are only 10 types of people in the world: those who understand binary and those who don’t.",
        ]
        return random.choice(jokes)

    if "weather" in low:
        return "I can't check live weather here, but I hope it's nice where you are!"

    if "name" in low:
        return "I'm Streamlit SimpleBot. Nice to meet you!"

    return (
        "I'm a simple small-talk bot. You can ask me for the time, a joke, my name, "
        "or switch to Calculator mode for math."
    )


def friendly_helper(text: str) -> str:
    """A very simple friendly helper with a few smarts."""
    low = text.lower().strip()

    # Try to detect plain math even in Friendly mode if it's clearly an expression
    if re.fullmatch(r"[0-9\.\+\-\*\/%\(\)\s]+", text):
        try:
            result = safe_eval(text)
            return f"Here's the result: {result}"
        except Exception:
            pass

    # Simple tips
    if low.endswith("?"):
        return (
            "That's a great question! I'm a lightweight local bot, so I can handle small talk and simple math. "
            "Try asking for the time, a joke, or enter a math expression like (2+3)*4."
        )

    # If user asks for help
    if "help" in low:
        return "I can chat casually and do quick calculations. Switch modes from the sidebar to explore."

    # Default friendly echo with a light rephrase
    return f"I hear you: '{text}'. How would you like me to help with that?"


def calculator_response(text: str) -> str:
    """Use safe_eval to compute the result or provide guidance."""
    try:
        result = safe_eval(text)
        return f"{result}"
    except Exception as e:
        return (
            "I can calculate expressions with +, -, *, /, %, //, ** and parentheses.\n"
            "Example: (2 + 3) * 4\n"
            f"Error: {e}"
        )


def generate_reply(user_text: str, mode: str) -> str:
    """Route user input to the selected bot mode."""
    if mode == "Echo":
        return f"You said: {user_text}"
    if mode == "Calculator":
        return calculator_response(user_text)
    if mode == "Small talk":
        return small_talk_response(user_text)
    # Default: Friendly helper
    return friendly_helper(user_text)


def init_chat(greeting: str):
    st.session_state.messages = [{"role": "assistant", "content": greeting}]


def export_chat_as_text(messages) -> str:
    lines = []
    for m in messages:
        speaker = "You" if m["role"] == "user" else "Assistant"
        lines.append(f"{speaker}: {m['content']}")
    return "\n\n".join(lines)


# -----------------------------
# App UI
# -----------------------------
st.set_page_config(page_title="Simple Streamlit Chatbot", page_icon="💬", layout="centered")

st.title("💬 Simple Streamlit Chatbot")

with st.sidebar:
    st.header("Settings")
    mode = st.radio(
        "Bot mode",
        ["Friendly", "Echo", "Calculator", "Small talk"],
        index=0,
        help="Choose how the bot should respond.",
        key="mode_selection",
    )

    # Initialize state and allow clearing chat
    if "messages" not in st.session_state:
        init_chat("Hi! I'm a simple chatbot. Ask me something, or try me in Calculator mode.")

    if st.button("Clear conversation", type="primary", use_container_width=True):
        init_chat("Chat cleared. How can I help you now?")
        st.rerun()

    # Download conversation
    chat_text = export_chat_as_text(st.session_state.messages)
    st.download_button(
        "Download conversation",
        data=chat_text.encode("utf-8"),
        file_name="conversation.txt",
        mime="text/plain",
        use_container_width=True,
    )

    st.caption("This chatbot runs locally with simple rule-based logic.")


# -----------------------------
# Message history
# -----------------------------
for msg in st.session_state.messages:
    with st.chat_message(msg["role"]):
        st.write(msg["content"])

# -----------------------------
# Input box
# -----------------------------
prompt = st.chat_input("Type your message here...")

if prompt:
    # Store the user's message
    st.session_state.messages.append({"role": "user", "content": prompt})

    # Generate and store the assistant's reply
    reply = generate_reply(prompt, st.session_state.get("mode_selection", "Friendly"))
    st.session_state.messages.append({"role": "assistant", "content": reply})

    # Rerun to display the new messages
    st.rerun()