import streamlit as st
import numpy as np
import math
import pandas as pd
import matplotlib.pyplot as plt

st.set_page_config(page_title="Advanced Calculator", layout="centered")

st.title("🧮 Advanced Calculator")
st.markdown("Multi-feature calculator for Hugging Face Streamlit deployment")

# -------------------------------
# Safe Expression Evaluation
# -------------------------------
allowed_names = {
    k: getattr(math, k) for k in dir(math) if not k.startswith("_")
}
allowed_names.update({
    "np": np,
    "abs": abs,
    "round": round
})

def safe_eval(expr):
    try:
        return eval(expr, {"__builtins__": {}}, allowed_names)
    except Exception as e:
        return f"Error: {e}"

# -------------------------------
# Sidebar Navigation
# -------------------------------
option = st.sidebar.selectbox(
    "Select Calculator Mode",
    ["Basic / Scientific", "Unit Converter", "Function Plotter", "History"]
)

# Session history
if "history" not in st.session_state:
    st.session_state.history = []

# -------------------------------
# BASIC & SCIENTIFIC CALCULATOR
# -------------------------------
if option == "Basic / Scientific":
    st.subheader("Basic & Scientific Calculator")

    expr = st.text_input(
        "Enter mathematical expression",
        placeholder="Example: sin(pi/2) + log(10)"
    )

    if st.button("Calculate"):
        result = safe_eval(expr)
        st.write("### Result:", result)

        st.session_state.history.append({
            "Expression": expr,
            "Result": result
        })

# -------------------------------
# UNIT CONVERTER
# -------------------------------
elif option == "Unit Converter":
    st.subheader("Unit Converter")

    conversion_type = st.selectbox(
        "Select Conversion Type",
        ["Length", "Weight", "Temperature"]
    )

    value = st.number_input("Enter Value")

    if conversion_type == "Length":
        units = st.selectbox("Convert From", ["Meters", "Kilometers", "Miles"])
        target = st.selectbox("Convert To", ["Meters", "Kilometers", "Miles"])

        conversion = {
            "Meters": 1,
            "Kilometers": 1000,
            "Miles": 1609.34
        }

        result = value * conversion[units] / conversion[target]
        st.write("### Result:", result)

    elif conversion_type == "Weight":
        units = st.selectbox("Convert From", ["Grams", "Kilograms", "Pounds"])
        target = st.selectbox("Convert To", ["Grams", "Kilograms", "Pounds"])

        conversion = {
            "Grams": 1,
            "Kilograms": 1000,
            "Pounds": 453.592
        }

        result = value * conversion[units] / conversion[target]
        st.write("### Result:", result)

    elif conversion_type == "Temperature":
        units = st.selectbox("Convert From", ["Celsius", "Fahrenheit", "Kelvin"])
        target = st.selectbox("Convert To", ["Celsius", "Fahrenheit", "Kelvin"])

        def temp_convert(val, u, t):
            if u == t:
                return val

            # Convert to Celsius first
            if u == "Fahrenheit":
                val = (val - 32) * 5/9
            elif u == "Kelvin":
                val = val - 273.15

            # Convert from Celsius to target
            if t == "Fahrenheit":
                return val * 9/5 + 32
            elif t == "Kelvin":
                return val + 273.15
            return val

        st.write("### Result:", temp_convert(value, units, target))

# -------------------------------
# FUNCTION PLOTTER
# -------------------------------
elif option == "Function Plotter":
    st.subheader("Function Plotter")

    func_expr = st.text_input(
        "Enter function in terms of x",
        placeholder="Example: sin(x) or x**2 + 3*x"
    )

    x_min = st.number_input("X min", value=-10.0)
    x_max = st.number_input("X max", value=10.0)

    if st.button("Plot Function"):
        try:
            x = np.linspace(x_min, x_max, 400)
            y = eval(func_expr, {"__builtins__": {}}, {**allowed_names, "x": x})

            fig, ax = plt.subplots()
            ax.plot(x, y)
            ax.set_xlabel("x")
            ax.set_ylabel("y")
            ax.set_title(f"Plot of {func_expr}")
            ax.grid(True)

            st.pyplot(fig)

        except Exception as e:
            st.error(f"Plot Error: {e}")

# -------------------------------
# HISTORY
# -------------------------------
elif option == "History":
    st.subheader("Calculation History")

    if st.session_state.history:
        df = pd.DataFrame(st.session_state.history)
        st.dataframe(df, use_container_width=True)

        if st.button("Clear History"):
            st.session_state.history = []
    else:
        st.info("No calculations yet.")