import streamlit as st
import math

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

# ---------- STATE ----------
if "expr" not in st.session_state:
    st.session_state.expr = ""

def press(key):
    if key == "C":
        st.session_state.expr = ""
    elif key == "=":
        try:
            st.session_state.expr = str(eval(st.session_state.expr))
        except:
            st.session_state.expr = "Error"
    elif key == "√":
        try:
            st.session_state.expr = str(math.sqrt(float(st.session_state.expr)))
        except:
            st.session_state.expr = "Error"
    elif key == "x²":
        try:
            st.session_state.expr = str(float(st.session_state.expr) ** 2)
        except:
            st.session_state.expr = "Error"
    elif key == "log":
        try:
            st.session_state.expr = str(math.log10(float(st.session_state.expr)))
        except:
            st.session_state.expr = "Error"
    else:
        st.session_state.expr += key

# ---------- DISPLAY ----------
st.markdown(
    f"""
    <div style="
        background:#111;
        color:white;
        padding:18px;
        font-size:30px;
        border-radius:12px;
        text-align:right;
        margin-bottom:12px;
    ">
        {st.session_state.expr or "0"}
    </div>
    """,
    unsafe_allow_html=True
)

# ---------- BUTTON GRID ----------
layout = [
    ["C", "√", "x²", "/"],
    ["7", "8", "9", "*"],
    ["4", "5", "6", "-"],
    ["1", "2", "3", "+"],
    ["0", ".", "log", "="]
]

for row in layout:
    cols = st.columns(4)
    for i, key in enumerate(row):
        if cols[i].button(key, use_container_width=True):
            press(key)
            st.rerun()