import streamlit as st
import math
import pandas as pd

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

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

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

# ---------------- SAFE EVAL ----------------
def safe_eval(expr):
    allowed = {
        "sqrt": math.sqrt,
        "sin": math.sin,
        "cos": math.cos,
        "tan": math.tan,
        "log": math.log10,
        "pi": math.pi,
        "e": math.e
    }
    try:
        return eval(expr, {"__builtins__": None}, allowed)
    except:
        return "Error"

# ---------------- STYLE ----------------
st.markdown("""
<style>
body {background-color:#0f172a;}
.display {
    background:#1e293b;
    color:white;
    padding:20px;
    border-radius:20px;
    font-size:32px;
    text-align:right;
    margin-bottom:15px;
}
.stButton>button {
    height:65px;
    border-radius:20px;
    font-size:22px;
    font-weight:bold;
}
</style>
""", unsafe_allow_html=True)

st.title("🧮 Advanced Mobile Calculator")

# ---------------- DISPLAY ----------------
st.markdown(f"<div class='display'>{st.session_state.expression or '0'}</div>", unsafe_allow_html=True)

if st.session_state.expression:
    st.write("Result:", safe_eval(st.session_state.expression))

# ---------------- BUTTON FUNCTIONS ----------------
def add(val):
    st.session_state.expression += str(val)

def clear():
    st.session_state.expression = ""

def delete():
    st.session_state.expression = st.session_state.expression[:-1]

def calculate():
    result = safe_eval(st.session_state.expression)
    st.session_state.history.append(f"{st.session_state.expression} = {result}")
    st.session_state.expression = str(result)

# ---------------- FIXED MOBILE GRID ----------------
layout = [
    ["C", "DEL", "(", ")"],
    ["7", "8", "9", "/"],
    ["4", "5", "6", "*"],
    ["1", "2", "3", "-"],
    ["0", ".", "+", "="],
]

for r, row in enumerate(layout):
    cols = st.columns(4)
    for c, button in enumerate(row):

        key_name = f"btn_{r}_{c}"

        if button == "C":
            cols[c].button(button, key=key_name, on_click=clear)

        elif button == "DEL":
            cols[c].button(button, key=key_name, on_click=delete)

        elif button == "=":
            cols[c].button(button, key=key_name, on_click=calculate)

        else:
            cols[c].button(
                button,
                key=key_name,
                on_click=add,
                args=(button,)
            )

st.markdown("---")

# ---------------- SCIENTIFIC BUTTONS ----------------
st.subheader("Scientific")

sci_buttons = ["sqrt(", "sin(", "cos(", "tan(", "log(", "pi", "e"]

cols = st.columns(len(sci_buttons))

for i, btn in enumerate(sci_buttons):
    cols[i].button(
        btn,
        key=f"sci_{i}",
        on_click=add,
        args=(btn,)
    )

st.markdown("---")

# ---------------- HISTORY ----------------
st.subheader("History")

if st.session_state.history:
    for item in reversed(st.session_state.history):
        st.write(item)

    df = pd.DataFrame(st.session_state.history, columns=["Calculations"])
    st.download_button(
        "Download History",
        df.to_csv(index=False),
        file_name="history.csv"
    )
else:
    st.info("No calculations yet.")