import streamlit as st
import pandas as pd
import os
import plotly.express as px
from datetime import datetime

# -------------------------------
# CONFIG & STYLES
# -------------------------------
st.set_page_config(page_title="💸 Expense Tracker", layout="wide")

st.markdown(
    """
    <style>
    body {
        background-color: #f8f9fa;
    }
    .title {
        font-size: 40px;
        font-weight: bold;
        color: #2c3e50;
        text-align: center;
        margin-bottom: 10px;
    }
    .subtitle {
        font-size: 18px;
        color: #7f8c8d;
        text-align: center;
        margin-bottom: 30px;
    }
    .metric-card {
        background: black;
        padding: 20px;
        border-radius: 15px;
        text-align: center;
        box-shadow: 0px 2px 6px rgba(0,0,0,0.1);
    }
    </style>
    """,
    unsafe_allow_html=True,
)

# -------------------------------
# FILE SETUP
# -------------------------------
CSV_FILE = "expenses.csv"

if not os.path.exists(CSV_FILE):
    df = pd.DataFrame(columns=["date", "category", "amount", "description"])
    df.to_csv(CSV_FILE, index=False)

# -------------------------------
# LOAD DATA
# -------------------------------
df = pd.read_csv(CSV_FILE)

# -------------------------------
# SIDEBAR NAVIGATION
# -------------------------------
st.sidebar.title("📌 Navigation")
page = st.sidebar.radio("Go to", ["➕ Add Expense", "📊 Dashboard", "📂 Expense Table"])

st.sidebar.markdown("---")
st.sidebar.write("💡 Tip: Use filters to explore your expenses easily!")

# -------------------------------
# PAGE: ADD EXPENSE
# -------------------------------
if page == "➕ Add Expense":
    st.markdown("<div class='title'>Add New Expense</div>", unsafe_allow_html=True)

    with st.form("expense_form", clear_on_submit=True):
        col1, col2 = st.columns(2)
        with col1:
            date = st.date_input("Date", datetime.today())
            category = st.selectbox("Category", ["Food", "Transport", "Bills", "Entertainment", "Other"])
        with col2:
            amount = st.number_input("Amount", min_value=0.0, step=0.01)
            description = st.text_input("Description")

        submitted = st.form_submit_button("💾 Save Expense")

        if submitted:
            new_expense = pd.DataFrame(
                [[date, category, amount, description]],
                columns=["date", "category", "amount", "description"],
            )
            new_expense.to_csv(CSV_FILE, mode="a", header=False, index=False)
            st.success("✅ Expense saved successfully!")

# -------------------------------
# PAGE: DASHBOARD
# -------------------------------
elif page == "📊 Dashboard":
    st.markdown("<div class='title'>Expense Dashboard</div>", unsafe_allow_html=True)
    st.markdown("<div class='subtitle'>Visualize your spending habits</div>", unsafe_allow_html=True)

    if df.empty:
        st.warning("⚠️ No data available yet. Add some expenses first.")
    else:
        # Metrics Row
        col1, col2, col3 = st.columns(3)
        with col1:
            st.markdown(f"<div class='metric-card'><h3>Total Spent</h3><p>Rs {df['amount'].sum():,.2f}</p></div>", unsafe_allow_html=True)
        with col2:
            top_cat = df.groupby("category")["amount"].sum().idxmax()
            st.markdown(f"<div class='metric-card'><h3>Top Category</h3><p>{top_cat}</p></div>", unsafe_allow_html=True)
        with col3:
            avg = df["amount"].mean()
            st.markdown(f"<div class='metric-card'><h3>Avg. Expense</h3><p>Rs {avg:,.2f}</p></div>", unsafe_allow_html=True)

        st.markdown("---")

        # Charts
        col1, col2 = st.columns(2)
        with col1:
            fig1 = px.pie(df, names="category", values="amount", title="Expenses by Category", hole=0.4)
            st.plotly_chart(fig1, use_container_width=True)

        with col2:
            df["date"] = pd.to_datetime(df["date"])
            fig2 = px.line(df, x="date", y="amount", title="Expenses Over Time", markers=True)
            st.plotly_chart(fig2, use_container_width=True)

# -------------------------------
# PAGE: EXPENSE TABLE
# -------------------------------
elif page == "📂 Expense Table":
    st.markdown("<div class='title'>Expense Records</div>", unsafe_allow_html=True)

    if df.empty:
        st.warning("⚠️ No expenses found. Add some first.")
    else:
        with st.expander("🔍 Filters", expanded=True):
            col1, col2 = st.columns(2)
            with col1:
                categories = st.multiselect("Filter by Category", df["category"].unique())
            with col2:
                date_range = st.date_input("Filter by Date Range", [])
            
            filtered = df.copy()
            if categories:
                filtered = filtered[filtered["category"].isin(categories)]
            if date_range:
                if len(date_range) == 2:
                    start, end = date_range
                    filtered = filtered[(pd.to_datetime(filtered["date"]) >= pd.to_datetime(start)) & 
                                        (pd.to_datetime(filtered["date"]) <= pd.to_datetime(end))]

        st.dataframe(filtered, use_container_width=True)