# =========================================================
# SIPXAR — PAPER TRADING (SESSION STATE ONLY)
# =========================================================

import math
import numpy as np
import pandas as pd
import yfinance as yf
import streamlit as st
from datetime import datetime

# =========================================================
# CONFIG
# =========================================================

MONTHLY_SIP = 10000

NIFTY = "NIFTYBEES.NS"
GOLD  = "GOLDBEES.NS"

SMA_MONTHS = 36

BASE_EQUITY = 0.60
TILT_MULT   = 1.5
MAX_TILT    = 0.25
MIN_EQUITY  = 0.20
MAX_EQUITY  = 0.90

# =========================================================
# DATA
# =========================================================

@st.cache_data(ttl=300)
def fetch_price(ticker):
    df = yf.download(
        ticker,
        period="5d",
        interval="1d",
        auto_adjust=True,
        progress=False
    )
    return float(df["Close"].iloc[-1].item())

@st.cache_data(ttl=3600)
def fetch_sma(ticker):
    df = yf.download(
        ticker,
        period=f"{SMA_MONTHS+2}mo",
        interval="1mo",
        auto_adjust=True,
        progress=False
    ).dropna()
    return float(df["Close"].tail(SMA_MONTHS).mean())

# =========================================================
# STRATEGY
# =========================================================

def compute_weights(n_price, g_price, n_sma, g_sma):
    dev_n = (n_price / n_sma) - 1
    dev_g = (g_price / g_sma) - 1
    rel = dev_n - dev_g

    tilt = np.clip(-rel * TILT_MULT, -MAX_TILT, MAX_TILT)
    eq_w = BASE_EQUITY * (1 + tilt)
    eq_w = min(max(eq_w, MIN_EQUITY), MAX_EQUITY)

    return eq_w, 1 - eq_w

# =========================================================
# SESSION STATE INIT
# =========================================================

if "nifty_units" not in st.session_state:
    st.session_state.nifty_units = 0
    st.session_state.gold_units = 0
    st.session_state.invested = 0
    st.session_state.ledger = []

# =========================================================
# STREAMLIT UI
# =========================================================

st.set_page_config(page_title="SIPXAR Paper Trading", layout="centered")
st.title("📊 SIPXAR — Paper Trading (Session Only)")

# Fetch market data
n_price = fetch_price(NIFTY)
g_price = fetch_price(GOLD)
n_sma   = fetch_sma(NIFTY)
g_sma   = fetch_sma(GOLD)

eq_w, g_w = compute_weights(n_price, g_price, n_sma, g_sma)

# Market snapshot
st.subheader("Market Snapshot")
st.write(f"**NIFTY:** ₹{n_price:.2f}")
st.write(f"**GOLD:** ₹{g_price:.2f}")

# Allocation
st.subheader("Allocation Weights")
st.progress(eq_w)
st.write(f"Equity: **{eq_w:.2%}** | Gold: **{g_w:.2%}**")

# =========================================================
# SIP ACTION
# =========================================================

if st.button("Run Paper SIP (Once)"):
    n_amt = MONTHLY_SIP * eq_w
    g_amt = MONTHLY_SIP * g_w

    n_qty = math.floor(n_amt / n_price)
    g_qty = math.floor(g_amt / g_price)

    if n_qty == 0 and g_qty == 0:
        st.warning(
            "SIP amount too small to buy ETF units at current prices."
        )
    else:
        st.session_state.nifty_units += n_qty
        st.session_state.gold_units += g_qty
        st.session_state.invested += MONTHLY_SIP

        port_value = (
            st.session_state.nifty_units * n_price +
            st.session_state.gold_units * g_price
        )

        st.session_state.ledger.append({
            "timestamp": datetime.now().strftime("%Y-%m-%d %H:%M:%S"),
            "nifty_units": st.session_state.nifty_units,
            "gold_units": st.session_state.gold_units,
            "invested": st.session_state.invested,
            "portfolio_value": port_value,
            "pnl": port_value - st.session_state.invested
        })

        st.success("Paper SIP executed")

# =========================================================
# PORTFOLIO VIEW
# =========================================================

if st.session_state.invested > 0:
    port_value = (
        st.session_state.nifty_units * n_price +
        st.session_state.gold_units * g_price
    )

    pnl = port_value - st.session_state.invested

    st.subheader("Portfolio Summary")
    st.metric("Total Invested", f"₹{st.session_state.invested:,.0f}")
    st.metric("Portfolio Value", f"₹{port_value:,.0f}")
    st.metric("PnL", f"₹{pnl:,.0f}")

    df = pd.DataFrame(st.session_state.ledger)

    st.subheader("Equity Curve")
    st.line_chart(df[["portfolio_value", "invested"]])

    st.subheader("Ledger")
    st.dataframe(df, use_container_width=True)
else:
    st.info("No SIPs yet. Click the button to start.")