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https://github.com/shawnkim1997/All-in-one-Financial-Analysis.git
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114 lines
4.0 KiB
Python
114 lines
4.0 KiB
Python
"""Tax simulation endpoints.
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These endpoints are educational calculators for personal planning. They are
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not tax advice and intentionally keep assumptions explicit in the payload.
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"""
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from __future__ import annotations
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from typing import Literal
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from fastapi import APIRouter, Query
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from server.routers.portfolio import _get_current_quote, _load_positions
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router = APIRouter()
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UK_CGT_ALLOWANCE_2026 = 3000.0
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UK_CGT_BASIC_RATE = 0.10
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UK_CGT_HIGHER_RATE = 0.20
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_FX_TO_GBP = {
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"GBP": 1.0,
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"GBX": 0.01,
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"USD": 0.80,
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"EUR": 0.86,
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"DKK": 0.115,
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"JPY": 0.0053,
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"KRW": 0.00058,
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"CHF": 0.90,
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"CAD": 0.58,
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"AUD": 0.52,
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}
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def _fx_to_gbp(currency: str) -> float:
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return _FX_TO_GBP.get((currency or "USD").upper(), _FX_TO_GBP["USD"])
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def _position_gain(position: dict) -> dict:
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ticker = str(position.get("ticker", "")).upper()
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quantity = float(position.get("quantity") or 0)
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avg_price = float(position.get("avg_price") or 0)
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exchange = str(position.get("exchange") or "")
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quote = _get_current_quote(ticker, exchange)
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current_price = float(quote.get("price") or avg_price)
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cost_currency = str(position.get("currency") or position.get("avg_price_currency") or quote.get("currency") or "USD").upper()
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current_currency = str(quote.get("currency") or cost_currency).upper()
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cost_gbp = quantity * avg_price * _fx_to_gbp(cost_currency)
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value_gbp = quantity * current_price * _fx_to_gbp(current_currency)
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gain_gbp = value_gbp - cost_gbp
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return {
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"ticker": ticker,
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"quantity": quantity,
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"avg_price": avg_price,
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"current_price": current_price,
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"cost_currency": cost_currency,
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"current_currency": current_currency,
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"cost_gbp": round(cost_gbp, 2),
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"value_gbp": round(value_gbp, 2),
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"gain_gbp": round(gain_gbp, 2),
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"gain_per_share_gbp": round(gain_gbp / quantity, 4) if quantity else 0,
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}
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def _optimal_realization(gains: list[dict], allowance: float) -> list[dict]:
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remaining = allowance
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suggestions = []
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positive = [item for item in gains if item["gain_gbp"] > 0 and item["quantity"] > 0]
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for item in sorted(positive, key=lambda row: row["gain_gbp"]):
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if remaining <= 0:
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break
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gain_per_share = item["gain_gbp"] / item["quantity"]
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if gain_per_share <= 0:
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continue
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shares = min(item["quantity"], remaining / gain_per_share)
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realized_gain = min(item["gain_gbp"], shares * gain_per_share)
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suggestions.append(
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{
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"ticker": item["ticker"],
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"shares_to_sell": round(shares, 6),
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"estimated_gain_gbp": round(realized_gain, 2),
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}
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)
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remaining -= realized_gain
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return suggestions
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@router.get("/uk/cgt/{user_id}", summary="UK CGT allowance simulator")
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async def simulate_uk_cgt(
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user_id: str,
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income_band: Literal["basic", "higher"] = Query("higher"),
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):
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positions = _load_positions()
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gains = [_position_gain(position) for position in positions if position.get("ticker")]
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total_gain = round(sum(item["gain_gbp"] for item in gains if item["gain_gbp"] > 0), 2)
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taxable = round(max(0.0, total_gain - UK_CGT_ALLOWANCE_2026), 2)
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rate = UK_CGT_HIGHER_RATE if income_band == "higher" else UK_CGT_BASIC_RATE
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tax = round(taxable * rate, 2)
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return {
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"user_id": user_id,
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"income_band": income_band,
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"total_unrealized_gain_gbp": total_gain,
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"allowance": UK_CGT_ALLOWANCE_2026,
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"allowance_remaining": round(max(0.0, UK_CGT_ALLOWANCE_2026 - total_gain), 2),
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"taxable_if_sold_all": taxable,
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"tax_if_sold_all": tax,
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"rate": rate,
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"optimal_realization": _optimal_realization(gains, UK_CGT_ALLOWANCE_2026),
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"positions": gains,
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"tax_year_end": "2026-04-05",
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"fx_source": "static_estimate",
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"disclaimer": "Educational estimate only. Not tax advice. Consult HMRC guidance or a qualified adviser.",
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}
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