fire-planner/fire_planner/api/simulate.py
Viktor Barzin eb0dd3ddbf
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fire-planner: life-event spending bumps now reflected in fan + auto-
refresh on scenario edits

Two fixes for the user's report that adding a £100k life-event spend
didn't change the chart:

Engine (simulator.py)
- New `extra_outflows` param. cashflow_adjustments still drains the
  portfolio at start-of-year as before, but the simulator now ALSO
  records the spending in `withdrawal_hist[p, y]` so the chart's red
  median-withdrawal trace shows the bump. Without this, the £100k
  silently came out of the portfolio but the user-facing withdrawal
  trace stayed at the strategy's flat 4% draw.
- simulate.py wires extra_outflows = essential + discretionary
  category outflows from life events.

UX (ScenarioDetail.tsx)
- New auto-refresh: when life events / income streams / flex rules
  change for a scenario, the page fires `/simulate` automatically
  with 2,000 paths and uses the result as the primary fan/year-stats
  source. The persisted MC run is only consulted as a fallback for
  scenarios with no overrides.
- Fan chart title gains a "live preview · Xs · Ny" pill while a sim
  is current, and "re-running…" while a fresh one is in flight.
- Removed the now-redundant "Live preview run" duplicate card lower
  down — the main chart IS the live preview.
- Year-stats badge row reads from sim.data when available so changes
  propagate immediately to NW / Δ NW / Spending / Taxes.

247 pytest pass (+1 new); mypy + ruff clean; frontend typecheck/test/
build green.
2026-05-10 19:17:57 +00:00

272 lines
11 KiB
Python

"""Sync simulate + multi-scenario compare.
Unlike the persisted Cartesian recompute (`/recompute`), these run a
single scenario inline and return the result immediately. The React UI
uses these for what-if exploration — no DB write.
Returns a fan-chart series in the same shape as
`GET /scenarios/{id}/projection`, so frontend chart code is shared.
"""
from __future__ import annotations
import asyncio
import time
from decimal import Decimal
from pathlib import Path
import numpy as np
from fastapi import APIRouter, HTTPException
from sqlalchemy.ext.asyncio import async_sessionmaker
from fire_planner.api.schemas import (
CompareRequest,
CompareResult,
GoalProbability,
ProjectionPoint,
SimulateRequest,
SimulateResult,
)
from fire_planner.flex_spending import FlexRule as EngineFlexRule
from fire_planner.glide_path import static
from fire_planner.goals_eval import evaluate_goals
from fire_planner.income_streams import IncomeStreamInput, streams_to_arrays
from fire_planner.ingest.wealthfolio_pg import create_wf_sync_engine_from_env
from fire_planner.life_events import (
EventInput,
events_to_cashflow_array,
events_to_category_outflows,
)
from fire_planner.returns.bootstrap import block_bootstrap
from fire_planner.returns.shiller import load_from_csv, synthetic_returns
from fire_planner.returns.wealthfolio_returns import (
compute_annual_returns_from_pg,
constant_real_return_paths,
)
from fire_planner.scenarios import build_regime_schedule, build_strategy
from fire_planner.simulator import SimulationResult, build_fixed_paths, simulate
router = APIRouter(tags=["simulate"])
_RETURNS_CSV = Path("/data/shiller_returns.csv")
def _shiller_paths(seed: int, n_paths: int, n_years: int) -> np.ndarray:
bundle = (load_from_csv(_RETURNS_CSV) if _RETURNS_CSV.exists() else synthetic_returns(seed=42))
rng = np.random.default_rng(seed)
return block_bootstrap(bundle, n_paths=n_paths, n_years=n_years, block_size=5, rng=rng)
async def _wealthfolio_paths(seed: int, n_paths: int, n_years: int) -> np.ndarray:
"""Block-bootstrap the user's actual blended real returns. With
typically <10 distinct annual samples, block_size=1 is appropriate
— there's no serial-correlation signal to preserve."""
eng = create_wf_sync_engine_from_env()
try:
factory = async_sessionmaker(eng, expire_on_commit=False)
async with factory() as wf_sess:
bundle = await compute_annual_returns_from_pg(wf_sess)
finally:
await eng.dispose()
rng = np.random.default_rng(seed)
return block_bootstrap(bundle, n_paths=n_paths, n_years=n_years, block_size=1, rng=rng)
async def _build_paths(req: SimulateRequest) -> np.ndarray:
if req.rates_mode == "fixed":
return build_fixed_paths(
n_paths=req.n_paths,
n_years=req.horizon_years,
inflation_pct=float(req.inflation_pct),
stocks_growth_pct=float(req.stocks_growth_pct),
stocks_dividend_pct=float(req.stocks_dividend_pct),
bonds_growth_pct=float(req.bonds_growth_pct),
bonds_dividend_pct=float(req.bonds_dividend_pct),
)
if req.returns_mode == "manual":
if req.manual_real_return_pct is None:
raise HTTPException(
status_code=400,
detail="manual_real_return_pct is required when returns_mode='manual'",
)
return constant_real_return_paths(
n_paths=req.n_paths,
n_years=req.horizon_years,
real_return_pct=float(req.manual_real_return_pct),
)
if req.returns_mode == "wealthfolio":
try:
return await _wealthfolio_paths(req.seed, req.n_paths, req.horizon_years)
except ValueError as e:
raise HTTPException(
status_code=400,
detail=f"Wealthfolio history insufficient: {e}",
) from e
return _shiller_paths(req.seed, req.n_paths, req.horizon_years)
def _project(req: SimulateRequest, paths: np.ndarray) -> tuple[SimulationResult, float]:
annual_savings = (np.full(req.horizon_years, float(req.savings_per_year_gbp), dtype=np.float64)
if req.savings_per_year_gbp > 0 else None)
floor = float(req.floor_gbp) if req.floor_gbp is not None else None
cashflow_adjustments = None
discretionary_outflows = None
extra_outflows = None
if req.life_events:
engine_events = [
EventInput(
year_start=ev.year_start,
year_end=ev.year_end,
delta_gbp_per_year=float(ev.delta_gbp_per_year),
one_time_amount_gbp=(float(ev.one_time_amount_gbp)
if ev.one_time_amount_gbp is not None else None),
category=ev.category,
enabled=ev.enabled,
) for ev in req.life_events
]
cashflow_adjustments = events_to_cashflow_array(engine_events, req.horizon_years)
category_outflows = events_to_category_outflows(engine_events, req.horizon_years)
discretionary_outflows = category_outflows.get("discretionary")
# extra_outflows feeds the withdrawal-trace display: total of
# essential + discretionary spending events surfaces alongside
# the strategy's draw on the chart.
essential = category_outflows.get("essential")
if essential is not None and discretionary_outflows is not None:
extra_outflows = essential + discretionary_outflows
engine_flex = [
EngineFlexRule(
from_ath_pct=float(r.from_ath_pct),
cut_discretionary_pct=float(r.cut_discretionary_pct),
) for r in req.flex_rules
] if req.flex_rules else None
income_inflows = None
income_taxable = None
if req.income_streams:
engine_streams = [
IncomeStreamInput(
kind=s.kind,
start_year=s.start_year,
end_year=s.end_year,
amount_gbp_per_year=float(s.amount_gbp_per_year),
growth_pct=float(s.growth_pct),
tax_treatment=s.tax_treatment,
enabled=s.enabled,
) for s in req.income_streams
]
income_inflows, income_taxable = streams_to_arrays(engine_streams, req.horizon_years)
strategy = build_strategy(
req.strategy,
floor=floor,
annual_real_adjust_pct=float(req.annual_real_adjust_pct),
guardrail_threshold_pct=(float(req.guardrail_threshold_pct)
if req.guardrail_threshold_pct is not None else None),
guardrail_cut_pct=float(req.guardrail_cut_pct),
)
glide_alloc = float(req.stocks_allocation) if req.rates_mode == "fixed" else 1.0
started = time.perf_counter()
result = simulate(
paths=paths,
initial_portfolio=float(req.nw_seed_gbp),
spending_target=float(req.spending_gbp),
glide=static(glide_alloc),
strategy=strategy,
regime=build_regime_schedule(req.jurisdiction, req.leave_uk_year),
horizon_years=req.horizon_years,
annual_savings=annual_savings,
cashflow_adjustments=cashflow_adjustments,
income_inflows=income_inflows,
income_taxable=income_taxable,
discretionary_outflows=discretionary_outflows,
extra_outflows=extra_outflows,
flex_rules=engine_flex,
)
elapsed = time.perf_counter() - started
return result, elapsed
def _to_response(
result: SimulationResult,
elapsed: float,
req: SimulateRequest | None = None,
) -> SimulateResult:
# portfolio_real has n_years+1 columns (year 0 = seed, year k = end-of-year k).
# withdrawal_real / tax_real have n_years columns (year k = withdrawn in year k+1).
# Yearly point k describes "end of year k+1": portfolio after withdrawal & growth.
pcts = [10, 25, 50, 75, 90]
portfolio_quantiles = {p: np.percentile(result.portfolio_real, p, axis=0) for p in pcts}
median_wd = np.percentile(result.withdrawal_real, 50, axis=0)
median_tax = np.percentile(result.tax_real, 50, axis=0)
n_years = result.n_years
survival_path = (result.success_mask.astype(np.float64).mean(axis=0) if
result.success_mask.ndim == 2 else np.ones(n_years))
yearly = [
ProjectionPoint(
year_idx=y,
p10_portfolio_gbp=Decimal(str(round(float(portfolio_quantiles[10][y + 1]), 2))),
p25_portfolio_gbp=Decimal(str(round(float(portfolio_quantiles[25][y + 1]), 2))),
p50_portfolio_gbp=Decimal(str(round(float(portfolio_quantiles[50][y + 1]), 2))),
p75_portfolio_gbp=Decimal(str(round(float(portfolio_quantiles[75][y + 1]), 2))),
p90_portfolio_gbp=Decimal(str(round(float(portfolio_quantiles[90][y + 1]), 2))),
p50_withdrawal_gbp=Decimal(str(round(float(median_wd[y]), 2))),
p50_tax_gbp=Decimal(str(round(float(median_tax[y]), 2))),
survival_rate=Decimal(str(round(float(survival_path[y]), 4))),
) for y in range(n_years)
]
median_ytr = result.median_years_to_ruin()
goals_probability: list[GoalProbability] = []
if req is not None and req.goals:
evaluations = evaluate_goals(result, req.goals, req.horizon_years)
goals_probability = [
GoalProbability(
goal_id=None,
name=ev.name,
kind=ev.kind,
probability=Decimal(str(round(ev.probability, 4))),
threshold=Decimal(str(round(ev.threshold, 4))),
passed=ev.passed,
) for ev in evaluations
]
return SimulateResult(
success_rate=Decimal(str(round(float(result.success_rate), 4))),
p10_ending_gbp=Decimal(str(round(float(result.ending_percentile(10)), 2))),
p50_ending_gbp=Decimal(str(round(float(result.ending_percentile(50)), 2))),
p90_ending_gbp=Decimal(str(round(float(result.ending_percentile(90)), 2))),
median_lifetime_tax_gbp=Decimal(str(round(float(result.median_lifetime_tax()), 2))),
median_years_to_ruin=(Decimal(str(round(float(median_ytr), 2)))
if median_ytr is not None else None),
elapsed_seconds=Decimal(str(round(elapsed, 3))),
yearly=yearly,
goals_probability=goals_probability,
)
@router.post("/simulate", response_model=SimulateResult)
async def simulate_one(req: SimulateRequest) -> SimulateResult:
"""Run one scenario synchronously, no DB write. ~1-3s for 5k paths."""
paths = await _build_paths(req)
try:
result, elapsed = await asyncio.to_thread(_project, req, paths)
except KeyError as e:
raise HTTPException(status_code=400, detail=f"Unknown name: {e}") from None
return _to_response(result, elapsed, req)
@router.post("/compare", response_model=CompareResult)
async def compare_scenarios(req: CompareRequest) -> CompareResult:
"""Run 2-5 scenarios in parallel, return all results."""
async def one(s: SimulateRequest) -> SimulateResult:
paths = await _build_paths(s)
result, elapsed = await asyncio.to_thread(_project, s, paths)
return _to_response(result, elapsed, s)
try:
results = await asyncio.gather(*(one(s) for s in req.scenarios))
except KeyError as e:
raise HTTPException(status_code=400, detail=f"Unknown name: {e}") from None
return CompareResult(results=results)