"""Progress overlay — actual NW from `account_snapshot` vs the persisted
projection fan.

Used by the left-sidebar "Progress" page. The alignment anchor is the
earliest available snapshot date (year 0 of the projection); subsequent
snapshots are bucketed into the projection's calendar-year axis so the
overlay lines up.
"""
from __future__ import annotations

from collections import defaultdict
from datetime import date
from decimal import Decimal

from fastapi import APIRouter, Depends, HTTPException
from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from fire_planner.api.dependencies import get_session
from fire_planner.api.schemas import (
    ProgressActualPoint,
    ProgressProjectedPoint,
    ProgressResponse,
    ProgressVariancePoint,
)
from fire_planner.db import AccountSnapshot, McRun, ProjectionYearly, Scenario

router = APIRouter(prefix="/scenarios", tags=["progress"])


@router.get("/{scenario_id}/progress", response_model=ProgressResponse)
async def get_progress(
    scenario_id: int,
    session: AsyncSession = Depends(get_session),
) -> ProgressResponse:
    scen = await session.get(Scenario, scenario_id)
    if scen is None:
        raise HTTPException(status_code=404, detail="Scenario not found")

    actuals_rows = (await session.execute(
        select(
            AccountSnapshot.snapshot_date,
            AccountSnapshot.market_value_gbp,
        ))).all()

    by_date: dict[date, Decimal] = defaultdict(lambda: Decimal("0"))
    for snap_date, value in actuals_rows:
        by_date[snap_date] += Decimal(str(value))

    actual = [
        ProgressActualPoint(snapshot_date=d, total_gbp=by_date[d]) for d in sorted(by_date.keys())
    ]
    if actual:
        anchor = actual[0].snapshot_date
    else:
        anchor = scen.created_at.date() if scen.created_at is not None else date.today()

    run = (await session.execute(
        select(McRun).where(McRun.scenario_id == scenario_id).order_by(
            McRun.run_at.desc()).limit(1))).scalar_one_or_none()
    projected: list[ProgressProjectedPoint] = []
    yearly_rows: list[ProjectionYearly] = []
    if run is not None:
        rows = (await session.execute(
            select(ProjectionYearly).where(ProjectionYearly.mc_run_id == run.id).order_by(
                ProjectionYearly.year_idx))).scalars().all()
        yearly_rows = list(rows)
        projected = [
            ProgressProjectedPoint(
                year_idx=r.year_idx,
                p10_portfolio_gbp=r.p10_portfolio_gbp,
                p50_portfolio_gbp=r.p50_portfolio_gbp,
                p90_portfolio_gbp=r.p90_portfolio_gbp,
            ) for r in yearly_rows
        ]

    variance: list[ProgressVariancePoint] = []
    if yearly_rows and actual:
        actuals_by_year: dict[int, list[Decimal]] = defaultdict(list)
        for pt in actual:
            year_idx = (pt.snapshot_date.year - anchor.year)
            if year_idx >= 0:
                actuals_by_year[year_idx].append(pt.total_gbp)
        for r in yearly_rows:
            samples = actuals_by_year.get(r.year_idx)
            if not samples:
                continue
            avg = sum(samples, Decimal("0")) / Decimal(len(samples))
            projected_p50 = Decimal(str(r.p50_portfolio_gbp))
            variance.append(
                ProgressVariancePoint(
                    year_idx=r.year_idx,
                    actual_avg_gbp=avg,
                    projected_p50_gbp=projected_p50,
                    delta_gbp=avg - projected_p50,
                ))

    return ProgressResponse(
        scenario_id=scenario_id,
        alignment_anchor=anchor,
        actual=actual,
        projected=projected,
        variance=variance,
    )