"""Scenario CRUD + projection read.

Mixed surface:
- GET /scenarios                  list (filter by kind)
- GET /scenarios/{id}             single
- POST /scenarios                 create user scenario
- PATCH /scenarios/{id}           update user scenario
- DELETE /scenarios/{id}          delete user scenario (cartesian protected)
- GET /scenarios/{id}/projection  latest MC run + per-year fan
"""
from __future__ import annotations

import uuid

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

from fire_planner.api.dependencies import get_session
from fire_planner.api.schemas import (
    ProjectionPoint,
    ScenarioCreate,
    ScenarioOut,
    ScenarioPatch,
    ScenarioProjection,
)
from fire_planner.db import McRun, ProjectionYearly, Scenario

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


@router.get("", response_model=list[ScenarioOut])
async def list_scenarios(
    kind: str | None = None,
    session: AsyncSession = Depends(get_session),
) -> list[Scenario]:
    """List all scenarios. Filter `kind=user` or `kind=cartesian`."""
    stmt = select(Scenario).order_by(Scenario.id)
    if kind is not None:
        stmt = stmt.where(Scenario.kind == kind)
    rows = (await session.execute(stmt)).scalars().all()
    return list(rows)


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


@router.post(
    "",
    response_model=ScenarioOut,
    status_code=201,
)
async def create_scenario(
    payload: ScenarioCreate,
    session: AsyncSession = Depends(get_session),
) -> Scenario:
    """Create a user scenario. Cartesian scenarios come from the engine,
    not the API."""
    if payload.parent_scenario_id is not None:
        parent = await session.get(Scenario, payload.parent_scenario_id)
        if parent is None:
            raise HTTPException(status_code=400, detail="parent_scenario_id not found")

    scen = Scenario(
        external_id=f"user-{uuid.uuid4().hex[:12]}",
        kind="user",
        name=payload.name,
        description=payload.description,
        parent_scenario_id=payload.parent_scenario_id,
        jurisdiction=payload.jurisdiction,
        strategy=payload.strategy,
        leave_uk_year=payload.leave_uk_year,
        glide_path=payload.glide_path,
        spending_gbp=payload.spending_gbp,
        horizon_years=payload.horizon_years,
        nw_seed_gbp=payload.nw_seed_gbp,
        savings_per_year_gbp=payload.savings_per_year_gbp,
        config_json=payload.config_json,
    )
    session.add(scen)
    await session.commit()
    await session.refresh(scen)
    return scen


@router.patch(
    "/{scenario_id}",
    response_model=ScenarioOut,
)
async def patch_scenario(
    scenario_id: int,
    payload: ScenarioPatch,
    session: AsyncSession = Depends(get_session),
) -> Scenario:
    scen = await session.get(Scenario, scenario_id)
    if scen is None:
        raise HTTPException(status_code=404, detail="Scenario not found")
    if scen.kind != "user":
        raise HTTPException(status_code=400,
                            detail="Cannot patch cartesian scenarios — they're auto-generated")
    updates = payload.model_dump(exclude_unset=True)
    for k, v in updates.items():
        setattr(scen, k, v)
    await session.commit()
    await session.refresh(scen)
    return scen


@router.delete(
    "/{scenario_id}",
    status_code=204,
    response_model=None,
)
async def delete_scenario(
    scenario_id: int,
    session: AsyncSession = Depends(get_session),
) -> None:
    scen = await session.get(Scenario, scenario_id)
    if scen is None:
        raise HTTPException(status_code=404, detail="Scenario not found")
    if scen.kind != "user":
        raise HTTPException(
            status_code=400,
            detail="Cannot delete cartesian scenarios — they re-appear on recompute",
        )
    await session.execute(delete(Scenario).where(Scenario.id == scenario_id))
    await session.commit()


@router.get("/{scenario_id}/projection", response_model=ScenarioProjection)
async def get_scenario_projection(
    scenario_id: int,
    session: AsyncSession = Depends(get_session),
) -> ScenarioProjection:
    """Latest MC run for this scenario + the per-year fan series."""
    scen = await session.get(Scenario, scenario_id)
    if scen is None:
        raise HTTPException(status_code=404, detail="Scenario not found")
    run = (await session.execute(
        select(McRun).where(McRun.scenario_id == scenario_id).order_by(
            McRun.run_at.desc()).limit(1))).scalar_one_or_none()
    if run is None:
        raise HTTPException(status_code=404, detail="No MC runs persisted for this scenario yet")
    yearly_rows = (await session.execute(
        select(ProjectionYearly).where(ProjectionYearly.mc_run_id == run.id).order_by(
            ProjectionYearly.year_idx))).scalars().all()
    return ScenarioProjection(
        scenario_id=scen.id,
        external_id=scen.external_id,
        mc_run_id=run.id,
        run_at=run.run_at,
        n_paths=run.n_paths,
        success_rate=run.success_rate,
        p10_ending_gbp=run.p10_ending_gbp,
        p50_ending_gbp=run.p50_ending_gbp,
        p90_ending_gbp=run.p90_ending_gbp,
        median_lifetime_tax_gbp=run.median_lifetime_tax_gbp,
        median_years_to_ruin=run.median_years_to_ruin,
        yearly=[ProjectionPoint.model_validate(y) for y in yearly_rows],
    )