"""Item decisions — 1:1 with line items.

State machine (P1 cross-endpoint rules):
    pending -> chosen (requires chosen_item_termsheet_id of the SAME line item)
    pending -> rejected
    chosen/rejected -> pending/anything-else = 409
"""
from fastapi import APIRouter, Depends
from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from app.db.engine import get_db
from app.models.procurement import ItemDecision, ItemTermsheet, LineItem
from app.schemas.procurement import DecisionPatch, DecisionPut, DecisionStatusUpdate
from app.services.expand_service import decision_full
from app.services.quote_service import utcnow
from app.utils.errors import ConflictError, NotFoundError, ValidationError

router = APIRouter(
    prefix="/quotes/{quote_id}/line-items/{line_item_id}/decision",
    tags=["item-decisions"],
)


async def _line_item_or_404(db: AsyncSession, quote_id, line_item_id) -> LineItem:
    li = await db.scalar(
        select(LineItem).where(LineItem.id == line_item_id, LineItem.quote_id == quote_id)
    )
    if li is None:
        raise NotFoundError("خط آیتم یافت نشد")
    return li


async def _get_or_create_pending(db: AsyncSession, line_item_id) -> ItemDecision:
    decision = await db.scalar(select(ItemDecision).where(ItemDecision.line_item_id == line_item_id))
    if decision is None:
        decision = ItemDecision(line_item_id=line_item_id, status="pending")
        db.add(decision)
        await db.flush()
    return decision


async def _validate_chosen_link(db: AsyncSession, line_item_id, item_termsheet_id) -> None:
    """chosen_item_termsheet_id must reference an item_termsheets row of the SAME line item."""
    if item_termsheet_id is None:
        raise ValidationError("برای وضعیت chosen، chosen_item_termsheet_id الزامی است", field="chosen_item_termsheet_id")
    it = await db.scalar(
        select(ItemTermsheet).where(ItemTermsheet.id == item_termsheet_id, ItemTermsheet.line_item_id == line_item_id)
    )
    if it is None:
        raise ValidationError("اتصال قیمت باید متعلق به همین خط آیتم باشد", field="chosen_item_termsheet_id")


@router.get("")
async def get_decision(quote_id, line_item_id, db: AsyncSession = Depends(get_db)):
    """Always returns a record — pending is auto-created (P0 contract)."""
    await _line_item_or_404(db, quote_id, line_item_id)
    decision = await _get_or_create_pending(db, line_item_id)
    return {"data": decision_full(decision)}


@router.put("")
async def put_decision(
    quote_id, line_item_id, payload: DecisionPut, db: AsyncSession = Depends(get_db)
):
    """UPSERT — pending -> chosen | pending -> rejected."""
    created = False
    async with db.begin():
        await _line_item_or_404(db, quote_id, line_item_id)
        decision = await db.scalar(
            select(ItemDecision).where(ItemDecision.line_item_id == line_item_id).with_for_update()
        )
        if decision is None:
            decision = ItemDecision(line_item_id=line_item_id, status="pending")
            db.add(decision)
            await db.flush()
            created = True
        if decision.status != "pending":
            raise ConflictError(
                f"بازگشت از وضعیت {decision.status} به {payload.status} مجاز نیست"
            )
        if payload.status == "chosen":
            await _validate_chosen_link(db, line_item_id, payload.chosen_item_termsheet_id)
            decision.chosen_item_termsheet_id = payload.chosen_item_termsheet_id
            decision.adjusted_unit_price = payload.adjusted_unit_price
            decision.adjusted_notes = payload.adjusted_notes
        else:  # rejected
            decision.chosen_item_termsheet_id = None
            decision.adjusted_unit_price = None
            decision.adjusted_notes = payload.adjusted_notes
        decision.status = payload.status
        decision.decided_at = utcnow()
    return {"data": decision_full(decision), "status_code_hint": 201 if created else 200}


@router.patch("/status")
async def patch_decision_status(
    quote_id, line_item_id, payload: DecisionStatusUpdate, db: AsyncSession = Depends(get_db)
):
    """Status-only transition; chosen requires chosen_item_termsheet_id already set."""
    async with db.begin():
        await _line_item_or_404(db, quote_id, line_item_id)
        decision = await db.scalar(
            select(ItemDecision).where(ItemDecision.line_item_id == line_item_id).with_for_update()
        )
        if decision is None:
            raise NotFoundError("تصمیمی برای این خط آیتم ثبت نشده است")
        if decision.status != "pending":
            raise ConflictError(
                f"بازگشت از وضعیت {decision.status} به {payload.status} مجاز نیست"
            )
        if payload.status == "chosen" and decision.chosen_item_termsheet_id is None:
            raise ValidationError(
                "برای انتخاب، ابتدا باید chosen_item_termsheet_id تنظیم شود", field="chosen_item_termsheet_id"
            )
        decision.status = payload.status
        decision.decided_at = utcnow()
    return {"data": decision_full(decision)}


@router.patch("")
async def patch_decision(
    quote_id, line_item_id, payload: DecisionPatch, db: AsyncSession = Depends(get_db)
):
    """Update chosen link / adjusted fields — status is NOT changeable here."""
    await _line_item_or_404(db, quote_id, line_item_id)
    decision = await db.scalar(select(ItemDecision).where(ItemDecision.line_item_id == line_item_id))
    if decision is None:
        raise NotFoundError("تصمیمی برای این خط آیتم ثبت نشده است")
    if payload.chosen_item_termsheet_id is not None:
        await _validate_chosen_link(db, line_item_id, payload.chosen_item_termsheet_id)
        decision.chosen_item_termsheet_id = payload.chosen_item_termsheet_id
    if payload.adjusted_unit_price is not None:
        decision.adjusted_unit_price = payload.adjusted_unit_price
    if payload.adjusted_notes is not None:
        decision.adjusted_notes = payload.adjusted_notes
    await db.flush()
    return {"data": decision_full(decision)}