from datetime import datetime, timezone

from fastapi import APIRouter, Depends, HTTPException, Query
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy import select, func
from pydantic import BaseModel
from app.core.database import get_db
from app.core.deps import get_current_user, require_roles
from app.models.maintenance import SparePart, WarehouseTransaction
from app.models.user import User

router = APIRouter(prefix="/warehouse", tags=["仓库管理"])


# ── Pydantic Schemas ────────────────────────────────────────────────

class PartCreate(BaseModel):
    name: str
    code: str | None = None
    category: str | None = None
    unit: str | None = None
    current_stock: int = 0
    min_stock: int = 0
    location: str | None = None
    supplier: str | None = None
    unit_price: float | None = None
    specs: dict | None = None
    notes: str | None = None


class PartUpdate(BaseModel):
    name: str | None = None
    code: str | None = None
    category: str | None = None
    unit: str | None = None
    min_stock: int | None = None
    location: str | None = None
    supplier: str | None = None
    unit_price: float | None = None
    specs: dict | None = None
    notes: str | None = None


class TransactionCreate(BaseModel):
    spare_part_id: int
    type: str  # "in" or "out"
    quantity: int
    reason: str | None = None
    related_order_id: int | None = None
    operator_id: int | None = None
    notes: str | None = None


# ── Helpers ─────────────────────────────────────────────────────────

def _part_to_dict(p: SparePart) -> dict:
    return {
        "id": p.id, "name": p.name, "code": p.code,
        "category": p.category, "unit": p.unit,
        "current_stock": p.current_stock, "min_stock": p.min_stock,
        "location": p.location, "supplier": p.supplier,
        "unit_price": p.unit_price, "specs": p.specs, "notes": p.notes,
        "created_at": str(p.created_at) if p.created_at else None,
        "updated_at": str(p.updated_at) if p.updated_at else None,
    }


def _transaction_to_dict(t: WarehouseTransaction) -> dict:
    return {
        "id": t.id, "spare_part_id": t.spare_part_id,
        "type": t.type, "quantity": t.quantity,
        "reason": t.reason, "related_order_id": t.related_order_id,
        "operator_id": t.operator_id, "notes": t.notes,
        "created_at": str(t.created_at) if t.created_at else None,
    }


# ── Spare Parts ────────────────────────────────────────────────────

@router.get("/parts")
async def list_parts(
    category: str | None = None,
    search: str | None = None,
    low_stock_only: bool = False,
    page: int = Query(1, ge=1),
    page_size: int = Query(20, ge=1, le=100),
    db: AsyncSession = Depends(get_db),
    user: User = Depends(get_current_user),
):
    query = select(SparePart)
    if category:
        query = query.where(SparePart.category == category)
    if search:
        query = query.where(SparePart.name.ilike(f"%{search}%"))
    if low_stock_only:
        query = query.where(SparePart.current_stock <= SparePart.min_stock)

    count_q = select(func.count()).select_from(query.subquery())
    total = (await db.execute(count_q)).scalar()

    query = query.order_by(SparePart.id.desc()).offset((page - 1) * page_size).limit(page_size)
    result = await db.execute(query)
    return {
        "total": total,
        "items": [_part_to_dict(p) for p in result.scalars().all()],
    }


@router.get("/parts/{part_id}")
async def get_part(
    part_id: int,
    db: AsyncSession = Depends(get_db),
    user: User = Depends(get_current_user),
):
    result = await db.execute(select(SparePart).where(SparePart.id == part_id))
    part = result.scalar_one_or_none()
    if not part:
        raise HTTPException(status_code=404, detail="备件不存在")
    return _part_to_dict(part)


@router.post("/parts")
async def create_part(
    data: PartCreate,
    db: AsyncSession = Depends(get_db),
    user: User = Depends(require_roles("admin", "energy_manager")),
):
    part = SparePart(**data.model_dump())
    db.add(part)
    await db.flush()
    return _part_to_dict(part)


@router.put("/parts/{part_id}")
async def update_part(
    part_id: int,
    data: PartUpdate,
    db: AsyncSession = Depends(get_db),
    user: User = Depends(require_roles("admin", "energy_manager")),
):
    result = await db.execute(select(SparePart).where(SparePart.id == part_id))
    part = result.scalar_one_or_none()
    if not part:
        raise HTTPException(status_code=404, detail="备件不存在")
    for k, v in data.model_dump(exclude_unset=True).items():
        setattr(part, k, v)
    return _part_to_dict(part)


# ── Warehouse Transactions ─────────────────────────────────────────

@router.get("/transactions")
async def list_transactions(
    spare_part_id: int | None = None,
    type: str | None = None,
    start_date: str | None = None,
    end_date: str | None = None,
    page: int = Query(1, ge=1),
    page_size: int = Query(20, ge=1, le=100),
    db: AsyncSession = Depends(get_db),
    user: User = Depends(get_current_user),
):
    query = select(WarehouseTransaction)
    if spare_part_id:
        query = query.where(WarehouseTransaction.spare_part_id == spare_part_id)
    if type:
        query = query.where(WarehouseTransaction.type == type)
    if start_date:
        query = query.where(WarehouseTransaction.created_at >= datetime.fromisoformat(start_date))
    if end_date:
        query = query.where(WarehouseTransaction.created_at <= datetime.fromisoformat(end_date))

    count_q = select(func.count()).select_from(query.subquery())
    total = (await db.execute(count_q)).scalar()

    query = query.order_by(WarehouseTransaction.id.desc()).offset((page - 1) * page_size).limit(page_size)
    result = await db.execute(query)
    return {
        "total": total,
        "items": [_transaction_to_dict(t) for t in result.scalars().all()],
    }


@router.post("/transactions")
async def create_transaction(
    data: TransactionCreate,
    db: AsyncSession = Depends(get_db),
    user: User = Depends(get_current_user),
):
    # Fetch the spare part
    result = await db.execute(select(SparePart).where(SparePart.id == data.spare_part_id))
    part = result.scalar_one_or_none()
    if not part:
        raise HTTPException(status_code=404, detail="备件不存在")

    # Validate stock for outbound
    if data.type == "out" and part.current_stock < data.quantity:
        raise HTTPException(status_code=400, detail=f"库存不足，当前库存: {part.current_stock}")

    # Update stock
    if data.type == "in":
        part.current_stock += data.quantity
    elif data.type == "out":
        part.current_stock -= data.quantity
    else:
        raise HTTPException(status_code=400, detail="类型必须为 'in' 或 'out'")

    txn = WarehouseTransaction(**data.model_dump())
    if not txn.operator_id:
        txn.operator_id = user.id
    db.add(txn)
    await db.flush()
    return _transaction_to_dict(txn)


# ── Statistics ─────────────────────────────────────────────────────

@router.get("/stats")
async def warehouse_stats(
    db: AsyncSession = Depends(get_db),
    user: User = Depends(get_current_user),
):
    # Total parts count
    total_q = select(func.count()).select_from(SparePart)
    total_parts = (await db.execute(total_q)).scalar() or 0

    # Low stock alerts
    low_q = select(func.count()).select_from(SparePart).where(
        SparePart.current_stock <= SparePart.min_stock
    )
    low_stock_count = (await db.execute(low_q)).scalar() or 0

    # Recent transactions (last 30 days)
    from datetime import timedelta
    cutoff = datetime.now(timezone.utc) - timedelta(days=30)
    recent_q = select(func.count()).select_from(WarehouseTransaction).where(
        WarehouseTransaction.created_at >= cutoff
    )
    recent_transactions = (await db.execute(recent_q)).scalar() or 0

    return {
        "total_parts": total_parts,
        "low_stock_count": low_stock_count,
        "recent_transactions": recent_transactions,
    }