import uuid
from datetime import datetime, date
from sqlalchemy import String, DateTime, Date, Float, Integer, Text, ForeignKey, func
from sqlalchemy.orm import Mapped, mapped_column, relationship
from app.database import Base


class PurchaseRequest(Base):
    __tablename__ = "purchase_requests"
    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
    request_number: Mapped[str] = mapped_column(String(30), unique=True)
    requested_by: Mapped[str] = mapped_column(ForeignKey("users.id"))
    department: Mapped[str | None] = mapped_column(String(50), nullable=True)
    status: Mapped[str] = mapped_column(String(20), default="pending")
    notes: Mapped[str | None] = mapped_column(Text, nullable=True)
    created_at: Mapped[datetime] = mapped_column(DateTime, server_default=func.now())


class PurchaseOrder(Base):
    __tablename__ = "purchase_orders"
    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
    po_number: Mapped[str] = mapped_column(String(30), unique=True)
    supplier_id: Mapped[str] = mapped_column(ForeignKey("suppliers.id"))
    order_date: Mapped[date] = mapped_column(Date)
    expected_date: Mapped[date | None] = mapped_column(Date, nullable=True)
    total: Mapped[float] = mapped_column(Float, default=0.0)
    status: Mapped[str] = mapped_column(String(20), default="draft")
    notes: Mapped[str | None] = mapped_column(Text, nullable=True)
    branch_id: Mapped[str | None] = mapped_column(String(36), nullable=True, index=True)
    created_by: Mapped[str] = mapped_column(ForeignKey("users.id"))
    created_at: Mapped[datetime] = mapped_column(DateTime, server_default=func.now())
    updated_at: Mapped[datetime] = mapped_column(DateTime, server_default=func.now(), onupdate=func.now())
    items = relationship("PurchaseItem", back_populates="order", cascade="all, delete-orphan")


class PurchaseItem(Base):
    __tablename__ = "purchase_items"
    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
    order_id: Mapped[str] = mapped_column(ForeignKey("purchase_orders.id"))
    inventory_id: Mapped[str | None] = mapped_column(ForeignKey("inventory.id"), nullable=True)
    description: Mapped[str] = mapped_column(String(200))
    quantity: Mapped[int] = mapped_column(Integer, default=1)
    unit_price: Mapped[float] = mapped_column(Float, default=0.0)
    total: Mapped[float] = mapped_column(Float, default=0.0)
    order = relationship("PurchaseOrder", back_populates="items")


class GoodsReceiptNote(Base):
    __tablename__ = "grn"
    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
    grn_number: Mapped[str] = mapped_column(String(30), unique=True)
    purchase_order_id: Mapped[str | None] = mapped_column(ForeignKey("purchase_orders.id"), nullable=True)
    supplier_id: Mapped[str] = mapped_column(ForeignKey("suppliers.id"))
    received_date: Mapped[date] = mapped_column(Date)
    total: Mapped[float] = mapped_column(Float, default=0.0)
    status: Mapped[str] = mapped_column(String(20), default="received")
    notes: Mapped[str | None] = mapped_column(Text, nullable=True)
    branch_id: Mapped[str | None] = mapped_column(String(36), nullable=True, index=True)
    received_by: Mapped[str] = mapped_column(ForeignKey("users.id"))
    created_at: Mapped[datetime] = mapped_column(DateTime, server_default=func.now())

    items = relationship("GRNItem", back_populates="grn", cascade="all, delete-orphan")


class GRNItem(Base):
    """Received-quantity snapshot per PO line at GRN time (Phase 3 addition)."""
    __tablename__ = "grn_items"
    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
    grn_id: Mapped[str] = mapped_column(ForeignKey("grn.id"), index=True)
    po_item_id: Mapped[str | None] = mapped_column(String(36), nullable=True)
    inventory_id: Mapped[str | None] = mapped_column(ForeignKey("inventory.id"), nullable=True)
    description: Mapped[str] = mapped_column(String(200), default="")
    quantity: Mapped[int] = mapped_column(Integer, default=0)
    unit_price: Mapped[float] = mapped_column(Float, default=0.0)
    total: Mapped[float] = mapped_column(Float, default=0.0)
    grn = relationship("GoodsReceiptNote", back_populates="items")