from typing import Any, Optional
from fastapi import APIRouter, Depends, HTTPException, status, Header
from sqlalchemy.orm import Session, joinedload
from datetime import datetime, timezone

from app.db.base import get_db
from app.models.user import User
from app.models.product import Product
from app.models.cart import Cart, CartItem, Coupon
from app.schemas.cart import (
    CartResponse, CartItemCreate, CartItemUpdate, 
    CartItemResponse, CouponApply, CouponResponse
)
from app.schemas.product import ProductListItem
from app.core.security import get_optional_current_user

router = APIRouter(tags=["Cart"])

TAX_RATE = 0.0  # Tax removed (0%)
SHIPPING_FLAT_RATE = 20.0  # Flat shipping rate
FREE_SHIPPING_THRESHOLD = 500.0  # Free shipping over 500


def calculate_cart_totals(cart: Cart, db: Session) -> dict:
    from app.models.settings import StoreSettings
    settings = db.query(StoreSettings).first()
    global_multiplier = (1 - (settings.global_discount / 100.0)) if settings else 1.0

    subtotal = sum(item.quantity * item.unit_price * global_multiplier for item in cart.items)
    
    # Calculate discount
    discount_amount = 0.0
    applied_coupon = None
    if cart.coupon and cart.coupon.is_active:
        if cart.coupon.expires_at is None or cart.coupon.expires_at > datetime.now(timezone.utc):
            discount_amount = subtotal * (cart.coupon.discount_percent / 100.0)
            applied_coupon = CouponResponse.model_validate(cart.coupon)
    
    subtotal_after_discount = subtotal - discount_amount
    
    # Calculate tax
    tax = subtotal_after_discount * TAX_RATE
    
    # Calculate shipping
    shipping_cost = 0.0 if subtotal_after_discount >= FREE_SHIPPING_THRESHOLD or subtotal_after_discount == 0 else SHIPPING_FLAT_RATE
    
    total = subtotal_after_discount + tax + shipping_cost

    return {
        "subtotal": round(subtotal, 2),
        "tax": round(tax, 2),
        "shipping_cost": round(shipping_cost, 2),
        "discount_amount": round(discount_amount, 2),
        "total": round(total, 2),
        "applied_coupon": applied_coupon,
        "global_discount_multiplier": global_multiplier
    }

def get_or_create_cart(db: Session, user_id: Optional[int] = None, session_id: Optional[str] = None) -> Cart:
    """Get or create a cart for either an authenticated user or a guest session."""
    if user_id:
        cart = db.query(Cart).filter(Cart.user_id == user_id).first()
        if not cart:
            cart = Cart(user_id=user_id)
            db.add(cart)
            db.commit()
            db.refresh(cart)
        return cart
    elif session_id:
        cart = db.query(Cart).filter(Cart.session_id == session_id).first()
        if not cart:
            cart = Cart(session_id=session_id)
            db.add(cart)
            db.commit()
            db.refresh(cart)
        return cart
    else:
        raise HTTPException(status_code=400, detail="Either login or provide X-Cart-ID header")


def _get_primary_image(product) -> Optional[str]:
    """Extract the primary image URL from a product's images relationship."""
    if not product:
        return None
    if product.images:
        sorted_imgs = sorted(product.images, key=lambda x: x.sort_order)
        return sorted_imgs[0].image_url if sorted_imgs else None
    return None


@router.get("/cart", response_model=dict)
def get_cart(
    current_user_id: Optional[int] = Depends(get_optional_current_user),
    x_cart_id: Optional[str] = Header(None),
    db: Session = Depends(get_db)
) -> Any:
    """Get the current user's (or guest session's) shopping cart."""
    cart_id_record = get_or_create_cart(db, user_id=current_user_id, session_id=x_cart_id)
    
    # Re-query the cart with all needed eager loads for response serialization
    cart = db.query(Cart).options(
        joinedload(Cart.items)
            .joinedload(CartItem.product)
            .joinedload(Product.images),
        joinedload(Cart.items)
            .joinedload(CartItem.product)
            .joinedload(Product.category),
        joinedload(Cart.coupon)
    ).filter(Cart.id == cart_id_record.id).first()

    # Cleanup: Remove orphaned items (where product was deleted)
    orphaned_items = [item for item in cart.items if not item.product]
    if orphaned_items:
        for item in orphaned_items:
            db.delete(item)
        db.commit()
        db.refresh(cart)

    totals = calculate_cart_totals(cart, db)
    
    # Build response manually as plain dicts to guarantee image_url is included
    items_list = []
    for item in cart.items:
        # We checked if item.product exists above, but let's be safe
        if not item.product:
            continue
            
        primary_image = _get_primary_image(item.product)
        
        multiplier = totals.get("global_discount_multiplier", 1.0)
        
        product_original_price = item.unit_price # Use the stored unit price (handles variants)
        product_original_compare = item.product.compare_price if item.product.compare_price else item.unit_price

        product_dict = {
            "id": item.product.id,
            "name_ar": item.product.name_ar,
            "name_en": item.product.name_en,
            "price": round(product_original_price * multiplier, 2),
            "compare_price": round(product_original_compare, 2) if (multiplier < 1.0 or item.product.compare_price) else None,
            "stock": item.product.stock,
            "category_id": item.product.category_id,
            "category": None,
            "rating": item.product.rating,
            "rating_count": item.product.rating_count,
            "is_featured": item.product.is_featured,
            "image_url": primary_image,
            "created_at": item.product.created_at.isoformat() if item.product.created_at else None,
        }
        if item.product.category:
            product_dict["category"] = {
                "id": item.product.category.id,
                "name_ar": item.product.category.name_ar,
                "name_en": item.product.category.name_en,
                "icon": item.product.category.icon,
                "sort_order": item.product.category.sort_order,
            }
        
        items_list.append({
            "id": item.id,
            "cart_id": item.cart_id,
            "product_id": item.product_id,
            "variant_label": item.variant_label,
            "variant_id": item.variant_id,
            "quantity": item.quantity,
            "unit_price": round(item.unit_price * multiplier, 2),
            "total_price": round(item.quantity * item.unit_price * multiplier, 2),
            "product": product_dict,
        })
    
    response_value = {
        "id": cart.id,
        "user_id": cart.user_id,
        "items": items_list,
        **totals
    }
    
    return {
        "isSuccess": True,
        "value": response_value,
        "statusCode": 200
    }

@router.post("/cart/items", response_model=dict)
def add_item_to_cart(
    item_in: CartItemCreate,
    current_user_id: Optional[int] = Depends(get_optional_current_user),
    x_cart_id: Optional[str] = Header(None),
    db: Session = Depends(get_db)
) -> Any:
    """Add a product to the cart."""
    cart = get_or_create_cart(db, user_id=current_user_id, session_id=x_cart_id)
    
    # Check product availability
    product = db.query(Product).filter(Product.id == item_in.product_id).first()
    if not product:
        raise HTTPException(status_code=404, detail="Product not found")
    if not product.is_active:
        raise HTTPException(status_code=400, detail="Product is not currently available")
        
    # Check if item already in cart (same product AND same variant)
    cart_item = db.query(CartItem).filter(
        CartItem.cart_id == cart.id,
        CartItem.product_id == item_in.product_id,
        CartItem.variant_id == item_in.variant_id
    ).first()
    
    # Calculate variant price if applicable
    final_price = product.price
    variant_label = item_in.variant_label
    
    if item_in.variant_id and product.specs:
        variants = product.specs.get("variants") or product.specs.get("options", [{}])[0].get("values")
        if variants and isinstance(variants, list):
            matched_variant = None
            
            # 1. Try matching by ID string
            for v in variants:
                if str(v.get("id")) == str(item_in.variant_id):
                    matched_variant = v
                    break
            
            # 2. Try matching by index if variant_id is numeric and no ID match found
            if not matched_variant and str(item_in.variant_id).isdigit():
                idx = int(item_in.variant_id)
                if 0 <= idx < len(variants):
                    matched_variant = variants[idx]
            
            if matched_variant:
                # Update price
                if matched_variant.get("price_modifier") is not None:
                    final_price += float(matched_variant.get("price_modifier", 0))
                elif matched_variant.get("price") is not None:
                    final_price = float(matched_variant.get("price"))
                
                # Auto-assign label if not provided
                if not variant_label:
                    variant_label = matched_variant.get("name_ar") or matched_variant.get("name_en") or matched_variant.get("label")

    if cart_item:
        if cart_item.quantity + item_in.quantity > product.stock:
            raise HTTPException(status_code=400, detail=f"Not enough stock. Only {product.stock} available.")
        cart_item.quantity += item_in.quantity
        cart_item.unit_price = final_price
        cart_item.variant_label = variant_label
    else:
        if item_in.quantity > product.stock:
            raise HTTPException(status_code=400, detail=f"Not enough stock. Only {product.stock} available.")
        cart_item = CartItem(
            cart_id=cart.id,
            product_id=item_in.product_id,
            quantity=item_in.quantity,
            unit_price=final_price,
            variant_id=item_in.variant_id,
            variant_label=variant_label
        )
        db.add(cart_item)
        
    db.commit()
    return {"isSuccess": True, "value": {"message": "Item added to cart"}, "statusCode": 200}

@router.put("/cart/items/{item_id}", response_model=dict)
def update_cart_item(
    item_id: int,
    item_in: CartItemUpdate,
    current_user_id: Optional[int] = Depends(get_optional_current_user),
    x_cart_id: Optional[str] = Header(None),
    db: Session = Depends(get_db)
) -> Any:
    """Update quantity of an item in the cart."""
    cart = get_or_create_cart(db, user_id=current_user_id, session_id=x_cart_id)
    
    cart_item = db.query(CartItem).filter(
        CartItem.id == item_id,
        CartItem.cart_id == cart.id
    ).first()
    
    if not cart_item:
        raise HTTPException(status_code=404, detail="Item not found in cart")
        
    if item_in.quantity > cart_item.product.stock:
        raise HTTPException(status_code=400, detail=f"Not enough stock. Only {cart_item.product.stock} available.")
        
    cart_item.quantity = item_in.quantity
    db.commit()
    
    return {"isSuccess": True, "value": {"message": "Cart updated"}, "statusCode": 200}

@router.delete("/cart/items/{item_id}", response_model=dict)
def remove_cart_item(
    item_id: int,
    current_user_id: Optional[int] = Depends(get_optional_current_user),
    x_cart_id: Optional[str] = Header(None),
    db: Session = Depends(get_db)
) -> Any:
    """Remove an item from the cart."""
    cart = get_or_create_cart(db, user_id=current_user_id, session_id=x_cart_id)
    
    cart_item = db.query(CartItem).filter(
        CartItem.id == item_id,
        CartItem.cart_id == cart.id
    ).first()
    
    if not cart_item:
        raise HTTPException(status_code=404, detail="Item not found in cart")
        
    db.delete(cart_item)
    db.commit()
    
    return {"isSuccess": True, "value": {"message": "Item removed from cart"}, "statusCode": 200}

@router.post("/cart/coupon", response_model=dict)
def apply_coupon(
    coupon_in: CouponApply,
    current_user_id: Optional[int] = Depends(get_optional_current_user),
    x_cart_id: Optional[str] = Header(None),
    db: Session = Depends(get_db)
) -> Any:
    """Apply a discount coupon to the cart."""
    cart = get_or_create_cart(db, user_id=current_user_id, session_id=x_cart_id)
    
    coupon = db.query(Coupon).filter(Coupon.code == coupon_in.code.upper()).first()
    if not coupon or not coupon.is_active:
        raise HTTPException(status_code=400, detail="Invalid coupon code")
        
    if coupon.expires_at and coupon.expires_at < datetime.now(timezone.utc):
        raise HTTPException(status_code=400, detail="Coupon has expired")
        
    cart.coupon_id = coupon.id
    db.commit()
    
    return {"isSuccess": True, "value": {"message": f"Coupon {coupon.code} applied successfully"}, "statusCode": 200}

@router.delete("/cart/clear", response_model=dict)
def clear_cart(
    current_user_id: Optional[int] = Depends(get_optional_current_user),
    x_cart_id: Optional[str] = Header(None),
    db: Session = Depends(get_db)
) -> Any:
    """Remove all items from the cart and detach coupons."""
    cart = get_or_create_cart(db, user_id=current_user_id, session_id=x_cart_id)
    
    db.query(CartItem).filter(CartItem.cart_id == cart.id).delete()
    cart.coupon_id = None
    db.commit()
    
    return {"isSuccess": True, "value": {"message": "Cart cleared"}, "statusCode": 200}