from django.shortcuts import render, redirect, get_object_or_404
from django.contrib.auth.decorators import login_required, permission_required
from django.contrib import messages
from django.http import HttpResponse
from django.db.models import Sum, Q, Count, F
from datetime import timedelta
from django.utils import timezone
from django import forms
from django.forms import inlineformset_factory
from decimal import Decimal
from .models import Supplier, PurchaseOrder, PurchaseOrderItem, GoodsReceipt, GoodsReceiptItem
from apps.inventory.models import Product, Warehouse, Inventory, StockMovement


class SupplierForm(forms.ModelForm):
    class Meta:
        model = Supplier
        fields = ['code', 'name', 'contact_person', 'email', 'phone', 'address', 'tax_id', 'payment_terms', 'is_active']
        widgets = {
            'address': forms.Textarea(attrs={'rows': 3}),
            'payment_terms': forms.Textarea(attrs={'rows': 2}),
        }


class PurchaseOrderItemForm(forms.ModelForm):
    class Meta:
        model = PurchaseOrderItem
        fields = ['product', 'quantity', 'unit_price']
        widgets = {
            'quantity': forms.NumberInput(attrs={'step': '0.01', 'min': '0'}),
            'unit_price': forms.NumberInput(attrs={'step': '0.01', 'min': '0'}),
        }

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.fields['product'].queryset = Product.objects.filter(is_active=True)


class PurchaseOrderForm(forms.ModelForm):
    class Meta:
        model = PurchaseOrder
        fields = ['supplier', 'order_date', 'expected_delivery_date', 'notes']
        widgets = {
            'order_date': forms.DateInput(attrs={'type': 'date'}),
            'expected_delivery_date': forms.DateInput(attrs={'type': 'date'}),
            'notes': forms.Textarea(attrs={'rows': 3}),
        }


PurchaseOrderItemFormSet = inlineformset_factory(
    PurchaseOrder,
    PurchaseOrderItem,
    form=PurchaseOrderItemForm,
    extra=0,
    can_delete=True,
    min_num=1,
    validate_min=True
)


@login_required
def purchasing_dashboard(request):
    """Purchasing dashboard view"""
    suppliers = Supplier.objects.filter(is_active=True)
    pending_orders = PurchaseOrder.objects.filter(
        Q(status='ordered') | Q(status='processing')
    )
    recent_orders = PurchaseOrder.objects.select_related('supplier').order_by('-created_at')[:5]

    # Calculate total value of recent orders (last 30 days)
    thirty_days_ago = timezone.now() - timedelta(days=30)
    total_value = PurchaseOrder.objects.filter(
        created_at__gte=thirty_days_ago
    ).aggregate(total=Sum('total_amount'))['total'] or 0

    # Get top suppliers by order count
    top_suppliers = Supplier.objects.annotate(
        order_count=Count('purchaseorder')
    ).order_by('-order_count')[:5]

    context = {
        'module_title': 'Purchasing Management',
        'suppliers': suppliers,
        'pending_orders': pending_orders,
        'recent_orders': recent_orders,
        'total_value': total_value,
        'top_suppliers': top_suppliers,
    }
    return render(request, 'purchasing/dashboard.html', context)


# Supplier Views
@login_required
@permission_required('purchasing.view_supplier', raise_exception=True)
def supplier_list_view(request):
    """List all suppliers"""
    suppliers = Supplier.objects.all()
    context = {
        'module_title': 'Supplier List',
        'suppliers': suppliers,
    }
    return render(request, 'purchasing/supplier_list.html', context)


@login_required
def create_supplier_view(request):
    """Create a new supplier"""
    if request.method == 'POST':
        form = SupplierForm(request.POST)
        if form.is_valid():
            supplier = form.save()
            messages.success(request, f'Supplier "{supplier.name}" created successfully!')
            return redirect('purchasing:supplier_detail', supplier_id=supplier.id)
    else:
        form = SupplierForm()

    context = {
        'form': form,
        'module_title': 'Create Supplier',
        'is_create': True,
    }
    return render(request, 'purchasing/supplier_form.html', context)


@login_required
@permission_required('purchasing.view_supplier', raise_exception=True)
def supplier_detail_view(request, supplier_id):
    """View supplier details"""
    try:
        supplier = Supplier.objects.get(id=supplier_id)
        context = {
            'module_title': 'Supplier Details',
            'supplier': supplier,
        }
        return render(request, 'purchasing/supplier_detail.html', context)
    except Supplier.DoesNotExist:
        messages.error(request, 'Supplier not found')
        return redirect('purchasing:supplier_list')


@login_required
def edit_supplier_view(request, supplier_id):
    """Edit supplier details"""
    supplier = get_object_or_404(Supplier, id=supplier_id)

    if request.method == 'POST':
        form = SupplierForm(request.POST, instance=supplier)
        if form.is_valid():
            supplier = form.save()
            messages.success(request, f'Supplier "{supplier.name}" updated successfully!')
            return redirect('purchasing:supplier_detail', supplier_id=supplier.id)
    else:
        form = SupplierForm(instance=supplier)

    context = {
        'form': form,
        'supplier': supplier,
        'module_title': 'Edit Supplier',
        'is_create': False,
    }
    return render(request, 'purchasing/supplier_form.html', context)


@login_required
def delete_supplier_view(request, supplier_id):
    """Delete a supplier"""
    supplier = get_object_or_404(Supplier, id=supplier_id)

    if request.method == 'POST':
        supplier_name = supplier.name
        supplier.delete()
        messages.success(request, f'Supplier "{supplier_name}" deleted successfully!')
        return redirect('purchasing:supplier_list')

    # Get supplier statistics for confirmation
    supplier_order_count = PurchaseOrder.objects.filter(supplier=supplier).count()
    supplier_total_value = PurchaseOrder.objects.filter(supplier=supplier).aggregate(
        total=Sum('total_amount')
    )['total'] or 0

    context = {
        'supplier': supplier,
        'module_title': 'Delete Supplier',
        'supplier_order_count': supplier_order_count,
        'supplier_total_value': supplier_total_value,
    }
    return render(request, 'purchasing/supplier_confirm_delete.html', context)


# Purchase Order Views
@login_required
@permission_required('purchasing.view_purchaseorder', raise_exception=True)
def po_list_view(request):
    """List all purchase orders"""
    pos = PurchaseOrder.objects.select_related('supplier').all()

    # Calculate statistics
    total_value = pos.aggregate(total=Sum('total_amount'))['total'] or 0
    pending_orders = pos.filter(status__in=['ordered', 'processing']).count()

    context = {
        'module_title': 'Purchase Order List',
        'pos': pos,
        'total_value': total_value,
        'pending_orders': pending_orders,
    }
    return render(request, 'purchasing/po_list.html', context)


@login_required
def create_po_view(request):
    """Create a new purchase order"""
    if request.method == 'POST':
        form = PurchaseOrderForm(request.POST)
        formset = PurchaseOrderItemFormSet(request.POST)

        if form.is_valid() and formset.is_valid():
            # Save the purchase order
            po = form.save(commit=False)
            po.created_by = request.user
            po.save()

            # Save the items
            items = formset.save(commit=False)
            for item in items:
                item.po = po
                item.save()

            # Calculate totals
            po.subtotal = sum(item.total_price for item in po.items.all())
            po.tax_amount = po.subtotal * Decimal('0.11')  # 11% tax
            po.total_amount = po.subtotal + po.tax_amount
            po.save()

            messages.success(request, f'Purchase Order "{po.po_number}" created successfully!')
            return redirect('purchasing:po_detail', po_number=po.po_number)
    else:
        form = PurchaseOrderForm()
        formset = PurchaseOrderItemFormSet()

    context = {
        'form': form,
        'formset': formset,
        'module_title': 'Create Purchase Order',
        'is_create': True,
    }
    return render(request, 'purchasing/po_form.html', context)


@login_required
@permission_required('purchasing.view_purchaseorder', raise_exception=True)
def po_detail_view(request, po_number):
    """View purchase order details"""
    try:
        po = PurchaseOrder.objects.get(po_number=po_number)
        context = {
            'module_title': 'Purchase Order Details',
            'po': po,
        }
        return render(request, 'purchasing/po_detail.html', context)
    except PurchaseOrder.DoesNotExist:
        messages.error(request, 'Purchase order not found')
        return redirect('purchasing:po_list')


@login_required
def edit_po_view(request, po_number):
    """Edit purchase order details"""
    po = get_object_or_404(PurchaseOrder, po_number=po_number)

    if request.method == 'POST':
        form = PurchaseOrderForm(request.POST, instance=po)
        formset = PurchaseOrderItemFormSet(request.POST, instance=po)

        # Custom validation to skip deleted items
        formset_valid = True
        for i, form_item in enumerate(formset):
            # Check if this item is marked for deletion in POST data
            delete_field_name = f'form-{i}-DELETE'
            is_deleted = request.POST.get(delete_field_name, 'off') == 'on'

            if not is_deleted:
                # Only validate non-deleted items
                if not form_item.is_valid():
                    formset_valid = False

        if form.is_valid() and formset_valid:
            # Save the purchase order
            po = form.save(commit=False)
            po.save()

            # Save the items (excluding deleted ones)
            items = formset.save(commit=False)
            for item in items:
                item.po = po
                item.save()

            # Delete items marked for deletion
            for deleted_item in formset.deleted_objects:
                deleted_item.delete()

            # Recalculate totals
            po.subtotal = sum(item.total_price for item in po.items.all())
            po.tax_amount = po.subtotal * Decimal('0.11')  # 11% tax
            po.total_amount = po.subtotal + po.tax_amount
            po.save()

            messages.success(request, f'Purchase Order "{po.po_number}" updated successfully!')
            return redirect('purchasing:po_detail', po_number=po.po_number)
    else:
        form = PurchaseOrderForm(instance=po)
        formset = PurchaseOrderItemFormSet(instance=po)

    context = {
        'form': form,
        'formset': formset,
        'po': po,
        'module_title': 'Edit Purchase Order',
        'is_create': False,
    }
    return render(request, 'purchasing/po_form.html', context)


@login_required
def approve_po_view(request, po_number):
    """Approve a purchase order"""
    po = get_object_or_404(PurchaseOrder, po_number=po_number)

    if request.method == 'POST':
        if po.status == 'ordered':
            po.status = 'approved'
            po.save()
            messages.success(request, f'Purchase Order "{po.po_number}" has been approved successfully!')

            # Log the approval
            # You could add audit logging here

        else:
            messages.warning(request, f'Purchase Order "{po.po_number}" cannot be approved in its current status.')

        return redirect('purchasing:po_detail', po_number=po.po_number)

    context = {
        'po': po,
        'action': 'approve',
        'action_title': 'Approve Purchase Order',
        'action_message': f'Are you sure you want to approve Purchase Order "{po.po_number}"?',
        'action_button': 'Approve Order',
        'action_class': 'success',
    }
    return render(request, 'purchasing/po_action_confirm.html', context)


@login_required
def cancel_po_view(request, po_number):
    """Cancel a purchase order"""
    po = get_object_or_404(PurchaseOrder, po_number=po_number)

    if request.method == 'POST':
        if po.status in ['ordered', 'approved']:
            po.status = 'cancelled'
            po.save()
            messages.success(request, f'Purchase Order "{po.po_number}" has been cancelled successfully!')

            # Log the cancellation
            # You could add audit logging here

        else:
            messages.warning(request, f'Purchase Order "{po.po_number}" cannot be cancelled in its current status.')

        return redirect('purchasing:po_detail', po_number=po.po_number)

    context = {
        'po': po,
        'action': 'cancel',
        'action_title': 'Cancel Purchase Order',
        'action_message': f'Are you sure you want to cancel Purchase Order "{po.po_number}"? This action cannot be undone.',
        'action_button': 'Cancel Order',
        'action_class': 'danger',
    }
    return render(request, 'purchasing/po_action_confirm.html', context)


@login_required
def delete_po_view(request, po_number):
    """Delete a purchase order"""
    po = get_object_or_404(PurchaseOrder, po_number=po_number)

    if request.method == 'POST':
        po_number = po.po_number
        po.delete()
        messages.success(request, f'Purchase Order "{po_number}" deleted successfully!')
        return redirect('purchasing:po_list')

    context = {
        'po': po,
        'module_title': 'Delete Purchase Order',
    }
    return render(request, 'purchasing/po_confirm_delete.html', context)


# Goods Receipt Views
@login_required
@permission_required('purchasing.view_goodsreceipt', raise_exception=True)
def gr_list_view(request):
    """List all goods receipts"""
    grs = GoodsReceipt.objects.all()
    context = {
        'module_title': 'Goods Receipt List',
        'grs': grs,
    }
    return render(request, 'purchasing/gr_list.html', context)


@login_required
def create_gr_view(request, po_number):
    """Create a new goods receipt"""
    po = get_object_or_404(PurchaseOrder, po_number=po_number)

    # Check if PO can have goods receipt
    if po.status not in ['ordered', 'approved']:
        messages.error(request, f'Cannot create goods receipt for Purchase Order in "{po.get_status_display()}" status.')
        return redirect('purchasing:po_detail', po_number=po.po_number)

    if request.method == 'POST':
        # Generate GR number (simple auto-increment)
        last_gr = GoodsReceipt.objects.order_by('-id').first()
        gr_number = f"GR{str(last_gr.id + 1).zfill(4)}" if last_gr else "GR0001"

        # Create goods receipt
        gr = GoodsReceipt.objects.create(
            gr_number=gr_number,
            po=po,
            receipt_date=request.POST.get('receipt_date', timezone.now().date()),
            received_by=request.user,
            notes=request.POST.get('notes', '')
        )

        # Create goods receipt items and update inventory
        for po_item in po.items.all():
            # Convert Indonesian format (comma) to standard format (dot) for Decimal
            quantity_str = request.POST.get(f'quantity_{po_item.id}', '0').replace(',', '.')
            received_qty = Decimal(quantity_str) if quantity_str else Decimal('0')

            if received_qty > 0:
                # Create GR item
                GoodsReceiptItem.objects.create(
                    receipt=gr,
                    po_item=po_item,
                    received_quantity=received_qty,
                    notes=request.POST.get(f'notes_{po_item.id}', '')
                )

                # Update PO item received quantity
                po_item.received_quantity += received_qty
                po_item.save()

                # Update inventory
                warehouse = Warehouse.objects.first()  # Default to first warehouse if not specified
                inventory, created = Inventory.objects.get_or_create(
                    product=po_item.product,
                    warehouse=warehouse,
                    defaults={'quantity': 0}
                )
                inventory.quantity += received_qty
                inventory.save()

                # Create stock movement record
                StockMovement.objects.create(
                    product=po_item.product,
                    warehouse=warehouse,
                    movement_type='in',
                    quantity=received_qty,
                    reference_number=f"GR{gr.gr_number}",
                    notes=f"Goods receipt from PO {po.po_number}",
                    created_by=request.user
                )

        # Check if PO is fully received
        total_received = sum(item.received_quantity for item in po.items.all())
        total_ordered = sum(item.quantity for item in po.items.all())

        if total_received >= total_ordered:
            po.status = 'completed'
            po.save()
            messages.success(request, f'Goods Receipt "{gr.gr_number}" created successfully! Purchase Order is now completed.')
        else:
            messages.success(request, f'Goods Receipt "{gr.gr_number}" created successfully! Partial receipt recorded.')

        return redirect('purchasing:gr_detail', gr_number=gr.gr_number)

    context = {
        'po': po,
        'module_title': f'Create Goods Receipt for {po.po_number}',
        'today': timezone.now().date(),
    }
    return render(request, 'purchasing/gr_form.html', context)


@login_required
@permission_required('purchasing.view_goodsreceipt', raise_exception=True)
def gr_detail_view(request, gr_number):
    """View goods receipt details"""
    try:
        gr = GoodsReceipt.objects.get(gr_number=gr_number)

        # Calculate totals
        total_quantity = sum(item.received_quantity for item in gr.items.all())
        total_value = sum(item.po_item.unit_price * item.received_quantity for item in gr.items.all())

        # Calculate previously received quantities and item totals for each item
        for item in gr.items.all():
            # Previously received = current total received - this receipt quantity
            item.previously_received = item.po_item.received_quantity - item.received_quantity
            # Calculate item total value
            item.item_total = item.po_item.unit_price * item.received_quantity

        context = {
            'module_title': 'Goods Receipt Details',
            'gr': gr,
            'total_quantity': total_quantity,
            'total_value': total_value,
        }
        return render(request, 'purchasing/gr_detail.html', context)
    except GoodsReceipt.DoesNotExist:
        messages.error(request, 'Goods receipt not found')
        return redirect('purchasing:gr_list')