"""JSON serializers for Part app"""

import imghdr
from decimal import Decimal

from django.db import models, transaction
from django.db.models import (ExpressionWrapper, F, FloatField, Func, OuterRef,
                              Q, Subquery)
from django.db.models.functions import Coalesce
from django.urls import reverse_lazy
from django.utils.translation import gettext_lazy as _

from djmoney.contrib.django_rest_framework import MoneyField
from rest_framework import serializers
from sql_util.utils import SubqueryCount, SubquerySum

from common.settings import currency_code_default, currency_code_mappings
from InvenTree.serializers import (DataFileExtractSerializer,
                                   DataFileUploadSerializer,
                                   InvenTreeAttachmentSerializer,
                                   InvenTreeAttachmentSerializerField,
                                   InvenTreeDecimalField,
                                   InvenTreeImageSerializerField,
                                   InvenTreeModelSerializer,
                                   InvenTreeMoneySerializer)
from InvenTree.status_codes import (BuildStatus, PurchaseOrderStatus,
                                    SalesOrderStatus)
from stock.models import StockItem

from .models import (BomItem, BomItemSubstitute, Part, PartAttachment,
                     PartCategory, PartCategoryParameterTemplate,
                     PartInternalPriceBreak, PartParameter,
                     PartParameterTemplate, PartRelated, PartSellPriceBreak,
                     PartStar, PartTestTemplate)


class CategorySerializer(InvenTreeModelSerializer):
    """Serializer for PartCategory"""

    def __init__(self, *args, **kwargs):

        super().__init__(*args, **kwargs)

    def get_starred(self, category):
        """Return True if the category is directly "starred" by the current user"""

        return category in self.context.get('starred_categories', [])

    url = serializers.CharField(source='get_absolute_url', read_only=True)

    parts = serializers.IntegerField(source='item_count', read_only=True)

    level = serializers.IntegerField(read_only=True)

    starred = serializers.SerializerMethodField()

    class Meta:
        model = PartCategory
        fields = [
            'pk',
            'name',
            'description',
            'default_location',
            'default_keywords',
            'level',
            'parent',
            'parts',
            'pathstring',
            'starred',
            'url',
        ]


class CategoryTree(InvenTreeModelSerializer):
    """Serializer for PartCategory tree"""

    class Meta:
        model = PartCategory
        fields = [
            'pk',
            'name',
            'parent',
        ]


class PartAttachmentSerializer(InvenTreeAttachmentSerializer):
    """Serializer for the PartAttachment class"""

    class Meta:
        model = PartAttachment

        fields = [
            'pk',
            'part',
            'attachment',
            'filename',
            'link',
            'comment',
            'upload_date',
        ]

        read_only_fields = [
            'upload_date',
        ]


class PartTestTemplateSerializer(InvenTreeModelSerializer):
    """Serializer for the PartTestTemplate class"""

    key = serializers.CharField(read_only=True)

    class Meta:
        model = PartTestTemplate

        fields = [
            'pk',
            'key',
            'part',
            'test_name',
            'description',
            'required',
            'requires_value',
            'requires_attachment',
        ]


class PartSalePriceSerializer(InvenTreeModelSerializer):
    """Serializer for sale prices for Part model."""

    quantity = InvenTreeDecimalField()

    price = InvenTreeMoneySerializer(
        allow_null=True
    )

    price_currency = serializers.ChoiceField(
        choices=currency_code_mappings(),
        default=currency_code_default,
        label=_('Currency'),
        help_text=_('Purchase currency of this stock item'),
    )

    price_string = serializers.CharField(source='price', read_only=True)

    class Meta:
        model = PartSellPriceBreak
        fields = [
            'pk',
            'part',
            'quantity',
            'price',
            'price_currency',
            'price_string',
        ]


class PartInternalPriceSerializer(InvenTreeModelSerializer):
    """Serializer for internal prices for Part model."""

    quantity = InvenTreeDecimalField()

    price = InvenTreeMoneySerializer(
        allow_null=True
    )

    price_currency = serializers.ChoiceField(
        choices=currency_code_mappings(),
        default=currency_code_default,
        label=_('Currency'),
        help_text=_('Purchase currency of this stock item'),
    )

    price_string = serializers.CharField(source='price', read_only=True)

    class Meta:
        model = PartInternalPriceBreak
        fields = [
            'pk',
            'part',
            'quantity',
            'price',
            'price_currency',
            'price_string',
        ]


class PartThumbSerializer(serializers.Serializer):
    """Serializer for the 'image' field of the Part model.

    Used to serve and display existing Part images.
    """

    image = serializers.URLField(read_only=True)
    count = serializers.IntegerField(read_only=True)


class PartThumbSerializerUpdate(InvenTreeModelSerializer):
    """Serializer for updating Part thumbnail"""

    def validate_image(self, value):
        """Check that file is an image."""
        validate = imghdr.what(value)
        if not validate:
            raise serializers.ValidationError("File is not an image")
        return value

    image = InvenTreeAttachmentSerializerField(required=True)

    class Meta:
        model = Part
        fields = [
            'image',
        ]


class PartParameterTemplateSerializer(InvenTreeModelSerializer):
    """JSON serializer for the PartParameterTemplate model"""

    class Meta:
        model = PartParameterTemplate
        fields = [
            'pk',
            'name',
            'units',
        ]


class PartParameterSerializer(InvenTreeModelSerializer):
    """JSON serializers for the PartParameter model"""

    template_detail = PartParameterTemplateSerializer(source='template', many=False, read_only=True)

    class Meta:
        model = PartParameter
        fields = [
            'pk',
            'part',
            'template',
            'template_detail',
            'data'
        ]


class PartBriefSerializer(InvenTreeModelSerializer):
    """Serializer for Part (brief detail)"""

    thumbnail = serializers.CharField(source='get_thumbnail_url', read_only=True)

    stock = serializers.FloatField(source='total_stock')

    class Meta:
        model = Part
        fields = [
            'pk',
            'IPN',
            'default_location',
            'name',
            'revision',
            'full_name',
            'description',
            'thumbnail',
            'active',
            'assembly',
            'is_template',
            'purchaseable',
            'salable',
            'stock',
            'trackable',
            'virtual',
            'units',
        ]


class PartSerializer(InvenTreeModelSerializer):
    """Serializer for complete detail information of a part.

    Used when displaying all details of a single component.
    """

    def get_api_url(self):
        return reverse_lazy('api-part-list')

    def __init__(self, *args, **kwargs):
        """Custom initialization method for PartSerializer, so that we can optionally pass extra fields based on the query."""
        self.starred_parts = kwargs.pop('starred_parts', [])

        category_detail = kwargs.pop('category_detail', False)

        parameters = kwargs.pop('parameters', False)

        super().__init__(*args, **kwargs)

        if category_detail is not True:
            self.fields.pop('category_detail')

        if parameters is not True:
            self.fields.pop('parameters')

    @staticmethod
    def annotate_queryset(queryset):
        """Add some extra annotations to the queryset.

        Performing database queries as efficiently as possible, to reduce database trips.
        """
        # Annotate with the total 'in stock' quantity
        queryset = queryset.annotate(
            in_stock=Coalesce(
                SubquerySum('stock_items__quantity', filter=StockItem.IN_STOCK_FILTER),
                Decimal(0),
                output_field=models.DecimalField(),
            ),
        )

        # Annotate with the total number of stock items
        queryset = queryset.annotate(
            stock_item_count=SubqueryCount('stock_items')
        )

        # Annotate with the total variant stock quantity
        variant_query = StockItem.objects.filter(
            part__tree_id=OuterRef('tree_id'),
            part__lft__gt=OuterRef('lft'),
            part__rght__lt=OuterRef('rght'),
        ).filter(StockItem.IN_STOCK_FILTER)

        queryset = queryset.annotate(
            variant_stock=Coalesce(
                Subquery(
                    variant_query.annotate(
                        total=Func(F('quantity'), function='SUM', output_field=FloatField())
                    ).values('total')),
                0,
                output_field=FloatField(),
            )
        )

        # Filter to limit builds to "active"
        build_filter = Q(
            status__in=BuildStatus.ACTIVE_CODES
        )

        # Annotate with the total 'building' quantity
        queryset = queryset.annotate(
            building=Coalesce(
                SubquerySum('builds__quantity', filter=build_filter),
                Decimal(0),
                output_field=models.DecimalField(),
            )
        )

        # Filter to limit orders to "open"
        order_filter = Q(
            order__status__in=PurchaseOrderStatus.OPEN
        )

        # Annotate with the total 'on order' quantity
        queryset = queryset.annotate(
            ordering=Coalesce(
                SubquerySum('supplier_parts__purchase_order_line_items__quantity', filter=order_filter),
                Decimal(0),
                output_field=models.DecimalField(),
            ) - Coalesce(
                SubquerySum('supplier_parts__purchase_order_line_items__received', filter=order_filter),
                Decimal(0),
                output_field=models.DecimalField(),
            )
        )

        # Annotate with the number of 'suppliers'
        queryset = queryset.annotate(
            suppliers=Coalesce(
                SubqueryCount('supplier_parts'),
                Decimal(0),
                output_field=models.DecimalField(),
            ),
        )

        """
        Annotate with the number of stock items allocated to sales orders.
        This annotation is modeled on Part.sales_order_allocations() method:

        - Only look for "open" orders
        - Stock items have not been "shipped"
        """
        so_allocation_filter = Q(
            line__order__status__in=SalesOrderStatus.OPEN,  # LineItem points to an OPEN order
            shipment__shipment_date=None,  # Allocated item has *not* been shipped out
        )

        queryset = queryset.annotate(
            allocated_to_sales_orders=Coalesce(
                SubquerySum('stock_items__sales_order_allocations__quantity', filter=so_allocation_filter),
                Decimal(0),
                output_field=models.DecimalField(),
            )
        )

        """
        Annotate with the number of stock items allocated to build orders.
        This annotation is modeled on Part.build_order_allocations() method
        """
        bo_allocation_filter = Q(
            build__status__in=BuildStatus.ACTIVE_CODES,
        )

        queryset = queryset.annotate(
            allocated_to_build_orders=Coalesce(
                SubquerySum('stock_items__allocations__quantity', filter=bo_allocation_filter),
                Decimal(0),
                output_field=models.DecimalField(),
            )
        )

        # Annotate with the total 'available stock' quantity
        # This is the current stock, minus any allocations
        queryset = queryset.annotate(
            unallocated_stock=ExpressionWrapper(
                F('in_stock') - F('allocated_to_sales_orders') - F('allocated_to_build_orders'),
                output_field=models.DecimalField(),
            )
        )

        return queryset

    def get_starred(self, part):
        """Return "true" if the part is starred by the current user."""
        return part in self.starred_parts

    # Extra detail for the category
    category_detail = CategorySerializer(source='category', many=False, read_only=True)

    # Calculated fields
    allocated_to_build_orders = serializers.FloatField(read_only=True)
    allocated_to_sales_orders = serializers.FloatField(read_only=True)
    unallocated_stock = serializers.FloatField(read_only=True)
    building = serializers.FloatField(read_only=True)
    in_stock = serializers.FloatField(read_only=True)
    variant_stock = serializers.FloatField(read_only=True)
    ordering = serializers.FloatField(read_only=True)
    stock_item_count = serializers.IntegerField(read_only=True)
    suppliers = serializers.IntegerField(read_only=True)

    image = InvenTreeImageSerializerField(required=False, allow_null=True)
    thumbnail = serializers.CharField(source='get_thumbnail_url', read_only=True)
    starred = serializers.SerializerMethodField()

    # PrimaryKeyRelated fields (Note: enforcing field type here results in much faster queries, somehow...)
    category = serializers.PrimaryKeyRelatedField(queryset=PartCategory.objects.all())

    parameters = PartParameterSerializer(
        many=True,
        read_only=True,
    )

    class Meta:
        model = Part
        partial = True
        fields = [
            'active',
            'allocated_to_build_orders',
            'allocated_to_sales_orders',
            'assembly',
            'category',
            'category_detail',
            'component',
            'default_expiry',
            'default_location',
            'default_supplier',
            'description',
            'full_name',
            'image',
            'in_stock',
            'variant_stock',
            'ordering',
            'building',
            'IPN',
            'is_template',
            'keywords',
            'link',
            'minimum_stock',
            'name',
            'notes',
            'parameters',
            'pk',
            'purchaseable',
            'revision',
            'salable',
            'starred',
            'stock_item_count',
            'suppliers',
            'thumbnail',
            'trackable',
            'unallocated_stock',
            'units',
            'variant_of',
            'virtual',
        ]


class PartRelationSerializer(InvenTreeModelSerializer):
    """Serializer for a PartRelated model"""

    part_1_detail = PartSerializer(source='part_1', read_only=True, many=False)
    part_2_detail = PartSerializer(source='part_2', read_only=True, many=False)

    class Meta:
        model = PartRelated
        fields = [
            'pk',
            'part_1',
            'part_1_detail',
            'part_2',
            'part_2_detail',
        ]


class PartStarSerializer(InvenTreeModelSerializer):
    """Serializer for a PartStar object"""

    partname = serializers.CharField(source='part.full_name', read_only=True)
    username = serializers.CharField(source='user.username', read_only=True)

    class Meta:
        model = PartStar
        fields = [
            'pk',
            'part',
            'partname',
            'user',
            'username',
        ]


class BomItemSubstituteSerializer(InvenTreeModelSerializer):
    """Serializer for the BomItemSubstitute class"""

    part_detail = PartBriefSerializer(source='part', read_only=True, many=False)

    class Meta:
        model = BomItemSubstitute
        fields = [
            'pk',
            'bom_item',
            'part',
            'part_detail',
        ]


class BomItemSerializer(InvenTreeModelSerializer):
    """Serializer for BomItem object"""

    price_range = serializers.CharField(read_only=True)

    quantity = InvenTreeDecimalField(required=True)

    def validate_quantity(self, quantity):
        if quantity <= 0:
            raise serializers.ValidationError(_("Quantity must be greater than zero"))

        return quantity

    part = serializers.PrimaryKeyRelatedField(queryset=Part.objects.filter(assembly=True))

    substitutes = BomItemSubstituteSerializer(many=True, read_only=True)

    part_detail = PartBriefSerializer(source='part', many=False, read_only=True)

    sub_part = serializers.PrimaryKeyRelatedField(queryset=Part.objects.filter(component=True))

    sub_part_detail = PartBriefSerializer(source='sub_part', many=False, read_only=True)

    validated = serializers.BooleanField(read_only=True, source='is_line_valid')

    purchase_price_min = MoneyField(max_digits=19, decimal_places=4, read_only=True)

    purchase_price_max = MoneyField(max_digits=19, decimal_places=4, read_only=True)

    purchase_price_avg = serializers.SerializerMethodField()

    purchase_price_range = serializers.SerializerMethodField()

    # Annotated fields for available stock
    available_stock = serializers.FloatField(read_only=True)
    available_substitute_stock = serializers.FloatField(read_only=True)
    available_variant_stock = serializers.FloatField(read_only=True)

    def __init__(self, *args, **kwargs):
        # part_detail and sub_part_detail serializers are only included if requested.
        # This saves a bunch of database requests

        part_detail = kwargs.pop('part_detail', False)
        sub_part_detail = kwargs.pop('sub_part_detail', False)
        include_pricing = kwargs.pop('include_pricing', False)

        super(BomItemSerializer, self).__init__(*args, **kwargs)

        if part_detail is not True:
            self.fields.pop('part_detail')

        if sub_part_detail is not True:
            self.fields.pop('sub_part_detail')

        if not include_pricing:
            # Remove all pricing related fields
            self.fields.pop('price_range')
            self.fields.pop('purchase_price_min')
            self.fields.pop('purchase_price_max')
            self.fields.pop('purchase_price_avg')
            self.fields.pop('purchase_price_range')

    @staticmethod
    def setup_eager_loading(queryset):
        queryset = queryset.prefetch_related('part')
        queryset = queryset.prefetch_related('part__category')
        queryset = queryset.prefetch_related('part__stock_items')

        queryset = queryset.prefetch_related('sub_part')
        queryset = queryset.prefetch_related('sub_part__category')

        queryset = queryset.prefetch_related(
            'sub_part__stock_items',
            'sub_part__stock_items__allocations',
            'sub_part__stock_items__sales_order_allocations',
        )

        queryset = queryset.prefetch_related(
            'substitutes',
            'substitutes__part__stock_items',
        )

        queryset = queryset.prefetch_related('sub_part__supplier_parts__pricebreaks')
        return queryset

    @staticmethod
    def annotate_queryset(queryset):
        """Annotate the BomItem queryset with extra information:

        Annotations:
            available_stock: The amount of stock available for the sub_part Part object
        """

        """
        Construct an "available stock" quantity:
        available_stock = total_stock - build_order_allocations - sales_order_allocations
        """
        build_order_filter = Q(build__status__in=BuildStatus.ACTIVE_CODES)
        sales_order_filter = Q(
            line__order__status__in=SalesOrderStatus.OPEN,
            shipment__shipment_date=None,
        )

        # Calculate "total stock" for the referenced sub_part
        # Calculate the "build_order_allocations" for the sub_part
        # Note that these fields are only aliased, not annotated
        queryset = queryset.alias(
            total_stock=Coalesce(
                SubquerySum(
                    'sub_part__stock_items__quantity',
                    filter=StockItem.IN_STOCK_FILTER
                ),
                Decimal(0),
                output_field=models.DecimalField(),
            ),
            allocated_to_sales_orders=Coalesce(
                SubquerySum(
                    'sub_part__stock_items__sales_order_allocations__quantity',
                    filter=sales_order_filter,
                ),
                Decimal(0),
                output_field=models.DecimalField(),
            ),
            allocated_to_build_orders=Coalesce(
                SubquerySum(
                    'sub_part__stock_items__allocations__quantity',
                    filter=build_order_filter,
                ),
                Decimal(0),
                output_field=models.DecimalField(),
            ),
        )

        # Calculate 'available_stock' based on previously annotated fields
        queryset = queryset.annotate(
            available_stock=ExpressionWrapper(
                F('total_stock') - F('allocated_to_sales_orders') - F('allocated_to_build_orders'),
                output_field=models.DecimalField(),
            )
        )

        # Extract similar information for any 'substitute' parts
        queryset = queryset.alias(
            substitute_stock=Coalesce(
                SubquerySum(
                    'substitutes__part__stock_items__quantity',
                    filter=StockItem.IN_STOCK_FILTER,
                ),
                Decimal(0),
                output_field=models.DecimalField(),
            ),
            substitute_build_allocations=Coalesce(
                SubquerySum(
                    'substitutes__part__stock_items__allocations__quantity',
                    filter=build_order_filter,
                ),
                Decimal(0),
                output_field=models.DecimalField(),
            ),
            substitute_sales_allocations=Coalesce(
                SubquerySum(
                    'substitutes__part__stock_items__sales_order_allocations__quantity',
                    filter=sales_order_filter,
                ),
                Decimal(0),
                output_field=models.DecimalField(),
            ),
        )

        # Calculate 'available_substitute_stock' field
        queryset = queryset.annotate(
            available_substitute_stock=ExpressionWrapper(
                F('substitute_stock') - F('substitute_build_allocations') - F('substitute_sales_allocations'),
                output_field=models.DecimalField(),
            )
        )

        # Annotate the queryset with 'available variant stock' information
        variant_stock_query = StockItem.objects.filter(
            part__tree_id=OuterRef('sub_part__tree_id'),
            part__lft__gt=OuterRef('sub_part__lft'),
            part__rght__lt=OuterRef('sub_part__rght'),
        ).filter(StockItem.IN_STOCK_FILTER)

        queryset = queryset.alias(
            variant_stock_total=Coalesce(
                Subquery(
                    variant_stock_query.annotate(
                        total=Func(F('quantity'), function='SUM', output_field=FloatField())
                    ).values('total')),
                0,
                output_field=FloatField()
            ),
            variant_stock_build_order_allocations=Coalesce(
                Subquery(
                    variant_stock_query.annotate(
                        total=Func(F('sales_order_allocations__quantity'), function='SUM', output_field=FloatField()),
                    ).values('total')),
                0,
                output_field=FloatField(),
            ),
            variant_stock_sales_order_allocations=Coalesce(
                Subquery(
                    variant_stock_query.annotate(
                        total=Func(F('allocations__quantity'), function='SUM', output_field=FloatField()),
                    ).values('total')),
                0,
                output_field=FloatField(),
            )
        )

        queryset = queryset.annotate(
            available_variant_stock=ExpressionWrapper(
                F('variant_stock_total') - F('variant_stock_build_order_allocations') - F('variant_stock_sales_order_allocations'),
                output_field=FloatField(),
            )
        )

        return queryset

    def get_purchase_price_range(self, obj):
        """Return purchase price range"""
        try:
            purchase_price_min = obj.purchase_price_min
        except AttributeError:
            return None

        try:
            purchase_price_max = obj.purchase_price_max
        except AttributeError:
            return None

        if purchase_price_min and not purchase_price_max:
            # Get price range
            purchase_price_range = str(purchase_price_max)
        elif not purchase_price_min and purchase_price_max:
            # Get price range
            purchase_price_range = str(purchase_price_max)
        elif purchase_price_min and purchase_price_max:
            # Get price range
            if purchase_price_min >= purchase_price_max:
                # If min > max: use min only
                purchase_price_range = str(purchase_price_min)
            else:
                purchase_price_range = str(purchase_price_min) + " - " + str(purchase_price_max)
        else:
            purchase_price_range = '-'

        return purchase_price_range

    def get_purchase_price_avg(self, obj):
        """Return purchase price average"""
        try:
            purchase_price_avg = obj.purchase_price_avg
        except AttributeError:
            return None

        if purchase_price_avg:
            # Get string representation of price average
            purchase_price_avg = str(purchase_price_avg)
        else:
            purchase_price_avg = '-'

        return purchase_price_avg

    class Meta:
        model = BomItem
        fields = [
            'allow_variants',
            'inherited',
            'note',
            'optional',
            'overage',
            'pk',
            'part',
            'part_detail',
            'purchase_price_avg',
            'purchase_price_max',
            'purchase_price_min',
            'purchase_price_range',
            'quantity',
            'reference',
            'sub_part',
            'sub_part_detail',
            'substitutes',
            'price_range',
            'validated',

            # Annotated fields describing available quantity
            'available_stock',
            'available_substitute_stock',
            'available_variant_stock',

        ]


class CategoryParameterTemplateSerializer(InvenTreeModelSerializer):
    """Serializer for PartCategoryParameterTemplate"""

    parameter_template = PartParameterTemplateSerializer(many=False,
                                                         read_only=True)

    category_detail = CategorySerializer(source='category', many=False, read_only=True)

    class Meta:
        model = PartCategoryParameterTemplate
        fields = [
            'pk',
            'category',
            'category_detail',
            'parameter_template',
            'default_value',
        ]


class PartCopyBOMSerializer(serializers.Serializer):
    """Serializer for copying a BOM from another part"""

    class Meta:
        fields = [
            'part',
            'remove_existing',
            'copy_substitutes',
            'include_inherited',
            'skip_invalid',
        ]

    part = serializers.PrimaryKeyRelatedField(
        queryset=Part.objects.all(),
        many=False,
        required=True,
        allow_null=False,
        label=_('Part'),
        help_text=_('Select part to copy BOM from'),
    )

    def validate_part(self, part):
        """Check that a 'valid' part was selected"""
        return part

    remove_existing = serializers.BooleanField(
        label=_('Remove Existing Data'),
        help_text=_('Remove existing BOM items before copying'),
        default=True,
    )

    include_inherited = serializers.BooleanField(
        label=_('Include Inherited'),
        help_text=_('Include BOM items which are inherited from templated parts'),
        default=False,
    )

    skip_invalid = serializers.BooleanField(
        label=_('Skip Invalid Rows'),
        help_text=_('Enable this option to skip invalid rows'),
        default=False,
    )

    copy_substitutes = serializers.BooleanField(
        label=_('Copy Substitute Parts'),
        help_text=_('Copy substitute parts when duplicate BOM items'),
        default=True,
    )

    def save(self):
        """Actually duplicate the BOM"""
        base_part = self.context['part']

        data = self.validated_data

        base_part.copy_bom_from(
            data['part'],
            clear=data.get('remove_existing', True),
            skip_invalid=data.get('skip_invalid', False),
            include_inherited=data.get('include_inherited', False),
            copy_substitutes=data.get('copy_substitutes', True),
        )


class BomImportUploadSerializer(DataFileUploadSerializer):
    """Serializer for uploading a file and extracting data from it."""

    TARGET_MODEL = BomItem

    class Meta:
        fields = [
            'data_file',
            'part',
            'clear_existing_bom',
        ]

    part = serializers.PrimaryKeyRelatedField(
        queryset=Part.objects.all(),
        required=True,
        allow_null=False,
        many=False,
    )

    clear_existing_bom = serializers.BooleanField(
        label=_('Clear Existing BOM'),
        help_text=_('Delete existing BOM items before uploading')
    )

    def save(self):

        data = self.validated_data

        if data.get('clear_existing_bom', False):
            part = data['part']

            with transaction.atomic():
                part.bom_items.all().delete()


class BomImportExtractSerializer(DataFileExtractSerializer):
    """
    """

    TARGET_MODEL = BomItem

    def validate_extracted_columns(self):
        super().validate_extracted_columns()

        part_columns = ['part', 'part_name', 'part_ipn', 'part_id']

        if not any([col in self.columns for col in part_columns]):
            # At least one part column is required!
            raise serializers.ValidationError(_("No part column specified"))

    def process_row(self, row):

        # Skip any rows which are at a lower "level"
        level = row.get('level', None)

        if level is not None:
            try:
                level = int(level)
                if level != 1:
                    # Skip this row
                    return None
            except:
                pass

        # Attempt to extract a valid part based on the provided data
        part_id = row.get('part_id', row.get('part', None))
        part_name = row.get('part_name', row.get('part', None))
        part_ipn = row.get('part_ipn', None)

        part = None

        if part_id is not None:
            try:
                part = Part.objects.get(pk=part_id)
            except (ValueError, Part.DoesNotExist):
                pass

        # No direct match, where else can we look?
        if part is None and (part_name or part_ipn):
            queryset = Part.objects.all()

            if part_name:
                queryset = queryset.filter(name=part_name)

            if part_ipn:
                queryset = queryset.filter(IPN=part_ipn)

            if queryset.exists():
                if queryset.count() == 1:
                    part = queryset.first()
                else:
                    row['errors']['part'] = _('Multiple matching parts found')

        if part is None:
            row['errors']['part'] = _('No matching part found')
        else:
            if not part.component:
                row['errors']['part'] = _('Part is not designated as a component')

        # Update the 'part' value in the row
        row['part'] = part.pk if part is not None else None

        # Check the provided 'quantity' value
        quantity = row.get('quantity', None)

        if quantity is None:
            row['errors']['quantity'] = _('Quantity not provided')
        else:
            try:
                quantity = Decimal(quantity)

                if quantity <= 0:
                    row['errors']['quantity'] = _('Quantity must be greater than zero')
            except:
                row['errors']['quantity'] = _('Invalid quantity')

        return row


class BomImportSubmitSerializer(serializers.Serializer):
    """Serializer for uploading a BOM against a specified part.

    A "BOM" is a set of BomItem objects which are to be validated together as a set
    """

    items = BomItemSerializer(many=True, required=True)

    def validate(self, data):

        items = data['items']

        if len(items) == 0:
            raise serializers.ValidationError(_("At least one BOM item is required"))

        data = super().validate(data)

        return data

    def save(self):

        data = self.validated_data

        items = data['items']

        try:
            with transaction.atomic():

                for item in items:

                    part = item['part']
                    sub_part = item['sub_part']

                    # Ignore duplicate BOM items
                    if BomItem.objects.filter(part=part, sub_part=sub_part).exists():
                        continue

                    # Create a new BomItem object
                    BomItem.objects.create(**item)

        except Exception as e:
            raise serializers.ValidationError(detail=serializers.as_serializer_error(e))