from django.contrib.contenttypes.fields import GenericForeignKey
from django.contrib.postgres.indexes import GistIndex
from django.core.exceptions import ValidationError
from django.core.validators import MaxValueValidator, MinValueValidator
from django.db import models
from django.utils.translation import gettext_lazy as _

from dcim.choices import *
from dcim.constants import *
from dcim.models.base import PortMappingBase
from dcim.models.mixins import InterfaceValidationMixin
from dcim.utils import get_module_bay_positions, resolve_module_placeholder
from netbox.models import ChangeLoggedModel
from netbox.models.features import ChangeLoggingMixin
from netbox.models.ltree import LtreeManager, LtreeModel
from utilities.exceptions import AbortRequest
from utilities.fields import ColorField, NaturalOrderingField
from utilities.ordering import naturalize_interface
from utilities.tracking import TrackingModelMixin
from wireless.choices import WirelessRoleChoices

from .device_components import (
    ConsolePort,
    ConsoleServerPort,
    DeviceBay,
    FrontPort,
    Interface,
    InventoryItem,
    ModuleBay,
    PowerOutlet,
    PowerPort,
    RearPort,
)

__all__ = (
    'ConsolePortTemplate',
    'ConsoleServerPortTemplate',
    'DeviceBayTemplate',
    'FrontPortTemplate',
    'InterfaceTemplate',
    'InventoryItemTemplate',
    'ModuleBayTemplate',
    'PortTemplateMapping',
    'PowerOutletTemplate',
    'PowerPortTemplate',
    'RearPortTemplate',
)


class ComponentTemplateModel(ChangeLoggedModel, TrackingModelMixin):
    device_type = models.ForeignKey(
        to='dcim.DeviceType',
        on_delete=models.CASCADE,
        related_name='%(class)ss'
    )
    name = models.CharField(
        verbose_name=_('name'),
        max_length=64,
        help_text=_(
            "{module} is accepted as a substitution for the module bay position when attached to a module type."
        ),
        db_collation="natural_sort"
    )
    label = models.CharField(
        verbose_name=_('label'),
        max_length=64,
        blank=True,
        help_text=_('Physical label')
    )
    description = models.CharField(
        verbose_name=_('description'),
        max_length=200,
        blank=True
    )

    class Meta:
        abstract = True
        ordering = ('device_type', 'name')
        constraints = (
            models.UniqueConstraint(
                fields=('device_type', 'name'),
                name='%(app_label)s_%(class)s_unique_device_type_name'
            ),
        )

    def __str__(self):
        if self.label:
            return f"{self.name} ({self.label})"
        return self.name

    def instantiate(self, device):
        """
        Instantiate a new component on the specified Device.
        """
        raise NotImplementedError()

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

        # Cache the original DeviceType ID for reference under clean()
        self._original_device_type = self.__dict__.get('device_type_id')

    def to_objectchange(self, action):
        objectchange = super().to_objectchange(action)
        objectchange.related_object = self.device_type
        return objectchange

    def clean(self):
        super().clean()

        if not self._state.adding and self._original_device_type != self.device_type_id:
            raise ValidationError({
                "device_type": _("Component templates cannot be moved to a different device type.")
            })


class ModularComponentTemplateModel(ComponentTemplateModel):
    """
    A ComponentTemplateModel which supports optional assignment to a ModuleType.
    """
    device_type = models.ForeignKey(
        to='dcim.DeviceType',
        on_delete=models.CASCADE,
        related_name='%(class)ss',
        blank=True,
        null=True
    )
    module_type = models.ForeignKey(
        to='dcim.ModuleType',
        on_delete=models.CASCADE,
        related_name='%(class)ss',
        blank=True,
        null=True
    )

    class Meta:
        abstract = True
        ordering = ('device_type', 'module_type', 'name')
        constraints = (
            models.UniqueConstraint(
                fields=('device_type', 'name'),
                name='%(app_label)s_%(class)s_unique_device_type_name'
            ),
            models.UniqueConstraint(
                fields=('module_type', 'name'),
                name='%(app_label)s_%(class)s_unique_module_type_name'
            ),
        )
        indexes = (
            models.Index(fields=('device_type', 'module_type', 'name')),  # Default ordering
        )

    def to_objectchange(self, action):
        objectchange = super().to_objectchange(action)
        if self.device_type is not None:
            objectchange.related_object = self.device_type
        elif self.module_type is not None:
            objectchange.related_object = self.module_type
        return objectchange

    def clean(self):
        super().clean()

        # A component template must belong to a DeviceType *or* to a ModuleType
        if self.device_type and self.module_type:
            raise ValidationError(
                _("A component template cannot be associated with both a device type and a module type.")
            )
        if not self.device_type and not self.module_type:
            raise ValidationError(
                _("A component template must be associated with either a device type or a module type.")
            )

    @staticmethod
    def _resolve_vc_position(value: str, device) -> str:
        """
        Resolves {vc_position} and {vc_position:X} tokens.

        If the device has a vc_position, replaces the token with that value.
        Otherwise uses the explicit fallback X if given, else '0'.
        """
        def replacer(match):
            explicit_fallback = match.group(1)
            if (
                device is not None
                and device.virtual_chassis is not None
                and device.vc_position is not None
            ):
                return str(device.vc_position)
            return explicit_fallback if explicit_fallback is not None else '0'

        return VC_POSITION_RE.sub(replacer, value)

    def _resolve_all_placeholders(self, value, module=None, device=None):
        has_module = MODULE_TOKEN in value
        has_vc = VC_POSITION_RE.search(value) is not None
        if not has_module and not has_vc:
            return value
        if has_module and module:
            # Reached only from Module._save_new(); AbortRequest is what the view/viewset catches.
            try:
                positions = get_module_bay_positions(module.module_bay)
            except ValueError as e:
                raise AbortRequest(str(e)) from e
            value = resolve_module_placeholder(value, positions)
        if has_vc:
            resolved_device = (module.device if module else None) or device
            value = self._resolve_vc_position(value, resolved_device)
        return value

    def resolve_name(self, module=None, device=None):
        return self._resolve_all_placeholders(self.name, module, device)

    def resolve_label(self, module=None, device=None):
        return self._resolve_all_placeholders(self.label, module, device)

    def resolve_position(self, module=None, device=None):
        return self._resolve_all_placeholders(self.position, module, device)


class ConsolePortTemplate(ModularComponentTemplateModel):
    """
    A template for a ConsolePort to be created for a new Device.
    """
    type = models.CharField(
        verbose_name=_('type'),
        max_length=50,
        choices=ConsolePortTypeChoices,
        blank=True,
        null=True
    )

    component_model = ConsolePort

    class Meta(ModularComponentTemplateModel.Meta):
        verbose_name = _('console port template')
        verbose_name_plural = _('console port templates')

    def instantiate(self, **kwargs):
        return self.component_model(
            name=self.resolve_name(kwargs.get('module'), kwargs.get('device')),
            label=self.resolve_label(kwargs.get('module'), kwargs.get('device')),
            type=self.type,
            **kwargs
        )

    def to_yaml(self):
        return {
            'name': self.name,
            'type': self.type,
            'label': self.label,
            'description': self.description,
        }


class ConsoleServerPortTemplate(ModularComponentTemplateModel):
    """
    A template for a ConsoleServerPort to be created for a new Device.
    """
    type = models.CharField(
        verbose_name=_('type'),
        max_length=50,
        choices=ConsolePortTypeChoices,
        blank=True,
        null=True
    )

    component_model = ConsoleServerPort

    class Meta(ModularComponentTemplateModel.Meta):
        verbose_name = _('console server port template')
        verbose_name_plural = _('console server port templates')

    def instantiate(self, **kwargs):
        return self.component_model(
            name=self.resolve_name(kwargs.get('module'), kwargs.get('device')),
            label=self.resolve_label(kwargs.get('module'), kwargs.get('device')),
            type=self.type,
            **kwargs
        )
    instantiate.do_not_call_in_templates = True

    def to_yaml(self):
        return {
            'name': self.name,
            'type': self.type,
            'label': self.label,
            'description': self.description,
        }


class PowerPortTemplate(ModularComponentTemplateModel):
    """
    A template for a PowerPort to be created for a new Device.
    """
    type = models.CharField(
        verbose_name=_('type'),
        max_length=50,
        choices=PowerPortTypeChoices,
        blank=True,
        null=True
    )
    maximum_draw = models.PositiveIntegerField(
        verbose_name=_('maximum draw'),
        blank=True,
        null=True,
        validators=[MinValueValidator(1)],
        help_text=_('Maximum power draw (watts)')
    )
    allocated_draw = models.PositiveIntegerField(
        verbose_name=_('allocated draw'),
        blank=True,
        null=True,
        validators=[MinValueValidator(1)],
        help_text=_('Allocated power draw (watts)')
    )

    component_model = PowerPort

    class Meta(ModularComponentTemplateModel.Meta):
        verbose_name = _('power port template')
        verbose_name_plural = _('power port templates')

    def instantiate(self, **kwargs):
        return self.component_model(
            name=self.resolve_name(kwargs.get('module'), kwargs.get('device')),
            label=self.resolve_label(kwargs.get('module'), kwargs.get('device')),
            type=self.type,
            maximum_draw=self.maximum_draw,
            allocated_draw=self.allocated_draw,
            **kwargs
        )
    instantiate.do_not_call_in_templates = True

    def clean(self):
        super().clean()

        if self.maximum_draw is not None and self.allocated_draw is not None:
            if self.allocated_draw > self.maximum_draw:
                raise ValidationError({
                    'allocated_draw': _(
                        "Allocated draw cannot exceed the maximum draw ({maximum_draw}W)."
                    ).format(maximum_draw=self.maximum_draw)
                })

    def to_yaml(self):
        return {
            'name': self.name,
            'type': self.type,
            'maximum_draw': self.maximum_draw,
            'allocated_draw': self.allocated_draw,
            'label': self.label,
            'description': self.description,
        }


class PowerOutletTemplate(ModularComponentTemplateModel):
    """
    A template for a PowerOutlet to be created for a new Device.
    """
    type = models.CharField(
        verbose_name=_('type'),
        max_length=50,
        choices=PowerOutletTypeChoices,
        blank=True,
        null=True
    )
    color = ColorField(
        verbose_name=_('color'),
        blank=True
    )
    power_port = models.ForeignKey(
        to='dcim.PowerPortTemplate',
        on_delete=models.SET_NULL,
        blank=True,
        null=True,
        related_name='poweroutlet_templates'
    )
    feed_leg = models.CharField(
        verbose_name=_('feed leg'),
        max_length=50,
        choices=PowerOutletFeedLegChoices,
        blank=True,
        null=True,
        help_text=_('Phase (for three-phase feeds)')
    )

    component_model = PowerOutlet

    class Meta(ModularComponentTemplateModel.Meta):
        verbose_name = _('power outlet template')
        verbose_name_plural = _('power outlet templates')

    def clean(self):
        super().clean()

        # Validate power port assignment
        if self.power_port:
            if self.device_type and self.power_port.device_type != self.device_type:
                raise ValidationError(
                    _("Parent power port ({power_port}) must belong to the same device type").format(
                        power_port=self.power_port
                    )
                )
            if self.module_type and self.power_port.module_type != self.module_type:
                raise ValidationError(
                    _("Parent power port ({power_port}) must belong to the same module type").format(
                        power_port=self.power_port
                    )
                )

    def instantiate(self, **kwargs):
        if self.power_port:
            power_port_name = self.power_port.resolve_name(kwargs.get('module'), kwargs.get('device'))
            power_port = PowerPort.objects.get(name=power_port_name, **kwargs)
        else:
            power_port = None
        return self.component_model(
            name=self.resolve_name(kwargs.get('module'), kwargs.get('device')),
            label=self.resolve_label(kwargs.get('module'), kwargs.get('device')),
            type=self.type,
            color=self.color,
            power_port=power_port,
            feed_leg=self.feed_leg,
            **kwargs
        )
    instantiate.do_not_call_in_templates = True

    def to_yaml(self):
        return {
            'name': self.name,
            'type': self.type,
            'color': self.color,
            'power_port': self.power_port.name if self.power_port else None,
            'feed_leg': self.feed_leg,
            'label': self.label,
            'description': self.description,
        }


class InterfaceTemplate(InterfaceValidationMixin, ModularComponentTemplateModel):
    """
    A template for a physical data interface on a new Device.
    """
    # Override ComponentTemplateModel._name to specify naturalize_interface function
    _name = NaturalOrderingField(
        target_field='name',
        naturalize_function=naturalize_interface,
        max_length=100,
        blank=True
    )
    type = models.CharField(
        verbose_name=_('type'),
        max_length=50,
        choices=InterfaceTypeChoices
    )
    channels = models.PositiveSmallIntegerField(
        verbose_name=_('channels'),
        blank=True,
        null=True,
        validators=(
            MinValueValidator(INTERFACE_CHANNELS_MIN),
            MaxValueValidator(INTERFACE_CHANNELS_MAX)
        ),
        help_text=_('The number of channels into which this interface is channelized')
    )
    channel_id = models.PositiveSmallIntegerField(
        verbose_name=_('channel ID'),
        blank=True,
        null=True,
        validators=(
            MinValueValidator(INTERFACE_CHANNELS_MIN),
            MaxValueValidator(INTERFACE_CHANNELS_MAX)
        ),
        help_text=_('The channel on the parent interface to which this subinterface is bound')
    )
    enabled = models.BooleanField(
        verbose_name=_('enabled'),
        default=True
    )
    mgmt_only = models.BooleanField(
        default=False,
        verbose_name=_('management only')
    )
    parent = models.ForeignKey(
        to='self',
        on_delete=models.RESTRICT,
        related_name='child_interfaces',
        null=True,
        blank=True,
        verbose_name=_('parent interface')
    )
    bridge = models.ForeignKey(
        to='self',
        on_delete=models.SET_NULL,
        related_name='bridge_interfaces',
        null=True,
        blank=True,
        verbose_name=_('bridge interface')
    )
    poe_mode = models.CharField(
        max_length=50,
        choices=InterfacePoEModeChoices,
        blank=True,
        null=True,
        verbose_name=_('PoE mode')
    )
    poe_type = models.CharField(
        max_length=50,
        choices=InterfacePoETypeChoices,
        blank=True,
        null=True,
        verbose_name=_('PoE type')
    )
    rf_role = models.CharField(
        max_length=30,
        choices=WirelessRoleChoices,
        blank=True,
        null=True,
        verbose_name=_('wireless role')
    )

    component_model = Interface

    class Meta(ModularComponentTemplateModel.Meta):
        constraints = (
            *ModularComponentTemplateModel.Meta.constraints,
            models.UniqueConstraint(
                fields=('parent', 'channel_id'),
                name='%(app_label)s_%(class)s_unique_parent_channel_id'
            ),
        )
        verbose_name = _('interface template')
        verbose_name_plural = _('interface templates')

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

        # Cache the original channel count for use by InterfaceValidationMixin.clean() to detect a channel-count
        # reduction that would orphan a bound subinterface.
        self._original_channels = self.__dict__.get('channels')

    def clean(self):
        super().clean()

        # Self-reference and interface-type restrictions are enforced by InterfaceValidationMixin
        if self.parent:
            if self.device_type and self.device_type != self.parent.device_type:
                raise ValidationError({
                    'parent': _(
                        "Parent interface ({parent}) must belong to the same device type"
                    ).format(parent=self.parent)
                })
            if self.module_type and self.module_type != self.parent.module_type:
                raise ValidationError({
                    'parent': _(
                        "Parent interface ({parent}) must belong to the same module type"
                    ).format(parent=self.parent)
                })

        if self.bridge:
            if self.device_type and self.device_type != self.bridge.device_type:
                raise ValidationError({
                    'bridge': _(
                        "Bridge interface ({bridge}) must belong to the same device type"
                    ).format(bridge=self.bridge)
                })
            if self.module_type and self.module_type != self.bridge.module_type:
                raise ValidationError({
                    'bridge': _(
                        "Bridge interface ({bridge}) must belong to the same module type"
                    ).format(bridge=self.bridge)
                })

    def instantiate(self, **kwargs):
        return self.component_model(
            name=self.resolve_name(kwargs.get('module'), kwargs.get('device')),
            label=self.resolve_label(kwargs.get('module'), kwargs.get('device')),
            type=self.type,
            channels=self.channels,
            channel_id=self.channel_id,
            enabled=self.enabled,
            mgmt_only=self.mgmt_only,
            poe_mode=self.poe_mode,
            poe_type=self.poe_type,
            rf_role=self.rf_role,
            **kwargs
        )
    instantiate.do_not_call_in_templates = True

    def to_yaml(self):
        return {
            'name': self.name,
            'type': self.type,
            'channels': self.channels,
            'channel_id': self.channel_id,
            'enabled': self.enabled,
            'mgmt_only': self.mgmt_only,
            'label': self.label,
            'description': self.description,
            'parent': self.parent.name if self.parent else None,
            'bridge': self.bridge.name if self.bridge else None,
            'poe_mode': self.poe_mode,
            'poe_type': self.poe_type,
            'rf_role': self.rf_role,
        }


class PortTemplateMapping(ChangeLoggingMixin, PortMappingBase):
    """
    Maps a FrontPortTemplate & position to a RearPortTemplate & position.
    """
    device_type = models.ForeignKey(
        to='dcim.DeviceType',
        on_delete=models.CASCADE,
        related_name='port_mappings',
        blank=True,
        null=True,
    )
    module_type = models.ForeignKey(
        to='dcim.ModuleType',
        on_delete=models.CASCADE,
        related_name='port_mappings',
        blank=True,
        null=True,
    )
    front_port = models.ForeignKey(
        to='dcim.FrontPortTemplate',
        on_delete=models.CASCADE,
        related_name='mappings',
    )
    rear_port = models.ForeignKey(
        to='dcim.RearPortTemplate',
        on_delete=models.CASCADE,
        related_name='mappings',
    )

    class Meta(PortMappingBase.Meta):
        # Inherit the unique constraints from PortMappingBase.Meta.
        pass

    def clean(self):
        super().clean()

        # Validate rear port assignment
        if self.front_port.device_type_id != self.rear_port.device_type_id:
            raise ValidationError({
                "rear_port": _("Rear port ({rear_port}) must belong to the same device type").format(
                    rear_port=self.rear_port
                )
            })

    def save(self, *args, **kwargs):
        # Associate the mapping with the parent DeviceType/ModuleType
        self.device_type = self.front_port.device_type
        self.module_type = self.front_port.module_type
        super().save(*args, **kwargs)

    def to_yaml(self):
        return {
            'front_port': self.front_port.name,
            'front_port_position': self.front_port_position,
            'rear_port': self.rear_port.name,
            'rear_port_position': self.rear_port_position,
        }


class FrontPortTemplate(ModularComponentTemplateModel):
    """
    Template for a pass-through port on the front of a new Device.
    """
    type = models.CharField(
        verbose_name=_('type'),
        max_length=50,
        choices=PortTypeChoices
    )
    color = ColorField(
        verbose_name=_('color'),
        blank=True
    )
    positions = models.PositiveSmallIntegerField(
        verbose_name=_('positions'),
        default=1,
        validators=[
            MinValueValidator(PORT_POSITION_MIN),
            MaxValueValidator(PORT_POSITION_MAX)
        ],
    )

    component_model = FrontPort

    class Meta(ModularComponentTemplateModel.Meta):
        constraints = (
            models.UniqueConstraint(
                fields=('device_type', 'name'),
                name='%(app_label)s_%(class)s_unique_device_type_name'
            ),
            models.UniqueConstraint(
                fields=('module_type', 'name'),
                name='%(app_label)s_%(class)s_unique_module_type_name'
            ),
        )
        verbose_name = _('front port template')
        verbose_name_plural = _('front port templates')

    def clean(self):
        super().clean()

        # Check that positions is greater than or equal to the number of associated RearPortTemplates
        if not self._state.adding:
            mapping_count = self.mappings.count()
            if self.positions < mapping_count:
                raise ValidationError({
                    "positions": _(
                        "The number of positions cannot be less than the number of mapped rear port templates ({count})"
                    ).format(count=mapping_count)
                })

    def instantiate(self, **kwargs):
        return self.component_model(
            name=self.resolve_name(kwargs.get('module'), kwargs.get('device')),
            label=self.resolve_label(kwargs.get('module'), kwargs.get('device')),
            type=self.type,
            color=self.color,
            positions=self.positions,
            **kwargs
        )
    instantiate.do_not_call_in_templates = True

    def to_yaml(self):
        return {
            'name': self.name,
            'type': self.type,
            'color': self.color,
            'positions': self.positions,
            'label': self.label,
            'description': self.description,
        }


class RearPortTemplate(ModularComponentTemplateModel):
    """
    Template for a pass-through port on the rear of a new Device.
    """
    type = models.CharField(
        verbose_name=_('type'),
        max_length=50,
        choices=PortTypeChoices
    )
    color = ColorField(
        verbose_name=_('color'),
        blank=True
    )
    positions = models.PositiveSmallIntegerField(
        verbose_name=_('positions'),
        default=1,
        validators=[
            MinValueValidator(PORT_POSITION_MIN),
            MaxValueValidator(PORT_POSITION_MAX)
        ],
    )

    component_model = RearPort

    class Meta(ModularComponentTemplateModel.Meta):
        verbose_name = _('rear port template')
        verbose_name_plural = _('rear port templates')

    def clean(self):
        super().clean()

        # Check that positions is greater than or equal to the number of associated FrontPortTemplates
        if not self._state.adding:
            mapping_count = self.mappings.count()
            if self.positions < mapping_count:
                raise ValidationError({
                    "positions": _(
                        "The number of positions cannot be less than the number of mapped front port templates "
                        "({count})"
                    ).format(count=mapping_count)
                })

    def instantiate(self, **kwargs):
        return self.component_model(
            name=self.resolve_name(kwargs.get('module'), kwargs.get('device')),
            label=self.resolve_label(kwargs.get('module'), kwargs.get('device')),
            type=self.type,
            color=self.color,
            positions=self.positions,
            **kwargs
        )
    instantiate.do_not_call_in_templates = True

    def to_yaml(self):
        return {
            'name': self.name,
            'type': self.type,
            'color': self.color,
            'positions': self.positions,
            'label': self.label,
            'description': self.description,
        }


class ModuleBayTemplate(ModularComponentTemplateModel):
    """
    A template for a ModuleBay to be created for a new parent Device.
    """
    position = models.CharField(
        verbose_name=_('position'),
        max_length=30,
        blank=True,
        help_text=_('Identifier to reference when renaming installed components')
    )
    enabled = models.BooleanField(
        verbose_name=_('enabled'),
        default=True,
    )
    module_bay_types = models.ManyToManyField(
        to='dcim.ModuleBayType',
        related_name='module_bay_templates',
        blank=True,
        verbose_name=_('module bay types'),
        help_text=_('Types of modules that can be installed in this bay (empty = unconstrained)'),
    )

    component_model = ModuleBay

    class Meta(ModularComponentTemplateModel.Meta):
        verbose_name = _('module bay template')
        verbose_name_plural = _('module bay templates')

    def instantiate(self, **kwargs):
        module = kwargs.get('module')
        instance = self.component_model(
            name=self.resolve_name(module, kwargs.get('device')),
            label=self.resolve_label(module, kwargs.get('device')),
            position=self.resolve_position(module, kwargs.get('device')),
            enabled=self.enabled,
            # A module bay created for an installed module nests under that module's
            # bay. bulk_create() bypasses ModuleBay.save() (which would otherwise set
            # this), so the parent must be assigned here for the path trigger to nest
            # it correctly. Device-level bays are instantiated without a module and
            # remain roots (parent=None).
            parent=module.module_bay if module else None,
            **kwargs
        )
        # Stash reference so callers (Module.save, Device._instantiate_components) can
        # copy M2M fields (e.g. module_bay_types) that bulk_create cannot handle.
        instance._source_template = self
        return instance
    instantiate.do_not_call_in_templates = True

    def to_yaml(self):
        return {
            'name': self.name,
            'label': self.label,
            'position': self.position,
            'enabled': self.enabled,
            'description': self.description,
        }


class DeviceBayTemplate(ComponentTemplateModel):
    """
    A template for a DeviceBay to be created for a new parent Device.
    """
    enabled = models.BooleanField(
        verbose_name=_('enabled'),
        default=True,
    )

    component_model = DeviceBay

    class Meta(ComponentTemplateModel.Meta):
        verbose_name = _('device bay template')
        verbose_name_plural = _('device bay templates')

    def instantiate(self, device):
        return self.component_model(
            device=device,
            name=self.name,
            label=self.label,
            enabled=self.enabled,
        )
    instantiate.do_not_call_in_templates = True

    def clean(self):
        if self.device_type and self.device_type.subdevice_role != SubdeviceRoleChoices.ROLE_PARENT:
            raise ValidationError(
                _(
                    'Subdevice role of device type ({device_type}) must be set to "parent" to allow device bays.'
                ).format(device_type=self.device_type)
            )

    def to_yaml(self):
        return {
            'name': self.name,
            'label': self.label,
            'enabled': self.enabled,
            'description': self.description,
        }


class InventoryItemTemplate(LtreeModel, ComponentTemplateModel):
    """
    A template for an InventoryItem to be created for a new parent Device.
    """
    parent = models.ForeignKey(
        to='self',
        on_delete=models.CASCADE,
        related_name='child_items',
        blank=True,
        null=True,
        db_index=True
    )
    component_type = models.ForeignKey(
        to='contenttypes.ContentType',
        on_delete=models.PROTECT,
        related_name='+',
        blank=True,
        null=True
    )
    component_id = models.PositiveBigIntegerField(
        blank=True,
        null=True
    )
    component = GenericForeignKey(
        ct_field='component_type',
        fk_field='component_id'
    )
    role = models.ForeignKey(
        to='dcim.InventoryItemRole',
        on_delete=models.PROTECT,
        related_name='inventory_item_templates',
        blank=True,
        null=True
    )
    manufacturer = models.ForeignKey(
        to='dcim.Manufacturer',
        on_delete=models.PROTECT,
        related_name='inventory_item_templates',
        blank=True,
        null=True
    )
    part_id = models.CharField(
        max_length=50,
        verbose_name=_('part ID'),
        blank=True,
        help_text=_('Manufacturer-assigned part identifier')
    )

    objects = LtreeManager()
    component_model = InventoryItem

    class Meta:
        ordering = ('device_type__id', 'parent__id', 'name')
        indexes = (
            models.Index(fields=('component_type', 'component_id')),
            GistIndex(fields=['path'], name='dcim_inv_item_tmpl_path_gist'),
        )
        constraints = (
            models.UniqueConstraint(
                fields=('device_type', 'parent', 'name'),
                name='%(app_label)s_%(class)s_unique_device_type_parent_name'
            ),
        )
        verbose_name = _('inventory item template')
        verbose_name_plural = _('inventory item templates')

    def instantiate(self, **kwargs):
        parent = InventoryItem.objects.get(name=self.parent.name, **kwargs) if self.parent else None
        if self.component:
            model = self.component.component_model
            component = model.objects.get(name=self.component.name, **kwargs)
        else:
            component = None
        return self.component_model(
            parent=parent,
            name=self.name,
            label=self.label,
            component=component,
            role=self.role,
            manufacturer=self.manufacturer,
            part_id=self.part_id,
            **kwargs
        )
    instantiate.do_not_call_in_templates = True
