samcli/lib/providers/sam_function_provider.py

"""
Class that provides functions from a given SAM template
"""

import logging
from pathlib import Path
from typing import Any, Dict, Iterator, List, Optional, cast

from samtranslator.policy_template_processor.exceptions import TemplateNotFoundException

from samcli.commands._utils.template import TemplateFailedParsingException
from samcli.commands.local.cli_common.user_exceptions import InvalidLayerVersionArn
from samcli.lib.build.exceptions import MissingFunctionHandlerException
from samcli.lib.providers.exceptions import InvalidLayerReference, MissingFunctionNameException
from samcli.lib.utils.colors import Colored, Colors
from samcli.lib.utils.file_observer import FileObserver
from samcli.lib.utils.packagetype import IMAGE, ZIP
from samcli.lib.utils.path_utils import check_path_valid_type
from samcli.lib.utils.resources import (
    AWS_LAMBDA_FUNCTION,
    AWS_LAMBDA_LAYERVERSION,
    AWS_SERVERLESS_FUNCTION,
    AWS_SERVERLESS_LAYERVERSION,
)

from ..build.constants import DEPRECATED_RUNTIMES
from .provider import Function, LayerVersion, Stack, get_full_path, get_function_build_info
from .sam_base_provider import SamBaseProvider
from .sam_stack_provider import SamLocalStackProvider

LOG = logging.getLogger(__name__)


class SamFunctionProvider(SamBaseProvider):
    """
    Fetches and returns Lambda Functions from a SAM Template. The SAM template passed to this provider is assumed
    to be valid, normalized and a dictionary.

    It may or may not contain a function.
    """

    def __init__(
        self,
        stacks: List[Stack],
        use_raw_codeuri: bool = False,
        ignore_code_extraction_warnings: bool = False,
        locate_layer_nested: bool = False,
    ) -> None:
        """
        Initialize the class with SAM template data. The SAM template passed to this provider is assumed
        to be valid, normalized and a dictionary. It should be normalized by running all pre-processing
        before passing to this class. The process of normalization will remove structures like ``Globals``, resolve
        intrinsic functions etc.
        This class does not perform any syntactic validation of the template.

        After the class is initialized, any changes to the ``template_dict`` will not be reflected in here.
        You need to explicitly update the class with new template, if necessary.

        :param dict stacks: List of stacks functions are extracted from
        :param bool use_raw_codeuri: Do not resolve adjust core_uri based on the template path, use the raw uri.
            Note(xinhol): use_raw_codeuri is temporary to fix a bug, and will be removed for a permanent solution.
        :param bool ignore_code_extraction_warnings: Ignores Log warnings
        :param bool locate_layer_nested: resolved nested layer reference to their actual location in the nested stack
        """

        self._stacks = stacks

        for stack in stacks:
            LOG.debug("%d resources found in the stack %s", len(stack.resources), stack.stack_path)

        # Store a map of function full_path to function information for quick reference
        self.functions = SamFunctionProvider._extract_functions(
            self._stacks, use_raw_codeuri, ignore_code_extraction_warnings, locate_layer_nested
        )

        self._colored = Colored()

    @property
    def stacks(self) -> List[Stack]:
        """
        Returns the list of stacks (including the root stack and all children stacks)

        :return list: list of stacks
        """
        return self._stacks

    def update(
        self,
        stacks: List[Stack],
        use_raw_codeuri: bool = False,
        ignore_code_extraction_warnings: bool = False,
        locate_layer_nested: bool = False,
    ) -> None:
        """
        Hydrate the function provider with updated stacks
        :param dict stacks: List of stacks functions are extracted from
        :param bool use_raw_codeuri: Do not resolve adjust core_uri based on the template path, use the raw uri.
            Note(xinhol): use_raw_codeuri is temporary to fix a bug, and will be removed for a permanent solution.
        :param bool ignore_code_extraction_warnings: Ignores Log warnings
        :param bool locate_layer_nested: resolved nested layer reference to their actual location in the nested stack
        """
        self._stacks = stacks
        self.functions = SamFunctionProvider._extract_functions(
            self._stacks, use_raw_codeuri, ignore_code_extraction_warnings, locate_layer_nested
        )

    def get(self, name: str) -> Optional[Function]:
        """
        Returns the function given name or LogicalId of the function. Every SAM resource has a logicalId, but it may
        also have a function name. This method searches only for LogicalID and returns the function that matches.
        If it is in a nested stack, "name" can be prefixed with stack path to avoid ambiguity.
        For example, if a function with name "FunctionA" is located in StackN, which is a nested stack in root stack,
          either "StackN/FunctionA" or "FunctionA" can be used.

        :param string name: Name of the function
        :return Function: namedtuple containing the Function information if function is found.
                          None, if function is not found
        :raises ValueError If name is not given
        """

        if not name:
            LOG.debug("Function name is not defined, unable to fetch Lambda function.")
            raise MissingFunctionNameException()

        resolved_function = None

        if name in self.functions:
            # support lookup by full_path
            resolved_function = self.functions.get(name)

        if not resolved_function:
            # If function is not found by full path, search through all functions

            found_fs = []

            for f in self.get_all():
                if name in (f.function_id, f.name, f.functionname):
                    found_fs.append(f)

            # If multiple functions are found, only return one of them
            if len(found_fs) > 1:
                found_fs.sort(key=lambda f0: f0.full_path.lower())

                message = (
                    f"Multiple functions found with keyword {name}! Function {found_fs[0].full_path} will be "
                    f"invoked! If it's not the function you are going to invoke, please choose one of them from"
                    f" below:"
                )
                LOG.warning(Colored().yellow(message))

                for found_f in found_fs:
                    LOG.warning(Colored().yellow(found_f.full_path))

                resolved_function = found_fs[0]

            elif len(found_fs) == 1:
                resolved_function = found_fs[0]

        if resolved_function:
            self._deprecate_notification(resolved_function.runtime)

        return resolved_function

    def _deprecate_notification(self, runtime: Optional[str]) -> None:
        if runtime in DEPRECATED_RUNTIMES:
            message = (
                f"WARNING: {runtime} is no longer supported by AWS Lambda, please update to a newer supported "
                "runtime. For more information please check AWS Lambda Runtime Support Policy: "
                "https://docs.aws.amazon.com/lambda/latest/dg/runtime-support-policy.html"
            )
            LOG.warning(self._colored.color_log(msg=message, color=Colors.WARNING), extra=dict(markup=True))

    def get_all(self) -> Iterator[Function]:
        """
        Yields all the Lambda functions available in the SAM Template.

        :yields Function: namedtuple containing the function information
        """

        for _, function in self.functions.items():
            yield function

    @staticmethod
    def _extract_functions(
        stacks: List[Stack],
        use_raw_codeuri: bool = False,
        ignore_code_extraction_warnings: bool = False,
        locate_layer_nested: bool = False,
    ) -> Dict[str, Function]:
        """
        Extracts and returns function information from the given dictionary of SAM/CloudFormation resources. This
        method supports functions defined with AWS::Serverless::Function and AWS::Lambda::Function

        :param stacks: List of SAM/CloudFormation stacks to extract functions from
        :param bool use_raw_codeuri: Do not resolve adjust core_uri based on the template path, use the raw uri.
        :param bool ignore_code_extraction_warnings: suppress log statements on code extraction from resources.
        :param bool locate_layer_nested: resolved nested layer reference to their actual location in the nested stack
        :return dict(string : samcli.commands.local.lib.provider.Function): Dictionary of function full_path to the
            Function configuration object
        """

        result: Dict[str, Function] = {}  # a dict with full_path as key and extracted function as value
        for stack in stacks:
            for name, resource in stack.resources.items():
                resource_type = resource.get("Type")
                resource_properties = resource.get("Properties", {})
                resource_metadata = resource.get("Metadata", None)
                # Add extra metadata information to properties under a separate field.
                if resource_metadata:
                    resource_properties["Metadata"] = resource_metadata

                if resource_type in [AWS_SERVERLESS_FUNCTION, AWS_LAMBDA_FUNCTION]:
                    resource_package_type = resource_properties.get("PackageType", ZIP)

                    code_property_key = SamBaseProvider.CODE_PROPERTY_KEYS[resource_type]
                    image_property_key = SamBaseProvider.IMAGE_PROPERTY_KEYS[resource_type]

                    if resource_package_type == ZIP and SamBaseProvider._is_s3_location(
                        resource_properties.get(code_property_key)
                    ):
                        # CodeUri can be a dictionary of S3 Bucket/Key or a S3 URI, neither of which are supported
                        if not ignore_code_extraction_warnings:
                            SamFunctionProvider._warn_code_extraction(resource_type, name, code_property_key)
                        continue

                    if (
                        resource_package_type == IMAGE
                        and SamBaseProvider._is_ecr_uri(resource_properties.get(image_property_key))
                        and not SamFunctionProvider._metadata_has_necessary_entries_for_image_function_to_be_built(
                            resource_metadata
                        )
                    ):
                        # ImageUri can be an ECR uri, which is not supported
                        if not ignore_code_extraction_warnings:
                            SamFunctionProvider._warn_imageuri_extraction(resource_type, name, image_property_key)
                        continue

                if resource_type == AWS_SERVERLESS_FUNCTION:
                    layers = SamFunctionProvider._parse_layer_info(
                        stack,
                        resource_properties.get("Layers", []),
                        use_raw_codeuri,
                        ignore_code_extraction_warnings=ignore_code_extraction_warnings,
                        locate_layer_nested=locate_layer_nested,
                        stacks=stacks if locate_layer_nested else None,
                        function_id=resource_metadata.get("SamResourceId", "") if locate_layer_nested else None,
                    )
                    function = SamFunctionProvider._convert_sam_function_resource(
                        stack,
                        name,
                        resource_properties,
                        layers,
                        use_raw_codeuri,
                    )
                    result[function.full_path] = function

                elif resource_type == AWS_LAMBDA_FUNCTION:
                    layers = SamFunctionProvider._parse_layer_info(
                        stack,
                        resource_properties.get("Layers", []),
                        use_raw_codeuri,
                        ignore_code_extraction_warnings=ignore_code_extraction_warnings,
                        locate_layer_nested=locate_layer_nested,
                        stacks=stacks if locate_layer_nested else None,
                        function_id=resource_metadata.get("SamResourceId", "") if locate_layer_nested else None,
                    )
                    function = SamFunctionProvider._convert_lambda_function_resource(
                        stack, name, resource_properties, layers, use_raw_codeuri
                    )
                    result[function.full_path] = function

                # We don't care about other resource types. Just ignore them

        return result

    @staticmethod
    def _convert_sam_function_resource(
        stack: Stack,
        name: str,
        resource_properties: Dict,
        layers: List[LayerVersion],
        use_raw_codeuri: bool = False,
    ) -> Function:
        """
        Converts a AWS::Serverless::Function resource to a Function configuration usable by the provider.

        Parameters
        ----------
        name str
            LogicalID of the resource NOTE: This is *not* the function name because not all functions declare a name
        resource_properties dict
            Properties of this resource
        layers List(samcli.commands.local.lib.provider.Layer)
            List of the Layer objects created from the template and layer list defined on the function.

        Returns
        -------
        samcli.commands.local.lib.provider.Function
            Function configuration
        """
        codeuri: Optional[str] = SamFunctionProvider.DEFAULT_CODEURI
        inlinecode = resource_properties.get("InlineCode")
        imageuri = None
        function_id = SamFunctionProvider._get_function_id(resource_properties, name)
        packagetype = resource_properties.get("PackageType", ZIP)
        if packagetype == ZIP:
            if inlinecode:
                LOG.debug("Found Serverless function with name='%s' and InlineCode", name)
                codeuri = None
            else:
                codeuri = SamBaseProvider._extract_codeuri(resource_properties, "CodeUri")
                LOG.debug("Found Serverless function with name='%s' and CodeUri='%s'", name, codeuri)
        elif packagetype == IMAGE:
            imageuri = SamFunctionProvider._extract_sam_function_imageuri(resource_properties, "ImageUri")
            LOG.debug("Found Serverless function with name='%s' and ImageUri='%s'", name, imageuri)

        return SamFunctionProvider._build_function_configuration(
            stack, function_id, name, codeuri, resource_properties, layers, inlinecode, imageuri, use_raw_codeuri
        )

    @staticmethod
    def _get_function_id(resource_properties: Dict, logical_id: str) -> str:
        """
        Get unique id for Function resource.
        For CFN/SAM project, this function id is the logical id.
        For CDK project, this function id is the user-defined resource id, or the logical id if the resource id is not
        found.

        Parameters
        ----------
        resource_properties str
            Properties of this resource
        logical_id str
            LogicalID of the resource

        Returns
        -------
        str
            The unique function id
        """
        function_id = resource_properties.get("Metadata", {}).get("SamResourceId")
        if isinstance(function_id, str) and function_id:
            return function_id

        return logical_id

    @staticmethod
    def _convert_lambda_function_resource(
        stack: Stack,
        name: str,
        resource_properties: Dict,
        layers: List[LayerVersion],
        use_raw_codeuri: bool = False,
    ) -> Function:
        """
        Converts a AWS::Lambda::Function resource to a Function configuration usable by the provider.

        Parameters
        ----------
        name str
            LogicalID of the resource NOTE: This is *not* the function name because not all functions declare a name
        resource_properties dict
            Properties of this resource
        layers List(samcli.commands.local.lib.provider.Layer)
            List of the Layer objects created from the template and layer list defined on the function.
        use_raw_codeuri
            Do not resolve adjust core_uri based on the template path, use the raw uri.

        Returns
        -------
        samcli.commands.local.lib.provider.Function
            Function configuration
        """

        # CodeUri is set to "." in order to get code locally from current directory. AWS::Lambda::Function's ``Code``
        # property does not support specifying a local path
        codeuri: Optional[str] = SamFunctionProvider.DEFAULT_CODEURI
        inlinecode = None
        imageuri = None
        function_id = SamFunctionProvider._get_function_id(resource_properties, name)
        packagetype = resource_properties.get("PackageType", ZIP)
        if packagetype == ZIP:
            if (
                "Code" in resource_properties
                and isinstance(resource_properties["Code"], dict)
                and resource_properties["Code"].get("ZipFile")
            ):
                inlinecode = resource_properties["Code"]["ZipFile"]
                LOG.debug("Found Lambda function with name='%s' and Code ZipFile", name)
                codeuri = None
            else:
                codeuri = SamBaseProvider._extract_codeuri(resource_properties, "Code")
                LOG.debug("Found Lambda function with name='%s' and CodeUri='%s'", name, codeuri)
        elif packagetype == IMAGE:
            imageuri = SamFunctionProvider._extract_lambda_function_imageuri(resource_properties, "Code")
            LOG.debug("Found Lambda function with name='%s' and Imageuri='%s'", name, imageuri)

        return SamFunctionProvider._build_function_configuration(
            stack, function_id, name, codeuri, resource_properties, layers, inlinecode, imageuri, use_raw_codeuri
        )

    @staticmethod
    def _build_function_configuration(
        stack: Stack,
        function_id: str,
        name: str,
        codeuri: Optional[str],
        resource_properties: Dict,
        layers: List,
        inlinecode: Optional[str],
        imageuri: Optional[str],
        use_raw_codeuri: bool = False,
    ) -> Function:
        """
        Builds a Function configuration usable by the provider.

        Parameters
        ----------
        name str
            LogicalID of the resource NOTE: This is *not* the function name because not all functions declare a name
        function_id str
            Unique function id
        codeuri str
            Representing the local code path
        resource_properties dict
            Properties of this resource
        layers List(samcli.commands.local.lib.provider.Layer)
            List of the Layer objects created from the template and layer list defined on the function.
        use_raw_codeuri
            Do not resolve adjust core_uri based on the template path, use the raw uri.

        Returns
        -------
        samcli.commands.local.lib.provider.Function
            Function configuration
        """
        metadata = resource_properties.get("Metadata", None)
        if metadata and "DockerContext" in metadata and not use_raw_codeuri:
            LOG.debug(
                "--base-dir is not presented, adjusting uri %s relative to %s",
                metadata["DockerContext"],
                stack.location,
            )
            metadata["DockerContext"] = SamLocalStackProvider.normalize_resource_path(
                stack.location, metadata["DockerContext"]
            )

        if codeuri and not use_raw_codeuri:
            LOG.debug("--base-dir is not presented, adjusting uri %s relative to %s", codeuri, stack.location)
            codeuri = SamLocalStackProvider.normalize_resource_path(stack.location, codeuri)

        if imageuri and check_path_valid_type(imageuri) and codeuri != ".":
            normalized_image_uri = SamLocalStackProvider.normalize_resource_path(stack.location, imageuri)
            if Path(normalized_image_uri).is_file():
                LOG.debug("--base-dir is not presented, adjusting uri %s relative to %s", codeuri, stack.location)
                imageuri = normalized_image_uri

        package_type = resource_properties.get("PackageType", ZIP)
        if package_type == ZIP and not resource_properties.get("Handler"):
            raise MissingFunctionHandlerException(f"Could not find handler for function: {name}")

        function_build_info = get_function_build_info(
            get_full_path(stack.stack_path, function_id), package_type, inlinecode, codeuri, imageuri, metadata
        )

        return Function(
            stack_path=stack.stack_path,
            function_id=function_id,
            name=name,
            functionname=resource_properties.get("FunctionName", name),
            packagetype=package_type,
            runtime=resource_properties.get("Runtime"),
            memory=resource_properties.get("MemorySize"),
            timeout=resource_properties.get("Timeout"),
            handler=resource_properties.get("Handler"),
            codeuri=codeuri,
            imageuri=imageuri if imageuri else resource_properties.get("ImageUri"),
            imageconfig=resource_properties.get("ImageConfig"),
            environment=resource_properties.get("Environment"),
            rolearn=resource_properties.get("Role"),
            events=resource_properties.get("Events"),
            layers=layers,
            metadata=metadata,
            inlinecode=inlinecode,
            codesign_config_arn=resource_properties.get("CodeSigningConfigArn", None),
            architectures=resource_properties.get("Architectures", None),
            function_url_config=resource_properties.get("FunctionUrlConfig"),
            runtime_management_config=resource_properties.get("RuntimeManagementConfig"),
            function_build_info=function_build_info,
            logging_config=resource_properties.get("LoggingConfig"),
        )

    @staticmethod
    def _parse_layer_info(
        stack: Stack,
        list_of_layers: List[Any],
        use_raw_codeuri: bool = False,
        ignore_code_extraction_warnings: bool = False,
        locate_layer_nested: bool = False,
        stacks: Optional[List[Stack]] = None,
        function_id: Optional[str] = None,
    ) -> List[LayerVersion]:
        """
        Creates a list of Layer objects that are represented by the resources and the list of layers

        Parameters
        ----------
        stack : Stack
            The stack the layer is defined in
        list_of_layers : List[Any]
            List of layers that are defined within the Layers Property on a function,
            layer can be defined as string or Dict, in case customers define it in other types, use "Any" here.
        use_raw_codeuri : bool
            Do not resolve adjust core_uri based on the template path, use the raw uri.
        ignore_code_extraction_warnings : bool
            Whether to print warning when codeuri is not a local pth
        locate_layer_nested: bool
            Resolved nested layer reference to their actual location in the nested stack
        stacks: List[Stack]
            List of stacks generates from templates
        function_id: str
            Logical id for the function resources

        Returns
        -------
        List(samcli.commands.local.lib.provider.Layer)
            List of the Layer objects created from the template and layer list defined on the function. The order
            of the layers does not change.

            I.E: list_of_layers = ["layer1", "layer2"] the return would be [Layer("layer1"), Layer("layer2")]
        """
        layers = []

        if locate_layer_nested and stacks and function_id:
            # The layer can be a parameter pass from parent stack, we need to locate to where the
            # layer is actually defined
            func_template = stack.template_dict.get("Resources", {}).get(function_id, {})
            a_list_of_layers = func_template.get("Properties", {}).get("Layers", [])
            for layer in a_list_of_layers:
                found_layer = SamFunctionProvider._locate_layer_from_nested(
                    stack, stacks, layer, use_raw_codeuri, ignore_code_extraction_warnings
                )
                if found_layer:
                    layers.append(found_layer)

        for layer in list_of_layers:
            if layer == "arn:aws:lambda:::awslayer:AmazonLinux1803":
                LOG.debug("Skipped arn:aws:lambda:::awslayer:AmazonLinux1803 as the containers are AmazonLinux1803")
                continue

            if layer == "arn:aws:lambda:::awslayer:AmazonLinux1703":
                raise InvalidLayerVersionArn(
                    "Building and invoking locally only supports AmazonLinux1803. See "
                    "https://aws.amazon.com/blogs/compute/upcoming-updates-to-the-aws-lambda-execution-environment/ "
                    "for more detials."
                )  # noqa: E501

            # If the layer is a string, assume it is the arn
            if isinstance(layer, str):
                if locate_layer_nested and "arn:" not in layer:
                    # the layer is not an arn
                    continue

                layers.append(
                    LayerVersion(
                        layer,
                        None,
                        stack_path=stack.stack_path,
                    )
                )
                continue

            # In the list of layers that is defined within a template, you can reference a LayerVersion resource.
            # When running locally, we need to follow that Ref so we can extract the local path to the layer code.
            if isinstance(layer, dict) and layer.get("Ref"):
                # if search_layer is set, this case should be resolved already
                if locate_layer_nested:
                    continue

                found_layer = SamFunctionProvider._locate_layer_from_ref(
                    stack, layer, use_raw_codeuri, ignore_code_extraction_warnings
                )
                if found_layer:
                    layers.append(found_layer)
            else:
                LOG.debug(
                    'layer "%s" is not recognizable, '
                    "it might be using intrinsic functions that we don't support yet. Skipping.",
                    str(layer),
                )

        return layers

    @staticmethod
    def _locate_layer_from_nested(  # pylint: disable=too-many-return-statements
        stack: Stack,
        stacks: List[Stack],
        layer: Any,
        use_raw_codeuri: bool = False,
        ignore_code_extraction_warnings: bool = False,
    ) -> Optional[LayerVersion]:
        """
        Search the layer reference through all the local templates and try to find it's actual location then create a
        layer object and return

        Right now this method does not support more complicated intrinsics like Fn:Sub and Fn:If, future task to
        expand support. One of possible solutions can be adding in an intrinsic resovler.

        TODO: this function have too many return statemnets, we may need to refactor it, break it down to multiple
        sub functions for example.

        Parameters
        ----------
        stack : Stack
            The stack the layer is defined in
        stacks: List[Stack]
            List of stacks generates from templates
        layer : Any
            layer that are defined within the Layers Property on a function,
            layer can be defined as string or Dict, in case customers define it in other types, use "Any" here.
        use_raw_codeuri : bool
            Do not resolve adjust core_uri based on the template path, use the raw uri.
        ignore_code_extraction_warnings : bool
            Whether to print warning when codeuri is not a local path

        Returns
        -------
        samcli.commands.local.lib.provider.Layer
            The Layer object created from the template and layer defined on the function.
        """

        if isinstance(layer, str):
            outputs = stack.template_dict.get("Outputs", {})
            # if the layer is not in the output section, it may be an layer arn and cannot be located in the template
            LOG.debug("Search layer %s in %s 's Output section", layer, stack.stack_path)
            if layer not in outputs:
                LOG.debug("Layer not in Output section, layer can not be located in templates")
                return None
            layer = outputs.get(layer).get("Value")
            LOG.debug("Layer found in Output section, try to search it in current stack %s", stack.stack_path)

        layer_reference = None
        # if the layer is in format {Ref:LayerName}, it is passed from the parent stack through parameter or is a
        # reference to the layer in current stack
        if isinstance(layer, dict) and layer.get("Ref"):
            layer_reference = layer.get("Ref")

        # if the layer is in the format {"Fn::GetAtt": ["LayerStackName", "Outputs.LayerName"]},
        # it is passed from another child stack inside the same parent stack
        elif isinstance(layer, dict) and layer.get("Fn::GetAtt"):
            layer_attribute: List = layer.get("Fn::GetAtt", [])
            if not SamFunctionProvider._validate_layer_get_attr_format(layer):
                return None
            layer_stack_reference = layer_attribute[0]
            layer_reference = layer_attribute[1].split(".")[1]
            LOG.debug("Search layer %s in child stack", layer_reference)

            child_stacks = Stack.get_child_stacks(stack, stacks)
            stack_prefix = stack.stack_path + "/" if stack.stack_path else ""
            stack_path = stack_prefix + layer_stack_reference
            child_stack = Stack.get_stack_by_full_path(stack_path, child_stacks)
            if not child_stack:
                LOG.debug("Child stack not found, layer can not be located in templates")
                return None
            # search in child stack
            LOG.debug("Child stack %s found", child_stack.stack_path)
            return SamFunctionProvider._locate_layer_from_nested(
                child_stack, stacks, layer_reference, use_raw_codeuri, ignore_code_extraction_warnings
            )

        # If the layer reference is not in the stack's parameters section, it must be a layer reference in current stack
        parameters: Dict = stack.template_dict.get("Parameters", {})
        if not parameters or (layer_reference and layer_reference not in parameters):
            LOG.debug("Resolved layer: %s in current stack %s", layer_reference, stack.stack_path)
            # layer reference should be in current stack
            try:
                resolve_layer = SamFunctionProvider._locate_layer_from_ref(
                    stack, layer, use_raw_codeuri, ignore_code_extraction_warnings
                )
            except InvalidLayerReference:
                LOG.debug("Layer reference (%s) can't be located in the template", layer)
                return None
            return resolve_layer

        # search in parent stack
        parent_stack = Stack.get_parent_stack(stack, stacks)
        LOG.debug("Search layer: %s in parent stack", layer_reference)
        # If it can't find the parent stack, it mean's the current stack is root stack and the layer reference may be a
        # layer arn passing from root stack's parameters, which means the actual layer can't be located in templates
        if not parent_stack:
            LOG.debug("Parent stack not found, layer can not be located in templates")
            return None
        LOG.debug("Found parent stack: %s", parent_stack.stack_path)
        layer = (
            parent_stack.template_dict.get("Resources", {})
            .get(stack.name, {})
            .get("Properties", {})
            .get("Parameters", {})
            .get(layer_reference)
        )

        return SamFunctionProvider._locate_layer_from_nested(
            parent_stack, stacks, layer, use_raw_codeuri, ignore_code_extraction_warnings
        )

    @staticmethod
    def _validate_layer_get_attr_format(layer: Dict) -> bool:
        # validate if the layer is in the format {"Fn::GetAtt": ["LayerStackName", "Outputs.LayerName"]}
        warn_message = "Fn::GetAtt with unsupported format in accelerate nested stack"
        layer_attribute = layer.get("Fn::GetAtt", [])
        required_layer_attr_length = 2
        reqauired_layer_reference_length = 2
        if not isinstance(layer_attribute, List):
            LOG.warning(warn_message)
            return False

        if len(layer_attribute) != required_layer_attr_length:
            LOG.warning(warn_message)
            return False
        layer_reference_array = layer_attribute[1].split(".")
        if len(layer_reference_array) != reqauired_layer_reference_length:
            LOG.warning(warn_message)
            return False
        return True

    @staticmethod
    def _locate_layer_from_ref(
        stack: Stack, layer: Dict, use_raw_codeuri: bool = False, ignore_code_extraction_warnings: bool = False
    ) -> Optional[LayerVersion]:
        layer_logical_id = cast(str, layer.get("Ref"))
        layer_resource = stack.resources.get(layer_logical_id)
        if not layer_resource or layer_resource.get("Type", "") not in (
            AWS_SERVERLESS_LAYERVERSION,
            AWS_LAMBDA_LAYERVERSION,
        ):
            raise InvalidLayerReference()

        layer_properties = layer_resource.get("Properties", {})
        resource_type = layer_resource.get("Type")
        compatible_runtimes = layer_properties.get("CompatibleRuntimes")
        codeuri: Optional[str] = None

        if resource_type in [AWS_LAMBDA_LAYERVERSION, AWS_SERVERLESS_LAYERVERSION]:
            code_property_key = SamBaseProvider.CODE_PROPERTY_KEYS[resource_type]
            if SamBaseProvider._is_s3_location(layer_properties.get(code_property_key)):
                # Content can be a dictionary of S3 Bucket/Key or a S3 URI, neither of which are supported
                if not ignore_code_extraction_warnings:
                    SamFunctionProvider._warn_code_extraction(resource_type, layer_logical_id, code_property_key)
                return None
            codeuri = SamBaseProvider._extract_codeuri(layer_properties, code_property_key)

        if codeuri and not use_raw_codeuri:
            LOG.debug("--base-dir is not presented, adjusting uri %s relative to %s", codeuri, stack.location)
            codeuri = SamLocalStackProvider.normalize_resource_path(stack.location, codeuri)

        return LayerVersion(
            layer_logical_id,
            codeuri,
            compatible_runtimes,
            layer_resource.get("Metadata", None),
            stack_path=stack.stack_path,
        )

    def get_resources_by_stack_path(self, stack_path: str) -> Dict:
        candidates = [stack.resources for stack in self._stacks if stack.stack_path == stack_path]
        if not candidates:
            raise RuntimeError(f"Cannot find resources with stack_path = {stack_path}")
        return candidates[0]

    @staticmethod
    def _metadata_has_necessary_entries_for_image_function_to_be_built(metadata: Optional[Dict[str, Any]]) -> bool:
        """
        > Note: If the PackageType property is set to Image, then either ImageUri is required,
          or you must build your application with necessary Metadata entries in the AWS SAM template file.
          https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-resource-function.html#sam-function-imageuri

        When ImageUri and Metadata are both provided, we will try to determine whether to treat the function
        as to be built or to be skipped. When we skip it whenever "ImageUri" is provided,
        we introduced a breaking change https://github.com/aws/aws-sam-cli/issues/3239

        This function is used to check whether there are the customers have "intention" to
        let AWS SAM CLI to build this image function.
        """
        return isinstance(metadata, dict) and bool(metadata.get("DockerContext"))


class RefreshableSamFunctionProvider(SamFunctionProvider):
    """
    Fetches and returns Lambda Functions from a SAM Template. The SAM template passed to this provider is assumed
    to be valid, normalized and a dictionary. It also detects any stack template change, and refreshes the loaded
    functions.

    It may or may not contain a function.
    """

    def __init__(
        self,
        stacks: List[Stack],
        parameter_overrides: Optional[Dict] = None,
        global_parameter_overrides: Optional[Dict] = None,
        use_raw_codeuri: bool = False,
        ignore_code_extraction_warnings: bool = False,
    ) -> None:
        """
        Initialize the class with SAM template data. The SAM template passed to this provider is assumed
        to be valid, normalized and a dictionary. It should be normalized by running all pre-processing
        before passing to this class. The process of normalization will remove structures like ``Globals``, resolve
        intrinsic functions etc.
        This class does not perform any syntactic validation of the template.

        This Class will also initialize watchers, to check the stack templates for any update, and refresh the loaded
        functions.

        :param dict stacks: List of stacks functions are extracted from
        :param bool use_raw_codeuri: Do not resolve adjust core_uri based on the template path, use the raw uri.
            Note(xinhol): use_raw_codeuri is temporary to fix a bug, and will be removed for a permanent solution.
        :param bool ignore_code_extraction_warnings: Ignores Log warnings
        """

        super().__init__(stacks, use_raw_codeuri, ignore_code_extraction_warnings)

        # initialize root templates. Usually it will be one template, as sam commands only support processing
        # one template. These templates will be fixed.
        self._use_raw_codeuri = use_raw_codeuri
        self._ignore_code_extraction_warnings = ignore_code_extraction_warnings
        self._parameter_overrides = parameter_overrides
        self._global_parameter_overrides = global_parameter_overrides
        self.parent_templates_paths = []
        for stack in self._stacks:
            if stack.is_root_stack:
                self.parent_templates_paths.append(stack.location)

        self.is_changed = False
        self._observer = FileObserver(self._set_templates_changed)
        self._observer.start()
        self._watch_stack_templates(stacks)

    @property
    def stacks(self) -> List[Stack]:
        """
        It Checks if any template got changed, then refresh the loaded stacks, and functions.

        Returns the list of stacks (including the root stack and all children stacks)

        :return list: list of stacks
        """
        if self.is_changed:
            self._refresh_loaded_functions()

        return super().stacks

    def get(self, name: str) -> Optional[Function]:
        """
        It Checks if any template got changed, then refresh the loaded functions before finding the required function.

        Returns the function given name or LogicalId of the function. Every SAM resource has a logicalId, but it may
        also have a function name. This method searches only for LogicalID and returns the function that matches.
        If it is in a nested stack, "name" can be prefixed with stack path to avoid ambiguity.
        For example, if a function with name "FunctionA" is located in StackN, which is a nested stack in root stack,
          either "StackN/FunctionA" or "FunctionA" can be used.

        :param string name: Name of the function
        :return Function: namedtuple containing the Function information if function is found.
                          None, if function is not found
        :raises ValueError If name is not given
        """

        if self.is_changed:
            self._refresh_loaded_functions()

        return super().get(name)

    def get_all(self) -> Iterator[Function]:
        """
        It Checks if any template got changed, then refresh the loaded functions before returning all available
        functions.

        Yields all the Lambda functions available in the SAM Template.

        :yields Function: namedtuple containing the function information
        """

        if self.is_changed:
            self._refresh_loaded_functions()

        return super().get_all()

    def get_resources_by_stack_path(self, stack_path: str) -> Dict:
        if self.is_changed:
            self._refresh_loaded_functions()
        return super().get_resources_by_stack_path(stack_path)

    def _set_templates_changed(self, paths: List[str]) -> None:
        LOG.info(
            "A change got detected in the templates %s. Mark templates as changed to be reloaded in the next invoke",
            ", ".join(paths),
        )
        self.is_changed = True
        for stack in self._stacks:
            self._observer.unwatch(stack.location)

    def _watch_stack_templates(self, stacks: List[Stack]) -> None:
        """
        initialize the list of stack template watchers
        """
        for stack in stacks:
            self._observer.watch(stack.location)

    def _refresh_loaded_functions(self) -> None:
        """
        Reload the stacks, and lambda functions from template files.
        """
        LOG.debug("A change got detected in one of the stack templates. Reload the lambda function resources")
        self._stacks = []

        for template_file in self.parent_templates_paths:
            try:
                template_stacks, _ = SamLocalStackProvider.get_stacks(
                    template_file,
                    parameter_overrides=self._parameter_overrides,
                    global_parameter_overrides=self._global_parameter_overrides,
                )
                self._stacks += template_stacks
            except (TemplateNotFoundException, TemplateFailedParsingException) as ex:
                raise ex

        self.is_changed = False
        self.functions = self._extract_functions(
            self._stacks, self._use_raw_codeuri, self._ignore_code_extraction_warnings
        )
        self._watch_stack_templates(self._stacks)

    def stop_observer(self) -> None:
        """
        Stop Observing.
        """
        self._observer.stop()