import uuid
import random

from datetime import datetime, timedelta

import sentry_sdk
from sentry_sdk.consts import INSTRUMENTER
from sentry_sdk.utils import is_valid_sample_rate, logger, nanosecond_time
from sentry_sdk._compat import PY2
from sentry_sdk.consts import SPANDATA
from sentry_sdk._types import TYPE_CHECKING


if TYPE_CHECKING:
    import typing

    from typing import Any
    from typing import Dict
    from typing import Iterator
    from typing import List
    from typing import Optional
    from typing import Tuple

    import sentry_sdk.profiler
    from sentry_sdk._types import Event, MeasurementUnit, SamplingContext


BAGGAGE_HEADER_NAME = "baggage"
SENTRY_TRACE_HEADER_NAME = "sentry-trace"


# Transaction source
# see https://develop.sentry.dev/sdk/event-payloads/transaction/#transaction-annotations
TRANSACTION_SOURCE_CUSTOM = "custom"
TRANSACTION_SOURCE_URL = "url"
TRANSACTION_SOURCE_ROUTE = "route"
TRANSACTION_SOURCE_VIEW = "view"
TRANSACTION_SOURCE_COMPONENT = "component"
TRANSACTION_SOURCE_TASK = "task"

# These are typically high cardinality and the server hates them
LOW_QUALITY_TRANSACTION_SOURCES = [
    TRANSACTION_SOURCE_URL,
]

SOURCE_FOR_STYLE = {
    "endpoint": TRANSACTION_SOURCE_COMPONENT,
    "function_name": TRANSACTION_SOURCE_COMPONENT,
    "handler_name": TRANSACTION_SOURCE_COMPONENT,
    "method_and_path_pattern": TRANSACTION_SOURCE_ROUTE,
    "path": TRANSACTION_SOURCE_URL,
    "route_name": TRANSACTION_SOURCE_COMPONENT,
    "route_pattern": TRANSACTION_SOURCE_ROUTE,
    "uri_template": TRANSACTION_SOURCE_ROUTE,
    "url": TRANSACTION_SOURCE_ROUTE,
}


class _SpanRecorder(object):
    """Limits the number of spans recorded in a transaction."""

    __slots__ = ("maxlen", "spans")

    def __init__(self, maxlen):
        # type: (int) -> None
        # FIXME: this is `maxlen - 1` only to preserve historical behavior
        # enforced by tests.
        # Either this should be changed to `maxlen` or the JS SDK implementation
        # should be changed to match a consistent interpretation of what maxlen
        # limits: either transaction+spans or only child spans.
        self.maxlen = maxlen - 1
        self.spans = []  # type: List[Span]

    def add(self, span):
        # type: (Span) -> None
        if len(self.spans) > self.maxlen:
            span._span_recorder = None
        else:
            self.spans.append(span)


class Span(object):
    """A span holds timing information of a block of code.
    Spans can have multiple child spans thus forming a span tree."""

    __slots__ = (
        "trace_id",
        "span_id",
        "parent_span_id",
        "same_process_as_parent",
        "sampled",
        "op",
        "description",
        "start_timestamp",
        "_start_timestamp_monotonic_ns",
        "status",
        "timestamp",
        "_tags",
        "_data",
        "_span_recorder",
        "hub",
        "_context_manager_state",
        "_containing_transaction",
    )

    def __new__(cls, **kwargs):
        # type: (**Any) -> Any
        """
        Backwards-compatible implementation of Span and Transaction
        creation.
        """

        # TODO: consider removing this in a future release.
        # This is for backwards compatibility with releases before Transaction
        # existed, to allow for a smoother transition.
        if "transaction" in kwargs:
            return object.__new__(Transaction)
        return object.__new__(cls)

    def __init__(
        self,
        trace_id=None,  # type: Optional[str]
        span_id=None,  # type: Optional[str]
        parent_span_id=None,  # type: Optional[str]
        same_process_as_parent=True,  # type: bool
        sampled=None,  # type: Optional[bool]
        op=None,  # type: Optional[str]
        description=None,  # type: Optional[str]
        hub=None,  # type: Optional[sentry_sdk.Hub]
        status=None,  # type: Optional[str]
        transaction=None,  # type: Optional[str] # deprecated
        containing_transaction=None,  # type: Optional[Transaction]
        start_timestamp=None,  # type: Optional[datetime]
    ):
        # type: (...) -> None
        self.trace_id = trace_id or uuid.uuid4().hex
        self.span_id = span_id or uuid.uuid4().hex[16:]
        self.parent_span_id = parent_span_id
        self.same_process_as_parent = same_process_as_parent
        self.sampled = sampled
        self.op = op
        self.description = description
        self.status = status
        self.hub = hub
        self._tags = {}  # type: Dict[str, str]
        self._data = {}  # type: Dict[str, Any]
        self._containing_transaction = containing_transaction
        self.start_timestamp = start_timestamp or datetime.utcnow()
        try:
            # profiling depends on this value and requires that
            # it is measured in nanoseconds
            self._start_timestamp_monotonic_ns = nanosecond_time()
        except AttributeError:
            pass

        #: End timestamp of span
        self.timestamp = None  # type: Optional[datetime]

        self._span_recorder = None  # type: Optional[_SpanRecorder]

    # TODO this should really live on the Transaction class rather than the Span
    # class
    def init_span_recorder(self, maxlen):
        # type: (int) -> None
        if self._span_recorder is None:
            self._span_recorder = _SpanRecorder(maxlen)

    def __repr__(self):
        # type: () -> str
        return (
            "<%s(op=%r, description:%r, trace_id=%r, span_id=%r, parent_span_id=%r, sampled=%r)>"
            % (
                self.__class__.__name__,
                self.op,
                self.description,
                self.trace_id,
                self.span_id,
                self.parent_span_id,
                self.sampled,
            )
        )

    def __enter__(self):
        # type: () -> Span
        hub = self.hub or sentry_sdk.Hub.current

        _, scope = hub._stack[-1]
        old_span = scope.span
        scope.span = self
        self._context_manager_state = (hub, scope, old_span)
        return self

    def __exit__(self, ty, value, tb):
        # type: (Optional[Any], Optional[Any], Optional[Any]) -> None
        if value is not None:
            self.set_status("internal_error")

        hub, scope, old_span = self._context_manager_state
        del self._context_manager_state

        self.finish(hub)
        scope.span = old_span

    @property
    def containing_transaction(self):
        # type: () -> Optional[Transaction]
        """The ``Transaction`` that this span belongs to.
        The ``Transaction`` is the root of the span tree,
        so one could also think of this ``Transaction`` as the "root span"."""

        # this is a getter rather than a regular attribute so that transactions
        # can return `self` here instead (as a way to prevent them circularly
        # referencing themselves)
        return self._containing_transaction

    def start_child(self, instrumenter=INSTRUMENTER.SENTRY, **kwargs):
        # type: (str, **Any) -> Span
        """
        Start a sub-span from the current span or transaction.

        Takes the same arguments as the initializer of :py:class:`Span`. The
        trace id, sampling decision, transaction pointer, and span recorder are
        inherited from the current span/transaction.
        """
        hub = self.hub or sentry_sdk.Hub.current
        client = hub.client
        configuration_instrumenter = client and client.options["instrumenter"]

        if instrumenter != configuration_instrumenter:
            return NoOpSpan()

        kwargs.setdefault("sampled", self.sampled)

        child = Span(
            trace_id=self.trace_id,
            parent_span_id=self.span_id,
            containing_transaction=self.containing_transaction,
            **kwargs
        )

        span_recorder = (
            self.containing_transaction and self.containing_transaction._span_recorder
        )
        if span_recorder:
            span_recorder.add(child)

        return child

    def new_span(self, **kwargs):
        # type: (**Any) -> Span
        """DEPRECATED: use :py:meth:`sentry_sdk.tracing.Span.start_child` instead."""
        logger.warning(
            "Deprecated: use Span.start_child instead of Span.new_span. This will be removed in the future."
        )
        return self.start_child(**kwargs)

    @classmethod
    def continue_from_environ(
        cls,
        environ,  # type: typing.Mapping[str, str]
        **kwargs  # type: Any
    ):
        # type: (...) -> Transaction
        """
        Create a Transaction with the given params, then add in data pulled from
        the ``sentry-trace`` and ``baggage`` headers from the environ (if any)
        before returning the Transaction.

        This is different from :py:meth:`~sentry_sdk.tracing.Span.continue_from_headers`
        in that it assumes header names in the form ``HTTP_HEADER_NAME`` -
        such as you would get from a WSGI/ASGI environ -
        rather than the form ``header-name``.

        :param environ: The ASGI/WSGI environ to pull information from.
        """
        if cls is Span:
            logger.warning(
                "Deprecated: use Transaction.continue_from_environ "
                "instead of Span.continue_from_environ."
            )
        return Transaction.continue_from_headers(EnvironHeaders(environ), **kwargs)

    @classmethod
    def continue_from_headers(
        cls,
        headers,  # type: typing.Mapping[str, str]
        **kwargs  # type: Any
    ):
        # type: (...) -> Transaction
        """
        Create a transaction with the given params (including any data pulled from
        the ``sentry-trace`` and ``baggage`` headers).

        :param headers: The dictionary with the HTTP headers to pull information from.
        """
        # TODO move this to the Transaction class
        if cls is Span:
            logger.warning(
                "Deprecated: use Transaction.continue_from_headers "
                "instead of Span.continue_from_headers."
            )

        # TODO-neel move away from this kwargs stuff, it's confusing and opaque
        # make more explicit
        baggage = Baggage.from_incoming_header(headers.get(BAGGAGE_HEADER_NAME))
        kwargs.update({BAGGAGE_HEADER_NAME: baggage})

        sentrytrace_kwargs = extract_sentrytrace_data(
            headers.get(SENTRY_TRACE_HEADER_NAME)
        )

        if sentrytrace_kwargs is not None:
            kwargs.update(sentrytrace_kwargs)

            # If there's an incoming sentry-trace but no incoming baggage header,
            # for instance in traces coming from older SDKs,
            # baggage will be empty and immutable and won't be populated as head SDK.
            baggage.freeze()

        transaction = Transaction(**kwargs)
        transaction.same_process_as_parent = False

        return transaction

    def iter_headers(self):
        # type: () -> Iterator[Tuple[str, str]]
        """
        Creates a generator which returns the span's ``sentry-trace`` and ``baggage`` headers.
        If the span's containing transaction doesn't yet have a ``baggage`` value,
        this will cause one to be generated and stored.
        """
        yield SENTRY_TRACE_HEADER_NAME, self.to_traceparent()

        if self.containing_transaction:
            baggage = self.containing_transaction.get_baggage().serialize()
            if baggage:
                yield BAGGAGE_HEADER_NAME, baggage

    @classmethod
    def from_traceparent(
        cls,
        traceparent,  # type: Optional[str]
        **kwargs  # type: Any
    ):
        # type: (...) -> Optional[Transaction]
        """
        DEPRECATED: Use :py:meth:`sentry_sdk.tracing.Span.continue_from_headers`.

        Create a ``Transaction`` with the given params, then add in data pulled from
        the given ``sentry-trace`` header value before returning the ``Transaction``.
        """
        logger.warning(
            "Deprecated: Use Transaction.continue_from_headers(headers, **kwargs) "
            "instead of from_traceparent(traceparent, **kwargs)"
        )

        if not traceparent:
            return None

        return cls.continue_from_headers(
            {SENTRY_TRACE_HEADER_NAME: traceparent}, **kwargs
        )

    def to_traceparent(self):
        # type: () -> str
        if self.sampled is True:
            sampled = "1"
        elif self.sampled is False:
            sampled = "0"
        else:
            sampled = None

        traceparent = "%s-%s" % (self.trace_id, self.span_id)
        if sampled is not None:
            traceparent += "-%s" % (sampled,)

        return traceparent

    def to_baggage(self):
        # type: () -> Optional[Baggage]
        """Returns the :py:class:`~sentry_sdk.tracing_utils.Baggage`
        associated with this ``Span``, if any. (Taken from the root of the span tree.)
        """
        if self.containing_transaction:
            return self.containing_transaction.get_baggage()
        return None

    def set_tag(self, key, value):
        # type: (str, Any) -> None
        self._tags[key] = value

    def set_data(self, key, value):
        # type: (str, Any) -> None
        self._data[key] = value

    def set_status(self, value):
        # type: (str) -> None
        self.status = value

    def set_http_status(self, http_status):
        # type: (int) -> None
        self.set_tag(
            "http.status_code", str(http_status)
        )  # we keep this for backwards compatability
        self.set_data(SPANDATA.HTTP_STATUS_CODE, http_status)

        if http_status < 400:
            self.set_status("ok")
        elif 400 <= http_status < 500:
            if http_status == 403:
                self.set_status("permission_denied")
            elif http_status == 404:
                self.set_status("not_found")
            elif http_status == 429:
                self.set_status("resource_exhausted")
            elif http_status == 413:
                self.set_status("failed_precondition")
            elif http_status == 401:
                self.set_status("unauthenticated")
            elif http_status == 409:
                self.set_status("already_exists")
            else:
                self.set_status("invalid_argument")
        elif 500 <= http_status < 600:
            if http_status == 504:
                self.set_status("deadline_exceeded")
            elif http_status == 501:
                self.set_status("unimplemented")
            elif http_status == 503:
                self.set_status("unavailable")
            else:
                self.set_status("internal_error")
        else:
            self.set_status("unknown_error")

    def is_success(self):
        # type: () -> bool
        return self.status == "ok"

    def finish(self, hub=None, end_timestamp=None):
        # type: (Optional[sentry_sdk.Hub], Optional[datetime]) -> Optional[str]
        # Note: would be type: (Optional[sentry_sdk.Hub]) -> None, but that leads
        # to incompatible return types for Span.finish and Transaction.finish.
        """Sets the end timestamp of the span.
        Additionally it also creates a breadcrumb from the span,
        if the span represents a database or HTTP request.

        :param hub: The hub to use for this transaction.
            If not provided, the current hub will be used.
        :param end_timestamp: Optional timestamp that should
            be used as timestamp instead of the current time.

        :return: Always ``None``. The type is ``Optional[str]`` to match
            the return value of :py:meth:`sentry_sdk.tracing.Transaction.finish`.
        """

        if self.timestamp is not None:
            # This span is already finished, ignore.
            return None

        hub = hub or self.hub or sentry_sdk.Hub.current

        try:
            if end_timestamp:
                self.timestamp = end_timestamp
            else:
                elapsed = nanosecond_time() - self._start_timestamp_monotonic_ns
                self.timestamp = self.start_timestamp + timedelta(
                    microseconds=elapsed / 1000
                )
        except AttributeError:
            self.timestamp = datetime.utcnow()

        maybe_create_breadcrumbs_from_span(hub, self)
        return None

    def to_json(self):
        # type: () -> Dict[str, Any]
        """Returns a JSON-compatible representation of the span."""

        rv = {
            "trace_id": self.trace_id,
            "span_id": self.span_id,
            "parent_span_id": self.parent_span_id,
            "same_process_as_parent": self.same_process_as_parent,
            "op": self.op,
            "description": self.description,
            "start_timestamp": self.start_timestamp,
            "timestamp": self.timestamp,
        }  # type: Dict[str, Any]

        if self.status:
            self._tags["status"] = self.status

        tags = self._tags
        if tags:
            rv["tags"] = tags

        data = self._data
        if data:
            rv["data"] = data

        return rv

    def get_trace_context(self):
        # type: () -> Any
        rv = {
            "trace_id": self.trace_id,
            "span_id": self.span_id,
            "parent_span_id": self.parent_span_id,
            "op": self.op,
            "description": self.description,
        }  # type: Dict[str, Any]
        if self.status:
            rv["status"] = self.status

        if self.containing_transaction:
            rv[
                "dynamic_sampling_context"
            ] = self.containing_transaction.get_baggage().dynamic_sampling_context()

        return rv


class Transaction(Span):
    """The Transaction is the root element that holds all the spans
    for Sentry performance instrumentation."""

    __slots__ = (
        "name",
        "source",
        "parent_sampled",
        # used to create baggage value for head SDKs in dynamic sampling
        "sample_rate",
        "_measurements",
        "_contexts",
        "_profile",
        "_baggage",
    )

    def __init__(
        self,
        name="",  # type: str
        parent_sampled=None,  # type: Optional[bool]
        baggage=None,  # type: Optional[Baggage]
        source=TRANSACTION_SOURCE_CUSTOM,  # type: str
        **kwargs  # type: Any
    ):
        # type: (...) -> None
        """Constructs a new Transaction.

        :param name: Identifier of the transaction.
            Will show up in the Sentry UI.
        :param parent_sampled: Whether the parent transaction was sampled.
            If True this transaction will be kept, if False it will be discarded.
        :param baggage: The W3C baggage header value.
            (see https://www.w3.org/TR/baggage/)
        :param source: A string describing the source of the transaction name.
            This will be used to determine the transaction's type.
            See https://develop.sentry.dev/sdk/event-payloads/transaction/#transaction-annotations
            for more information. Default "custom".
        """
        # TODO: consider removing this in a future release.
        # This is for backwards compatibility with releases before Transaction
        # existed, to allow for a smoother transition.
        if not name and "transaction" in kwargs:
            logger.warning(
                "Deprecated: use Transaction(name=...) to create transactions "
                "instead of Span(transaction=...)."
            )
            name = kwargs.pop("transaction")

        super(Transaction, self).__init__(**kwargs)

        self.name = name
        self.source = source
        self.sample_rate = None  # type: Optional[float]
        self.parent_sampled = parent_sampled
        self._measurements = {}  # type: Dict[str, Any]
        self._contexts = {}  # type: Dict[str, Any]
        self._profile = None  # type: Optional[sentry_sdk.profiler.Profile]
        self._baggage = baggage

    def __repr__(self):
        # type: () -> str
        return (
            "<%s(name=%r, op=%r, trace_id=%r, span_id=%r, parent_span_id=%r, sampled=%r, source=%r)>"
            % (
                self.__class__.__name__,
                self.name,
                self.op,
                self.trace_id,
                self.span_id,
                self.parent_span_id,
                self.sampled,
                self.source,
            )
        )

    def __enter__(self):
        # type: () -> Transaction
        super(Transaction, self).__enter__()

        if self._profile is not None:
            self._profile.__enter__()

        return self

    def __exit__(self, ty, value, tb):
        # type: (Optional[Any], Optional[Any], Optional[Any]) -> None
        if self._profile is not None:
            self._profile.__exit__(ty, value, tb)

        super(Transaction, self).__exit__(ty, value, tb)

    @property
    def containing_transaction(self):
        # type: () -> Transaction
        """The root element of the span tree.
        In the case of a transaction it is the transaction itself.
        """

        # Transactions (as spans) belong to themselves (as transactions). This
        # is a getter rather than a regular attribute to avoid having a circular
        # reference.
        return self

    def finish(self, hub=None, end_timestamp=None):
        # type: (Optional[sentry_sdk.Hub], Optional[datetime]) -> Optional[str]
        """Finishes the transaction and sends it to Sentry.
        All finished spans in the transaction will also be sent to Sentry.

        :param hub: The hub to use for this transaction.
            If not provided, the current hub will be used.
        :param end_timestamp: Optional timestamp that should
            be used as timestamp instead of the current time.

        :return: The event ID if the transaction was sent to Sentry,
            otherwise None.
        """
        if self.timestamp is not None:
            # This transaction is already finished, ignore.
            return None

        hub = hub or self.hub or sentry_sdk.Hub.current
        client = hub.client

        if client is None:
            # We have no client and therefore nowhere to send this transaction.
            return None

        # This is a de facto proxy for checking if sampled = False
        if self._span_recorder is None:
            logger.debug("Discarding transaction because sampled = False")

            # This is not entirely accurate because discards here are not
            # exclusively based on sample rate but also traces sampler, but
            # we handle this the same here.
            if client.transport and has_tracing_enabled(client.options):
                if client.monitor and client.monitor.downsample_factor > 0:
                    reason = "backpressure"
                else:
                    reason = "sample_rate"

                client.transport.record_lost_event(reason, data_category="transaction")

            return None

        if not self.name:
            logger.warning(
                "Transaction has no name, falling back to `<unlabeled transaction>`."
            )
            self.name = "<unlabeled transaction>"

        super(Transaction, self).finish(hub, end_timestamp)

        if not self.sampled:
            # At this point a `sampled = None` should have already been resolved
            # to a concrete decision.
            if self.sampled is None:
                logger.warning("Discarding transaction without sampling decision.")

            return None

        finished_spans = [
            span.to_json()
            for span in self._span_recorder.spans
            if span.timestamp is not None
        ]

        # we do this to break the circular reference of transaction -> span
        # recorder -> span -> containing transaction (which is where we started)
        # before either the spans or the transaction goes out of scope and has
        # to be garbage collected
        self._span_recorder = None

        contexts = {}
        contexts.update(self._contexts)
        contexts.update({"trace": self.get_trace_context()})

        event = {
            "type": "transaction",
            "transaction": self.name,
            "transaction_info": {"source": self.source},
            "contexts": contexts,
            "tags": self._tags,
            "timestamp": self.timestamp,
            "start_timestamp": self.start_timestamp,
            "spans": finished_spans,
        }  # type: Event

        if self._profile is not None and self._profile.valid():
            event["profile"] = self._profile
            self._profile = None

        event["measurements"] = self._measurements

        return hub.capture_event(event)

    def set_measurement(self, name, value, unit=""):
        # type: (str, float, MeasurementUnit) -> None
        self._measurements[name] = {"value": value, "unit": unit}

    def set_context(self, key, value):
        # type: (str, Any) -> None
        """Sets a context. Transactions can have multiple contexts
        and they should follow the format described in the "Contexts Interface"
        documentation.

        :param key: The name of the context.
        :param value: The information about the context.
        """
        self._contexts[key] = value

    def set_http_status(self, http_status):
        # type: (int) -> None
        """Sets the status of the Transaction according to the given HTTP status.

        :param http_status: The HTTP status code."""
        super(Transaction, self).set_http_status(http_status)
        self.set_context("response", {"status_code": http_status})

    def to_json(self):
        # type: () -> Dict[str, Any]
        """Returns a JSON-compatible representation of the transaction."""
        rv = super(Transaction, self).to_json()

        rv["name"] = self.name
        rv["source"] = self.source
        rv["sampled"] = self.sampled

        return rv

    def get_baggage(self):
        # type: () -> Baggage
        """Returns the :py:class:`~sentry_sdk.tracing_utils.Baggage`
        associated with the Transaction.

        The first time a new baggage with Sentry items is made,
        it will be frozen."""

        if not self._baggage or self._baggage.mutable:
            self._baggage = Baggage.populate_from_transaction(self)

        return self._baggage

    def _set_initial_sampling_decision(self, sampling_context):
        # type: (SamplingContext) -> None
        """
        Sets the transaction's sampling decision, according to the following
        precedence rules:

        1. If a sampling decision is passed to `start_transaction`
        (`start_transaction(name: "my transaction", sampled: True)`), that
        decision will be used, regardless of anything else

        2. If `traces_sampler` is defined, its decision will be used. It can
        choose to keep or ignore any parent sampling decision, or use the
        sampling context data to make its own decision or to choose a sample
        rate for the transaction.

        3. If `traces_sampler` is not defined, but there's a parent sampling
        decision, the parent sampling decision will be used.

        4. If `traces_sampler` is not defined and there's no parent sampling
        decision, `traces_sample_rate` will be used.
        """

        hub = self.hub or sentry_sdk.Hub.current
        client = hub.client
        options = (client and client.options) or {}
        transaction_description = "{op}transaction <{name}>".format(
            op=("<" + self.op + "> " if self.op else ""), name=self.name
        )

        # nothing to do if there's no client or if tracing is disabled
        if not client or not has_tracing_enabled(options):
            self.sampled = False
            return

        # if the user has forced a sampling decision by passing a `sampled`
        # value when starting the transaction, go with that
        if self.sampled is not None:
            self.sample_rate = float(self.sampled)
            return

        # we would have bailed already if neither `traces_sampler` nor
        # `traces_sample_rate` were defined, so one of these should work; prefer
        # the hook if so
        sample_rate = (
            options["traces_sampler"](sampling_context)
            if callable(options.get("traces_sampler"))
            else (
                # default inheritance behavior
                sampling_context["parent_sampled"]
                if sampling_context["parent_sampled"] is not None
                else options["traces_sample_rate"]
            )
        )

        # Since this is coming from the user (or from a function provided by the
        # user), who knows what we might get. (The only valid values are
        # booleans or numbers between 0 and 1.)
        if not is_valid_sample_rate(sample_rate, source="Tracing"):
            logger.warning(
                "[Tracing] Discarding {transaction_description} because of invalid sample rate.".format(
                    transaction_description=transaction_description,
                )
            )
            self.sampled = False
            return

        self.sample_rate = float(sample_rate)

        if client.monitor:
            self.sample_rate /= 2**client.monitor.downsample_factor

        # if the function returned 0 (or false), or if `traces_sample_rate` is
        # 0, it's a sign the transaction should be dropped
        if not self.sample_rate:
            logger.debug(
                "[Tracing] Discarding {transaction_description} because {reason}".format(
                    transaction_description=transaction_description,
                    reason=(
                        "traces_sampler returned 0 or False"
                        if callable(options.get("traces_sampler"))
                        else "traces_sample_rate is set to 0"
                    ),
                )
            )
            self.sampled = False
            return

        # Now we roll the dice. random.random is inclusive of 0, but not of 1,
        # so strict < is safe here. In case sample_rate is a boolean, cast it
        # to a float (True becomes 1.0 and False becomes 0.0)
        self.sampled = random.random() < self.sample_rate

        if self.sampled:
            logger.debug(
                "[Tracing] Starting {transaction_description}".format(
                    transaction_description=transaction_description,
                )
            )
        else:
            logger.debug(
                "[Tracing] Discarding {transaction_description} because it's not included in the random sample (sampling rate = {sample_rate})".format(
                    transaction_description=transaction_description,
                    sample_rate=self.sample_rate,
                )
            )


class NoOpSpan(Span):
    def __repr__(self):
        # type: () -> str
        return self.__class__.__name__

    @property
    def containing_transaction(self):
        # type: () -> Optional[Transaction]
        return None

    def start_child(self, instrumenter=INSTRUMENTER.SENTRY, **kwargs):
        # type: (str, **Any) -> NoOpSpan
        return NoOpSpan()

    def new_span(self, **kwargs):
        # type: (**Any) -> NoOpSpan
        return self.start_child(**kwargs)

    def to_traceparent(self):
        # type: () -> str
        return ""

    def to_baggage(self):
        # type: () -> Optional[Baggage]
        return None

    def get_baggage(self):
        # type: () -> Optional[Baggage]
        return None

    def iter_headers(self):
        # type: () -> Iterator[Tuple[str, str]]
        return iter(())

    def set_tag(self, key, value):
        # type: (str, Any) -> None
        pass

    def set_data(self, key, value):
        # type: (str, Any) -> None
        pass

    def set_status(self, value):
        # type: (str) -> None
        pass

    def set_http_status(self, http_status):
        # type: (int) -> None
        pass

    def is_success(self):
        # type: () -> bool
        return True

    def to_json(self):
        # type: () -> Dict[str, Any]
        return {}

    def get_trace_context(self):
        # type: () -> Any
        return {}

    def finish(self, hub=None, end_timestamp=None):
        # type: (Optional[sentry_sdk.Hub], Optional[datetime]) -> Optional[str]
        pass

    def set_measurement(self, name, value, unit=""):
        # type: (str, float, MeasurementUnit) -> None
        pass

    def set_context(self, key, value):
        # type: (str, Any) -> None
        pass

    def init_span_recorder(self, maxlen):
        # type: (int) -> None
        pass

    def _set_initial_sampling_decision(self, sampling_context):
        # type: (SamplingContext) -> None
        pass


def trace(func=None):
    # type: (Any) -> Any
    """
    Decorator to start a child span under the existing current transaction.
    If there is no current transaction, then nothing will be traced.

    .. code-block::
        :caption: Usage

        import sentry_sdk

        @sentry_sdk.trace
        def my_function():
            ...

        @sentry_sdk.trace
        async def my_async_function():
            ...
    """
    if PY2:
        from sentry_sdk.tracing_utils_py2 import start_child_span_decorator
    else:
        from sentry_sdk.tracing_utils_py3 import start_child_span_decorator

    # This patterns allows usage of both @sentry_traced and @sentry_traced(...)
    # See https://stackoverflow.com/questions/52126071/decorator-with-arguments-avoid-parenthesis-when-no-arguments/52126278
    if func:
        return start_child_span_decorator(func)
    else:
        return start_child_span_decorator


# Circular imports

from sentry_sdk.tracing_utils import (
    Baggage,
    EnvironHeaders,
    extract_sentrytrace_data,
    has_tracing_enabled,
    maybe_create_breadcrumbs_from_span,
)
