import uuid
import random

from datetime import 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 datetime_utcnow, PY2
from sentry_sdk.consts import SPANDATA
from sentry_sdk._types import TYPE_CHECKING


if TYPE_CHECKING:
    import typing

    from datetime import datetime
    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,
)
