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# to you under the Apache License, Version 2.0 (the
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#
#   http://www.apache.org/licenses/LICENSE-2.0
#
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# software distributed under the License is distributed on an
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from __future__ import annotations

import logging
import os
import time
from collections.abc import Generator, Iterator
from datetime import datetime, timezone
from functools import cached_property
from typing import TYPE_CHECKING

from airflow.configuration import conf
from airflow.utils.log.file_task_handler import FileTaskHandler, StructuredLogMessage
from airflow.utils.log.logging_mixin import ExternalLoggingMixin
from airflow.utils.state import TaskInstanceState

if TYPE_CHECKING:
    from typing import TypeAlias

    from airflow.models.taskinstance import TaskInstance
    from airflow.models.taskinstancehistory import TaskInstanceHistory
    from airflow.utils.log.file_task_handler import LogHandlerOutputStream, LogMetadata

LogReaderOutputStream: TypeAlias = Generator[str, None, None]

READ_BATCH_SIZE = 1024


class TaskLogReader:
    """Task log reader."""

    STREAM_LOOP_SLEEP_SECONDS = 1
    """Time to sleep between loops while waiting for more logs"""

    STREAM_LOOP_STOP_AFTER_EMPTY_ITERATIONS = 10
    """Number of empty loop iterations before stopping the stream"""

    @staticmethod
    def get_no_log_state_message(ti: TaskInstance | TaskInstanceHistory) -> Iterator[StructuredLogMessage]:
        """Yield standardized no-log messages for a given TI state."""
        if ti.state == TaskInstanceState.SKIPPED:
            msg = "Task was skipped — no logs available."
        elif ti.state == TaskInstanceState.UPSTREAM_FAILED:
            msg = "Task did not run because upstream task(s) failed."
        else:
            msg = "No logs available for this task."

        yield StructuredLogMessage(timestamp=None, event="::group::Log message source details")
        yield StructuredLogMessage(timestamp=None, event="::endgroup::")
        yield StructuredLogMessage(
            timestamp=ti.updated_at or datetime.now(timezone.utc),
            event=msg,
        )

    def read_log_chunks(
        self,
        ti: TaskInstance | TaskInstanceHistory,
        try_number: int | None,
        metadata: LogMetadata,
    ) -> tuple[LogHandlerOutputStream, LogMetadata]:
        """
        Read chunks of Task Instance logs.

        :param ti: The taskInstance
        :param try_number:
        :param metadata: A dictionary containing information about how to read the task log

        The following is an example of how to use this method to read log:

        .. code-block:: python

            logs, metadata = task_log_reader.read_log_chunks(ti, try_number, metadata)
            logs = logs[0] if try_number is not None else logs

        where task_log_reader is an instance of TaskLogReader. The metadata will always
        contain information about the task log which can enable you read logs to the
        end.
        """
        if try_number == 0:
            msg = self.get_no_log_state_message(ti)  # returns StructuredLogMessage
            # one message + tell the caller it's the end so stream stops
            return msg, {"end_of_log": True}

        return self.log_handler.read(ti, try_number, metadata=metadata)

    def read_log_stream(
        self,
        ti: TaskInstance | TaskInstanceHistory,
        try_number: int | None,
        metadata: LogMetadata,
    ) -> Iterator[str]:
        """
        Continuously read log to the end.

        :param ti: The Task Instance
        :param try_number: the task try number
        :param metadata: A dictionary containing information about how to read the task log
        """
        if try_number is None:
            try_number = ti.try_number

        # Handle skipped / upstream_failed case directly
        if try_number == 0:
            for msg in self.get_no_log_state_message(ti):
                yield f"{msg.model_dump_json()}\n"
            return

        for key in ("end_of_log", "max_offset", "offset", "log_pos"):
            # https://mypy.readthedocs.io/en/stable/typed_dict.html#supported-operations
            metadata.pop(key, None)  # type: ignore[misc]
        empty_iterations = 0

        while True:
            log_stream, out_metadata = self.read_log_chunks(ti, try_number, metadata)
            yield from (f"{log.model_dump_json()}\n" for log in log_stream)

            if not out_metadata.get("end_of_log", False) and ti.state not in (
                TaskInstanceState.RUNNING,
                TaskInstanceState.DEFERRED,
            ):
                if log_stream:
                    empty_iterations = 0
                else:
                    # we did not receive any logs in this loop
                    # sleeping to conserve resources / limit requests on external services
                    time.sleep(self.STREAM_LOOP_SLEEP_SECONDS)
                    empty_iterations += 1
                    if empty_iterations >= self.STREAM_LOOP_STOP_AFTER_EMPTY_ITERATIONS:
                        # we have not received any logs for a while, so we stop the stream
                        # this is emitted as json to avoid breaking the ndjson stream format
                        yield '{"event": "Log stream stopped - End of log marker not found; logs may be incomplete."}\n'
                        return
            else:
                # https://mypy.readthedocs.io/en/stable/typed_dict.html#supported-operations
                metadata.clear()  # type: ignore[attr-defined]
                metadata.update(out_metadata)
                return

    @cached_property
    def log_handler(self):
        """Get the log handler which is configured to read logs."""
        task_log_reader = conf.get("logging", "task_log_reader")

        def handlers():
            """
            Yield all handlers first from airflow.task logger then root logger.

            Depending on whether we're in a running task, it could be in either of these locations.
            """
            yield from logging.getLogger("airflow.task").handlers
            yield from logging.getLogger().handlers

            fallback = FileTaskHandler(os.devnull)
            fallback.name = task_log_reader
            yield fallback

        return next((h for h in handlers() if h.name == task_log_reader), None)

    @property
    def supports_read(self):
        """Checks if a read operation is supported by a current log handler."""
        return hasattr(self.log_handler, "read")

    @property
    def supports_external_link(self) -> bool:
        """Check if the logging handler supports external links (e.g. to Elasticsearch, Stackdriver, etc)."""
        if not isinstance(self.log_handler, ExternalLoggingMixin):
            return False

        return self.log_handler.supports_external_link
