#!/usr/bin/env python3

# © Copyright 2021-2022, Scott Gasch

"""Helpers for unittests.

.. note::

    When you import this we automatically wrap unittest.main()
    with a call to bootstrap.initialize so that we getLogger
    config, commandline args, logging control, etc... this works
    fine but it's a little hacky so caveat emptor.
"""

import contextlib
import functools
import inspect
import logging
import os
import pickle
import random
import statistics
import tempfile
import time
import unittest
import warnings
from abc import ABC, abstractmethod
from typing import Any, Callable, Dict, List, Literal, Optional

import sqlalchemy as sa

import bootstrap
import config
import function_utils
import scott_secrets

logger = logging.getLogger(__name__)
cfg = config.add_commandline_args(f'Logging ({__file__})', 'Args related to function decorators')
cfg.add_argument(
    '--unittests_ignore_perf',
    action='store_true',
    default=False,
    help='Ignore unittest perf regression in @check_method_for_perf_regressions',
)
cfg.add_argument(
    '--unittests_num_perf_samples',
    type=int,
    default=50,
    help='The count of perf timing samples we need to see before blocking slow runs on perf grounds',
)
cfg.add_argument(
    '--unittests_drop_perf_traces',
    type=str,
    nargs=1,
    default=None,
    help='The identifier (i.e. file!test_fixture) for which we should drop all perf data',
)
cfg.add_argument(
    '--unittests_persistance_strategy',
    choices=['FILE', 'DATABASE'],
    default='DATABASE',
    help='Should we persist perf data in a file or db?',
)
cfg.add_argument(
    '--unittests_perfdb_filename',
    type=str,
    metavar='FILENAME',
    default=f'{os.environ["HOME"]}/.python_unittest_performance_db',
    help='File in which to store perf data (iff --unittests_persistance_strategy is FILE)',
)
cfg.add_argument(
    '--unittests_perfdb_spec',
    type=str,
    metavar='DBSPEC',
    default='mariadb+pymysql://python_unittest:<PASSWORD>@db.house:3306/python_unittest_performance',
    help='Db connection spec for perf data (iff --unittest_persistance_strategy is DATABASE)',
)

# >>> This is the hacky business, FYI. <<<
unittest.main = bootstrap.initialize(unittest.main)


class PerfRegressionDataPersister(ABC):
    """A base class for a signature dealing with persisting perf
    regression data."""

    def __init__(self):
        pass

    @abstractmethod
    def load_performance_data(self, method_id: str) -> Dict[str, List[float]]:
        pass

    @abstractmethod
    def save_performance_data(self, method_id: str, data: Dict[str, List[float]]):
        pass

    @abstractmethod
    def delete_performance_data(self, method_id: str):
        pass


class FileBasedPerfRegressionDataPersister(PerfRegressionDataPersister):
    """A perf regression data persister that uses files."""

    def __init__(self, filename: str):
        super().__init__()
        self.filename = filename
        self.traces_to_delete: List[str] = []

    def load_performance_data(self, method_id: str) -> Dict[str, List[float]]:
        with open(self.filename, 'rb') as f:
            return pickle.load(f)

    def save_performance_data(self, method_id: str, data: Dict[str, List[float]]):
        for trace in self.traces_to_delete:
            if trace in data:
                data[trace] = []

        with open(self.filename, 'wb') as f:
            pickle.dump(data, f, pickle.HIGHEST_PROTOCOL)

    def delete_performance_data(self, method_id: str):
        self.traces_to_delete.append(method_id)


class DatabasePerfRegressionDataPersister(PerfRegressionDataPersister):
    """A perf regression data persister that uses a database backend."""

    def __init__(self, dbspec: str):
        super().__init__()
        self.dbspec = dbspec
        self.engine = sa.create_engine(self.dbspec)
        self.conn = self.engine.connect()

    def load_performance_data(self, method_id: str) -> Dict[str, List[float]]:
        results = self.conn.execute(
            sa.text(f'SELECT * FROM runtimes_by_function WHERE function = "{method_id}";')
        )
        ret: Dict[str, List[float]] = {method_id: []}
        for result in results.all():
            ret[method_id].append(result['runtime'])
        results.close()
        return ret

    def save_performance_data(self, method_id: str, data: Dict[str, List[float]]):
        self.delete_performance_data(method_id)
        for (mid, perf_data) in data.items():
            sql = 'INSERT INTO runtimes_by_function (function, runtime) VALUES '
            for perf in perf_data:
                self.conn.execute(sql + f'("{mid}", {perf});')

    def delete_performance_data(self, method_id: str):
        sql = f'DELETE FROM runtimes_by_function WHERE function = "{method_id}"'
        self.conn.execute(sql)


def check_method_for_perf_regressions(func: Callable) -> Callable:
    """
    This is meant to be used on a method in a class that subclasses
    unittest.TestCase.  When thus decorated it will time the execution
    of the code in the method, compare it with a database of
    historical perfmance, and fail the test with a perf-related
    message if it has become too slow.

    """

    @functools.wraps(func)
    def wrapper_perf_monitor(*args, **kwargs):
        if config.config['unittests_ignore_perf']:
            return func(*args, **kwargs)

        if config.config['unittests_persistance_strategy'] == 'FILE':
            filename = config.config['unittests_perfdb_filename']
            helper = FileBasedPerfRegressionDataPersister(filename)
        elif config.config['unittests_persistance_strategy'] == 'DATABASE':
            dbspec = config.config['unittests_perfdb_spec']
            dbspec = dbspec.replace('<PASSWORD>', scott_secrets.MARIADB_UNITTEST_PERF_PASSWORD)
            helper = DatabasePerfRegressionDataPersister(dbspec)
        else:
            raise Exception('Unknown/unexpected --unittests_persistance_strategy value')

        func_id = function_utils.function_identifier(func)
        func_name = func.__name__
        logger.debug('Watching %s\'s performance...', func_name)
        logger.debug('Canonical function identifier = "%s"', func_id)

        try:
            perfdb = helper.load_performance_data(func_id)
        except Exception as e:
            logger.exception(e)
            msg = 'Unable to load perfdb; skipping it...'
            logger.warning(msg)
            warnings.warn(msg)
            perfdb = {}

        # cmdline arg to forget perf traces for function
        drop_id = config.config['unittests_drop_perf_traces']
        if drop_id is not None:
            helper.delete_performance_data(drop_id)

        # Run the wrapped test paying attention to latency.
        start_time = time.perf_counter()
        value = func(*args, **kwargs)
        end_time = time.perf_counter()
        run_time = end_time - start_time

        # See if it was unexpectedly slow.
        hist = perfdb.get(func_id, [])
        if len(hist) < config.config['unittests_num_perf_samples']:
            hist.append(run_time)
            logger.debug('Still establishing a perf baseline for %s', func_name)
        else:
            stdev = statistics.stdev(hist)
            logger.debug('For %s, performance stdev=%.2f', func_name, stdev)
            slowest = hist[-1]
            logger.debug('For %s, slowest perf on record is %.2fs', func_name, slowest)
            limit = slowest + stdev * 4
            logger.debug('For %s, max acceptable runtime is %.2fs', func_name, limit)
            logger.debug('For %s, actual observed runtime was %.2fs', func_name, run_time)
            if run_time > limit:
                msg = f'''{func_id} performance has regressed unacceptably.
{slowest:f}s is the slowest runtime on record in {len(hist)} perf samples.
It just ran in {run_time:f}s which is 4+ stdevs slower than the slowest.
Here is the current, full db perf timing distribution:

'''
                for x in hist:
                    msg += f'{x:f}\n'
                logger.error(msg)
                slf = args[0]  # Peek at the wrapped function's self ref.
                slf.fail(msg)  # ...to fail the testcase.
            else:
                hist.append(run_time)

        # Don't spam the database with samples; just pick a random
        # sample from what we have and store that back.
        n = min(config.config['unittests_num_perf_samples'], len(hist))
        hist = random.sample(hist, n)
        hist.sort()
        perfdb[func_id] = hist
        helper.save_performance_data(func_id, perfdb)
        return value

    return wrapper_perf_monitor


def check_all_methods_for_perf_regressions(prefix='test_'):
    """Decorate unittests with this to pay attention to the perf of the
    testcode and flag perf regressions.  e.g.

    import unittest_utils as uu

    @uu.check_all_methods_for_perf_regressions()
    class TestMyClass(unittest.TestCase):

        def test_some_part_of_my_class(self):
            ...

    """

    def decorate_the_testcase(cls):
        if issubclass(cls, unittest.TestCase):
            for name, m in inspect.getmembers(cls, inspect.isfunction):
                if name.startswith(prefix):
                    setattr(cls, name, check_method_for_perf_regressions(m))
                    logger.debug('Wrapping %s:%s.', cls.__name__, name)
        return cls

    return decorate_the_testcase


class RecordStdout(contextlib.AbstractContextManager):
    """
    Record what is emitted to stdout.

    >>> with RecordStdout() as record:
    ...     print("This is a test!")
    >>> print({record().readline()})
    {'This is a test!\\n'}
    >>> record().close()
    """

    def __init__(self) -> None:
        super().__init__()
        self.destination = tempfile.SpooledTemporaryFile(mode='r+')
        self.recorder: Optional[contextlib.redirect_stdout] = None

    def __enter__(self) -> Callable[[], tempfile.SpooledTemporaryFile]:
        self.recorder = contextlib.redirect_stdout(self.destination)
        assert self.recorder is not None
        self.recorder.__enter__()
        return lambda: self.destination

    def __exit__(self, *args) -> Literal[False]:
        assert self.recorder is not None
        self.recorder.__exit__(*args)
        self.destination.seek(0)
        return False


class RecordStderr(contextlib.AbstractContextManager):
    """
    Record what is emitted to stderr.

    >>> import sys
    >>> with RecordStderr() as record:
    ...     print("This is a test!", file=sys.stderr)
    >>> print({record().readline()})
    {'This is a test!\\n'}
    >>> record().close()
    """

    def __init__(self) -> None:
        super().__init__()
        self.destination = tempfile.SpooledTemporaryFile(mode='r+')
        self.recorder: Optional[contextlib.redirect_stdout[Any]] = None

    def __enter__(self) -> Callable[[], tempfile.SpooledTemporaryFile]:
        self.recorder = contextlib.redirect_stderr(self.destination)  # type: ignore
        assert self.recorder is not None
        self.recorder.__enter__()
        return lambda: self.destination

    def __exit__(self, *args) -> Literal[False]:
        assert self.recorder is not None
        self.recorder.__exit__(*args)
        self.destination.seek(0)
        return False


class RecordMultipleStreams(contextlib.AbstractContextManager):
    """
    Record the output to more than one stream.
    """

    def __init__(self, *files) -> None:
        super().__init__()
        self.files = [*files]
        self.destination = tempfile.SpooledTemporaryFile(mode='r+')
        self.saved_writes: List[Callable[..., Any]] = []

    def __enter__(self) -> Callable[[], tempfile.SpooledTemporaryFile]:
        for f in self.files:
            self.saved_writes.append(f.write)
            f.write = self.destination.write
        return lambda: self.destination

    def __exit__(self, *args) -> Literal[False]:
        for f in self.files:
            f.write = self.saved_writes.pop()
        self.destination.seek(0)
        return False


if __name__ == '__main__':
    import doctest

    doctest.testmod()