# Copyright 2023 Amazon.com, Inc. or its affiliates. All Rights Reserved.
# SPDX-License-Identifier: Apache-2.0

"""Fixture to send metrics to AWS CloudWatch

We use the aws-embedded-metrics library although it has some sharp corners,
namely:

1. It uses asyncio, which complicates the flushing a bit.

2. It has an stateful API. Setting dimensions will override previous ones.

Example:

    set_dimensions("instance")
    put_metric("duration", 1)
    set_dimensions("cpu")
    put_metric("duration", 1)

This will end with 2 identical metrics with dimension "cpu" (the last one). The
correct way of doing it is:

    set_dimensions("instance")
    put_metric("duration", 1)
    flush()
    set_dimensions("cpu")
    put_metric("duration", 1)

This is not very intuitive, but we assume all metrics within a test will have
the same dimensions.

# Debugging

You can override the destination of the metrics to stdout with:

    AWS_EMF_NAMESPACE=$USER-test
    AWS_EMF_ENVIRONMENT=local ./tools/devtest test

# References:

- https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Embedded_Metric_Format_Specification.html
- https://github.com/awslabs/aws-embedded-metrics-python
"""

import asyncio
import os

from aws_embedded_metrics.logger.metrics_logger_factory import create_metrics_logger


class MetricsWrapperDummy:
    """Send metrics to /dev/null"""

    def set_dimensions(self, *args, **kwargs):
        """Set dimensions"""

    def put_metric(self, *args, **kwargs):
        """Put a datapoint with given dimensions"""

    def set_property(self, *args, **kwargs):
        """Set a property"""

    def flush(self):
        """Flush any remaining metrics"""


class MetricsWrapper:
    """A convenient metrics logger"""

    def __init__(self, logger):
        self.logger = logger

    def __getattr__(self, attr):
        """Dispatch methods to logger instance"""
        if attr not in self.__dict__:
            return getattr(self.logger, attr)
        return getattr(self, attr)

    def flush(self):
        """Flush any remaining metrics"""
        asyncio.run(self.logger.flush())


def get_metrics_logger():
    """Get a new metrics logger object"""
    # if no metrics namespace, don't output metrics
    if "AWS_EMF_NAMESPACE" not in os.environ:
        return MetricsWrapperDummy()
    logger = create_metrics_logger()
    logger.reset_dimensions(False)
    return MetricsWrapper(logger)