"""
StatsD connector.

Statsd and Graphite allows to graph data based on a specific key. This feature
is handy when you need to keep track of performance, number of times an
endpoint is fetched and more.

For local environments (unless the STATSD_CLIENT, STATSDPORT, and STATSD_PREFIX
is specified), no metrics are sent to our report server (this is meant so none
of our production metrics are polluted.)

Please: do not enable this on `api-dev`.
"""
import time

import statsd

from analytics import config


connection = None

if config.STATSD_CLIENT and config.STATSD_PORT and config.STATSD_PREFIX:
    connection = statsd.StatsClient(
        host=config.STATSD_CLIENT,
        port=config.STATSD_PORT,
        prefix=config.STATSD_PREFIX)


def metric(metric_key, count=1):
    """Define a decorator for metrics.

    Args:
        key (str): the metric key name.
        count (int): the count to add.
    Returns:
        callable: The decorator.

    """
    def decorator(fn):
        def wrapper(*args, **kwargs):
            response = fn(*args, **kwargs)
            send_metric(key(metric_key).format(key=key), count=count)
            return response
        return wrapper
    return decorator


def timing(metric_key):
    """Time an execution.

    Performance profiling is important: it allows to know how much time is
    spent on specific endpoints or methods.

    Args:
        metric_key: the metric key name.
    Returns:
        callable: the decorator

    """
    def decorator(fn):
        def wrapper(*args, **kwargs):
            start_time = time.time() * 1000
            response = fn(*args, **kwargs)
            end_time = time.time() * 1000
            send_timer(
                key(metric_key),
                delta=end_time - start_time)
            return response
        return wrapper
    return decorator


def key(metric_key):
    """Create a namespaced key for grass.

    Args:
        metric_key (str): the metric key.
    Returns:
        str: the key.

    """
    return 'ows.analytics.{metric_key}'.format(metric_key=metric_key)


def send_metric(key, count=1):
    """Sent metric to graphite.

    Calling this method, the metric is immediately sent to graphite.

    Args:
        key (str): the metric key name.
        count (int): the number to add to the metric.

    """
    if not connection:
        return

    assert key.startswith('ows.analytics.')
    connection.incr(key, count=count)


def send_timer(key, delta):
    """Send a timer to statsd.

    Add information on how long a process took.

    Args:
        key (str): the metric key name.
        delta (int): the time difference (in ms)

    """
    if not connection:
        return

    assert key.startswith('ows.analytics.')
    connection.timing(key, delta=delta)