# (C) Datadog, Inc. 2018-present
# All rights reserved
# Licensed under Simplified BSD License (see LICENSE)
from __future__ import division

import bmemcached
import pkg_resources
from six import iteritems, itervalues

from datadog_checks.base import AgentCheck, ConfigurationError


class BadResponseError(ConfigurationError):
    pass


class InvalidConfigError(ConfigurationError):
    pass


class Memcache(AgentCheck):

    SOURCE_TYPE_NAME = 'memcached'

    DEFAULT_PORT = 11211

    GAUGES = [
        "total_items",
        "curr_items",
        "limit_maxbytes",
        "uptime",
        "bytes",
        "curr_connections",
        "connection_structures",
        "threads",
        "pointer_size",
    ]

    RATES = [
        "rusage_user",
        "rusage_system",
        "cmd_get",
        "cmd_set",
        "cmd_flush",
        "get_hits",
        "get_misses",
        "delete_misses",
        "delete_hits",
        "evictions",
        "bytes_read",
        "bytes_written",
        "cas_misses",
        "cas_hits",
        "cas_badval",
        "total_connections",
        "listen_disabled_num",
    ]

    ITEMS_RATES = [
        "evicted",
        "evicted_nonzero",
        "expired_unfetched",
        "evicted_unfetched",
        "outofmemory",
        "tailrepairs",
        "moves_to_cold",
        "moves_to_warm",
        "moves_within_lru",
        "reclaimed",
        "crawler_reclaimed",
        "lrutail_reflocked",
        "direct_reclaims",
    ]

    ITEMS_GAUGES = ["number", "number_hot", "number_warm", "number_cold", "number_noexp", "age", "evicted_time"]

    SLABS_RATES = [
        "get_hits",
        "cmd_set",
        "delete_hits",
        "incr_hits",
        "decr_hits",
        "cas_hits",
        "cas_badval",
        "touch_hits",
        "used_chunks",
    ]

    SLABS_GAUGES = [
        "chunk_size",
        "chunks_per_page",
        "total_pages",
        "total_chunks",
        "used_chunks",
        "free_chunks",
        "free_chunks_end",
        "mem_requested",
        "active_slabs",
        "total_malloced",
    ]

    # format - "key": (rates, gauges, handler)
    OPTIONAL_STATS = {"items": [ITEMS_RATES, ITEMS_GAUGES, None], "slabs": [SLABS_RATES, SLABS_GAUGES, None]}

    SERVICE_CHECK = 'memcache.can_connect'

    @classmethod
    def get_library_versions(cls):
        return {"memcache": pkg_resources.get_distribution("python-binary-memcached").version}

    def _process_response(self, response):
        """
        Examine the response and raise an error is something is off
        """
        if len(response) != 1:
            raise BadResponseError("Malformed response: {}".format(response))

        stats = list(itervalues(response))[0]
        if not len(stats):
            raise BadResponseError("Malformed response for host: {}".format(stats))

        if 'version' in stats:
            self.set_metadata('version', stats['version'].decode('utf-8'))
        else:
            self.log.debug('Cannot determine Memcached version')
        return stats

    def _get_metrics(self, client, tags, service_check_tags=None):
        try:
            stats = self._process_response(client.stats())
            for metric in stats:
                # Check if metric is a gauge or rate
                if metric in self.GAUGES:
                    our_metric = self.normalize(metric.lower(), 'memcache')
                    self.gauge(our_metric, float(stats[metric]), tags=tags)

                # Tweak the name if it's a rate so that we don't use the exact
                # same metric name as the memcache documentation
                if metric in self.RATES:
                    our_metric = self.normalize("{0}_rate".format(metric.lower()), 'memcache')
                    self.rate(our_metric, float(stats[metric]), tags=tags)

            # calculate some metrics based on other metrics.
            # stats should be present, but wrap in try/except
            # and log an exception just in case.
            try:
                self.gauge(
                    "memcache.get_hit_percent", 100.0 * float(stats["get_hits"]) / float(stats["cmd_get"]), tags=tags
                )
            except ZeroDivisionError:
                pass

            try:
                self.gauge(
                    "memcache.fill_percent", 100.0 * float(stats["bytes"]) / float(stats["limit_maxbytes"]), tags=tags
                )
            except ZeroDivisionError:
                pass

            try:
                self.gauge("memcache.avg_item_size", float(stats["bytes"]) / float(stats["curr_items"]), tags=tags)
            except ZeroDivisionError:
                pass

            uptime = stats.get("uptime", 0)
            self.service_check(
                self.SERVICE_CHECK,
                AgentCheck.OK,
                tags=service_check_tags,
                message="Server has been up for %s seconds" % uptime,
            )
        except BadResponseError:
            raise

    def _get_optional_metrics(self, client, tags, options=None):
        for arg, metrics_args in iteritems(self.OPTIONAL_STATS):
            if not options or options.get(arg, False):
                try:
                    optional_rates = metrics_args[0]
                    optional_gauges = metrics_args[1]
                    optional_fn = metrics_args[2]

                    stats = self._process_response(client.stats(arg))
                    prefix = "memcache.{}".format(arg)

                    for metric, val in iteritems(stats):
                        # Check if metric is a gauge or rate
                        metric_tags = []
                        if optional_fn:
                            metric, metric_tags, val = optional_fn(metric, val)

                        if optional_gauges and metric in optional_gauges:
                            our_metric = self.normalize(metric.lower(), prefix)
                            self.gauge(our_metric, float(val), tags=tags + metric_tags)

                        if optional_rates and metric in optional_rates:
                            our_metric = self.normalize("{0}_rate".format(metric.lower()), prefix)
                            self.rate(our_metric, float(val), tags=tags + metric_tags)
                except BadResponseError:
                    self.log.warning(
                        "Unable to retrieve optional stats from memcache instance, "
                        "running 'stats %s' they could be empty or bad configuration.",
                        arg,
                    )
                except Exception as e:
                    self.log.exception("Unable to retrieve optional stats from memcache instance: %s", e)

    @staticmethod
    def get_items_stats(key, value):
        """
        Optional metric handler for 'items' stats

        key: "items:<slab_id>:<metric_name>" format
        value: return untouched

        Like all optional metric handlers returns metric, tags, value
        """
        itemized_key = key.split(':')
        slab_id = itemized_key[1]
        metric = itemized_key[2]

        tags = ["slab:{}".format(slab_id)]

        return metric, tags, value

    @staticmethod
    def get_slabs_stats(key, value):
        """
        Optional metric handler for 'items' stats

        key: "items:<slab_id>:<metric_name>" format
        value: return untouched

        Like all optional metric handlers returns metric, tags, value
        """
        slabbed_key = key.split(':')
        tags = []
        if len(slabbed_key) == 2:
            slab_id = slabbed_key[0]
            metric = slabbed_key[1]
            tags = ["slab:{}".format(slab_id)]
        else:
            metric = slabbed_key[0]

        return metric, tags, value

    def check(self, instance):
        socket = instance.get('socket')
        server = instance.get('url')
        options = instance.get('options', {})
        username = instance.get('username')
        password = instance.get('password')

        if not server and not socket:
            raise InvalidConfigError('Either "url" or "socket" must be configured')

        if socket:
            server = 'unix'
            port = socket
            connection_server = "{}".format(port)
        else:
            port = int(instance.get('port', self.DEFAULT_PORT))
            connection_server = "{}:{}".format(server, port)
        custom_tags = instance.get('tags') or []

        tags = ["url:{0}:{1}".format(server, port)] + custom_tags
        service_check_tags = ["host:%s" % server, "port:%s" % port] + custom_tags

        try:
            self.log.debug("Connecting to %s, tags:%s", connection_server, tags)
            client = bmemcached.Client(connection_server, username, password)

            self._get_metrics(client, tags, service_check_tags)
            if options:
                # setting specific handlers
                self.OPTIONAL_STATS["items"][2] = Memcache.get_items_stats
                self.OPTIONAL_STATS["slabs"][2] = Memcache.get_slabs_stats
                self._get_optional_metrics(client, tags, options)
        except BadResponseError as e:
            self.service_check(
                self.SERVICE_CHECK,
                AgentCheck.CRITICAL,
                tags=service_check_tags,
                message="Unable to fetch stats from server",
            )
            raise ConfigurationError(
                "Unable to retrieve stats from memcache instance: {}:{}."
                "Please check your configuration. ({})".format(server, port, e)
            )
        else:
            client.disconnect_all()
            self.log.debug("Disconnected from memcached")

        del client
