# Copyright 2020 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Exports fields as Prometheus gauges and enums."""

import enum
import time

import pint
import prometheus_client

from . import defs

_UNITS = {
    '%': 'percent',
    '°C': 'celcius',
    '0.01 kWh': 'DWh',
}


class Filter:
    def __init__(self):
        self._acc = None
        self._tau = 0.05

    def step(self, v: float) -> float:
        if self._acc is None:
            self._acc = v

        self._acc = self._acc * (1 - self._tau) + v * self._tau
        return self._acc


def _is_enum(v: object) -> bool:
    try:
        return issubclass(v, enum.Enum)
    except TypeError:
        return False


class Exporter:
    def __init__(self):
        self._metrics = None
        self._filters = {}

    def _config(self, fields):
        metrics = {}
        labels = ['serial_number', 'product_id']

        for f in defs.FIELDS:
            label = f.label.replace('#', '')
            name = 'victron_%s' % label.lower()
            kind = f.kind()
            if isinstance(kind, pint.Quantity):
                unit = str(kind.units)
            else:
                unit = _UNITS.get(f.unit, f.unit)

            if unit == 'hour * watt':
                unit = 'wh'

            if kind == str:
                metrics[f.label] = prometheus_client.Info(name,
                                                          f.description,
                                                          labelnames=labels)
            elif _is_enum(kind):
                states = [x.name.lower() for x in kind]
                metrics[f.label] = prometheus_client.Enum(
                    name,
                    f.description,
                    labelnames=['serial_number', 'product_id'],
                    states=states)
                metrics[f.label + '_value'] = prometheus_client.Gauge(
                    name + '_value',
                    f.description,
                    labelnames=['serial_number', 'product_id'])
            else:
                metrics[f.label] = prometheus_client.Gauge(
                    name,
                    f.description,
                    labelnames=['serial_number', 'product_id'],
                    unit=unit)

        updated = prometheus_client.Gauge(
            'victron_updated',
            'Last time a block was received from the device',
            labelnames=labels)
        blocks = prometheus_client.Counter(
            'victron_blocks',
            'Number of blocks received from the device',
            labelnames=labels)

        return metrics, updated, blocks

    def export(self, fields):
        if self._metrics is None:
            self._metrics, self._updated, self._blocks = self._config(fields)

        ser = fields[defs.SER.label]
        pid = fields[defs.PID.label]
        self._updated.labels(ser, pid).set(time.time())
        self._blocks.labels(ser, pid).inc()

        for label, value in fields.items():
            gauge = self._metrics[label]
            if isinstance(value, pint.Quantity):
                f = self._filters.setdefault(label, Filter())
                m = f.step(value.m)
                gauge.labels(ser, pid).set(round(m, 3))
            elif isinstance(gauge, prometheus_client.Info):
                gauge.labels(ser,
                             pid).info({label.lower().replace('#', ''): value})
            elif isinstance(gauge, prometheus_client.Enum):
                gauge.labels(ser, pid).state(value.name.lower())
                self._metrics[label + '_value'].labels(ser,
                                                       pid).set(value.value)
            elif isinstance(value, int):
                gauge.labels(ser, pid).set(value)
            else:
                print(repr(value))