#!/usr/bin/env python3

"""A check plugin for Nagios/Icinga/etc. that queries Home Assistant for the current state of entities."""

import argparse
import dataclasses
import logging
import re
import sys
from urllib.parse import urljoin
from typing import Optional
from pathlib import Path

import requests
import nagiosplugin

_log = logging.getLogger("nagiosplugin")


class ScalarOrUnknownContext(nagiosplugin.ScalarContext):
    """
    Same as a :class:`nagiosplugin.ScalarContext`, but returns UNKNOWN when the
    value is not an int or float
    """

    def evaluate(self, metric: nagiosplugin.Metric, resource: nagiosplugin.Resource):
        if isinstance(metric.value, (int, float)):
            return super().evaluate(metric, resource)
        else:
            return self.result_cls(
                nagiosplugin.state.Unknown, "non-scalar value", metric
            )

    def performance(self, metric: nagiosplugin.Metric, resource: nagiosplugin.Resource):
        if isinstance(metric.value, (int, float)):
            return super().performance(metric, resource)
        else:
            return nagiosplugin.Performance(
                metric.name,
                "U",
                metric.uom,
                self.warning,
                self.critical,
                metric.min,
                metric.max,
            )


@dataclasses.dataclass
class AttributeFilter:
    attribute: str
    value: str
    negated: bool

    @classmethod
    def from_str(cls, arg: str):
        k, _, v = arg.partition("=")
        if k.endswith("!"):
            return cls(k.removesuffix("!"), v, True)
        else:
            return cls(k, v, False)

    def check(self, attributes: dict[str, str]) -> bool:
        return self.negated ^ (attributes.get(self.attribute) == self.value)


@dataclasses.dataclass
class Entities(nagiosplugin.Resource):
    url: str
    token: str
    device_class: str
    numeric: bool
    filters: list[AttributeFilter]
    attribute: Optional[str]
    friendly_name: bool
    ignore_missing: bool
    include: list[str]
    exclude: list[str]
    min: Optional[float] = None
    max: Optional[float] = None

    def hass_get(self, endpoint: str) -> requests.Response:
        headers = {
            "Authorization": "Bearer " + self.token,
            "Content-Type": "application/json",
        }

        r = requests.get(urljoin(self.url, endpoint), headers=headers)
        if not r.ok:
            raise Exception("Failed to query Home Assistant API: " + r.text)

        return r.json()

    def check_api(self):
        message = self.hass_get("/api/").get("message")
        if message != "API running.":
            print("ERROR: " + message)
            sys.exit(1)
        else:
            print("OK: " + message)

    def _state_to_metric(self, state):
        """Convert a state into a metric"""
        if self.attribute is not None:
            if self.ignore_missing and self.attribute not in state["attributes"]:
                return
            else:
                value = state["attributes"].get(self.attribute, "missing attribute")
            uom = None
        else:
            if self.numeric:
                try:
                    value = float(state["state"])
                except ValueError:
                    value = state["state"]
            else:
                value = state["state"]
            uom = state["attributes"].get("unit_of_measurement")

        if self.friendly_name:
            name = (
                state["attributes"]
                .get("friendly_name", state["entity_id"])
                .translate({ord(c): "_" for c in "'="})
            )
        else:
            name = state["entity_id"]

        yield nagiosplugin.Metric(
            name,
            value,
            uom,
            context=self.device_class,
            min=self.min,
            max=self.max,
        )

    def probe(self):
        response = self.hass_get("/api/states")
        for state in response:
            if (
                state["attributes"].get("device_class") == self.device_class
                and all(filter.check(state["attributes"]) for filter in self.filters)
                and (len(self.include) == 0 or state["entity_id"] in self.include)
                and state["entity_id"] not in self.exclude
            ):
                yield from self._state_to_metric(state)


class RegexContext(nagiosplugin.Context):
    def __init__(
        self,
        name: str,
        ok: str = None,
        warning: str = None,
        critical: str = None,
        fmt_metric=None,
        result_cls=nagiosplugin.Result,
    ):
        super().__init__(name, fmt_metric=fmt_metric, result_cls=result_cls)
        # '.^' should match nothing
        self.ok = re.compile(ok or ".^")
        self.warning = re.compile(warning or ".^")
        self.critical = re.compile(critical or ".^")

    def fmt_reason(self, regex: re.Pattern, metric: nagiosplugin.Metric) -> str:
        return f"{metric.name} matched regex '{regex.pattern}' ({metric.value})"

    def evaluate(self, metric: nagiosplugin.Metric, resource):
        if self.critical.match(metric.value):
            return self.result_cls(
                nagiosplugin.Critical, self.fmt_reason(self.critical, metric), metric
            )
        elif self.warning.match(metric.value):
            return self.result_cls(
                nagiosplugin.Warn, self.fmt_reason(self.warning, metric), metric
            )
        elif self.ok.match(metric.value):
            return self.result_cls(
                nagiosplugin.Ok, self.fmt_reason(self.ok, metric), metric
            )
        else:
            return self.result_cls(
                nagiosplugin.Unknown,
                f"{metric.name} did not match any defined patterns ({metric.value})",
                metric,
            )


class Icinga2ConfAction(argparse.Action):
    def __init__(
        self,
        option_strings,
        dest=argparse.SUPPRESS,
        default=argparse.SUPPRESS,
        help="Generate conf file for icinga2 CheckCommand",
    ):
        super().__init__(
            option_strings=option_strings,
            dest=dest,
            default=default,
            nargs=0,
            help=help,
        )

    def _format_actions(
        self,
        param_prefix: str,
        parser: argparse.ArgumentParser,
        order: Optional[int] = None,
    ):
        for action in parser._actions:
            if action.dest in [self.dest, "help", "version"] or isinstance(
                action, argparse._SubParsersAction
            ):
                continue

            arg_str = action.option_strings[-1]
            icinga2_var = arg_str.lstrip("-").replace("-", "_")
            print(f'    "{arg_str}" = {{')

            if action.required:
                print("      required = true")

            if isinstance(
                action,
                (
                    argparse._StoreConstAction,
                    argparse._CountAction,
                    argparse._AppendConstAction,
                ),
            ):
                print(f'      set_if = "${param_prefix}_{icinga2_var}$"')
            else:
                print(f'      value = "${param_prefix}_{icinga2_var}$"')

            print(f'      description = "{action.help}"')

            if order is not None:
                print(f"      order = {order}")

            print("    }")

    def __call__(
        self, parser: argparse.ArgumentParser, namespace, values, option_string=None
    ):
        filename = Path(__file__).absolute()
        command_name = filename.stem.removeprefix("check_")
        # FIXME: assumes that script will be in a subdirectory of PluginContribDir
        command_path = filename.relative_to(filename.parents[1])

        if parser._subparsers:
            # TODO: this seems a bit more hacky than it needs to be
            choices = parser._subparsers._group_actions[0].choices
            for subname, subparser in choices.items():
                print(f'object CheckCommand "{command_name}_{subname}" {{')
                print(f'  command = [ PluginContribDir + "/{command_path}" ]')

                print("  arguments = {")

                self._format_actions(command_name, parser, order=-2)
                print(f'    "{subname}" = {{')
                print("      set_if = true")
                print("      order = -1")
                print("    }")
                self._format_actions(f"{command_name}_{subname}", subparser)

                print("  }\n}")
        else:
            print(f'object CheckCommand "{command_name}" {{')
            print(f'  command = [ PluginContribDir + "/{command_path}" ]')

            print("  arguments = {")

            self._format_actions(command_name, parser)

            print("  }\n}")

        parser.exit()


@nagiosplugin.guarded
def main():
    argp = argparse.ArgumentParser(description=__doc__)

    argp.add_argument("--version", action="version", version="0.2.0")
    argp.add_argument("-v", "--verbose", action="count", default=0)
    argp.add_argument("--make-icinga-conf", action=Icinga2ConfAction)

    argp.add_argument(
        "-t",
        "--token",
        required=True,
        type=str,
        help="token for Home Assistant REST API (see https://developers.home-assistant.io/docs/api/rest/)",
    )
    argp.add_argument(
        "-u", "--url", required=True, type=str, help="URL for Home Assistant"
    )

    shared_parser = argparse.ArgumentParser(add_help=False)
    common_args = shared_parser.add_argument_group(
        "Common Arguments", "Arguments shared between metric types"
    )
    common_args.add_argument(
        "-d",
        "--device-class",
        type=str,
        required=True,
        help="device class of entities to monitor",
    )
    common_args.add_argument(
        "-a", "--attribute", type=str, help="check attribute instead of value"
    )
    common_args.add_argument(
        "-f",
        "--filter",
        type=AttributeFilter.from_str,
        default=[],
        nargs="*",
        help="filter by 'attribute=value' (may be specified multiple times). Use != to negate the match",
    )
    common_args.add_argument(
        "-i",
        "--include",
        default=[],
        nargs="*",
        help="explicitly include entities by id. Other entities will not be considered if this is specified. Listed entities must also match the specified device class",
    )
    common_args.add_argument(
        "-e",
        "--exclude",
        default=[],
        nargs="*",
        help="exclude entities by id",
    )
    common_args.add_argument(
        "--friendly",
        action="store_true",
        help="use friendly name, when available",
    )
    common_args.add_argument(
        "--ignore-missing", action="store_true", help="Ignore missing attributes"
    )

    subparsers = argp.add_subparsers(
        title="Query type", required=True, dest="subparser_name"
    )

    scalar_parser = subparsers.add_parser(
        "scalar", help="Numeric metrics", parents=[shared_parser]
    )
    scalar_parser.add_argument(
        "-w",
        "--warning",
        metavar="RANGE",
        required=True,
        help="return warning if value is outside %(metavar)s",
    )
    scalar_parser.add_argument(
        "-c",
        "--critical",
        metavar="RANGE",
        required=True,
        help="return critical if value is outside %(metavar)s",
    )
    scalar_parser.add_argument(
        "--min",
        type=float,
        help="min for performance data",
    )
    scalar_parser.add_argument(
        "--max",
        type=float,
        help="max for performance data",
    )

    text_parser = subparsers.add_parser(
        "text", help="Textual metrics", parents=[shared_parser]
    )
    text_parser.add_argument(
        "-o",
        "--ok",
        metavar="REGEX",
        help="return ok if value matches %(metavar)s",
    )
    text_parser.add_argument(
        "-w",
        "--warning",
        metavar="REGEX",
        help="return warning if value matches %(metavar)s",
    )
    text_parser.add_argument(
        "-c",
        "--critical",
        metavar="REGEX",
        help="return critical if value matches %(metavar)s",
    )

    args = argp.parse_args()
    parsed_common_args = {
        "device_class": args.device_class,
        "attribute": args.attribute,
        "filters": args.filter,
        "include": args.include,
        "exclude": args.exclude,
        "friendly_name": args.friendly,
        "ignore_missing": args.ignore_missing,
    }
    if args.subparser_name == "scalar":
        check = nagiosplugin.Check(
            Entities(
                url=args.url,
                token=args.token,
                numeric=True,
                min=args.min,
                max=args.max,
                **parsed_common_args,
            ),
            ScalarOrUnknownContext(args.device_class, args.warning, args.critical),
        )
    elif args.subparser_name == "text":
        check = nagiosplugin.Check(
            Entities(
                url=args.url,
                token=args.token,
                numeric=False,
                **parsed_common_args,
            ),
            RegexContext(args.device_class, args.ok, args.warning, args.critical),
        )

    check.main(args.verbose)


if __name__ == "__main__":
    main()