#!/usr/bin/env python3
"""
Module to act as a Prometheus Exporter for Docker containers with a
healthcheck configured
"""

import argparse
import os
import os.path
import sys
from http.server import HTTPServer
from typing import Any

import docker  # type: ignore[import]
import numpy
from prometheus_client import CollectorRegistry  # type: ignore[import]
from prometheus_client import Gauge, MetricsHandler, generate_latest

LISTEN_PORT = int(os.environ.get("DOCKSTAT_LISTEN_PORT", 8080))
HEALTHY_STR = "healthy"


class HTTPHandler(MetricsHandler):  # type: ignore[misc]
    """
    Class to encompass the requirements of a Prometheus Exporter
        for Docker containers with a healthcheck configured
    """

    def __init__(self, *args: Any, **kwargs: Any):
        self.docker_api: docker.APIClient = docker.APIClient()
        self.docker_client = docker.from_env()
        super().__init__(*args, **kwargs)

    # Override built-in method
    def do_GET(self) -> None:
        """
        Handle GET requests
        """
        if self.path == "/metrics":
            try:
                self._metrics()
            except docker.errors.NotFound:
                pass

        if self.path == "/healthcheck":
            if not healthy():
                print("ERROR: Check requirements")
                self._respond(500, "ERR")

            self._respond(200, "OK")

    def _respond(self, status: int, message: str) -> None:
        """
        Output a simple HTTP status and string to the client

        e.g. 200 OK

        Args:
            status (int): HTTP status to output
            message (str): String to output
        """
        self.send_response(int(status) or 500)
        self.end_headers()
        try:
            self.wfile.write(bytes(str(message).encode()))
        except BrokenPipeError:
            pass

    def _metrics(self) -> None:
        """
        Handle the request for metrics
        """
        if not healthy:
            print("ERROR: Check requirements")
            self._respond(500, "Server not configured correctly")
            return

        registry = CollectorRegistry()

        health_gauge = Gauge(
            "container_inspect_state_health_status",
            "Container's healthcheck value (binary)",
            labelnames=["id", "name", "value"],
            registry=registry,
        )
        status_gauge = Gauge(
            "container_inspect_state_running",
            "Container's running state (binary)",
            labelnames=["id", "name"],
            registry=registry,
        )
        started_at_gauge = Gauge(
            "container_inspect_state_started_at",
            "Container's start time (int)",
            labelnames=["id", "name"],
            registry=registry,
        )
        exit_code_gauge = Gauge(
            "container_inspect_state_exit_code",
            "Container's exit code (int)",
            labelnames=["id", "name"],
            registry=registry,
        )
        alert_threshold_gauge = Gauge(
            "container_inspect_downtime_alert_threshold",
            "Container's downtime alert threshold in seconds (int)",
            labelnames=["id", "name"],
            registry=registry,
        )

        for container in self.docker_client.containers.list(all=True):
            try:
                data = self.docker_api.inspect_container(container.id)
            except docker.errors.NotFound:
                print(f"WARNING: Container {container.id} does not exist. Skipping.")
                continue

            running = bool(data["State"]["Running"])
            started_at = data["State"]["StartedAt"]
            exit_code = int(data["State"]["ExitCode"])
            alert_threshold = int(
                data["Config"]["Labels"].get("io.prometheus.alert.downtime", 3600)
            )
            starttime: numpy.longlong = numpy.datetime64(started_at, "s").astype("long")

            status_gauge.labels(
                container.id,
                container.name,
            ).set(int(running))
            started_at_gauge.labels(
                container.id,
                container.name,
            ).set(starttime)
            exit_code_gauge.labels(
                container.id,
                container.name,
            ).set(int(exit_code))
            alert_threshold_gauge.labels(
                container.id,
                container.name,
            ).set(alert_threshold)

            try:
                health_str = data["State"]["Health"]["Status"]
                health_gauge.labels(
                    container.id,
                    container.name,
                    health_str,
                ).set(int(health_str == HEALTHY_STR))
            except KeyError:
                pass

        self._respond(200, generate_latest(registry).decode())


def healthy() -> bool:
    """
    Simple funtion to return if all the requirements are met

    Returns:
        bool: True if healthy or False if unhealthy
    """
    return all(
        [
            os.path.exists("/var/run/docker.sock"),
        ]
    )


if __name__ == "__main__":

    def cli_parse() -> argparse.Namespace:
        """
        Parse the CLI

        Returns:
            argparse.Namespace: Arguments from the CLI
        """
        parser = argparse.ArgumentParser()

        parser.add_argument(
            "-H",
            "--healthcheck",
            action="store_true",
            help="Simply exit with 0 for healthy or 1 when unhealthy",
        )

        return parser.parse_args()

    def main() -> int:
        """
        main()
        """
        args: argparse.Namespace = cli_parse()

        if args.healthcheck:
            # Invert the sense of 'healthy' for Unix CLI usage
            return not healthy()

        print(f"Starting web server on port {LISTEN_PORT}")
        try:
            HTTPServer(("", LISTEN_PORT), HTTPHandler).serve_forever()
        except KeyboardInterrupt:
            print("Exiting")

        return 0

    sys.exit(main())