// Copyright 2015 The Prometheus Authors
// 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
//
// http://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.

//go:build !nosystemd
// +build !nosystemd

package collector

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"math"
	"regexp"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/alecthomas/kingpin/v2"
	"github.com/coreos/go-systemd/v22/dbus"
	"github.com/prometheus/client_golang/prometheus"
)

const (
	// minSystemdVersionSystemState is the minimum SystemD version for availability of
	// the 'SystemState' manager property and the timer property 'LastTriggerUSec'
	// https://github.com/prometheus/node_exporter/issues/291
	minSystemdVersionSystemState = 212
)

var (
	systemdUnitIncludeSet bool
	systemdUnitInclude    = kingpin.Flag("collector.systemd.unit-include", "Regexp of systemd units to include. Units must both match include and not match exclude to be included.").Default(".+").PreAction(func(c *kingpin.ParseContext) error {
		systemdUnitIncludeSet = true
		return nil
	}).String()
	oldSystemdUnitInclude = kingpin.Flag("collector.systemd.unit-whitelist", "DEPRECATED: Use --collector.systemd.unit-include").Hidden().String()
	systemdUnitExcludeSet bool
	systemdUnitExclude    = kingpin.Flag("collector.systemd.unit-exclude", "Regexp of systemd units to exclude. Units must both match include and not match exclude to be included.").Default(".+\\.(automount|device|mount|scope|slice)").PreAction(func(c *kingpin.ParseContext) error {
		systemdUnitExcludeSet = true
		return nil
	}).String()
	oldSystemdUnitExclude  = kingpin.Flag("collector.systemd.unit-blacklist", "DEPRECATED: Use collector.systemd.unit-exclude").Hidden().String()
	systemdPrivate         = kingpin.Flag("collector.systemd.private", "Establish a private, direct connection to systemd without dbus (Strongly discouraged since it requires root. For testing purposes only).").Hidden().Bool()
	enableTaskMetrics      = kingpin.Flag("collector.systemd.enable-task-metrics", "Enables service unit tasks metrics unit_tasks_current and unit_tasks_max").Bool()
	enableRestartsMetrics  = kingpin.Flag("collector.systemd.enable-restarts-metrics", "Enables service unit metric service_restart_total").Bool()
	enableStartTimeMetrics = kingpin.Flag("collector.systemd.enable-start-time-metrics", "Enables service unit metric unit_start_time_seconds").Bool()

	systemdVersionRE = regexp.MustCompile(`[0-9]{3,}(\.[0-9]+)?`)
)

type systemdCollector struct {
	unitDesc                      *prometheus.Desc
	unitStartTimeDesc             *prometheus.Desc
	unitTasksCurrentDesc          *prometheus.Desc
	unitTasksMaxDesc              *prometheus.Desc
	systemRunningDesc             *prometheus.Desc
	summaryDesc                   *prometheus.Desc
	nRestartsDesc                 *prometheus.Desc
	timerLastTriggerDesc          *prometheus.Desc
	socketAcceptedConnectionsDesc *prometheus.Desc
	socketCurrentConnectionsDesc  *prometheus.Desc
	socketRefusedConnectionsDesc  *prometheus.Desc
	systemdVersionDesc            *prometheus.Desc
	// Use regexps for more flexibility than device_filter.go allows
	systemdUnitIncludePattern *regexp.Regexp
	systemdUnitExcludePattern *regexp.Regexp
	logger                    *slog.Logger
}

var unitStatesName = []string{"active", "activating", "deactivating", "inactive", "failed"}

func init() {
	registerCollector("systemd", defaultDisabled, NewSystemdCollector)
}

// NewSystemdCollector returns a new Collector exposing systemd statistics.
func NewSystemdCollector(logger *slog.Logger) (Collector, error) {
	const subsystem = "systemd"

	unitDesc := prometheus.NewDesc(
		prometheus.BuildFQName(namespace, subsystem, "unit_state"),
		"Systemd unit", []string{"name", "state", "type"}, nil,
	)
	unitStartTimeDesc := prometheus.NewDesc(
		prometheus.BuildFQName(namespace, subsystem, "unit_start_time_seconds"),
		"Start time of the unit since unix epoch in seconds.", []string{"name"}, nil,
	)
	unitTasksCurrentDesc := prometheus.NewDesc(
		prometheus.BuildFQName(namespace, subsystem, "unit_tasks_current"),
		"Current number of tasks per Systemd unit", []string{"name"}, nil,
	)
	unitTasksMaxDesc := prometheus.NewDesc(
		prometheus.BuildFQName(namespace, subsystem, "unit_tasks_max"),
		"Maximum number of tasks per Systemd unit", []string{"name"}, nil,
	)
	systemRunningDesc := prometheus.NewDesc(
		prometheus.BuildFQName(namespace, subsystem, "system_running"),
		"Whether the system is operational (see 'systemctl is-system-running')",
		nil, nil,
	)
	summaryDesc := prometheus.NewDesc(
		prometheus.BuildFQName(namespace, subsystem, "units"),
		"Summary of systemd unit states", []string{"state"}, nil)
	nRestartsDesc := prometheus.NewDesc(
		prometheus.BuildFQName(namespace, subsystem, "service_restart_total"),
		"Service unit count of Restart triggers", []string{"name"}, nil)
	timerLastTriggerDesc := prometheus.NewDesc(
		prometheus.BuildFQName(namespace, subsystem, "timer_last_trigger_seconds"),
		"Seconds since epoch of last trigger.", []string{"name"}, nil)
	socketAcceptedConnectionsDesc := prometheus.NewDesc(
		prometheus.BuildFQName(namespace, subsystem, "socket_accepted_connections_total"),
		"Total number of accepted socket connections", []string{"name"}, nil)
	socketCurrentConnectionsDesc := prometheus.NewDesc(
		prometheus.BuildFQName(namespace, subsystem, "socket_current_connections"),
		"Current number of socket connections", []string{"name"}, nil)
	socketRefusedConnectionsDesc := prometheus.NewDesc(
		prometheus.BuildFQName(namespace, subsystem, "socket_refused_connections_total"),
		"Total number of refused socket connections", []string{"name"}, nil)
	systemdVersionDesc := prometheus.NewDesc(
		prometheus.BuildFQName(namespace, subsystem, "version"),
		"Detected systemd version", []string{"version"}, nil)

	if *oldSystemdUnitExclude != "" {
		if !systemdUnitExcludeSet {
			logger.Warn("--collector.systemd.unit-blacklist is DEPRECATED and will be removed in 2.0.0, use --collector.systemd.unit-exclude")
			*systemdUnitExclude = *oldSystemdUnitExclude
		} else {
			return nil, errors.New("--collector.systemd.unit-blacklist and --collector.systemd.unit-exclude are mutually exclusive")
		}
	}
	if *oldSystemdUnitInclude != "" {
		if !systemdUnitIncludeSet {
			logger.Warn("--collector.systemd.unit-whitelist is DEPRECATED and will be removed in 2.0.0, use --collector.systemd.unit-include")
			*systemdUnitInclude = *oldSystemdUnitInclude
		} else {
			return nil, errors.New("--collector.systemd.unit-whitelist and --collector.systemd.unit-include are mutually exclusive")
		}
	}
	logger.Info("Parsed flag --collector.systemd.unit-include", "flag", *systemdUnitInclude)
	systemdUnitIncludePattern := regexp.MustCompile(fmt.Sprintf("^(?:%s)$", *systemdUnitInclude))
	logger.Info("Parsed flag --collector.systemd.unit-exclude", "flag", *systemdUnitExclude)
	systemdUnitExcludePattern := regexp.MustCompile(fmt.Sprintf("^(?:%s)$", *systemdUnitExclude))

	return &systemdCollector{
		unitDesc:                      unitDesc,
		unitStartTimeDesc:             unitStartTimeDesc,
		unitTasksCurrentDesc:          unitTasksCurrentDesc,
		unitTasksMaxDesc:              unitTasksMaxDesc,
		systemRunningDesc:             systemRunningDesc,
		summaryDesc:                   summaryDesc,
		nRestartsDesc:                 nRestartsDesc,
		timerLastTriggerDesc:          timerLastTriggerDesc,
		socketAcceptedConnectionsDesc: socketAcceptedConnectionsDesc,
		socketCurrentConnectionsDesc:  socketCurrentConnectionsDesc,
		socketRefusedConnectionsDesc:  socketRefusedConnectionsDesc,
		systemdVersionDesc:            systemdVersionDesc,
		systemdUnitIncludePattern:     systemdUnitIncludePattern,
		systemdUnitExcludePattern:     systemdUnitExcludePattern,
		logger:                        logger,
	}, nil
}

// Update gathers metrics from systemd.  Dbus collection is done in parallel
// to reduce wait time for responses.
func (c *systemdCollector) Update(ch chan<- prometheus.Metric) error {
	begin := time.Now()
	conn, err := newSystemdDbusConn()
	if err != nil {
		return fmt.Errorf("couldn't get dbus connection: %w", err)
	}
	defer conn.Close()

	systemdVersion, systemdVersionFull := c.getSystemdVersion(conn)
	if systemdVersion < minSystemdVersionSystemState {
		c.logger.Debug("Detected systemd version is lower than minimum, some systemd state and timer metrics will not be available", "current", systemdVersion, "minimum", minSystemdVersionSystemState)
	}
	ch <- prometheus.MustNewConstMetric(
		c.systemdVersionDesc,
		prometheus.GaugeValue,
		systemdVersion,
		systemdVersionFull,
	)

	allUnits, err := c.getAllUnits(conn)
	if err != nil {
		return fmt.Errorf("couldn't get units: %w", err)
	}
	c.logger.Debug("getAllUnits took", "duration_seconds", time.Since(begin).Seconds())

	begin = time.Now()
	summary := summarizeUnits(allUnits)
	c.collectSummaryMetrics(ch, summary)
	c.logger.Debug("collectSummaryMetrics took", "duration_seconds", time.Since(begin).Seconds())

	begin = time.Now()
	units := filterUnits(allUnits, c.systemdUnitIncludePattern, c.systemdUnitExcludePattern, c.logger)
	c.logger.Debug("filterUnits took", "duration_seconds", time.Since(begin).Seconds())

	var wg sync.WaitGroup
	defer wg.Wait()

	wg.Add(1)
	go func() {
		defer wg.Done()
		begin = time.Now()
		c.collectUnitStatusMetrics(conn, ch, units)
		c.logger.Debug("collectUnitStatusMetrics took", "duration_seconds", time.Since(begin).Seconds())
	}()

	if *enableStartTimeMetrics {
		wg.Add(1)
		go func() {
			defer wg.Done()
			begin = time.Now()
			c.collectUnitStartTimeMetrics(conn, ch, units)
			c.logger.Debug("collectUnitStartTimeMetrics took", "duration_seconds", time.Since(begin).Seconds())
		}()
	}

	if *enableTaskMetrics {
		wg.Add(1)
		go func() {
			defer wg.Done()
			begin = time.Now()
			c.collectUnitTasksMetrics(conn, ch, units)
			c.logger.Debug("collectUnitTasksMetrics took", "duration_seconds", time.Since(begin).Seconds())
		}()
	}

	if systemdVersion >= minSystemdVersionSystemState {
		wg.Add(1)
		go func() {
			defer wg.Done()
			begin = time.Now()
			c.collectTimers(conn, ch, units)
			c.logger.Debug("collectTimers took", "duration_seconds", time.Since(begin).Seconds())
		}()
	}

	wg.Add(1)
	go func() {
		defer wg.Done()
		begin = time.Now()
		c.collectSockets(conn, ch, units)
		c.logger.Debug("collectSockets took", "duration_seconds", time.Since(begin).Seconds())
	}()

	if systemdVersion >= minSystemdVersionSystemState {
		begin = time.Now()
		err = c.collectSystemState(conn, ch)
		c.logger.Debug("collectSystemState took", "duration_seconds", time.Since(begin).Seconds())
	}

	return err
}

func (c *systemdCollector) collectUnitStatusMetrics(conn *dbus.Conn, ch chan<- prometheus.Metric, units []unit) {
	for _, unit := range units {
		serviceType := ""
		if strings.HasSuffix(unit.Name, ".service") {
			serviceTypeProperty, err := conn.GetUnitTypePropertyContext(context.TODO(), unit.Name, "Service", "Type")
			if err != nil {
				c.logger.Debug("couldn't get unit type", "unit", unit.Name, "err", err)
			} else {
				serviceType = serviceTypeProperty.Value.Value().(string)
			}
		} else if strings.HasSuffix(unit.Name, ".mount") {
			serviceTypeProperty, err := conn.GetUnitTypePropertyContext(context.TODO(), unit.Name, "Mount", "Type")
			if err != nil {
				c.logger.Debug("couldn't get unit type", "unit", unit.Name, "err", err)
			} else {
				serviceType = serviceTypeProperty.Value.Value().(string)
			}
		}
		for _, stateName := range unitStatesName {
			isActive := 0.0
			if stateName == unit.ActiveState {
				isActive = 1.0
			}
			ch <- prometheus.MustNewConstMetric(
				c.unitDesc, prometheus.GaugeValue, isActive,
				unit.Name, stateName, serviceType)
		}
		if *enableRestartsMetrics && strings.HasSuffix(unit.Name, ".service") {
			// NRestarts wasn't added until systemd 235.
			restartsCount, err := conn.GetUnitTypePropertyContext(context.TODO(), unit.Name, "Service", "NRestarts")
			if err != nil {
				c.logger.Debug("couldn't get unit NRestarts", "unit", unit.Name, "err", err)
			} else {
				ch <- prometheus.MustNewConstMetric(
					c.nRestartsDesc, prometheus.CounterValue,
					float64(restartsCount.Value.Value().(uint32)), unit.Name)
			}
		}
	}
}

func (c *systemdCollector) collectSockets(conn *dbus.Conn, ch chan<- prometheus.Metric, units []unit) {
	for _, unit := range units {
		if !strings.HasSuffix(unit.Name, ".socket") {
			continue
		}

		acceptedConnectionCount, err := conn.GetUnitTypePropertyContext(context.TODO(), unit.Name, "Socket", "NAccepted")
		if err != nil {
			c.logger.Debug("couldn't get unit NAccepted", "unit", unit.Name, "err", err)
			continue
		}
		ch <- prometheus.MustNewConstMetric(
			c.socketAcceptedConnectionsDesc, prometheus.CounterValue,
			float64(acceptedConnectionCount.Value.Value().(uint32)), unit.Name)

		currentConnectionCount, err := conn.GetUnitTypePropertyContext(context.TODO(), unit.Name, "Socket", "NConnections")
		if err != nil {
			c.logger.Debug("couldn't get unit NConnections", "unit", unit.Name, "err", err)
			continue
		}
		ch <- prometheus.MustNewConstMetric(
			c.socketCurrentConnectionsDesc, prometheus.GaugeValue,
			float64(currentConnectionCount.Value.Value().(uint32)), unit.Name)

		// NRefused wasn't added until systemd 239.
		refusedConnectionCount, err := conn.GetUnitTypePropertyContext(context.TODO(), unit.Name, "Socket", "NRefused")
		if err == nil {
			ch <- prometheus.MustNewConstMetric(
				c.socketRefusedConnectionsDesc, prometheus.GaugeValue,
				float64(refusedConnectionCount.Value.Value().(uint32)), unit.Name)
		}
	}
}

func (c *systemdCollector) collectUnitStartTimeMetrics(conn *dbus.Conn, ch chan<- prometheus.Metric, units []unit) {
	var startTimeUsec uint64

	for _, unit := range units {
		if unit.ActiveState != "active" {
			startTimeUsec = 0
		} else {
			timestampValue, err := conn.GetUnitPropertyContext(context.TODO(), unit.Name, "ActiveEnterTimestamp")
			if err != nil {
				c.logger.Debug("couldn't get unit StartTimeUsec", "unit", unit.Name, "err", err)
				continue
			}
			startTimeUsec = timestampValue.Value.Value().(uint64)
		}

		ch <- prometheus.MustNewConstMetric(
			c.unitStartTimeDesc, prometheus.GaugeValue,
			float64(startTimeUsec)/1e6, unit.Name)
	}
}

func (c *systemdCollector) collectUnitTasksMetrics(conn *dbus.Conn, ch chan<- prometheus.Metric, units []unit) {
	var val uint64
	for _, unit := range units {
		if strings.HasSuffix(unit.Name, ".service") {
			tasksCurrentCount, err := conn.GetUnitTypePropertyContext(context.TODO(), unit.Name, "Service", "TasksCurrent")
			if err != nil {
				c.logger.Debug("couldn't get unit TasksCurrent", "unit", unit.Name, "err", err)
			} else {
				val = tasksCurrentCount.Value.Value().(uint64)
				// Don't set if tasksCurrent if dbus reports MaxUint64.
				if val != math.MaxUint64 {
					ch <- prometheus.MustNewConstMetric(
						c.unitTasksCurrentDesc, prometheus.GaugeValue,
						float64(val), unit.Name)
				}
			}
			tasksMaxCount, err := conn.GetUnitTypePropertyContext(context.TODO(), unit.Name, "Service", "TasksMax")
			if err != nil {
				c.logger.Debug("couldn't get unit TasksMax", "unit", unit.Name, "err", err)
			} else {
				val = tasksMaxCount.Value.Value().(uint64)
				// Don't set if tasksMax if dbus reports MaxUint64.
				if val != math.MaxUint64 {
					ch <- prometheus.MustNewConstMetric(
						c.unitTasksMaxDesc, prometheus.GaugeValue,
						float64(val), unit.Name)
				}
			}
		}
	}
}

func (c *systemdCollector) collectTimers(conn *dbus.Conn, ch chan<- prometheus.Metric, units []unit) {
	for _, unit := range units {
		if !strings.HasSuffix(unit.Name, ".timer") {
			continue
		}

		lastTriggerValue, err := conn.GetUnitTypePropertyContext(context.TODO(), unit.Name, "Timer", "LastTriggerUSec")
		if err != nil {
			c.logger.Debug("couldn't get unit LastTriggerUSec", "unit", unit.Name, "err", err)
			continue
		}

		ch <- prometheus.MustNewConstMetric(
			c.timerLastTriggerDesc, prometheus.GaugeValue,
			float64(lastTriggerValue.Value.Value().(uint64))/1e6, unit.Name)
	}
}

func (c *systemdCollector) collectSummaryMetrics(ch chan<- prometheus.Metric, summary map[string]float64) {
	for stateName, count := range summary {
		ch <- prometheus.MustNewConstMetric(
			c.summaryDesc, prometheus.GaugeValue, count, stateName)
	}
}

func (c *systemdCollector) collectSystemState(conn *dbus.Conn, ch chan<- prometheus.Metric) error {
	systemState, err := conn.GetManagerProperty("SystemState")
	if err != nil {
		return fmt.Errorf("couldn't get system state: %w", err)
	}
	isSystemRunning := 0.0
	if systemState == `"running"` {
		isSystemRunning = 1.0
	}
	ch <- prometheus.MustNewConstMetric(c.systemRunningDesc, prometheus.GaugeValue, isSystemRunning)
	return nil
}

func newSystemdDbusConn() (*dbus.Conn, error) {
	if *systemdPrivate {
		return dbus.NewSystemdConnectionContext(context.TODO())
	}
	return dbus.NewWithContext(context.TODO())
}

type unit struct {
	dbus.UnitStatus
}

func (c *systemdCollector) getAllUnits(conn *dbus.Conn) ([]unit, error) {
	allUnits, err := conn.ListUnitsContext(context.TODO())
	if err != nil {
		return nil, err
	}

	result := make([]unit, 0, len(allUnits))
	for _, status := range allUnits {
		unit := unit{
			UnitStatus: status,
		}
		result = append(result, unit)
	}

	return result, nil
}

func summarizeUnits(units []unit) map[string]float64 {
	summarized := make(map[string]float64)

	for _, unitStateName := range unitStatesName {
		summarized[unitStateName] = 0.0
	}

	for _, unit := range units {
		summarized[unit.ActiveState] += 1.0
	}

	return summarized
}

func filterUnits(units []unit, includePattern, excludePattern *regexp.Regexp, logger *slog.Logger) []unit {
	filtered := make([]unit, 0, len(units))
	for _, unit := range units {
		if includePattern.MatchString(unit.Name) && !excludePattern.MatchString(unit.Name) && unit.LoadState == "loaded" {
			logger.Debug("Adding unit", "unit", unit.Name)
			filtered = append(filtered, unit)
		} else {
			logger.Debug("Ignoring unit", "unit", unit.Name)
		}
	}

	return filtered
}

func (c *systemdCollector) getSystemdVersion(conn *dbus.Conn) (float64, string) {
	version, err := conn.GetManagerProperty("Version")
	if err != nil {
		c.logger.Debug("Unable to get systemd version property, defaulting to 0")
		return 0, ""
	}
	version = strings.TrimPrefix(strings.TrimSuffix(version, `"`), `"`)
	c.logger.Debug("Got systemd version", "version", version)
	parsedVersion := systemdVersionRE.FindString(version)
	v, err := strconv.ParseFloat(parsedVersion, 64)
	if err != nil {
		c.logger.Debug("Got invalid systemd version", "version", version)
		return 0, ""
	}
	return v, version
}