//go:build linux

package cgroups

import (
	"errors"
	"fmt"
	"io/fs"
	"path/filepath"
	"strings"
	"time"

	"github.com/containerd/cgroups/v3/cgroup2"
	"github.com/opencontainers/runtime-spec/specs-go"
	"github.com/prometheus/client_golang/prometheus"
	"gitlab.com/gitlab-org/gitaly/v16/internal/gitaly/config"
	cgroupscfg "gitlab.com/gitlab-org/gitaly/v16/internal/gitaly/config/cgroups"
	"gitlab.com/gitlab-org/gitaly/v16/internal/kernel"
	"gitlab.com/gitlab-org/gitaly/v16/internal/log"
)

type cgroupV2Handler struct {
	cfg    cgroupscfg.Config
	logger log.Logger

	*cgroupsMetrics
	pid             int
	cloneIntoCgroup bool
}

func newV2Handler(cfg cgroupscfg.Config, logger log.Logger, pid int) *cgroupV2Handler {
	cloneIntoCgroup, err := kernel.IsAtLeast(kernel.Version{Major: 5, Minor: 7})
	if err != nil {
		// Log the error for now as we're only rolling out functionality behind feature flag.
		logger.WithError(err).Error("failed detecting kernel version, CLONE_INTO_CGROUP support disabled")
	}

	return &cgroupV2Handler{
		cfg:             cfg,
		logger:          logger,
		pid:             pid,
		cgroupsMetrics:  newV2CgroupsMetrics(),
		cloneIntoCgroup: cloneIntoCgroup,
	}
}

func (cvh *cgroupV2Handler) setupParent(parentResources *specs.LinuxResources) error {
	if _, err := cgroup2.NewManager(cvh.cfg.Mountpoint, "/"+cvh.currentProcessCgroup(), cgroup2.ToResources(parentResources)); err != nil {
		return fmt.Errorf("failed creating parent cgroup: %w", err)
	}

	return nil
}

func (cvh *cgroupV2Handler) createCgroup(reposResources *specs.LinuxResources, cgroupPath string) error {
	_, err := cgroup2.NewManager(
		cvh.cfg.Mountpoint,
		"/"+cgroupPath,
		cgroup2.ToResources(reposResources),
	)

	return err
}

func (cvh *cgroupV2Handler) addToCgroup(pid int, cgroupPath string) error {
	control, err := cvh.loadCgroup(cgroupPath)
	if err != nil {
		return err
	}

	if err := control.AddProc(uint64(pid)); err != nil {
		// Command could finish so quickly before we can add it to a cgroup, so
		// we don't consider it an error.
		if strings.Contains(err.Error(), "no such process") {
			return nil
		}
		return fmt.Errorf("failed adding process to cgroup: %w", err)
	}

	return nil
}

func (cvh *cgroupV2Handler) loadCgroup(cgroupPath string) (*cgroup2.Manager, error) {
	control, err := cgroup2.Load("/"+cgroupPath, cgroup2.WithMountpoint(cvh.cfg.Mountpoint))
	if err != nil {
		return nil, fmt.Errorf("failed loading %s cgroup: %w", cgroupPath, err)
	}
	return control, nil
}

func (cvh *cgroupV2Handler) collect(repoPath string, ch chan<- prometheus.Metric) {
	logger := cvh.logger.WithField("cgroup_path", repoPath)
	control, err := cvh.loadCgroup(repoPath)
	if err != nil {
		logger.WithError(err).Warn("unable to load cgroup controller")
		return
	}

	if metrics, err := control.Stat(); err != nil {
		logger.WithError(err).Warn("unable to get cgroup stats")
	} else {
		cpuUserMetric := cvh.cpuUsage.WithLabelValues(repoPath, "user")
		cpuUserMetric.Set(float64(metrics.CPU.UserUsec))
		ch <- cpuUserMetric

		ch <- prometheus.MustNewConstMetric(
			cvh.cpuCFSPeriods,
			prometheus.CounterValue,
			float64(metrics.CPU.NrPeriods),
			repoPath,
		)

		ch <- prometheus.MustNewConstMetric(
			cvh.cpuCFSThrottledPeriods,
			prometheus.CounterValue,
			float64(metrics.CPU.NrThrottled),
			repoPath,
		)

		ch <- prometheus.MustNewConstMetric(
			cvh.cpuCFSThrottledTime,
			prometheus.CounterValue,
			float64(metrics.CPU.ThrottledUsec)/float64(time.Second),
			repoPath,
		)

		cpuKernelMetric := cvh.cpuUsage.WithLabelValues(repoPath, "kernel")
		cpuKernelMetric.Set(float64(metrics.CPU.SystemUsec))
		ch <- cpuKernelMetric
	}

	if subsystems, err := control.Controllers(); err != nil {
		logger.WithError(err).Warn("unable to get cgroup hierarchy")
	} else {
		processes, err := control.Procs(true)
		if err != nil {
			logger.WithError(err).
				Warn("unable to get process list")
			return
		}

		for _, subsystem := range subsystems {
			procsMetric := cvh.procs.WithLabelValues(repoPath, subsystem)
			procsMetric.Set(float64(len(processes)))
			ch <- procsMetric
		}
	}
}

func (cvh *cgroupV2Handler) repoPath(groupID int) string {
	return filepath.Join(cvh.currentProcessCgroup(), fmt.Sprintf("repos-%d", groupID))
}

func (cvh *cgroupV2Handler) currentProcessCgroup() string {
	return config.GetGitalyProcessTempDir(cvh.cfg.HierarchyRoot, cvh.pid)
}

func (cvh *cgroupV2Handler) stats() (Stats, error) {
	processCgroupPath := cvh.currentProcessCgroup()

	control, err := cvh.loadCgroup(processCgroupPath)
	if err != nil {
		return Stats{}, err
	}

	metrics, err := control.Stat()
	if err != nil {
		return Stats{}, fmt.Errorf("failed to fetch metrics %s: %w", processCgroupPath, err)
	}

	stats := Stats{
		ParentStats: CgroupStats{
			CPUThrottledCount:    metrics.CPU.NrThrottled,
			CPUThrottledDuration: float64(metrics.CPU.ThrottledUsec) / float64(time.Second),
			MemoryUsage:          metrics.Memory.Usage,
			MemoryLimit:          metrics.Memory.UsageLimit,
			// memory.stat breaks down the cgroup's memory footprint into different types of memory. In
			// Cgroup V2, this file includes the consumption of the cgroup’s entire subtree. Total_* stats
			// were removed.
			TotalAnon:         metrics.Memory.Anon,
			TotalActiveAnon:   metrics.Memory.ActiveAnon,
			TotalInactiveAnon: metrics.Memory.InactiveAnon,
			TotalFile:         metrics.Memory.File,
			TotalActiveFile:   metrics.Memory.ActiveFile,
			TotalInactiveFile: metrics.Memory.InactiveFile,
		},
	}

	if metrics.MemoryEvents != nil {
		stats.ParentStats.OOMKills = metrics.MemoryEvents.OomKill
	}
	return stats, nil
}

func (cvh *cgroupV2Handler) supportsCloneIntoCgroup() bool {
	return cvh.cloneIntoCgroup
}

func pruneOldCgroupsV2(cfg cgroupscfg.Config, logger log.Logger) {
	if err := config.PruneOldGitalyProcessDirectories(
		logger,
		filepath.Join(cfg.Mountpoint, cfg.HierarchyRoot),
	); err != nil {
		var pathError *fs.PathError
		if !errors.As(err, &pathError) {
			logger.WithError(err).Error("failed to clean up cpu cgroups")
		}
	}
}