// +build linux

/*
   Copyright The containerd 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.
*/

package cgroups

import (
	"errors"
	"fmt"
	"sync"

	"github.com/containerd/cgroups"
	"github.com/containerd/containerd/log"
	metrics "github.com/docker/go-metrics"
	"github.com/prometheus/client_golang/prometheus"
)

var (
	// ErrAlreadyCollected is returned when a cgroups is already being monitored
	ErrAlreadyCollected = errors.New("cgroup is already being collected")
	// ErrCgroupNotExists is returns when a cgroup no longer exists
	ErrCgroupNotExists = errors.New("cgroup does not exist in the collector")
)

// Trigger will be called when an event happens and provides the cgroup
// where the event originated from
type Trigger func(string, string, cgroups.Cgroup)

// newCollector registers the collector with the provided namespace and returns it so
// that cgroups can be added for collection
func newCollector(ns *metrics.Namespace) *collector {
	if ns == nil {
		return &collector{}
	}
	// add machine cpus and memory info
	c := &collector{
		ns:      ns,
		cgroups: make(map[string]*task),
	}
	c.metrics = append(c.metrics, pidMetrics...)
	c.metrics = append(c.metrics, cpuMetrics...)
	c.metrics = append(c.metrics, memoryMetrics...)
	c.metrics = append(c.metrics, hugetlbMetrics...)
	c.metrics = append(c.metrics, blkioMetrics...)
	c.storedMetrics = make(chan prometheus.Metric, 100*len(c.metrics))
	ns.Add(c)
	return c
}

type task struct {
	id        string
	namespace string
	cgroup    cgroups.Cgroup
}

func taskID(id, namespace string) string {
	return fmt.Sprintf("%s-%s", id, namespace)
}

// collector provides the ability to collect container stats and export
// them in the prometheus format
type collector struct {
	mu sync.RWMutex

	cgroups       map[string]*task
	ns            *metrics.Namespace
	metrics       []*metric
	storedMetrics chan prometheus.Metric
}

func (c *collector) Describe(ch chan<- *prometheus.Desc) {
	for _, m := range c.metrics {
		ch <- m.desc(c.ns)
	}
}

func (c *collector) Collect(ch chan<- prometheus.Metric) {
	c.mu.RLock()
	wg := &sync.WaitGroup{}
	for _, t := range c.cgroups {
		wg.Add(1)
		go c.collect(t.id, t.namespace, t.cgroup, ch, true, wg)
	}
storedLoop:
	for {
		// read stored metrics until the channel is flushed
		select {
		case m := <-c.storedMetrics:
			ch <- m
		default:
			break storedLoop
		}
	}
	c.mu.RUnlock()
	wg.Wait()
}

func (c *collector) collect(id, namespace string, cg cgroups.Cgroup, ch chan<- prometheus.Metric, block bool, wg *sync.WaitGroup) {
	if wg != nil {
		defer wg.Done()
	}

	stats, err := cg.Stat(cgroups.IgnoreNotExist)
	if err != nil {
		log.L.WithError(err).Errorf("stat cgroup %s", id)
		return
	}
	for _, m := range c.metrics {
		m.collect(id, namespace, stats, c.ns, ch, block)
	}
}

// Add adds the provided cgroup and id so that metrics are collected and exported
func (c *collector) Add(id, namespace string, cg cgroups.Cgroup) error {
	if c.ns == nil {
		return nil
	}
	c.mu.Lock()
	defer c.mu.Unlock()
	if _, ok := c.cgroups[taskID(id, namespace)]; ok {
		return ErrAlreadyCollected
	}
	c.cgroups[taskID(id, namespace)] = &task{
		id:        id,
		namespace: namespace,
		cgroup:    cg,
	}
	return nil
}

// Remove removes the provided cgroup by id from the collector
func (c *collector) Remove(id, namespace string) {
	if c.ns == nil {
		return
	}
	c.mu.Lock()
	defer c.mu.Unlock()
	delete(c.cgroups, taskID(id, namespace))
}
