/*
Copyright 2017 The Kubernetes 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 metrics

import (
	"fmt"
	"net/http"
	"sync"
	"time"
)

// HealthCheck contains information about last time of autoscaler activity and timeout
type HealthCheck struct {
	lastActivity time.Time
	mutex        *sync.Mutex
	timeout      time.Duration
	checkTimeout bool
}

// NewHealthCheck builds new HealthCheck object with given timeout
func NewHealthCheck(timeout time.Duration) *HealthCheck {
	return &HealthCheck{
		lastActivity: time.Now(),
		mutex:        &sync.Mutex{},
		timeout:      timeout,
		checkTimeout: false,
	}
}

// StartMonitoring activates checks for autoscaler inactivity
func (hc *HealthCheck) StartMonitoring() {
	hc.mutex.Lock()
	defer hc.mutex.Unlock()
	hc.checkTimeout = true
	now := time.Now()
	if now.After(hc.lastActivity) {
		hc.lastActivity = now
	}
}

// ServeHTTP implements http.Handler interface to provide a health-check endpoint
func (hc *HealthCheck) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	hc.mutex.Lock()
	lastActivity := hc.lastActivity
	timedOut := hc.checkTimeout && time.Now().After(lastActivity.Add(hc.timeout))
	hc.mutex.Unlock()

	if timedOut {
		w.WriteHeader(500)
		w.Write([]byte(fmt.Sprintf("Error: last activity more than %v ago", time.Now().Sub(lastActivity).String())))
	} else {
		w.WriteHeader(200)
		w.Write([]byte("OK"))
	}
}

// UpdateLastActivity updates last time of activity
func (hc *HealthCheck) UpdateLastActivity(timestamp time.Time) {
	hc.mutex.Lock()
	defer hc.mutex.Unlock()
	if timestamp.After(hc.lastActivity) {
		hc.lastActivity = timestamp
	}
}