/*
   Copyright 2014 CoreOS, Inc.

   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 stats

import (
	"encoding/json"
	"log"
	"math"
	"sync"
	"time"
)

// LeaderStats is used by the leader in an etcd cluster, and encapsulates
// statistics about communication with its followers
type LeaderStats struct {
	// TODO(jonboulle): clarify that these are IDs, not names
	Leader    string                    `json:"leader"`
	Followers map[string]*FollowerStats `json:"followers"`

	sync.Mutex
}

// NewLeaderStats generates a new LeaderStats with the given id as leader
func NewLeaderStats(id string) *LeaderStats {
	return &LeaderStats{
		Leader:    id,
		Followers: make(map[string]*FollowerStats),
	}
}

func (ls *LeaderStats) JSON() []byte {
	ls.Lock()
	stats := *ls
	ls.Unlock()
	b, err := json.Marshal(stats)
	// TODO(jonboulle): appropriate error handling?
	if err != nil {
		log.Printf("stats: error marshalling leader stats: %v", err)
	}
	return b
}

func (ls *LeaderStats) Follower(name string) *FollowerStats {
	ls.Lock()
	defer ls.Unlock()
	fs, ok := ls.Followers[name]
	if !ok {
		fs = &FollowerStats{}
		fs.Latency.Minimum = 1 << 63
		ls.Followers[name] = fs
	}
	return fs
}

// FollowerStats encapsulates various statistics about a follower in an etcd cluster
type FollowerStats struct {
	Latency struct {
		Current           float64 `json:"current"`
		Average           float64 `json:"average"`
		averageSquare     float64
		StandardDeviation float64 `json:"standardDeviation"`
		Minimum           float64 `json:"minimum"`
		Maximum           float64 `json:"maximum"`
	} `json:"latency"`

	Counts struct {
		Fail    uint64 `json:"fail"`
		Success uint64 `json:"success"`
	} `json:"counts"`

	sync.Mutex
}

// Succ updates the FollowerStats with a successful send
func (fs *FollowerStats) Succ(d time.Duration) {
	fs.Lock()
	defer fs.Unlock()

	total := float64(fs.Counts.Success) * fs.Latency.Average
	totalSquare := float64(fs.Counts.Success) * fs.Latency.averageSquare

	fs.Counts.Success++

	fs.Latency.Current = float64(d) / (1000000.0)

	if fs.Latency.Current > fs.Latency.Maximum {
		fs.Latency.Maximum = fs.Latency.Current
	}

	if fs.Latency.Current < fs.Latency.Minimum {
		fs.Latency.Minimum = fs.Latency.Current
	}

	fs.Latency.Average = (total + fs.Latency.Current) / float64(fs.Counts.Success)
	fs.Latency.averageSquare = (totalSquare + fs.Latency.Current*fs.Latency.Current) / float64(fs.Counts.Success)

	// sdv = sqrt(avg(x^2) - avg(x)^2)
	fs.Latency.StandardDeviation = math.Sqrt(fs.Latency.averageSquare - fs.Latency.Average*fs.Latency.Average)
}

// Fail updates the FollowerStats with an unsuccessful send
func (fs *FollowerStats) Fail() {
	fs.Lock()
	defer fs.Unlock()
	fs.Counts.Fail++
}