// Package bandwidth is a simple tool for keeping track of transmitted and
// received counts (ostensibly bytes).
package bandwidth

import (
	"errors"
	"sort"
	"time"
)

// Bandwidth keeps track of state for Rx and Tx (byte) counts. Instantiate
// a Bandwidth then feed values using the AddRx and AddTx channels. When the
// accumulated values are needed, simply read from the Rx or Tx chans. When the
// Bandwidth is no loner needed close the Quit chan.
type Bandwidth struct {
	// write number of bytes to us
	AddRx chan int
	AddTx chan int

	// read stats from us
	Rx chan []float64
	Tx chan []float64

	Quit chan interface{}

	rxSnap []float64
	txSnap []float64
	dt     time.Duration
	dts    []int

	curRx int
	curTx int

	rxstream []int
	txstream []int

	timeI int
	max   int
}

// NewBandwidth Returns a populated and ready to launch Bandwidth. seconds is
// a slice of multiples of dt on which to report (e.g. 1x, 10x, 60x dt). dt is
// also how often the values used to send to Rx and Tx are updated.
func NewBandwidth(dts []int, dt time.Duration) (*Bandwidth, error) {
	if len(dts) < 1 {
		return nil, errors.New("must specify at least one interval lenght")
	}
	sort.Ints(dts)
	max := dts[len(dts)-1]
	r := &Bandwidth{
		AddRx:    make(chan int, 1024),
		AddTx:    make(chan int, 1024),
		Rx:       make(chan []float64),
		Tx:       make(chan []float64),
		dt:       dt,
		dts:      dts,
		Quit:     make(chan interface{}),
		rxstream: make([]int, max),
		txstream: make([]int, max),
		max:      max,
	}
	return r, nil
}

// Run is a method of Bandwidth that must be started in a goroutine in order
// for things to be functional.
func (bw *Bandwidth) Run() {
	t := time.NewTicker(bw.dt)
outer:
	for {
		select {
		case <-t.C:
			bw.rxstream[bw.timeI] = bw.curRx
			bw.txstream[bw.timeI] = bw.curTx

			bw.rxSnap = bw.averages(bw.rxstream)
			bw.txSnap = bw.averages(bw.txstream)

			bw.curTx = 0
			bw.curRx = 0

			// n.b.: here we march forward through time by going backward in
			// our slice.
			bw.timeI = (bw.timeI - 1) % bw.max
			// lol: because modulo does unexpected things for negative numbers.
			if bw.timeI < 0 {
				bw.timeI = bw.timeI + bw.max
			}
			// log.Printf("%d %+v", bw.timeI, bw.rxstream)
		case bw.Rx <- bw.rxSnap:
		case bw.Tx <- bw.txSnap:
		case s := <-bw.AddRx:
			bw.curRx += s
		case s := <-bw.AddTx:
			bw.curTx += s
		case <-bw.Quit:
			break outer
		}
	}
	close(bw.AddRx)
	close(bw.AddTx)
	close(bw.Rx)
	close(bw.Tx)
}

func (bw *Bandwidth) averages(state []int) []float64 {
	r := []float64{}
	var i int = 0
	total := 0
	for _, ti := range bw.dts {
		for ; ; i++ {
			if i == ti {
				break
			}
			total += state[(bw.timeI+i)%bw.max]
		}
		r = append(r, float64(total)/float64(ti))
	}
	return r
}