package main

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

	"gonum.org/v1/plot"
	"gonum.org/v1/plot/plotter"
	"gonum.org/v1/plot/plotutil"
	"gonum.org/v1/plot/vg"
	"gonum.org/v1/plot/vg/draw"
	"gonum.org/v1/plot/vg/vgsvg"
)

type statSheet struct {
	Values []float64
	Ok     bool
}

type provider struct {
	Current int
	Values  [3600]statSheet
	Fetch   func() []float64

	NoVals  int
	ValTags []string

	Name string
	Y    string
}

func (p *provider) Run() {
	tick := time.NewTicker(time.Second)

	for {
		<-tick.C

		vals := p.Fetch()
		// fmt.Println("tick", p.Name, vals)

		p.Values[p.Current] = statSheet{vals, true}
		p.Current++

		if p.Current >= 3600 {
			p.Current = 0
		}
	}
}

var xypool = sync.Pool{
	New: func() interface{} {
		return make(plotter.XYs, 3600)
	},
}

func (prov *provider) Render(w http.ResponseWriter, r *http.Request) {
	p := plot.New()
	p.Legend.Top = true
	p.Title.Text = prov.Name
	p.X.Label.Text = "Time (seconds)"
	p.Y.Label.Text = prov.Y

	var points = make([]plotter.XYs, prov.NoVals)
	var allocs = make([]plotter.XYs, prov.NoVals)
	defer func() {
		for _, x := range allocs {
			xypool.Put(x)
		}
	}()
	for i := range points {
		alloc := xypool.Get().(plotter.XYs)
		points[i] = alloc
		allocs[i] = alloc
	}
	for i, x := range prov.Values {
		if !x.Ok {
			for yi := range points {
				points[yi] = points[yi][:i]
			}
			break
		}
		for yi, y := range x.Values {
			points[yi][i] = plotter.XY{
				Y: y,
				X: float64(i),
			}
		}
	}

	for i, x := range points {
		line, err := plotter.NewLine(x)
		if err != nil {
			panic(err)
		}
		line.Color = plotutil.Color(i)
		line.Dashes = plotutil.Dashes(i)
		p.Add(line)
		p.Legend.Add(prov.ValTags[i], line)
	}

	canv := vgsvg.New(vg.Millimeter*290, vg.Millimeter*200)
	p.Draw(draw.New(canv))

	w.Header().Set("content-type", "image/svg+xml")
	canv.WriteTo(w)
}