//练习 1.12： 修改Lissajour服务，从URL读取变量，
//比如你可以访问 http://localhost:8000/?cycles=20 这个URL，
// 这样访问可以将程序里的cycles默认的5修改为20。
// 字符串转换为数字可以调用strconv.Atoi函数。
// 你可以在godoc里查看strconv.Atoi的详细说明。
package main

import (
	"image"
	"image/color"
	"image/gif"
	"io"
	"math"
	"math/rand"
	"os"
	"strconv"
)

//!-main
// Packages not needed by version in book.
import (
	"log"
	"net/http"
	"time"
)

//!+main

var palette = []color.Color{color.White, color.Black}

const (
	whiteIndex = 0 // first color in palette
	blackIndex = 1 // next color in palette
)

func main() {
	rand.Seed(time.Now().UTC().UnixNano())

	if len(os.Args) > 1 && os.Args[1] == "web" {
		//!+http
		handler := func(w http.ResponseWriter, r *http.Request) {
			lissajous(w, r)
		}
		http.HandleFunc("/", handler)
		//!-http
		log.Fatal(http.ListenAndServe("localhost:8000", nil))
		return
	}

}

func lissajous(out io.Writer, r *http.Request) {
	const (
		cycles  = 5     // number of complete x oscillator revolutions
		res     = 0.001 // angular resolution
		size    = 100   // image canvas covers [-size..+size]
		nframes = 64    // number of animation frames
		delay   = 8     // delay between frames in 10ms units
	)
	r.ParseForm()
	cyc := r.FormValue("cycles")
	if cyc == "" {
		cyc = "5"
	}
	cycValue, _ := strconv.Atoi(cyc)
	freq := rand.Float64() * 3.0 // relative frequency of y oscillator
	anim := gif.GIF{LoopCount: nframes}
	phase := 0.0 // phase difference
	for i := 0; i < nframes; i++ {
		rect := image.Rect(0, 0, 2*size+1, 2*size+1)
		img := image.NewPaletted(rect, palette)
		for t := 0.0; t < float64(cycValue)*2*math.Pi; t += res {
			x := math.Sin(t)
			y := math.Sin(t*freq + phase)
			img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5),
				blackIndex)
		}
		phase += 0.1
		anim.Delay = append(anim.Delay, delay)
		anim.Image = append(anim.Image, img)
	}
	gif.EncodeAll(out, &anim) // NOTE: ignoring encoding errors
}

//!-main
