package main

import (

	"fmt"

	"log"

	"net/http"

	"image/gif"

	"image"

	"math"

	"math/rand"

	"io"

	"image/color"

	"strconv"

)

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

const (

	whiteIndex = 0 // first color in palette

	blackIndex = 1 // next color in palette

)

func lissajous(out io.Writer, myCycles float64) { //接收 cycles参数

	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

	)

	if myCycles == 0 {

		myCycles = cycles //如果为零，则使用常亮定义的值

	}

	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 < myCycles*2*math.Pi; t += res { //使用myCycles变量

			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

}

func handler(w http.ResponseWriter, r *http.Request)  {

	fmt.Fprintf(w, "%s %s %s\n", r.Method, r.URL, r.Proto)

	fmt.Fprintf(w, "URL.Path = %q\n", r.URL.Path)

}

func handler_gif(w http.ResponseWriter,r *http.Request) {

	if err := r.ParseForm(); err != nil {

		log.Print(err)

	}

	if r.Form["cycles"] != nil { // 获取cycles参数，并转为int型

		cycles,err := strconv.Atoi(r.Form["cycles"][0])

		if err != nil {

			lissajous(w,float64(cycles))

		}

	}

	lissajous(w,float64(0))

}

func main() {

	http.HandleFunc("/", handler) // each request calls handler

	http.HandleFunc("/gif", handler_gif) // each request calls handler

	log.Println("localhost:8000")

	log.Fatal(http.ListenAndServe("localhost:8000", nil))

}