package main
import (
	"bufio"
	"fmt"
	"log"
	"math"
	"math/rand"
	"os"
	"time"
)
const (
	n_particles int     = 2048
	n_steps     int     = 1000000
	dt          float64 = 1.0
	v0          float64 = 0.50
	radius      float64 = 1.0
	f_intensity float64 = 1.8
	scale       float64 = 32.0
	alpha       float64 = 1.0 / 36.0
)
var (
	x      [n_particles + 1]float64
	y      [n_particles + 1]float64
	angles [n_particles + 1]float64
	vx     [n_particles + 1]float64
	vy     [n_particles + 1]float64
	order  [n_steps + 1]float64
)
func main() {
	/////randomizer
	vstart := time.Now()
	rsource := rand.NewSource(time.Now().UnixNano())
	randomizer := rand.New(rsource)
	for i := 0; i <= n_particles; i++ {
		x[i] = (randomizer.Float64()) * scale
		y[i] = (randomizer.Float64()) * scale
		angles[i] = (randomizer.Float64()) * math.Pi * 2
		sin, cos := math.Sincos(angles[i])
		vx[i] = v0 * cos
		vy[i] = v0 * sin
	}
	//////main loop
	for i := 0; i <= n_steps; i++ {
		start := time.Now()
		for j := 0; j <= n_particles; j++ {
			x[j] = x[j] + (vx[j] * dt)
			//x[j] = math.Mod(x[j], scale)
			if x[j] < 0.0 {
				x[j] = x[j] + scale
			}
			if x[j] >= scale {
				x[j] = x[j] - scale
			}
			y[j] = y[j] + (vy[j] * dt)
			//y[j] = math.Mod(x[j], scale)
			if y[j] < 0.0 {
				y[j] = y[j] + scale
			}
			if y[j] >= scale {
				y[j] = y[j] - scale
			}
		}
		type intpos struct {
			x, y int64
		}
		adjacencyIndex := make(map[intpos][]int)
		////getting each boxes particles
		for j := 0; j <= n_particles; j++ {
			// . . .
			ix, iy := int64(math.Floor(x[j])), int64(math.Floor(y[j]))                 // getting particle box
			adjacencyIndex[intpos{ix, iy}] = append(adjacencyIndex[intpos{ix, iy}], j) // adding particles to boxes
		}
		/////////
		m_angles := angles
		

////particle loop - I WANT FOLLOWING LOOP PARALLEL
for j := 0; j <= n_particles; j++ {
sumanglesx := 0.0
sumanglesy := 0.0
ix, iy := int64(math.Floor(x[j])), int64(math.Floor(y[j]))
// fxi = math.Floor(x[j])
// fyi = math.Floor(y[j])
for dx := -1; dx <= 1; dx++ {
for dy := -1; dy <= 1; dy++ {
adjacentParticles := adjacencyIndex[intpos{ix + int64(dx), iy + int64(dy)}]
for _, k := range adjacentParticles {
dist := ((x[k] - x[j]) * (x[k] - x[j])) + ((y[k] - y[j]) * (y[k] - y[j]))
if dist < radius {
sy, sx := math.Sincos(angles[k])
if k <= j {
sumanglesx = sumanglesx + sx
sumanglesy = sumanglesy + sy
} else {
sx = alpha * sx
sy = alpha * sy
sumanglesx = sumanglesx + sx
sumanglesy = sumanglesy + sy
}
}
}
}
}
bsource := rand.NewSource(time.Now().UnixNano())
bandomizer := rand.New(bsource)
sumanglesy = sumanglesy
sumanglesx = sumanglesx
r_angles := math.Atan2(sumanglesy, sumanglesx)
}
}
}

package main
import (
	"fmt"
	"sync"
)
func main() {
  waitGroupApproach()
  channelApproach()
}
func waitGroupApproach() {
	fmt.Println("waitGroupApproach")
	var waitgroup sync.WaitGroup
	
	result_table := make([]int, 6, 6)
	
	for j := 0; j <= 5; j++ {
		waitgroup.Add(1)
		
		go func(index int) {
			fmt.Println(index) // try putting here `j` instea of `index`
			result_table[index] = index*2
		
			waitgroup.Done()
		}(j) // you have to put any for-loop variables into closure
		// because otherwsie all routines inside will likely get the last j == n_particles + 1
		// as they will likely run after the loop has finished
	}
	
	fmt.Println("waiting")
	waitgroup.Wait()
	// process results further
	fmt.Println("finished")
	fmt.Println(result_table)
}
func channelApproach() {
	fmt.Println("\nchannelApproach")
	
	type intpos struct {
            x, y, index int
        }
	results := make(chan intpos)
	// initialize routines
	for j := 0; j <= 5; j++ {
		go func(index int) {
			// do processing
			results <- intpos{index*2, index*3, index}			
		}(j)
	}
	fmt.Println("Waiting..")
	
	// collect results, iterate the same number of times
	result_table := make([]int, 6)
	for j := 0; j <= 5; j++ {
		r := <- results
		// watch out order, migth not be the same as in invocation, 
		// so that's why I store j in results as well
		fmt.Println(r.index, r.x, r.y)
		result_table[r.index] = r.x
	}
	fmt.Println("Finished..")
	fmt.Println(result_table)
}