package main

import (
	"sync"
	"time"

	rl "github.com/gen2brain/raylib-go/raylib"
)

const MAXPOINTS = 100000
const MAXOBSTACLES = 20
const PI = 3.141592653589793

type quad struct {
	lu rl.Vector2
	ru rl.Vector2
	rd rl.Vector2
	ld rl.Vector2
}

func spawnParticlesAsGrid(particleWidth float32, particleHeight float32, particleColumnCount int, particleRowCount int, particleList *[MAXPOINTS]rl.Vector2) {
	var particleLeftCornerPos rl.Vector2 = rl.Vector2{500, 200}

	for y := 0; y < (particleColumnCount); y++ {
		for x := 0; x < particleRowCount; x++ {
			newParticle := rl.NewVector2(particleWidth*(float32(x)/float32(particleRowCount))+particleLeftCornerPos.X, particleHeight*(float32(y)/float32(particleColumnCount))+particleLeftCornerPos.Y)
			particleList[y*particleRowCount+x] = newParticle
		}
	}
}

func createRectangle(centerPoint rl.Vector2, width float32, height float32, rotation float32) quad {
	rectangle := quad{}
	rectangle.lu = rl.Vector2Add(
		centerPoint,
		rl.Vector2Rotate(rl.Vector2{-0.5 * width, -0.5 * height},
			rotation))
	rectangle.ru = rl.Vector2Add(
		centerPoint,
		rl.Vector2Rotate(rl.Vector2{0.5 * width, -0.5 * height},
			rotation))
	rectangle.rd = rl.Vector2Add(
		centerPoint,
		rl.Vector2Rotate(rl.Vector2{0.5 * width, 0.5 * height},
			rotation))
	rectangle.ld = rl.Vector2Add(
		centerPoint,
		rl.Vector2Rotate(rl.Vector2{-0.5 * width, 0.5 * height},
			rotation))
	return rectangle
}

func drawRec(rectangle *quad) {
	rl.DrawLineV((*rectangle).lu, (*rectangle).ru, rl.Black)
	rl.DrawLineV((*rectangle).ru, (*rectangle).rd, rl.Black)
	rl.DrawLineV((*rectangle).rd, (*rectangle).ld, rl.Black)
	rl.DrawLineV((*rectangle).ld, (*rectangle).lu, rl.Black)
}

func obstacleReflect(particlePos rl.Vector2, particleSpeed *rl.Vector2, obstacles *([MAXOBSTACLES](*quad)), particleRadius *float32, obstacleCount *int) {
	var friction float32 = 0.9

	for k := 0; k < *obstacleCount; k++ {
		if rl.CheckCollisionCircleLine(particlePos, *particleRadius, (*((*obstacles)[k])).lu, (*((*obstacles)[k])).ru) {
			var floorVector rl.Vector2 = rl.Vector2Subtract((*((*obstacles)[k])).ru, (*((*obstacles)[k])).lu)
			var normalFloor rl.Vector2 = rl.Vector2Normalize(rl.Vector2Rotate(floorVector, -PI/2))
			*particleSpeed = rl.Vector2Scale(rl.Vector2Reflect(*particleSpeed, normalFloor), friction)
		} else if rl.CheckCollisionCircleLine(particlePos, *particleRadius, (*((*obstacles)[k])).ru, (*((*obstacles)[k])).rd) {
			var floorVector rl.Vector2 = rl.Vector2Subtract((*((*obstacles)[k])).rd, (*((*obstacles)[k])).ru)
			var normalFloor rl.Vector2 = rl.Vector2Normalize(rl.Vector2Rotate(floorVector, -PI/2))
			*particleSpeed = rl.Vector2Scale(rl.Vector2Reflect(*particleSpeed, normalFloor), friction)
		} else if rl.CheckCollisionCircleLine(particlePos, *particleRadius, (*((*obstacles)[k])).rd, (*((*obstacles)[k])).ld) {
			var floorVector rl.Vector2 = rl.Vector2Subtract((*((*obstacles)[k])).ld, (*((*obstacles)[k])).rd)
			var normalFloor rl.Vector2 = rl.Vector2Normalize(rl.Vector2Rotate(floorVector, -PI/2))
			*particleSpeed = rl.Vector2Scale(rl.Vector2Reflect(*particleSpeed, normalFloor), friction)
		} else if rl.CheckCollisionCircleLine(particlePos, *particleRadius, (*((*obstacles)[k])).ld, (*((*obstacles)[k])).lu) {
			var floorVector rl.Vector2 = rl.Vector2Subtract((*((*obstacles)[k])).lu, (*((*obstacles)[k])).ld)
			var normalFloor rl.Vector2 = rl.Vector2Normalize(rl.Vector2Rotate(floorVector, -PI/2))
			*particleSpeed = rl.Vector2Scale(rl.Vector2Reflect(*particleSpeed, normalFloor), friction)
		}
	}
}

func physics(particleList *[MAXPOINTS]rl.Vector2, particleCount int, particleListKey *sync.Mutex, obstacles *([MAXOBSTACLES](*quad)), particleRadius *float32, obstacleCount *int) {
	var particleSpeed = [MAXPOINTS]rl.Vector2{{0, -300}} //pixel pro Sekunde
	var timeIncrement float64 = 0.01
	var gravity rl.Vector2 = rl.Vector2{0, 300}
	var newParticleList [MAXPOINTS]rl.Vector2
	var newParticleSpeed [MAXPOINTS]rl.Vector2

	for j := float64(0); j < 50; {
		var startTime time.Time = time.Now()

		// Snapshot der aktuellen Positionen für den parallelen Block (read-only)
		particleListKey.Lock()
		currentPositions := *particleList
		particleListKey.Unlock()

		var wg sync.WaitGroup

		for k := 0; k < particleCount; k++ {
			wg.Add(1)
			go func(i int) {
				defer wg.Done()

				// Jede Goroutine arbeitet nur auf Index i → kein Datenkonflikt
				obstacleReflect(currentPositions[i], &particleSpeed[i], obstacles, particleRadius, obstacleCount)

				newParticleList[i] = rl.Vector2Add(
					currentPositions[i],
					rl.Vector2Scale(particleSpeed[i], float32(timeIncrement)))

				newParticleSpeed[i] = rl.Vector2Add(
					particleSpeed[i],
					rl.Vector2Scale(gravity, float32(timeIncrement)))
			}(k)
		}

		wg.Wait()

		// Ergebnisse zurückschreiben — nur dieser Block muss gelockt sein
		particleListKey.Lock()
		*particleList = newParticleList
		particleListKey.Unlock()
		//fmt.Println(particleList)

		particleSpeed = newParticleSpeed

		j += timeIncrement
		var endTime time.Time = time.Now()
		var elapsed time.Duration = endTime.Sub(startTime)
		var waitTime float64 = timeIncrement - elapsed.Seconds()
		rl.WaitTime(waitTime)
		println((waitTime / timeIncrement))
		//rl.ClearBackground(rl.RayWhite)
	}
}

func main() {
	rl.InitWindow(1200, 800, "raylib [core] example - basic window")
	defer rl.CloseWindow()

	rl.SetTargetFPS(120)

	rl.BeginDrawing()
	rl.WaitTime(1)
	rl.ClearBackground(rl.RayWhite)
	rl.DrawText("Congrats! You created your first window!", 190, 200, 20, rl.LightGray)

	rl.EndDrawing()

	var particleWidth float32 = 300
	var particleHeight float32 = 200
	var particleColumnCount int = 20
	var particleRowCount int = 20
	var particleCount int = particleRowCount * particleColumnCount
	var particleRadius float32 = 5
	var particleColor rl.Color = rl.Black
	var particleListKey sync.Mutex
	var obstacleCount int = 0

	//var stepSize float32 = 10

	var particleList = [MAXPOINTS]rl.Vector2{}

	spawnParticlesAsGrid(particleWidth, particleHeight, particleColumnCount, particleRowCount, &particleList)

	var floor quad = createRectangle(rl.Vector2{600, 700}, 1200, 100, 0*PI/8)
	var obstacles = [MAXOBSTACLES]*quad{}
	obstacles[0] = &floor
	obstacleCount++
	var hillLeft quad = createRectangle(rl.Vector2{500, 700}, 1200, 100, PI/6)
	obstacles[1] = &hillLeft
	obstacleCount++
	var hillRight quad = createRectangle(rl.Vector2{700, 700}, 1200, 100, -PI/6)
	obstacles[2] = &hillRight
	obstacleCount++

	go physics(&particleList, particleCount, &particleListKey, &obstacles, &particleRadius, &obstacleCount)

	for !rl.WindowShouldClose() {
		rl.ClearBackground(rl.RayWhite)

		particleListKey.Lock()

		rl.BeginDrawing()
		for i := 0; i < particleCount; i++ {
			rl.DrawCircleV(particleList[i], particleRadius, particleColor)
		}

		particleListKey.Unlock()
		drawRec(&floor)
		drawRec(&hillLeft)
		drawRec(&hillRight)
		rl.EndDrawing()
	}

}