package main

import (
	"time"

	"github.com/faiface/pixel"
	"github.com/faiface/pixel/imdraw"
	"github.com/faiface/pixel/pixelgl"
	"golang.org/x/image/colornames"
)

var (
	width  = 1000
	height = 800

	blob       pixel.Vec
	gridCanvas *pixelgl.Canvas
	gridSize   float64 = 50
	gridPos    pixel.Vec

	imd *imdraw.IMDraw
)

func run() {
	cfg := pixelgl.WindowConfig{
		Title:  "Agario Fake Grid",
		Bounds: pixel.R(0, 0, 1000, 800),
		VSync:  true,
	}
	win, err := pixelgl.NewWindow(cfg)
	if err != nil {
		panic(err)
	}

	gridCanvas = pixelgl.NewCanvas(pixel.R(0-2*gridSize, 0-2*gridSize, float64(width)+2*gridSize, float64(height)+2*gridSize))
	screenCenter := pixel.V(float64(width)/2, float64(height)/2)

	lineDraw := imdraw.New(nil)
	for x := gridCanvas.Bounds().Min.X; x <= gridCanvas.Bounds().Max.X; x += gridSize {
		lineDraw.Push(pixel.V(x, gridCanvas.Bounds().Min.Y), pixel.V(x, gridCanvas.Bounds().Max.Y))
		lineDraw.Line(2)
	}
	for y := gridCanvas.Bounds().Min.Y; y <= gridCanvas.Bounds().Max.Y; y += gridSize {
		lineDraw.Push(pixel.V(gridCanvas.Bounds().Min.X, y), pixel.V(gridCanvas.Bounds().Max.X, y))
		lineDraw.Line(2)
	}
	lineDraw.Draw(gridCanvas)

	imd = imdraw.New(nil)

	start := time.Now()
	now := start
	for !win.Closed() {
		last := now
		now = time.Now()
		dt := now.Sub(last).Seconds()

		if win.Pressed(pixelgl.KeyRight) {
			blob.X += 100 * dt
		}
		if win.Pressed(pixelgl.KeyLeft) {
			blob.X -= 100 * dt
		}
		if win.Pressed(pixelgl.KeyUp) {
			blob.Y += 100 * dt
		}
		if win.Pressed(pixelgl.KeyDown) {
			blob.Y -= 100 * dt
		}

		// Adjust grid pos in gridSize steps.
		if blob.X-gridPos.X >= gridSize {
			gridPos.X += gridSize
		} else if blob.X-gridPos.X <= -gridSize {
			gridPos.X -= gridSize
		}
		if blob.Y-gridPos.Y >= gridSize {
			gridPos.Y += gridSize
		} else if blob.Y-gridPos.Y <= -gridSize {
			gridPos.Y -= gridSize
		}

		win.Clear(colornames.Skyblue)

		gridMatrix := pixel.IM.Moved(gridPos)
		gridCanvas.Draw(win, gridMatrix)

		imd.Clear()
		imd.Color = colornames.Black
		imd.Push(blob)
		imd.Circle(25, 0)
		imd.Draw(win)

		centerCam := pixel.IM.Moved(screenCenter.Sub(blob))

		win.SetMatrix(centerCam)

		win.Update()
	}
}

func main() {
	pixelgl.Run(run)
}