//go:build example
// +build example

package system

import (
	"code.rocketnine.space/tslocum/gohan"
	"code.rocketnine.space/tslocum/gohan/examples/twinstick/component"
	"code.rocketnine.space/tslocum/gohan/examples/twinstick/world"
	"github.com/hajimehoshi/ebiten/v2"
)

type MovementSystem struct {
	Position *component.Position
	Velocity *component.Velocity
}

func NewMovementSystem() *MovementSystem {
	return &MovementSystem{}
}

func (s *MovementSystem) Update(entity gohan.Entity) error {
	bullet := entity != world.Player

	// Position the player at the center of the screen when the game starts.
	if !bullet && s.Position.X == -1 && s.Position.Y == -1 {
		s.Position.X, s.Position.Y = float64(world.ScreenW)/2-16, float64(world.ScreenH)/2-16
	}

	// Check for collision.
	if s.Position.X+s.Velocity.X < 16 {
		if bullet {
			entity.Remove()
			return nil
		}

		s.Position.X = 16
		s.Velocity.X = 0
	} else if s.Position.X+s.Velocity.X > world.ScreenW-16 {
		if bullet {
			entity.Remove()
			return nil
		}

		s.Position.X = world.ScreenW - 16
		s.Velocity.X = 0
	}
	if s.Position.Y+s.Velocity.Y < 16 {
		if bullet {
			entity.Remove()
			return nil
		}

		s.Position.Y = 16
		s.Velocity.Y = 0
	} else if s.Position.Y+s.Velocity.Y > world.ScreenH-16 {
		if bullet {
			entity.Remove()
			return nil
		}

		s.Position.Y = world.ScreenH - 16
		s.Velocity.Y = 0
	}

	s.Position.X, s.Position.Y = s.Position.X+s.Velocity.X, s.Position.Y+s.Velocity.Y

	if !bullet {
		s.Velocity.X *= 0.95
		s.Velocity.Y *= 0.95
	}

	return nil
}

func (_ *MovementSystem) Draw(_ gohan.Entity, _ *ebiten.Image) error {
	return gohan.ErrUnregister
}