//go:build example
// +build example

package system

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

type MovementSystem struct {
	ScreenW, ScreenH float64
	Player           gohan.Entity
}

func (_ *MovementSystem) Components() []gohan.ComponentID {
	return []gohan.ComponentID{
		component.PositionComponentID,
		component.VelocityComponentID,
	}
}

func (s *MovementSystem) Update(ctx *gohan.Context) error {
	position := component.Position(ctx)
	velocity := component.Velocity(ctx)

	bullet := ctx.Entity != s.Player

	// Check for collision.
	if position.X+velocity.X < 16 {
		if bullet {
			ctx.RemoveEntity()
			return nil
		}

		position.X = 16
		velocity.X = 0
	} else if position.X+velocity.X > s.ScreenW-16 {
		if bullet {
			ctx.RemoveEntity()
			return nil
		}

		position.X = s.ScreenW - 16
		velocity.X = 0
	}
	if position.Y+velocity.Y < 16 {
		if bullet {
			ctx.RemoveEntity()
			return nil
		}

		position.Y = 16
		velocity.Y = 0
	} else if position.Y+velocity.Y > s.ScreenH-16 {
		if bullet {
			ctx.RemoveEntity()
			return nil
		}

		position.Y = s.ScreenH - 16
		velocity.Y = 0
	}

	position.X, position.Y = position.X+velocity.X, position.Y+velocity.Y

	if !bullet {
		velocity.X *= 0.95
		velocity.Y *= 0.95
	}

	return nil
}

func (_ *MovementSystem) Draw(ctx *gohan.Context, _ *ebiten.Image) error {
	return gohan.ErrSystemWithoutDraw
}