openquell/systems/player_system.go

package systems

import (
	"log/slog"
	"openquell/components"
	. "openquell/components"
	. "openquell/config"
	"openquell/grid"
	"openquell/observers"

	"github.com/hajimehoshi/ebiten/v2"
	"github.com/hajimehoshi/ebiten/v2/inpututil"
	"github.com/mlange-42/arche/ecs"
	"github.com/mlange-42/arche/generic"
)

type PlayerSystem struct {
	World         *ecs.World
	Selector      *generic.Filter4[Position, Velocity, Player, Renderable]
	GridContainer *grid.GridContainer
}

func NewPlayerSystem(world *ecs.World, gridcontainer *grid.GridContainer) System {
	system := &PlayerSystem{
		Selector:      generic.NewFilter4[Position, Velocity, Player, Renderable](),
		GridContainer: gridcontainer,
		World:         world,
	}

	return system
}

func (system PlayerSystem) Update() error {
	var EntitiesToRemove []ecs.Entity

	// check if we need to switch player[s]
	system.SwitchPlayers()

	// check player movements etc
	query := system.Selector.Query(system.World)
	count := query.Count()

	for query.Next() {
		playerposition, velocity, player, _ := query.Get()

		if !player.IsPrimary {
			continue
		}

		// check if the user alters or initiates movement
		system.CheckMovement(velocity)

		// check if player collides with walls or edges
		system.CheckGridCollision(playerposition, velocity)

		if count > 1 {
			// check if player collides with another player, fuse them if any
			EntitiesToRemove = system.CheckPlayerCollision(playerposition, velocity, query.Entity())
		}
	}

	// 2nd pass: move player after obstacle or collectible updates
	query = system.Selector.Query(system.World)
	for query.Next() {
		playerposition, velocity, _, _ := query.Get()
		playerposition.Move(velocity)
	}

	// we may have lost players, remove them here

	for _, entity := range EntitiesToRemove {
		slog.Debug("remove player", "ent", entity.IsZero())
		system.World.RemoveEntity(entity)
	}

	return nil
}

func (system *PlayerSystem) Draw(screen *ebiten.Image) {
	// write the movable tiles
	op := &ebiten.DrawImageOptions{}
	query := system.Selector.Query(system.World)

	for query.Next() {
		pos, _, _, sprite := query.Get()

		op.GeoM.Reset()
		op.GeoM.Translate(float64(pos.X), float64(pos.Y))

		screen.DrawImage(sprite.Image, op)
	}
}

func (system *PlayerSystem) SwitchPlayers() {
	// first check if we need to switch player
	switchable := false
	query := system.Selector.Query(system.World)
	count := query.Count()

	for query.Next() {
		_, _, player, _ := query.Get()
		if !player.IsPrimary {
			switchable = true
		}
	}

	if switchable {
		query := system.Selector.Query(system.World)
		for query.Next() {
			_, _, player, render := query.Get()

			if count == 1 && !player.IsPrimary {
				// there's only one player left, make it the primary one
				player.IsPrimary = true
				render.Image = player.SwitchSprite()
			} else {
				// many players, switch when requested
				if inpututil.IsKeyJustPressed(ebiten.KeyTab) {
					slog.Debug("switch players")
					if player.IsPrimary {
						player.IsPrimary = false
						render.Image = player.SwitchSprite()
					} else {
						player.IsPrimary = true
						render.Image = player.SwitchSprite()
					}
				}
			}
		}
	}
}

func (system *PlayerSystem) CheckMovement(velocity *components.Velocity) {
	if !velocity.Moving() {
		switch {
		case ebiten.IsKeyPressed(ebiten.KeyRight):
			velocity.Change(East)
		case ebiten.IsKeyPressed(ebiten.KeyLeft):
			velocity.Change(West)
		case ebiten.IsKeyPressed(ebiten.KeyDown):
			velocity.Change(South)
		case ebiten.IsKeyPressed(ebiten.KeyUp):
			velocity.Change(North)
		}
	}
}

func (system *PlayerSystem) CheckGridCollision(
	playerposition *components.Position,
	velocity *components.Velocity) {

	if velocity.Moving() {
		ok, newpos := system.GridContainer.Grid.BumpEdge(playerposition, velocity)
		if ok {
			//slog.Debug("falling off the edge", "newpos", newpos)
			playerposition.Set(newpos)
		} else {
			ok, tilepos := system.GridContainer.Grid.GetSolidNeighborPosition(playerposition, velocity, true)
			if ok {
				slog.Debug("HaveSolidNeighbor", "ok", ok, "tilepos",
					tilepos.Point(), "playerpos", playerposition)
				intersects, newpos := tilepos.Intersects(playerposition, velocity)
				if intersects {
					// slog.Debug("collision detected", "tile",
					// 	tilepos, "player", playerposition, "new", newpos)

					playerposition.Set(newpos)
					velocity.Change(Stop)
				}
			}
		}
	}
}

func (system *PlayerSystem) CheckPlayerCollision(
	position *components.Position,
	velocity *components.Velocity,
	player ecs.Entity) []ecs.Entity {

	observer := observers.GetGameObserver(system.World)
	posID := ecs.ComponentID[components.Position](system.World)
	EntitiesToRemove := []ecs.Entity{}

	for _, otherplayer := range observer.GetPlayers() {
		if !system.World.Alive(otherplayer) {
			continue
		}

		if otherplayer == player {
			continue
		}

		otherposition := (*Position)(system.World.Get(otherplayer, posID))

		ok, _ := otherposition.Intersects(position, velocity)
		if ok {
			// keep displaying it until the two fully intersect
			EntitiesToRemove = append(EntitiesToRemove, otherplayer)
		}
	}

	// FIXME: add an animation highlighting the fusion
	return EntitiesToRemove
}