CHALLENGE 2: A Damage Flash Driven by the Health Signal
====================================================================

TASK
----
Add an AnimationPlayer to a Sprite2D with a short "flash" animation
(e.g. briefly changing modulate to red and back). Connect it to
Chapter 7's health_changed signal so the sprite flashes every time
take_damage() is called.

SETUP - the "flash" animation
----------------------------------
1. Add an AnimationPlayer as a sibling (or child) of the Sprite2D
   you want to flash.
2. In the Animation panel, create a new animation named "flash",
   about 0.3 seconds long.
3. Select the Sprite2D, and with the animation timeline open, add a
   keyframe for its "modulate" property at time 0.0 (white, the
   default), one at 0.1s (red), and one at 0.3s (back to white).

SCENE STRUCTURE
----------------
Root (Node2D)
|-- Health (Node)             <- health.gd, from Chapter 7
|-- PlayerSprite (Sprite2D)
    |-- AnimationPlayer       <- the "flash" animation
    |-- FlashController.gd    <- this script

SOLUTION CODE (attached to a Node under PlayerSprite, or PlayerSprite itself)
------------------------------------------------------------------------------------
extends Node

func _ready() -> void:
    get_parent().get_parent().get_node("Health").health_changed.connect(_on_health_changed)

func _on_health_changed(current: int, max_health: int) -> void:
    get_parent().get_node("AnimationPlayer").play("flash")

(A simpler, common alternative is to attach this logic directly to
the Sprite2D itself, in which case $AnimationPlayer.play("flash")
can be used directly, exactly as shown in the chapter.)

WHY THIS WORKS AS AN ANSWER
----------------------------
This connects to health_changed the same way every other listener
in this course has (Chapter 7's Challenge 3, Chapter 8's health
bar) - the sprite doesn't know or care why health changed, only that
it did, and reacts by playing its own "flash" animation every single
time the signal fires, regardless of whether current went up or
down.

$AnimationPlayer.play("flash") triggers the entire keyframed
sequence recorded in the editor with one call - the AnimationPlayer
itself handles smoothly interpolating the Sprite2D's modulate color
from white to red and back over the recorded 0.3 seconds, with no
manual per-frame color-blending code needed in the script at all.
Because this fires from health_changed rather than being called
directly from take_damage(), the exact same flash would also trigger
correctly if some other, entirely different part of the game later
called take_damage() through a completely different code path - the
flash is a property of "health changed," not of any one specific
call site.