extends RefCounted
## Particle and glow building blocks for the strategic buildings (G2). Every effect is a
## small, bounded GPUParticles3D (no per-frame physics debris): sparks, smoke, dust bursts,
## crystal shard bursts and rising motes, plus soft sprite materials. Effects are purely
## visual and never feed back into the simulation.

static var _soft: Texture2D
static var _cache: Dictionary = {}

## Radial soft dot used by smoke, dust, motes and flashes.
static func soft_texture() -> Texture2D:
	if _soft == null:
		var gradient := Gradient.new()
		gradient.set_color(0, Color(1, 1, 1, 1))
		gradient.set_color(1, Color(1, 1, 1, 0))
		gradient.add_point(.35, Color(1, 1, 1, .55))
		var texture := GradientTexture2D.new()
		texture.gradient = gradient
		texture.fill = GradientTexture2D.FILL_RADIAL
		texture.fill_from = Vector2(.5, .5)
		texture.fill_to = Vector2(1.0, .5)
		texture.width = 64
		texture.height = 64
		_soft = texture
	return _soft

## Billboard sprite material: additive glow (sparks, motes, flashes) or alpha (smoke, dust).
static func sprite_material(color: Color, additive: bool, energy: float = 1.0) -> StandardMaterial3D:
	var key: String = "%s:%s:%.2f" % [color.to_html(), additive, energy]
	if _cache.has(key):
		return _cache[key]
	var material := StandardMaterial3D.new()
	material.shading_mode = BaseMaterial3D.SHADING_MODE_UNSHADED
	material.transparency = BaseMaterial3D.TRANSPARENCY_ALPHA
	material.blend_mode = BaseMaterial3D.BLEND_MODE_ADD if additive else BaseMaterial3D.BLEND_MODE_MIX
	material.billboard_mode = BaseMaterial3D.BILLBOARD_PARTICLES
	material.vertex_color_use_as_albedo = true
	material.albedo_texture = soft_texture()
	material.albedo_color = Color(color.r * energy, color.g * energy, color.b * energy, color.a)
	material.no_depth_test = false
	material.disable_receive_shadows = true
	_cache[key] = material
	return material

static func _quad(size: float, material: Material) -> QuadMesh:
	var quad := QuadMesh.new()
	quad.size = Vector2(size, size)
	quad.material = material
	return quad

static func _ramp(stops: Array) -> GradientTexture1D:
	var gradient := Gradient.new()
	gradient.offsets = PackedFloat32Array(stops.map(func(s: Array) -> float: return s[0]))
	gradient.colors = PackedColorArray(stops.map(func(s: Array) -> Color: return s[1]))
	var texture := GradientTexture1D.new()
	texture.gradient = gradient
	return texture

static func _curve(points: Array) -> CurveTexture:
	var curve := Curve.new()
	for p: Vector2 in points:
		curve.add_point(p)
	var texture := CurveTexture.new()
	texture.curve = curve
	return texture

static func _base(name: String, amount: int, lifetime: float, box: AABB) -> GPUParticles3D:
	var particles := GPUParticles3D.new()
	particles.name = name
	particles.amount = amount
	particles.lifetime = lifetime
	particles.visibility_aabb = box
	particles.cast_shadow = GeometryInstance3D.SHADOW_CASTING_SETTING_OFF
	particles.local_coords = false
	particles.emitting = false
	return particles

## Continuous sparks falling from damaged masonry and metal.
static func sparks(color: Color, amount: int = 14, radius: float = 1.0, height: float = 2.0) -> GPUParticles3D:
	var particles := _base("Sparks", amount, .9, AABB(Vector3(-4, -1, -4), Vector3(8, 9, 8)))
	var process := ParticleProcessMaterial.new()
	process.emission_shape = ParticleProcessMaterial.EMISSION_SHAPE_RING
	process.emission_ring_axis = Vector3.UP
	process.emission_ring_radius = radius
	process.emission_ring_inner_radius = radius * .6
	process.emission_ring_height = height
	process.direction = Vector3(0, 1, 0)
	process.spread = 60.0
	process.initial_velocity_min = .6
	process.initial_velocity_max = 2.2
	process.gravity = Vector3(0, -5.5, 0)
	process.scale_min = .5
	process.scale_max = 1.0
	process.color_ramp = _ramp([[0.0, Color(1, 1, 1, 1)], [.5, Color(1, .8, .5, .9)], [1.0, Color(1, .4, .2, 0)]])
	particles.process_material = process
	particles.draw_pass_1 = _quad(.07, sprite_material(color, true, 3.0))
	return particles

## Thin rising smoke (damage) or a heavier plume (ruin, destruction).
static func smoke(amount: int = 10, radius: float = .8, dark: float = .22, size: float = 1.1, lifetime: float = 3.2) -> GPUParticles3D:
	var particles := _base("Smoke", amount, lifetime, AABB(Vector3(-5, -1, -5), Vector3(10, 14, 10)))
	var process := ParticleProcessMaterial.new()
	process.emission_shape = ParticleProcessMaterial.EMISSION_SHAPE_SPHERE
	process.emission_sphere_radius = radius
	process.direction = Vector3(0, 1, 0)
	process.spread = 18.0
	process.initial_velocity_min = .35
	process.initial_velocity_max = .8
	process.gravity = Vector3(.18, .25, .08)
	process.damping_min = .2
	process.damping_max = .5
	process.scale_min = .7
	process.scale_max = 1.3
	process.scale_curve = _curve([Vector2(0, .35), Vector2(1, 1.6)])
	process.angle_min = 0.0
	process.angle_max = 360.0
	process.color_ramp = _ramp([[0.0, Color(dark, dark, dark * 1.05, 0)], [.15, Color(dark, dark, dark * 1.05, .42)], [1.0, Color(dark * 1.3, dark * 1.3, dark * 1.35, 0)]])
	particles.process_material = process
	particles.draw_pass_1 = _quad(size, sprite_material(Color(1, 1, 1, 1), false))
	return particles

## One-shot dust and rubble burst at the foot of a collapsing structure.
static func dust_burst(amount: int = 36, radius: float = 1.4, size: float = 1.6, color: Color = Color(.62, .58, .52)) -> GPUParticles3D:
	var particles := _base("DustBurst", amount, 1.9, AABB(Vector3(-7, -1, -7), Vector3(14, 10, 14)))
	particles.one_shot = true
	particles.explosiveness = .85
	var process := ParticleProcessMaterial.new()
	process.emission_shape = ParticleProcessMaterial.EMISSION_SHAPE_RING
	process.emission_ring_axis = Vector3.UP
	process.emission_ring_radius = radius
	process.emission_ring_inner_radius = radius * .3
	process.emission_ring_height = .6
	process.direction = Vector3(0, .35, 0)
	process.spread = 80.0
	process.initial_velocity_min = 1.2
	process.initial_velocity_max = 3.4
	process.gravity = Vector3(0, -.6, 0)
	process.damping_min = 1.6
	process.damping_max = 2.6
	process.scale_curve = _curve([Vector2(0, .4), Vector2(1, 1.8)])
	process.angle_max = 360.0
	process.color_ramp = _ramp([[0.0, Color(color.r, color.g, color.b, .75)], [1.0, Color(color.r, color.g, color.b, 0)]])
	particles.process_material = process
	particles.draw_pass_1 = _quad(size, sprite_material(Color(1, 1, 1, 1), false))
	return particles

## One-shot burst of glowing crystal fragments (crystal failure, Ancient collapse).
static func shard_burst(color: Color, amount: int = 40, speed: float = 5.0) -> GPUParticles3D:
	var particles := _base("ShardBurst", amount, 1.3, AABB(Vector3(-9, -2, -9), Vector3(18, 14, 18)))
	particles.one_shot = true
	particles.explosiveness = .95
	var process := ParticleProcessMaterial.new()
	process.emission_shape = ParticleProcessMaterial.EMISSION_SHAPE_SPHERE
	process.emission_sphere_radius = .4
	process.direction = Vector3(0, 1, 0)
	process.spread = 180.0
	process.initial_velocity_min = speed * .4
	process.initial_velocity_max = speed
	process.gravity = Vector3(0, -7.0, 0)
	process.scale_min = .5
	process.scale_max = 1.2
	process.color_ramp = _ramp([[0.0, Color(1, 1, 1, 1)], [.6, Color(1, 1, 1, .8)], [1.0, Color(1, 1, 1, 0)]])
	particles.process_material = process
	var mesh := PrismMesh.new()
	mesh.size = Vector3(.06, .16, .06)
	var material := StandardMaterial3D.new()
	material.shading_mode = BaseMaterial3D.SHADING_MODE_UNSHADED
	material.vertex_color_use_as_albedo = true
	material.transparency = BaseMaterial3D.TRANSPARENCY_ALPHA
	material.albedo_color = Color(color.r * 1.35, color.g * 1.35, color.b * 1.35)
	mesh.material = material
	particles.draw_pass_1 = mesh
	return particles

## Slow rising motes of energy around crystals (ambient; few particles).
static func motes(color: Color, amount: int = 18, radius: float = 2.0, height: float = 3.0, lifetime: float = 4.0) -> GPUParticles3D:
	var particles := _base("Motes", amount, lifetime, AABB(Vector3(-6, -1, -6), Vector3(12, 14, 12)))
	var process := ParticleProcessMaterial.new()
	process.emission_shape = ParticleProcessMaterial.EMISSION_SHAPE_RING
	process.emission_ring_axis = Vector3.UP
	process.emission_ring_radius = radius
	process.emission_ring_inner_radius = radius * .3
	process.emission_ring_height = height
	process.direction = Vector3(0, 1, 0)
	process.spread = 25.0
	process.initial_velocity_min = .15
	process.initial_velocity_max = .45
	process.gravity = Vector3(0, .08, 0)
	process.tangential_accel_min = .2
	process.tangential_accel_max = .5
	process.scale_min = .6
	process.scale_max = 1.2
	process.color_ramp = _ramp([[0.0, Color(1, 1, 1, 0)], [.2, Color(1, 1, 1, 1)], [1.0, Color(1, 1, 1, 0)]])
	particles.process_material = process
	particles.draw_pass_1 = _quad(.09, sprite_material(color, true, 2.2))
	return particles

## Energy escaping from a cracked crystal: fast, bright sparks shooting upwards in bursts.
static func leak(color: Color, amount: int = 30, radius: float = .8) -> GPUParticles3D:
	var particles := _base("Leak", amount, 1.1, AABB(Vector3(-5, -2, -5), Vector3(10, 14, 10)))
	particles.explosiveness = .35
	particles.randomness = .6
	var process := ParticleProcessMaterial.new()
	process.emission_shape = ParticleProcessMaterial.EMISSION_SHAPE_SPHERE
	process.emission_sphere_radius = radius
	process.direction = Vector3(0, 1, 0)
	process.spread = 35.0
	process.initial_velocity_min = 2.2
	process.initial_velocity_max = 4.6
	process.gravity = Vector3(0, -1.2, 0)
	process.damping_min = .8
	process.damping_max = 1.6
	process.scale_min = .6
	process.scale_max = 1.3
	process.color_ramp = _ramp([[0.0, Color(1, 1, 1, 1)], [.6, Color(1, 1, 1, .7)], [1.0, Color(1, 1, 1, 0)]])
	particles.process_material = process
	particles.draw_pass_1 = _quad(.1, sprite_material(color, true, 3.2))
	return particles

## Additive billboard flash (impact, overload); animate its scale and transparency.
static func flash_mesh(color: Color, size: float = 1.0) -> MeshInstance3D:
	var flash := MeshInstance3D.new()
	var quad := QuadMesh.new()
	quad.size = Vector2(size, size)
	var material := StandardMaterial3D.new()
	material.shading_mode = BaseMaterial3D.SHADING_MODE_UNSHADED
	material.transparency = BaseMaterial3D.TRANSPARENCY_ALPHA
	material.blend_mode = BaseMaterial3D.BLEND_MODE_ADD
	material.billboard_mode = BaseMaterial3D.BILLBOARD_ENABLED
	material.albedo_texture = soft_texture()
	material.albedo_color = color
	material.disable_receive_shadows = true
	quad.material = material
	flash.mesh = quad
	flash.cast_shadow = GeometryInstance3D.SHADOW_CASTING_SETTING_OFF
	return flash

## Restarts a one-shot effect at a position.
static func fire(particles: GPUParticles3D, at: Vector3) -> void:
	particles.global_position = at
	particles.restart()
	particles.emitting = true