/**
 * Simple 2d knockback with unit collision detection.
 * By muzzel
 */
package Knockback
import Terrain
import LinkedList

@configurable constant string SFX_EARTH = "Objects\\Spawnmodels\\Undead\\ImpaleTargetDust\\ImpaleTargetDust.mdl"
@configurable constant string SFX_WATER = "Abilities\\Spells\\Undead\\AbsorbMana\\AbsorbManaBirthMissile.mdl"
@configurable constant string SFX_ATTACHPOINT = "origin"

/** Filter for unit collision. No collision action will be executed for units where this function returns false. */
@configurable function unitValid(unit u) returns boolean
		return not IsUnitType(u, UNIT_TYPE_DEAD) and (GetUnitTypeId(u) != DUMMY_UNIT_ID)

public interface UnitCollision
	/**
	 * Action that is run for every collision.
	 * unit knockbackUnit: unit currenly performing the knockback
	 * unit hitUnit: unit the knockbackUnit collided with
	 */
	function onCollide(unit knockbackUnit, unit hitUnit)


public class Knockback
	use Periodic
	unit u
	vec2 acc
	vec2 vel
	int steps
	boolean useEffects
	boolean stopImpassable
	effect sfx
	int sfxCurr
	UnitCollision collisionAction
	LinkedList<unit> collisionUnits
	real collisionSize

	/**
	 * Performs a simple 2d knockback. The knockback object is automatically destroyed afterwards.
	 * unit u: the unit to be knocked back.
	 * vec2 moveVec: defines the knockback distance and direction.
	 * real time: specifies the duration of the knockback.
	 * boolean useEffects: if true, if special effects should be displayed for knockbacks on the ground or shallow water.
	 * boolean stopImpassable: if true, the knockback is stopped if the unit is about to enter impassable terrain.
	 */
	construct(unit u, vec2 moveVec, real time, boolean useEffects, boolean stopImpassable)
		let speed = 2 * moveVec.length() / ((time / ANIMATION_PERIOD) + 1)
		let acceleration = speed / (time / ANIMATION_PERIOD)
		let dir = moveVec.norm()
		this.u = u
		this.acc = dir * acceleration
		this.vel = dir * speed
		this.steps = (time / ANIMATION_PERIOD).toInt()
		this.useEffects = useEffects
		this.stopImpassable = stopImpassable
		this.collisionAction = null
		if useEffects
			if isTerrainLand(u.getX(), u.getY())
				sfx = u.addEffect(SFX_EARTH, SFX_ATTACHPOINT)
				sfxCurr = 1
			else if isTerrainShallowWater(u.getX(), u.getY())
				sfx = u.addEffect(SFX_WATER, SFX_ATTACHPOINT)
				sfxCurr = 2
		startPeriodic(ANIMATION_PERIOD)

	/**
	 * Enables/disable collision for this knockback. Each unit can only collide once with each knockback.
	 * You can call this directly after creating a new Knockback object or at any other time.
	 * real size: range for collision checks, must be > 0.
	 * UnitCollision action: action that is executed for each collision. Use null to disable collision.
	 */
	function enableCollision(real size, UnitCollision action)
		if action == null // disable
			if this.collisionAction != null
				destroy this.collisionAction
				this.collisionAction = null
				destroy this.collisionUnits
		else // enable
			if this.collisionAction == null
				this.collisionAction = action
				this.collisionUnits = new LinkedList<unit>()
		this.collisionSize = size

	override function periodic()
		vel -= acc
		var newPos = u.getPos() + vel
		// effects:
		if useEffects
			if isTerrainLand(u.getX(), u.getY()) and sfxCurr != 1
				sfx.destr()
				sfx = u.addEffect(SFX_EARTH, SFX_ATTACHPOINT)
				sfxCurr = 1
			else if isTerrainShallowWater(u.getX(), u.getY()) and sfxCurr != 2
				sfx.destr()
				sfx = u.addEffect(SFX_WATER, SFX_ATTACHPOINT)
				sfxCurr = 2
		// terrain walkable check:
		if isTerrainWalkable(newPos.x, newPos.y)
			u.setXY(newPos)
		else
			if stopImpassable
				destroy this
				return
		// check for unit collisions
		if collisionAction != null
			if collisionSize > 0.
				ENUM_GROUP.clear()
				ENUM_GROUP.enumUnitsInRange(u.getPos(), collisionSize)
				for unit cu in ENUM_GROUP
					if unitValid(cu) and cu != u
						if not collisionUnits.contains(cu)
							collisionUnits.add(cu)
							collisionAction.onCollide(u, cu)
		// destroy if last iteration:
		steps--
		if steps <= 0
			destroy this

	ondestroy
		if sfx != null
			sfx.destr()
		if collisionUnits != null
			destroy collisionUnits
			collisionUnits = null