# We need this for 2D vectors
# Make sure you pass the correct include path to "bzzc -I <path1:path2> ..."
include "include/vec2.bzz"

# Lennard-Jones parameters
TARGET_KIN     = 283.0
EPSILON_KIN    = 150.0
TARGET_NONKIN  = 200.0
EPSILON_NONKIN = 100.0

# Lennard-Jones interaction magnitude
function lj_magnitude(dist, target, epsilon) {
  return -(epsilon / dist) * ((target / dist)^4 - (target / dist)^2)
}

# Neighbor data to LJ interaction vector
function lj_vector_kin(rid, data) {
  return math.vec2.newp(lj_magnitude(data.distance, TARGET_KIN, EPSILON_KIN), data.azimuth)
}

# Neighbor data to LJ interaction vector
function lj_vector_nonkin(rid, data) {
  return math.vec2.newp(lj_magnitude(data.distance, TARGET_NONKIN, EPSILON_NONKIN), data.azimuth)
}

# Accumulator of neighbor LJ interactions
function lj_sum(rid, data, accum) {
  return math.vec2.add(data, accum)
}

# Calculates and actuates the flocking interaction
function square() {
  # Calculate accumulator
  var accum = neighbors.kin().map(lj_vector_kin).reduce(lj_sum, math.vec2.new(0.0, 0.0))
  accum = neighbors.nonkin().map(lj_vector_nonkin).reduce(lj_sum, accum)
  if(neighbors.count() > 0)
    math.vec2.scale(accum, 1.0 / neighbors.count())
  # Move according to vector
  goto(accum.x, accum.y)
}

# Executed at init time
function init() {
  # Divide the swarm in two sub-swarms
  s1 = swarm.create(1)
  s1.select(id % 2 == 0)
  s2 = s1.others(2)
}

# Executed every time step
function step() {
  s1.exec(square)
  s2.exec(square)
}

# Execute at exit
function destroy() {
}