# steer.ludic - turning toward a point at a rate, a step along the facing that turns away from water
# and a climb; a walker leaves a print every 2.8 m (the way there and a target about home: way.ludic)
function wl_wrap(a: float) -> float {
  var r = a
  while r > 3.1415927 { r = r - WL_TAU }
  while r < -3.1415927 { r = r + WL_TAU }
  return r
}

function wl_face(a: WildAnimal, tx: float, tz: float, rate: float, dt: float) -> void {
  let want = Math.atan2(-(tx - a.x), -(tz - a.z))
  let r = rate * dt
  a.yaw = a.yaw + Math.clamp(wl_wrap(want - a.yaw), -r, r)
  a.goal_x = tx
  a.goal_z = tz
}

# true when it moved; a walker is slid round a still thing (a trunk, a tent), a bird is not

# a climb is judged over half a metre ahead, not one frame's step: a few centimetres of the drawn
# ground rise steeply over a pebble a walker steps across, and a frame's step shrinks with the rate
const WL_LOOK: float = 0.5
function wl_climb(a: WildAnimal, nx: float, nz: float) -> float {
  let dx = nx - a.x
  let dz = nz - a.z
  let l = Math.sqrt(dx * dx + dz * dz)
  return WildlifeWorld.ground(a.x + dx / l * WL_LOOK, a.z + dz / l * WL_LOOK) - a.y
}

function wl_step(wildlife_st: mut WildlifeState, a: WildAnimal, dt: float) -> bool {
  if a.crowd { return wl_crowd_step(a) }
  let d = a.speed * dt
  if d < 0.0001 { return false }
  var nx = a.x - Math.sin(a.yaw) * d
  var nz = a.z - Math.cos(a.yaw) * d
  let s = wl_sp(wildlife_st, a.sp)
  if not s.flies and wl_push(wildlife_st, a, s, nx, nz) {
    nx = wildlife_st.wl_out_x
    nz = wildlife_st.wl_out_z
  }
  let nh = WildlifeWorld.ground(nx, nz)
  let moved = Math.abs(nx - a.x) + Math.abs(nz - a.z)
  let wet = nh < WildlifeWorld.water(nx, nz) + 0.6
  let steep = moved > 0.0001 and wl_climb(a, nx, nz) > WL_LOOK * 1.2
  if wet or steep or moved < d * 0.2 {
    if wet { wildlife_st.wl_turned_wet += 1 } else if steep { wildlife_st.wl_turned_steep += 1 }
    a.yaw = a.yaw + Math.deg_to_rad(75.0)
    a.timer = 0.0
    wildlife_st.wl_turned += 1
    return false
  }
  a.x = nx
  a.z = nz
  a.y = nh
  wl_walked(wildlife_st, a, s, d)
  return true
}

# (x, z) pushed clear of every still thing for a body its size; wl_out_x / _z say where
function wl_push(wildlife_st: mut WildlifeState, a: WildAnimal, s: WildSpecies, x: float, z: float) -> bool {
  wildlife_st.wl_ask_x = x
  wildlife_st.wl_ask_z = z
  let k = Math.clamp(float(s.size), 0.0, 2.0)
  let r = (0.2 + 0.2 * k) * s.scale * a.scale
  let hit = WildlifeWorld.push(x, z, r, a.y + 0.1, a.y + (0.5 + 0.7 * k) * s.scale * a.scale)
  wildlife_st.wl_out_x = x
  wildlife_st.wl_out_z = z
  if hit {
    wildlife_st.wl_out_x = WildlifeWorld.pushed_x()
    wildlife_st.wl_out_z = WildlifeWorld.pushed_z()
  }
  return hit
}

function wl_at_target(a: WildAnimal, r: float) -> bool {
  let dx = a.tx - a.x
  let dz = a.tz - a.z
  return dx * dx + dz * dz < r * r
}

# back to wandering about home after `t` seconds of whatever it was doing
function wl_wander(wildlife_st: WildlifeState, a: WildAnimal, t: float) -> void {
  a.state = WILD_WANDER
  a.timer = t
  wl_pick_target(wildlife_st, a, wl_sp(wildlife_st, a.sp).home)
}

# home where it stands now, kept inside its range
function wl_rehome(wildlife_st: WildlifeState, a: WildAnimal) -> void {
  a.home_x = a.x
  a.home_z = a.z
  wl_clamp(wildlife_st, a)
}