# ============================================================================
# fx.ludic — Fx.*: engine-owned transient effects. A game asks for a burst of
# sparks or a floating number and the engine owns the rest: it ages and moves
# them every Update, draws them every Render (after the sprites, before a game's
# Overlay pass, through the camera / shake / clip chokepoints), and drops them
# when they expire. Nothing is an entity, so nothing needs a component, a model,
# a handler or a draw call. Deterministic: velocities and lifetimes come from the
# seeded RNG.
#
#   Fx.sparks(x, y, color, count)   a burst of `count` sparks flying out of (x, y)
#   Fx.number(x, y, value, color)   a number that floats up from (x, y) and fades
#   Fx.clear()                      drop every effect (a room change, a new run)
# ============================================================================

const FX_MAX_SPARKS:  int = 512
const FX_MAX_NUMBERS: int = 64
const FX_SPARK_LIFE:  int = 18     # frames, plus up to FX_SPARK_LIFE_JITTER
const FX_SPARK_LIFE_JITTER: int = 8
const FX_SPARK_SPEED: int = 3      # px per frame, each axis, either way
const FX_NUMBER_LIFE: int = 30     # frames; a number rises one pixel every other frame

var fx_ready: bool = false
var fx_sx: words = null
var fx_sy: words = null
var fx_svx: words = null
var fx_svy: words = null
var fx_slife: words = null
var fx_scolor: words = null
var fx_ssize: words = null
var fx_sn: int = 0
var fx_nx: words = null
var fx_ny: words = null
var fx_nvalue: words = null
var fx_nlife: words = null
var fx_ncolor: words = null
var fx_nn: int = 0

function fx_init() -> void {
  if fx_ready { return }
  fx_sx = words(FX_MAX_SPARKS);  fx_sy = words(FX_MAX_SPARKS)
  fx_svx = words(FX_MAX_SPARKS);  fx_svy = words(FX_MAX_SPARKS)
  fx_slife = words(FX_MAX_SPARKS);  fx_scolor = words(FX_MAX_SPARKS);  fx_ssize = words(FX_MAX_SPARKS)
  fx_nx = words(FX_MAX_NUMBERS);  fx_ny = words(FX_MAX_NUMBERS)
  fx_nvalue = words(FX_MAX_NUMBERS);  fx_nlife = words(FX_MAX_NUMBERS);  fx_ncolor = words(FX_MAX_NUMBERS)
  fx_ready = true
}

function fx_sparks(x: int, y: int, color: int, count: int) -> void {
  fx_init()
  var i = 0
  while i < count {
    if fx_sn >= FX_MAX_SPARKS { return }
    fx_sx[fx_sn] = x
    fx_sy[fx_sn] = y
    fx_svx[fx_sn] = rt_rng_range(-FX_SPARK_SPEED, FX_SPARK_SPEED)
    fx_svy[fx_sn] = rt_rng_range(-FX_SPARK_SPEED, FX_SPARK_SPEED)
    fx_slife[fx_sn] = FX_SPARK_LIFE + rt_rng_range(0, FX_SPARK_LIFE_JITTER)
    fx_scolor[fx_sn] = color
    fx_ssize[fx_sn] = 1 + rt_rng_range(0, 2)
    fx_sn += 1
    i += 1
  }
}

function fx_number(x: int, y: int, value: int, color: int) -> void {
  fx_init()
  if fx_nn >= FX_MAX_NUMBERS { return }
  fx_nx[fx_nn] = x
  fx_ny[fx_nn] = y
  fx_nvalue[fx_nn] = value
  fx_nlife[fx_nn] = FX_NUMBER_LIFE
  fx_ncolor[fx_nn] = color
  fx_nn += 1
}

function fx_clear() -> void { fx_sn = 0;  fx_nn = 0 }

# drop spark i by moving the last one into its slot
function fx_drop_spark(i: int) -> void {
  let last = fx_sn - 1
  fx_sx[i] = fx_sx[last];  fx_sy[i] = fx_sy[last]
  fx_svx[i] = fx_svx[last];  fx_svy[i] = fx_svy[last]
  fx_slife[i] = fx_slife[last];  fx_scolor[i] = fx_scolor[last];  fx_ssize[i] = fx_ssize[last]
  fx_sn = last
}
function fx_drop_number(i: int) -> void {
  let last = fx_nn - 1
  fx_nx[i] = fx_nx[last];  fx_ny[i] = fx_ny[last]
  fx_nvalue[i] = fx_nvalue[last];  fx_nlife[i] = fx_nlife[last];  fx_ncolor[i] = fx_ncolor[last]
  fx_nn = last
}

# once per Update: move and age everything, dropping what expired
function fx_tick() -> void {
  if not fx_ready { return }
  var i = 0
  while i < fx_sn {
    fx_sx[i] += fx_svx[i]
    fx_sy[i] += fx_svy[i]
    fx_slife[i] -= 1
    if fx_slife[i] <= 0 { fx_drop_spark(i) } else { i += 1 }
  }
  i = 0
  while i < fx_nn {
    fx_nlife[i] -= 1
    if fx_nlife[i] % 2 == 0 { fx_ny[i] -= 1 }
    if fx_nlife[i] <= 0 { fx_drop_number(i) } else { i += 1 }
  }
}

# once per Render, after the sprites: everything goes through the camera chokepoints
function fx_draw() -> void {
  if not fx_ready { return }
  var i = 0
  while i < fx_sn {
    rt_fill_rect(fx_sx[i], fx_sy[i], fx_ssize[i], fx_ssize[i], fx_scolor[i])
    i += 1
  }
  i = 0
  while i < fx_nn {
    rt_text_int(fx_nx[i] - 4, fx_ny[i] - 10, fx_nvalue[i], fx_ncolor[i], 1)
    i += 1
  }
}