# ============================================================================
# systems_light.ludic — the engine-owned 2D lighting render system (#47).
#
# This is the ECS-native shape the lighting follow-up asked for: a torch is just
# an entity carrying `Light2D` (and optionally `Position`), a wall is an entity
# carrying `Occluder`, and the engine runs the whole light pass for you at the
# end of the Render phase — no `Light.point` / `Light.occlude` calls wired by
# hand. It reuses the deterministic accumulation core shipped in #4 (light.ludic:
# light_ambient / light_occlude / light_point), consuming components through the
# by-name reflection ABI instead of imperative calls.
#
# Split from systems.ludic because it links against the light pass (light.ludic):
# a game that uses SpriteAnim/Motion but no lights must not pull light_point in,
# so esys_light2d lives in its own file, spliced only when Light2D / Occluder is
# declared (parse.ludic). It is inserted into the Render phase after the game's
# own draw handlers (emit_engine_systems_for_phase), so the scene is already on
# the framebuffer when the light pass runs; it finishes by presenting the frame,
# so an ECS-lit game leaves Screen.show to the engine.
#
# Component contracts:
#   property Ambient  { color: int }                       # optional, one entity
#   property Light2D  { x, y, radius, color, intensity }   # intensity is 0..100 %
#   property Occluder { x, y, w, h }
# A Light2D / Occluder reads its position from a `Position { x, y }` component on
# the same entity when the entity carries one, else from its own x / y fields —
# so "Position + Light2D" and a self-positioned Light2D both work.
# ============================================================================

# read entity `e`'s world x: a `Position { x }` component wins when present, else
# the component's own x field (fx) on prop `p`. Same idea for y below.
function esys_pos_x(e: int, p: int, fx: int) -> int {
  let pp = World.prop_id("Position")
  if pp >= 0 {
    if World.has(e, pp) != 0 {
      let f = World.field_id(pp, "x")
      if f >= 0 { return World.get(e, pp, f) }
    }
  }
  if fx >= 0 { return World.get(e, p, fx) }
  return 0
}
function esys_pos_y(e: int, p: int, fy: int) -> int {
  let pp = World.prop_id("Position")
  if pp >= 0 {
    if World.has(e, pp) != 0 {
      let f = World.field_id(pp, "y")
      if f >= 0 { return World.get(e, pp, f) }
    }
  }
  if fy >= 0 { return World.get(e, p, fy) }
  return 0
}

function esys_light2d(rt_core_st: mut RtCoreState, rt_light_st: mut RtLightState) -> void {
  let pl = World.prop_id("Light2D")
  if pl < 0 { return }

  # 1. ambient — a single `Ambient { color }` entity modulates the whole scene
  # toward its tint (night / cave). Absent: the scene keeps its drawn brightness.
  let pa = World.prop_id("Ambient")
  if pa >= 0 {
    let af = World.field_id(pa, "color")
    let ae = World.query_next(pa, 0)
    if ae >= 0 {
      if af >= 0 { light_ambient(rt_core_st, World.get(ae, pa, af)) }
    }
  }

  # 2. occluders — re-register every `Occluder` as a shadow caster this frame.
  light_clear_occluders(rt_light_st)
  let po = World.prop_id("Occluder")
  if po >= 0 {
    let oxf = World.field_id(po, "x")
    let oyf = World.field_id(po, "y")
    let owf = World.field_id(po, "w")
    let ohf = World.field_id(po, "h")
    var oe = World.query_next(po, 0)
    while oe >= 0 {
      let ox = esys_pos_x(oe, po, oxf)
      let oy = esys_pos_y(oe, po, oyf)
      var ow = 0
      var oh = 0
      if owf >= 0 { ow = World.get(oe, po, owf) }
      if ohf >= 0 { oh = World.get(oe, po, ohf) }
      light_occlude(rt_light_st, ox, oy, ow, oh)
      oe = World.query_next(po, oe + 1)
    }
  }

  # 3. lights — additively accumulate each `Light2D` as a radial glow, cut by the
  # occluders registered above (hard shadows). Beyond the core five fields, a
  # Light2D may carry optional tier fields, each defaulting off when absent so an
  # older five-field component still lights exactly as before:
  #   direction, spread — a cone/spot (spread < 0 or absent = omnidirectional)
  #   falloff           — brightness ramp exponent (1 = linear, absent = 1)
  #   softness          — penumbra radius in px (0 / absent = hard shadows)
  #   gel               — outer rim colour for a colour cookie (< 0 / absent = off)
  let lxf = World.field_id(pl, "x")
  let lyf = World.field_id(pl, "y")
  let lrf = World.field_id(pl, "radius")
  let lcf = World.field_id(pl, "color")
  let lif = World.field_id(pl, "intensity")
  let ldf = World.field_id(pl, "direction")
  let lsf = World.field_id(pl, "spread")
  let lff = World.field_id(pl, "falloff")
  let lkf = World.field_id(pl, "softness")
  let lgf = World.field_id(pl, "gel")
  var e = World.query_next(pl, 0)
  while e >= 0 {
    let x = esys_pos_x(e, pl, lxf)
    let y = esys_pos_y(e, pl, lyf)
    var radius = 0
    if lrf >= 0 { radius = World.get(e, pl, lrf) }
    var color = 16777215                              # 0xFFFFFF (white) default
    if lcf >= 0 { color = World.get(e, pl, lcf) }
    var energy = fixed(1)                             # full intensity default
    if lif >= 0 { energy = fixed(World.get(e, pl, lif)) / fixed(100) }

    # tier controls: apply per light, resetting to defaults each time so one
    # cone/soft light does not bleed its settings onto the next.
    var falloff = 1
    if lff >= 0 { falloff = World.get(e, pl, lff) }
    light_set_falloff(rt_light_st, falloff)
    var soft = 0
    if lkf >= 0 { soft = World.get(e, pl, lkf) }
    light_set_soft(rt_light_st, soft)
    if lgf >= 0 { light_set_gel(rt_light_st, World.get(e, pl, lgf)) } else { light_clear_gel(rt_light_st) }

    var spread = -1
    if lsf >= 0 { spread = World.get(e, pl, lsf) }
    var direction = 0
    if ldf >= 0 { direction = World.get(e, pl, ldf) }
    if spread >= 0 { light_spot(rt_core_st, rt_light_st, x, y, radius, color, energy, direction, spread) }
    else { light_point(rt_core_st, rt_light_st, x, y, radius, color, energy) }
    e = World.query_next(pl, e + 1)
  }

  # 4. present — the engine owns the flip for an ECS-lit frame.
  Screen.show()
}