# puzzles.ludic — RPG Module F: the recurring 2D puzzle primitives (#59).
#
# Sokoban pushables on the grid, plus a signal graph of switches / pressure plates
# driving gates — logic puzzles with no code: wire a Gate to a source and the gate
# opens when the source is on. Composes with the grid Mover (Module A).

const PZ_Q: int = 65536

property Pushable { }
property Switch { on: int = 0 }
property Pressure { on: int = 0, step: int = 16 }
property Gate { open: int = 0, src: int = -1 }

event BlockPushed { block: int = 0, dx: int = 0, dy: int = 0 }
event cancellable PushBlocked { block: int = 0 }
event SignalChanged { gate: int = 0, open: int = 0 }

function pz_pos(e: int, name: pointer) -> int {
  let P = World.prop_id("Position");  if P < 0 { return 0 }
  return World.get(e, P, World.field_id(P, name))
}
function pz_pos_set(e: int, name: pointer, v: int) -> void {
  let P = World.prop_id("Position");  if P < 0 { return }
  World.set(e, P, World.field_id(P, name), v)
}

# the pushable whose cell is exactly (x, y), or -1.
function pz_block_at(x: int, y: int) -> int {
  let P = World.prop_id("Pushable")
  if P < 0 { return -1 }
  var e = World.query_next(P, 0)
  while e >= 0 {
    if (pz_pos(e, "x") == x) and (pz_pos(e, "y") == y) { return e }
    e = World.query_next(P, e + 1)
  }
  return -1
}

# reuse the Mover module's tilemap walkability check when present.
function pz_walkable(nx: int, ny: int, step: int) -> int {
  let ps = World.prop_id("Solids")
  if ps < 0 { return 1 }
  let se = World.query_next(ps, 0)
  if se < 0 { return 1 }
  let ft = World.field_id(ps, "tile")
  let fw = World.field_id(ps, "wall")
  if (ft < 0) or (fw < 0) { return 1 }
  let ts = World.get(se, ps, ft)
  if ts <= 0 { return 1 }
  let wall = World.get(se, ps, fw)
  if Grid.blocked(nx / ts, ny / ts, wall) { return 0 }
  return 1
}

# Puzzle.push(bx, by, dx, dy, step) — push the block at (bx,by) one cell along
# (dx,dy) if the destination is free (no wall, no other block). Returns 1 on a move.
@Namespace(Puzzle) function puzzle_push(bx: int, by: int, dx: int, dy: int, step: int) -> int {
  let b = pz_block_at(bx, by)
  if b < 0 { return 0 }
  let nx = bx + dx * step
  let ny = by + dy * step
  if (pz_walkable(nx, ny, step) == 0) or (pz_block_at(nx, ny) >= 0) {
    emit PushBlocked(block: b)
    return 0
  }
  pz_pos_set(b, "x", nx);  pz_pos_set(b, "y", ny)
  emit BlockPushed(block: b, dx: dx, dy: dy)
  return 1
}

# Puzzle.link(gate, source) — a gate opens when its source (a Switch or Pressure) is on.
@Namespace(Puzzle) function puzzle_link(gate: int, source: int) -> void {
  let P = World.prop_id("Gate")
  if P < 0 { return }
  World.set(gate, P, World.field_id(P, "src"), source)
}
# Puzzle.switch(e, on) — set a manual switch.
@Namespace(Puzzle) function puzzle_switch(e: int, on: int) -> void {
  let P = World.prop_id("Switch")
  if P < 0 { return }
  World.set(e, P, World.field_id(P, "on"), on)
}
@Namespace(Puzzle) function puzzle_is_open(gate: int) -> int {
  let P = World.prop_id("Gate")
  if P < 0 { return 0 }
  return World.get(gate, P, World.field_id(P, "open"))
}

# read the "on" state of a signal source (Switch or Pressure), 0 if neither.
function pz_source_on(src: int) -> int {
  if src < 0 { return 0 }
  let PS = World.prop_id("Switch")
  if (PS >= 0) and (World.has(src, PS) != 0) { return World.get(src, PS, World.field_id(PS, "on")) }
  let PP = World.prop_id("Pressure")
  if (PP >= 0) and (World.has(src, PP) != 0) { return World.get(src, PP, World.field_id(PP, "on")) }
  return 0
}

# ===========================================================================
# esys_pressure (Update) — a plate is on while a Pushable or a Position-carrying
# body sits on its cell.
# ===========================================================================
@EngineSystem(Pressure, Update) function esys_pressure() -> void {
  let P = World.prop_id("Pressure")
  if P < 0 { return }
  let fon = World.field_id(P, "on")
  let fstep = World.field_id(P, "step")
  var e = World.query_next(P, 0)
  while e >= 0 {
    let px = pz_pos(e, "x");  let py = pz_pos(e, "y")
    let step = World.get(e, P, fstep)
    var on = 0
    # a pushable on the plate?
    if pz_block_at(px, py) >= 0 { on = 1 }
    # or any other Position entity within the same cell?
    if on == 0 {
      let PP = World.prop_id("Position")
      var o = World.query_next(PP, 0)
      while o >= 0 {
        if (o != e) and (World.has(o, P) == 0) {
          let ox = World.get(o, PP, World.field_id(PP, "x"))
          let oy = World.get(o, PP, World.field_id(PP, "y"))
          var adx = ox - px;  if adx < 0 { adx = -adx }
          var ady = oy - py;  if ady < 0 { ady = -ady }
          if (adx < step) and (ady < step) { on = 1;  o = -1 }
        }
        if o >= 0 { o = World.query_next(PP, o + 1) }
      }
    }
    World.set(e, P, fon, on)
    e = World.query_next(P, e + 1)
  }
}

# ===========================================================================
# esys_gate (Update, after pressure) — a gate mirrors its source's on-state.
# ===========================================================================
@EngineSystem(Gate, Update) function esys_gate() -> void {
  let P = World.prop_id("Gate")
  if P < 0 { return }
  let fopen = World.field_id(P, "open")
  let fsrc = World.field_id(P, "src")
  var e = World.query_next(P, 0)
  while e >= 0 {
    let want = pz_source_on(World.get(e, P, fsrc))
    if World.get(e, P, fopen) != want {
      World.set(e, P, fopen, want)
      emit SignalChanged(gate: e, open: want)
    }
    e = World.query_next(P, e + 1)
  }
}