# state.ludic - the port, the kinds and layers, the facts, and what the world holds
# what the package asks the world: the water's surface under a point and the current there.
# Unbound there is no water.
export port PhysWater {
  height: fn(float, float) -> float = fn ph_dry
  current_x: fn(float, float) -> float = fn ph_still
  current_z: fn(float, float) -> float = fn ph_still
}
function ph_dry(x: float, z: float) -> float { return PHYS_NONE }
function ph_still(x: float, z: float) -> float { return 0.0 }

export const PHYS_NONE: float = -1000000000.0   # no height: no water, nothing under a query

# what a query sees, as a mask: the ground, the still things on it, and what moves
export const PHYS_M_GROUND: int = 1
export const PHYS_M_STATIC: int = 2
export const PHYS_M_MOVING: int = 4
export const PHYS_M_SOLID: int = 3
export const PHYS_M_ALL: int = 7

# what happened
export const PHYS_HIT: int = 0        # two bodies met at least ph_hard metres a second apart
export const PHYS_SPLASH: int = 1     # a floating body reached the water

export property PhysFact {
  what: int = 0
  a: int = -1
  b: int = -1
  x: float = 0.0
  y: float = 0.0
  z: float = 0.0
  speed: float = 0.0
}

export const PH_CAP: int = 512        # contacts drained a step, queries' buffers

export state PhysicsState {
  ph_world: pointer = null
  @max(262144) ph_shapes: []pointer = new []pointer     # a shape id is its place here; null once freed
  @max(262144) ph_spare: []int = new []int              # the freed places, handed out again (shape_ids.ludic)
  @max(262144) ph_own: []int = new []int                # by a body's index: the shape it owns, freed with it (owned.ludic)
  ph_step: float = 0.016666668    # seconds a step
  ph_sub: int = 1                 # collision steps in each
  ph_max_steps: int = 4           # a slow frame catches up this far and no further
  ph_max: int = 0                 # the bodies the world was opened for: one more is a failure, not a -1
  ph_acc: float = 0.0
  ph_steps: int = 0
  ph_gen: int = 0                 # how many worlds have been opened: an id from an older one is stale
  ph_hard: float = 2.0            # metres a second: a contact under this is not a fact
  ph_floats: words = words(256)        # buoyant bodies' ids, the first ph_nf of them
  ph_float_k: floats = floats(256 * 4)  # and theirs: buoyancy, linear drag, angular drag, wet
  ph_nf: int = 0
  ph_rx: float = 0.0               # where the last phys_resolve put a body
  ph_rz: float = 0.0
  @max(64) ph_walkers: []pointer = new []pointer   # a walker id is its place here; null once removed
  ph_ids: []int = words(PH_CAP * 2)
  ph_vals: []float = floats(PH_CAP * 4)
  ph_facts: Queue<PhysFact> = ph_facts__new()
  @max(1024) ph_fpool: []PhysFact = ph_fpool_new()   # every fact record made, reused once no drain holds it
  @max(1024) ph_ffree: []PhysFact = ph_ffree_new()
  ph_fnext: int = 0
}

# the facts, oldest first
export function phys_facts(physics_st: PhysicsState) -> Queue<PhysFact> {
  return physics_st.ph_facts
}

function ph_buffers() -> void {
}

# a step's length, its collision steps, and how hard a contact must be to be a fact
export function phys_config(physics_st: mut PhysicsState, step: float, sub: int, hard: float) -> void {
  physics_st.ph_step = step
  physics_st.ph_sub = sub
  physics_st.ph_hard = hard
}
function ph_facts__new() -> Queue<PhysFact> { return queue_new("physics.facts") }

# what moves, sized: touching pairs, contact constraints and the step's temp heap (KB). A valley's still
# things make no pairs between them; drops, boats and the walkers do. Past a size a step fails loudly
export const PH_PAIRS: int = 4096
export const PH_CONTACTS: int = 2048
export const PH_TEMP_KB: int = 4096