class_name MapGen
extends RefCounted
## Builds a dungeon: generated rooms and corridors around a hand-authored boss
## arena (see [Rooms]).
##
## Deterministic from (seed, depth) alone, which is what makes a failing run
## reproducible from its log line. It does NOT mean the client can rebuild the
## map -- see the note on build().

## Tunnel widths, in tiles, rolled per leg of every corridor.
##
## The floor is 2 because a one-tile tunnel in a bullet hell is a shooting
## gallery: there is no side to step to, so anything fired down it lands. Each
## leg of an L rolls its own width, so a tunnel can open up or pinch at its
## bend rather than every connection in the map being the same pipe.
const CORRIDOR_MIN_WIDTH := 2
const CORRIDOR_MAX_WIDTH := 4


## The single entry point. SERVER-SIDE ONLY.
##
## This used to be described as "both sides call it with the same three
## integers" -- that is no longer true and has not been since map streaming
## landed. Handing a client the seed would let it regenerate the entire floor
## plan, which is a map hack with no work required, so the client is given the
## map's SIZE and nothing else and fills tiles in from streamed chunks as it
## walks. See ServerRuntime._stream_map.
##
## Generation is still deterministic from (kind, seed, depth), which is what
## makes a bad run reproducible from its log line; tests/unit/test_map_gen.gd
## pins that.
static func build(kind: Protocol.InstanceKind, seed_value: int, depth: int,
		arena: StringName = &"") -> Dictionary:
	if kind == Protocol.InstanceKind.LOBBY:
		return _build_lobby()
	return generate(seed_value, depth, arena)


static func _build_lobby() -> Dictionary:
	var stamp := Rooms.lobby()
	var size := Rooms.size_of(stamp)
	var grid := MapGrid.new(size.x, size.y, MapGrid.Kind.WALL)
	grid.centre_on_origin()
	var markers := Rooms.stamp(grid, stamp, Vector2i.ZERO)
	var spawn := grid.tile_centre(size.x / 2, size.y - 4)
	if not markers["S"].is_empty():
		var m: Vector2i = markers["S"][0]
		spawn = grid.tile_centre(m.x, m.y)
	# One portal per marker, in reading order, matched against Dungeons.ORDER.
	# A stamp with fewer markers than dungeons simply makes the extra ones
	# unreachable rather than crashing -- an unreachable dungeon is a content
	# bug, not a runtime one.
	var portals: Array[SimPortal] = []
	for i in (markers["P"] as Array).size():
		if i >= Dungeons.ORDER.size():
			break
		var m: Vector2i = markers["P"][i]
		portals.append(SimPortal.make(grid.tile_centre(m.x, m.y), Dungeons.ORDER[i]))
	if portals.is_empty():
		portals.append(SimPortal.make(
			grid.tile_centre(size.x / 2, 3), Dungeons.default_id()))
	var target := grid.tile_centre(size.x / 4, size.y / 2)
	if not markers["T"].is_empty():
		var m: Vector2i = markers["T"][0]
		target = grid.tile_centre(m.x, m.y)
	var npc := grid.tile_centre(size.x * 3 / 4, size.y / 2)
	if not markers["U"].is_empty():
		var m: Vector2i = markers["U"][0]
		npc = grid.tile_centre(m.x, m.y)
	return {
		"grid": grid,
		"rooms": [] as Array[Rect2i],
		"spawn": spawn,
		"portals": portals,
		"dummy": target,
		"npc": npc,
		"boss_pos": Vector2.ZERO,
		"boss_room": Rect2i(),
		"boss_id": &"",
	}


## Result keys: grid, rooms (Array[Rect2i]), spawn (Vector2), boss_pos
## (Vector2), boss_room (Rect2i).
## [param arena] names the boss arena to stamp, and therefore which boss the run
## ends with. Empty leaves it to the seed, which is what the Proving Grounds
## wants and nothing else does -- for a real dungeon the boss is the thing a
## player chose at the portal.
static func generate(seed_value: int, depth: int, arena: StringName = &"") -> Dictionary:
	var rng := RandomNumberGenerator.new()
	rng.seed = seed_value
	var d := maxi(depth, 1)

	# Size grows with depth. Depth 1 is a little under two screens across --
	# enough that fog and exploration mean something without a first run
	# becoming a hike.
	var w := 56 + d * 10
	var h := 36 + d * 7
	var grid := MapGrid.new(w, h, MapGrid.Kind.WALL)
	grid.centre_on_origin()

	# The boss arena is placed first and everything else works around it, so a
	# generated corridor can never carve through the authored fight.
	# Normally the dungeon says which arena it is; only the test harness leaves
	# it open, and then the seed decides.
	var chosen := arena
	if chosen.is_empty():
		chosen = &"warden_hall" if posmod(seed_value, 2) == 0 else &"choir_vault"
	var stamp := Rooms.warden_hall() if chosen == &"warden_hall" else Rooms.choir_vault()
	var bs := Rooms.size_of(stamp)
	var boss_origin := Vector2i(w - bs.x - 2, (h - bs.y) / 2)
	var markers := Rooms.stamp(grid, stamp, boss_origin)
	var boss_room := Rect2i(boss_origin, bs)
	var arena_id := chosen

	var boss_pos := grid.tile_centre(
		boss_origin.x + bs.x / 2, boss_origin.y + bs.y / 2)
	if not markers["B"].is_empty():
		var m: Vector2i = markers["B"][0]
		boss_pos = grid.tile_centre(m.x, m.y)

	var door := Vector2i(boss_origin.x, boss_origin.y + bs.y / 2)
	if not markers["D"].is_empty():
		door = markers["D"][0]

	# Generated rooms, confined to the space left of the arena.
	var rooms: Array[Rect2i] = []
	var usable_w := boss_origin.x - 2
	var attempts := 0
	var wanted := 5 + d
	while rooms.size() < wanted and attempts < wanted * 40:
		attempts += 1
		var rw := rng.randi_range(6, 12)
		var rh := rng.randi_range(5, 10)
		var rx := rng.randi_range(1, maxi(usable_w - rw - 1, 2))
		var ry := rng.randi_range(1, maxi(h - rh - 2, 2))
		var candidate := Rect2i(rx, ry, rw, rh)
		# One tile of padding so two rooms never share a wall and merge into an
		# ambiguous blob.
		var padded := candidate.grow(1)
		var clash := false
		for existing in rooms:
			if padded.intersects(existing.grow(1)):
				clash = true
				break
		if clash:
			continue
		rooms.append(candidate)
		grid.fill_rect(candidate, MapGrid.Kind.FLOOR)

	# Connect each room to the previous one, then the last to the arena door,
	# so every room is reachable by construction rather than by luck.
	var widths := PackedInt32Array()
	var legs: Array[Rect2i] = []
	for i in range(1, rooms.size()):
		var from := _centre_of(rooms[i - 1])
		widths.append_array(_carve_corridor(grid, rng, from, _centre_of(rooms[i]),
			(from.x + from.y) % 2 == 0, boss_room, legs))
	if not rooms.is_empty():
		# Aimed at the tile OUTSIDE the door, and always arriving along the
		# door's own row. Aiming at the door itself, an L that bent the other
		# way ran its second leg straight down the arena's west wall -- 45% of
		# generated arenas had a slit carved in an authored room. The arena is
		# also kept out of every carve, so a wide tunnel stops at its wall
		# rather than eating into it.
		var outside := door + Vector2i(-1, 0)
		widths.append_array(_carve_corridor(grid, rng,
			_centre_of(rooms[rooms.size() - 1]), outside, false, boss_room, legs))
		# The door tile itself, and the tile outside it, must be floor.
		grid.set_tile(door.x, door.y, MapGrid.Kind.FLOOR)
		grid.set_tile(outside.x, outside.y, MapGrid.Kind.FLOOR)

	_scatter_cover(grid, rooms, rng)

	var spawn := boss_pos
	if not rooms.is_empty():
		var c := _centre_of(rooms[0])
		# Cover is scattered before the spawn is chosen, so the spawn tile can
		# have had a pillar dropped on it. Clear it rather than hunting for a
		# free tile: this is the one tile in the map that must be standable.
		grid.set_tile(c.x, c.y, MapGrid.Kind.FLOOR)
		spawn = grid.tile_centre(c.x, c.y)

	return {
		"grid": grid,
		"rooms": rooms,
		"spawn": spawn,
		"portals": [] as Array[SimPortal],
		"dummy": Vector2.ZERO,
		"npc": Vector2.ZERO,
		"boss_pos": boss_pos,
		"boss_room": boss_room,
		# What every corridor leg was carved at. Not used by anything that
		# builds a world -- it is here so a test can check the widths actually
		# vary, which the tiles alone cannot say once tunnels overlap.
		"corridor_widths": widths,
		# The rectangle each tunnel leg was carved over. Overlaps the rooms it
		# joins at its ends, so whoever uses it decides what counts as tunnel --
		# Instance._populate_tunnels keeps only floor clear of every room.
		"tunnels": legs,
		# Which boss lives here follows from WHICH arena was stamped. Choosing
		# it anywhere else would let a dungeon put the Cantor in the Warden's
		# hall, where its patterns assume geometry that is not there.
		"boss_id": Rooms.boss_for_arena(arena_id),
	}


static func _centre_of(r: Rect2i) -> Vector2i:
	return Vector2i(r.position.x + r.size.x / 2, r.position.y + r.size.y / 2)


## L-shaped, with the corner order chosen by parity so corridors do not all
## bend the same way.
## An L-shaped tunnel from [param from] to [param to], each leg its own width.
## Returns the two widths it rolled.
##
## [param horizontal_first] picks which way the L bends. [param keep_out] is
## never carved: it is the boss arena, which is authored, and keeps exactly the
## walls it was drawn with.
static func _carve_corridor(grid: MapGrid, rng: RandomNumberGenerator,
		from: Vector2i, to: Vector2i, horizontal_first: bool,
		keep_out: Rect2i, legs: Array[Rect2i]) -> PackedInt32Array:
	var first := rng.randi_range(CORRIDOR_MIN_WIDTH, CORRIDOR_MAX_WIDTH)
	var second := rng.randi_range(CORRIDOR_MIN_WIDTH, CORRIDOR_MAX_WIDTH)
	var bend := Vector2i(to.x, from.y) if horizontal_first else Vector2i(from.x, to.y)
	# Each leg overshoots the bend by half the other's width, so the corner is
	# carved square. Cosmetic, not structural: the two legs always overlap on
	# the INNER side of the bend, so leaving this out never narrows a tunnel
	# below its width -- it just bevels the outer corner, which reads as a
	# notch rather than a turn.
	legs.append(_carve_leg(grid, from, bend, first, second / 2, keep_out))
	legs.append(_carve_leg(grid, bend, to, second, first / 2, keep_out))
	return PackedInt32Array([first, second])


## One straight leg of [param width] tiles between two points sharing a row or
## a column, extended [param overshoot] tiles past both ends.
##
## Never touches the map's outermost ring: out-of-bounds reads as wall, and the
## world is sealed by construction, so a wide tunnel that hugs the edge must
## stop one tile short of it rather than open the map to nothing.
static func _carve_leg(grid: MapGrid, a: Vector2i, b: Vector2i, width: int,
		overshoot: int, keep_out: Rect2i) -> Rect2i:
	# Width is laid across the leg, centred on its line: two tiles is the line
	# and the one after it, three is one either side, four leans one way.
	var lo := -(width - 1) / 2
	var hi := width / 2
	var rect: Rect2i
	if a.y == b.y:
		var x0 := mini(a.x, b.x) - overshoot
		var x1 := maxi(a.x, b.x) + overshoot
		rect = Rect2i(x0, a.y + lo, x1 - x0 + 1, hi - lo + 1)
	else:
		var y0 := mini(a.y, b.y) - overshoot
		var y1 := maxi(a.y, b.y) + overshoot
		rect = Rect2i(a.x + lo, y0, hi - lo + 1, y1 - y0 + 1)
	for y in range(maxi(rect.position.y, 1), mini(rect.end.y, grid.height - 1)):
		for x in range(maxi(rect.position.x, 1), mini(rect.end.x, grid.width - 1)):
			if keep_out.has_point(Vector2i(x, y)):
				continue
			grid.set_tile(x, y, MapGrid.Kind.FLOOR)
	return rect


## A few pillars and pits inside generated rooms, so open rooms still have
## something to fight around. Never placed on a room's edge, where they could
## seal a corridor mouth.
static func _scatter_cover(grid: MapGrid, rooms: Array[Rect2i], rng: RandomNumberGenerator) -> void:
	for r in rooms:
		if r.size.x < 7 or r.size.y < 6:
			continue
		var centre := _centre_of(r)
		var count := rng.randi_range(1, 3)
		for _i in count:
			var tx := rng.randi_range(r.position.x + 2, r.end.x - 3)
			var ty := rng.randi_range(r.position.y + 2, r.end.y - 3)
			# Room centres are where corridors meet and where the spawn goes;
			# blocking one can pinch a junction shut.
			if tx == centre.x and ty == centre.y:
				continue
			var kind := MapGrid.Kind.PILLAR if rng.randf() < 0.6 else MapGrid.Kind.PIT
			grid.set_tile(tx, ty, kind)