Sylpheed/port/scripts/menu_flow.gd

# Where the buttons go, and what the d-pad does.
#
# EVERYTHING IN HERE IS AUTHORED OR MEASURED -- none of it is on the disc.
# HANDOFF Q6 closed the "what drives the flow" question with a negative: the
# order is code, not data, in all four places it could have been. So this class
# reads `authored/flow.json` and holds no rule of its own.
#
# The split is deliberate and is the derived/authored contract in miniature:
#
#   * the ORDER of the items is DERIVED -- each screen file's `buttons`, which
#     the exporter fills from the button-role elements sorted by resting Y;
#   * WHERE an item goes, WHICH item opens focused, and WHAT (B) does are
#     AUTHORED, because they were measured off the running game or chosen.
#
# A rule that lived in GDScript instead would be invisible to the person whose
# job is to notice that we decided it.
class_name MenuFlow
extends RefCounted

## The authored `screens` map: screen name -> destinations, initial focus, (B).
var screens: Dictionary = {}
## The authored `navigation` block: wrap, left/right, input during a transition.
var navigation: Dictionary = {}

## Where we are and how we got here, oldest first. The last entry is current.
## (B) restores the focus recorded on the entry it pops back to -- HANDOFF Q5
## measured that the game does this, so the stack carries a focus, not just a
## name.
var stack: Array[Dictionary] = []

var error: String = ""

## Nothing happened. Returned rather than `null` so a caller reads one shape.
const NONE := {"kind": "none"}


func configure(flow: Variant) -> bool:
	if typeof(flow) != TYPE_DICTIONARY:
		error = "authored/flow.json did not parse to an object"
		return false
	if not flow.has("screens") or not flow.has("navigation"):
		error = "authored/flow.json has no `screens`/`navigation` block -- this build needs both"
		return false
	screens = flow["screens"]
	navigation = flow["navigation"]
	return true


func known(name: String) -> bool:
	return screens.has(name) and typeof(screens[name]) == TYPE_DICTIONARY


func current() -> String:
	return String(stack[stack.size() - 1]["screen"]) if not stack.is_empty() else ""


func focus() -> String:
	return String(stack[stack.size() - 1]["focus"]) if not stack.is_empty() else ""


## The item a screen opens on.
##
## Authored per screen. Where the authored value names a button this screen does
## not have -- a mistyped id, or an export whose buttons moved -- fall back to
## the first button rather than to nothing, and SAY SO: a menu that opens with
## no focus looks like a rendering bug, and this is the one place that mistake
## would hide.
func initial_focus(name: String, buttons: Array) -> String:
	if buttons.is_empty():
		return ""
	var want := String(screens.get(name, {}).get("initial_focus", ""))
	if want != "" and buttons.has(want):
		return want
	if want != "":
		push_warning("flow.json opens %s on %s, which is not one of its buttons %s" % [name, want, buttons])
	return String(buttons[0])


func enter(name: String, buttons: Array) -> void:
	stack.append({"screen": name, "focus": initial_focus(name, buttons)})


## Move the cursor. Returns true when it actually moved, so a caller can fire the
## move cue only on a real move (P6) rather than on every press.
##
## MEASURED, HANDOFF Q5: up/down move one item and WRAP at both ends -- on the
## 5-item main menu and the 3-item EXTRAS both, so it is a menu rule. `wrap` is
## read from `authored/flow.json` rather than written here, because it is a
## measurement and the day it is contradicted the fix is a data edit.
func move(step: int, buttons: Array) -> bool:
	if stack.is_empty() or buttons.size() < 2:
		return false
	var at := buttons.find(focus())
	if at < 0:
		at = 0
	var to := at + step
	if bool(navigation.get("wrap", true)):
		to = posmod(to, buttons.size())
	else:
		to = clampi(to, 0, buttons.size() - 1)
	if to == at:
		return false
	stack[stack.size() - 1]["focus"] = String(buttons[to])
	return true


## (A). Returns what the authored flow says the focused item opens.
##
##   {"kind": "enter",   "goto": <screen>, "label": …}  -- go there
##   {"kind": "blocked", "label": …, "why": …}          -- a real destination
##                                                          that is not in this
##                                                          export
##   {"kind": "video",   "video": …, "skipped": […],    -- the destination is
##                       "after": {…}}                      absent but its chain
##                                                          ends in a movie we
##                                                          DO have (P7)
##   {"kind": "none"}                                   -- nothing bound
##
## `blocked` is not an error and is not an unknown. Those five destinations were
## measured off the running game; they live in other archives and this milestone
## does not export them. Saying "blocked" rather than "none" keeps the two apart.
func accept(buttons: Array) -> Dictionary:
	if stack.is_empty():
		return NONE
	var screen: Dictionary = screens.get(current(), {})
	# A screen with no buttons -- the title -- can still take (A).
	if buttons.is_empty():
		return _target(screen.get("on_accept", null), "A")
	var button: Dictionary = screen.get("buttons", {}).get(focus(), {})
	if button.is_empty():
		return NONE
	var label := String(button.get("label", focus()))
	if button.get("goto", null) == null:
		# A destination this export does not carry, but whose CHAIN ends in
		# something it does: `NEW GAME` opens `DIFFICULTY`, then `SELECT DATA`,
		# and only then the new-game movie. The port has the movie and neither
		# screen (P7).
		#
		# This is returned as its own kind rather than folded into `blocked`,
		# because the caller has to announce the skip. A port that quietly
		# jumped from `NEW GAME` to the intro would be showing a sequence the
		# game does not have, and nothing on screen would say so.
		if button.get("then_video", null) != null:
			return {
				"kind": "video",
				"label": label,
				"video": String(button["then_video"]),
				"skipped": button.get("skipped_chain", []),
				"skippable": bool(button.get("skippable", false)),
				"after": button.get("after_video", {}),
			}
		return {"kind": "blocked", "label": label, "why": String(button.get("blocked", ""))}
	return {"kind": "enter", "goto": String(button["goto"]), "label": label}


## (B), and EXTRAS' own `BACK` item, which is treated as the same thing --
## nothing measured distinguishes them and inventing a difference would be a
## guess with no evidence behind it.
##
## MEASURED, HANDOFF Q5: (B) goes up one level and RESTORES FOCUS to the item you
## came from. So the target comes from the authored flow, but the focus comes
## from the STACK -- and only when the stack agrees about where we are going. A
## run that started straight on a submenu has no history to restore and enters
## the parent at its authored initial focus instead.
func cancel() -> Dictionary:
	if stack.is_empty():
		return NONE
	var target: Variant = screens.get(current(), {}).get("on_cancel", null)
	var out := _target(target, "B")
	if out["kind"] != "enter":
		return out
	if stack.size() >= 2 and String(stack[stack.size() - 2]["screen"]) == out["goto"]:
		out["restore_focus"] = String(stack[stack.size() - 2]["focus"])
		out["pop"] = true
	return out


## Pop back to the parent, keeping the focus it was left on.
func pop() -> void:
	if stack.size() >= 2:
		stack.pop_back()


static func _target(target: Variant, label: String) -> Dictionary:
	if typeof(target) != TYPE_DICTIONARY or target.get("goto", null) == null:
		return NONE
	return {"kind": "enter", "goto": String(target["goto"]), "label": label}