extends RefCounted
class_name NovaCompiler
# NOTE: Godot's docs for array states that `.resize` + direct assignment is faster
#       than repeatedly calling `append` and `push_back`.
static var prelude = """
extends RefCounted

var state = %s

func push(stack_symbol, symbol) -> void:
	state[stack_symbol].push_back(symbol)

func peek(stack_symbol, depth : int, symbol) -> bool:
	var stack = state[stack_symbol]
	if not stack: return false
	return stack[stack.size() - depth] == symbol

func pop(stack_symbol) -> void:
	state[stack_symbol].pop_back()
"""

static func compile(json_string: String) -> GDScript:
	var json = JSON.new()
	var error = json.parse(json_string)
	if error != OK:
		print("JSON Parse Error: ", json.get_error_message(), " in ", json_string, " at line ", json.get_error_line())
		return GDScript.new()

	var rules = json.data.rules
	var state = json.data.state

	var compiled_rules := PackedStringArray([prelude % state])
	var i := 0

	for rule in rules:
		var conditions = rule.conditions
		var results = rule.results
		compiled_rules.push_back("func _rule_%d() -> bool:" % i)
		var depths : Dictionary[String, int] = {}
		for condition in conditions:
			for action in condition.pattern:
				match action.type:
					"variable":
						# TODO: name mangle this
						compiled_rules.push_back("\tvar %s" % action.symbol)
		for condition in conditions:
			var stack : String = condition.stack.c_escape()
			for action in condition.pattern:
				var depth = depths.get_or_add(stack, 0)
				depths[stack] = depth + 1
				match action.type:
					"literal":
						compiled_rules.push_back("\tif not peek(\"%s\", %d, \"%s\"): return false" % [
							stack,
							depth,
							action.symbol.c_escape()
						])
					"variable":
						compiled_rules.push_back("\tif %s == null and peek(\"%s\", %d, \"%s\"): return false" % [
							action.symbol.c_escape(),
							stack,
							depth,
							action.symbol.c_escape()
						])
						compiled_rules.push_back("\t%s = peek(\"%s\", %d, \"%s\")" % [
							action.symbol.c_escape(),
							stack,
							depth,
							action.symbol.c_escape()
						])
		for condition in conditions:
			var stack : String = condition.stack.c_escape()
			for __ in range(condition.pattern.size()):
				compiled_rules.push_back("\tpop(\"%s\")" % stack)
		for result in results:
			var stack : String = result.stack
			for action in result.pattern:
				match action.type:
					"literal":
						compiled_rules.push_back("\tpush(\"%s\", \"%s\")" % [
							stack, action.symbol.c_escape()
						])
					"variable":
						compiled_rules.push_back("\tpush(\"%s\", %s if %s else \"%s\")" % [
							stack, action.symbol, action.symbol, action.symbol.c_escape()
						])
			pass
		print(conditions)
		print(results)
		print("\n".join(compiled_rules))

	return GDScript.new()