// SPDX-FileCopyrightText: 2025 The Project Pterodactyl Developers
//
// SPDX-License-Identifier: MPL-2.0

import Foundation

/// This is an abstraction of grammatical productions.
public protocol Grammar: Sendable {
	/// The kinds of tree that the production produces.
	static var kinds: [SyntaxTreeKind] { get }

	/// Indicates whether the current parser state is consistent with the grammatical production starting here. When a given grammatical element is optional, this can be used to avoid backtracking. This is a *precondition* for parsing.
	static func precondition(_ parser: inout Parser) -> Bool

	/// Parse the grammatical production, assuming the precondition indicated by ``precondition(_:)``. This function should not be called outside this module (instead, use ``parse(_:recovery:)`` and ``tryParse(_:recovery:)``.
	static func inside(_ parser: inout Parser, recovery: Set<TokenKind>) -> ParseResult
}

extension Grammar {
	public static func tryParse(_ parser: inout Parser, recovery: Set<TokenKind>) -> Bool {
		guard !parser.isEndOfFile && precondition(&parser) else { return false }
		parse(&parser, recovery: recovery)
		return true
	}

	public static func parse(_ parser: inout Parser, recovery: Set<TokenKind>) {
		let mark = parser.builder.open()
		let result = inside(&parser, recovery: recovery)
		parser.builder.close(mark: mark, kind: result.kind, metadata: result.metadata)
	}
}

public struct ParseResult {
	public var kind: SyntaxTreeKind
	public var metadata: SyntaxTreeMetadata? = nil

	public init(kind: SyntaxTreeKind, metadata: SyntaxTreeMetadata? = nil) {
		self.kind = kind
		self.metadata = metadata
	}
}