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

import Foundation

/// This is a “green tree” in the sense of Roslyn.
public struct SyntaxTree: Codable, Sendable {
	public let kind: SyntaxTreeKind
	public let metadata: SyntaxTreeMetadata?
	public let children: [Child]
	public let utf16Length: Int

	public enum Child: Codable, Sendable {
		case token(Token, metadata: TokenMetadata?)
		case tree(SyntaxTree)
	}

	public init(kind: SyntaxTreeKind, metadata: SyntaxTreeMetadata? = nil, children: [SyntaxTree.Child]) {
		self.kind = kind
		self.metadata = metadata
		self.children = children
		self.utf16Length = children.reduce(0) { length, child in
			length + child.utf16Length
		}
	}
}

extension SyntaxTree {
	/// A mutable version of ``SyntaxTree`` that does not keep track of textual length, for use when constructing trees.
	public struct MutableTree {
		public var kind: SyntaxTreeKind
		public var metadata: SyntaxTreeMetadata?
		public var children: [Child]
		
		var tree: SyntaxTree {
			SyntaxTree(kind: kind, metadata: metadata, children: children)
		}
	}
}

extension SyntaxTree {
	public var text: String {
		children.map(\.text).joined()
	}
}

extension SyntaxTree.Child {
	public var text: String {
		switch self {
		case let .token(tok, _): tok.text
		case let .tree(tree): tree.text
		}
	}
	
	public var tree: SyntaxTree? {
		switch self {
		case let .tree(tree): tree
		default: nil
		}
	}

	var token: (Token, TokenMetadata?)? {
		switch self {
		case let .token(token, metadata): (token, metadata)
		default: nil
		}
	}
	
	var utf16Length: Int {
		switch self {
		case let .token(token, _): token.utf16Length
		case let .tree(tree): tree.utf16Length
		}
	}
	
	var children: [Self] {
		switch self {
		case .token: []
		case let .tree(tree): tree.children
		}
	}
}

extension SyntaxTree: CustomStringConvertible {
	public var description: String {
		prettyPrint()
	}

	/// Pretty-print the tree with indentation.
	func prettyPrint(indent: String = "") -> String {
		var result = "\(indent)\(kind)"
		for child in children {
			switch child {
			case .token(let token, _):
				result += "\n\(indent)  \(token.kind): \(token.text.replacingOccurrences(of: "\n", with: "\\n"))"
			case .tree(let subtree):
				result += "\n" + subtree.prettyPrint(indent: indent + "  ")
			}
		}
		return result
	}
}