NetNewsWire/Modules/Parser/Sources/HTMLParser/HTMLLinkParser.swift

//
//  File.swift
//  
//
//  Created by Brent Simmons on 9/21/24.
//

import Foundation
import SAX

public final class HTMLLinkParser {

	public private(set) var links = [HTMLLink]()

	private let parserData: ParserData
	private let baseURL: URL?

	public static func htmlLinks(parserData: ParserData) -> [HTMLLink] {

		let parser = HTMLLinkParser(parserData)
		parser.parse()
		return parser.links
	}

	init(_ parserData: ParserData) {

		self.parserData = parserData
		self.baseURL = URL(string: parserData.url)
	}
}

private extension HTMLLinkParser {

	func parse() {

		let htmlParser = SAXHTMLParser(delegate: self, data: parserData.data)
		htmlParser.parse()
	}
}

private extension HTMLLinkParser: SAXHTMLParserDelegate {

	var currentLink: HTMLLink? {
		links.last
	}

	struct HTMLAttributeName {
		let href = "href"
		let title = "title"
	}

	func title(_ attributesDictionary: HTMLAttributesDictionary) -> String? {

		attributesDictionary.object(object(forCaseInsensitiveKey: HTMLAttributeName.title))
	}

	func urlString(_ attributesDictionary: HTMLAttributesDictionary) -> String? {

		guard let href = attributesDictionary.object(forCaseInsensitiveKey: HTMLAttributeName.href) else {
			return nil
		}

		guard let baseURL, let absoluteURL = URL(string: href, relativeTo: baseURL) else {
			assertionFailure("Expected to create URL")
			return nil
		}

		return absoluteURL.absoluteString
	}

	func handleLinkAttributes(_ attributesDictionary: HTMLAttributesDictionary) {

		guard let currentLink else {
			assertionFailure("currentLink must not be nil")
			return
		}

		link.urlString = urlString(attributesDictionary)
		link.title = title(attributesDictionary)
	}

	struct HTMLName {
		static let a = "a".utf8CString
	}

	func saxHTMLParser(_ saxHTMLParser: SAXHTMLParser, startElement name: XMLPointer, attributes: UnsafePointer<XMLPointer?>?) {

		guard SAXEqualTags(name, HTMLName.a) else {
			return
		}

		let link = HTMLLink()
		links.append(link)

		if let attributesDictionary = saxHTMLParser.attributesDictionary(attributes) {
			handleLinkAttributes(attributesDictionary)
		}

		saxHTMLParser.beginStoringCharacters()
	}

	func saxHTMLParser(_ saxHTMLParser: SAXHTMLParser, endElement name: XMLPointer) {

		guard SAXEqualTags(name, HTMLName.a) else {
			return
		}
		currentLink.text = saxHTMLParser.currentStringWithTrimmedWhitespace
	}

	func saxHTMLParser(_: SAXHTMLParser, charactersFound: XMLPointer, count: Int) {
		// Nothing needed.
	}
}