import Foundation
import libxml2


open class HTMLParser {
    
    enum Error: String, Swift.Error {
        case NoRootNode = "No root node"
    }

    /// Public initializer
    ///
    public init() { }


    /// Parses HTML data into an HTML Node representing the same data.
    ///
    /// - Parameters:
    ///     - html: the HTML string to parse.
    ///
    /// - Returns: the HTML root node.
    ///
    open func parse(_ html: String) -> RootNode {

        // We wrap the HTML into a special root node, since it helps avoid conversion issues
        // with libxml2, where the library would add custom tags to "fix" the HTML code we
        // provide.
        //
        let wrappedHTML = "<\(RootNode.name)>\(html)</\(RootNode.name)>"
        let data = wrappedHTML.data(using: String.Encoding.utf8)!

        let bufferSize = 1024
        let buffer = Array<Int8>(repeating: 0, count: bufferSize)
        let htmlPtr = (data as NSData).bytes.bindMemory(to: Int8.self, capacity: data.count)

        let parserContext = htmlCreateMemoryParserCtxt(buffer, 1024)
        
        defer {
            htmlFreeParserCtxt(parserContext)
        }

        // We don't want <p> tags added automattically.
        //
        htmlHandleOmittedElem(0)

        let document = htmlCtxtReadMemory(parserContext,
                                          htmlPtr,
                                          Int32(wrappedHTML.lengthOfBytes(using: String.Encoding.utf8)),
                                          "",
                                          "UTF-8",
                                          Int32(HTML_PARSE_RECOVER.rawValue | HTML_PARSE_NODEFDTD.rawValue | HTML_PARSE_NOERROR.rawValue | HTML_PARSE_NOWARNING.rawValue | HTML_PARSE_NOIMPLIED.rawValue | HTML_PARSE_NOBLANKS.rawValue))
        
        defer {
            xmlFreeDoc(document)
        }

        let errorPtr = xmlGetLastError()

        if errorPtr != nil {
            if let messagePtr = errorPtr?.pointee.message {
                let message = String(cString: messagePtr)

                NSLog("Message: \(message)")
            }

            // Some errors are really not a problem for us (like "misplaced HTML tag"), so let's
            // keep going.  In the future we should analyze the different errors here and decide
            // if there's a need to handle any of them in a different way.
            //
        }

        let rootNodePtr = xmlDocGetRootElement(document)
        let nodeConverter = InNodeConverter()

        guard let rootNode = rootNodePtr?.pointee,
            let node = nodeConverter.convert(rootNode) as? RootNode else {
                return RootNode(children: [TextNode(text: "")])
        }

        // Don't let this method return an empty root node.
        //
        if node.children.count == 0 {
            node.children.append(TextNode(text: html))
        }

        return node
    }
}