HTML-DSL.swift

import Foundation



@_functionBuilder struct XMLBuilder {
    
    static func buildBlock(_ content: String) -> String {
        return content
    }
    static func buildBlock(_ content: XMLElement...) -> [XMLElement] {
        return content.map{ $0 }
    }
    static func buildBlock(_ content: String, _ elements: XMLElement...) -> (String, [XMLElement]) {
        return (content, elements.map{$0} )
    }
}




extension XMLElement {
    convenience init(name: String, content: String, children: [XMLElement] = [], attributes: [XMLNode] = []) {
        self.init(name: name)
        if content != "" { stringValue = content } // yes, really.
        children.forEach(addChild)
        attributes.forEach(addAttribute)
    }
    convenience init(name: String, children: [XMLElement] = [], attributes: [XMLNode] = []) {
        self.init(name: name)
        children.forEach(addChild)
        attributes.forEach(addAttribute)
    }
    
}



enum HTMLLang : String {
    case en_GB = "en_GB"
}

enum HTMLAttribute {
    case `class` (String)
    case  id     (String)
}



func attributes( dict: [String : String] ) -> [XMLNode] {
    var nodes = [XMLNode]()
    for (k,v) in dict {
        let node = XMLNode(kind: .attribute)
        node.name        = k
        node.stringValue = v
        nodes.append(node)
    }
    return nodes
}

func attribute(htmlAttribute: HTMLAttribute) -> (String, String) {
    switch htmlAttribute {
        case .class(let value): return ("class",value)
        case .id   (let value): return ("id",   value)
    }
}

func attributes( htmlAttributes: [HTMLAttribute] ) -> [XMLNode] {
    var dict : [String : String] = [:]
    for attrib in htmlAttributes {
        let (k, v) = attribute(htmlAttribute: attrib)
        dict[k] = v
    }
    return attributes(dict: dict)
}




func html (lang: HTMLLang, @XMLBuilder _ content: () -> String) -> XMLElement {
    return XMLElement(name: "html", content: content(), attributes: attributes(dict: ["lang":lang.rawValue]))
}

func html (lang: HTMLLang, @XMLBuilder _ content: () -> [XMLElement] ) -> XMLElement {
    return XMLElement(name: "html", children: content(), attributes: attributes(dict: ["lang":lang.rawValue]))
}

func html (lang: HTMLLang, @XMLBuilder _ content: () -> (String, [XMLElement]) ) -> XMLElement {
    let (content, elements) = content()
    return XMLElement(name: "html", content: content, children: elements, attributes: attributes(dict: ["lang":lang.rawValue]))
}





func body (_ htmlAttributes: [HTMLAttribute] = [], @XMLBuilder _ content: () -> String) -> XMLElement {
    return XMLElement(name: "body", content: content(), attributes: attributes( htmlAttributes: htmlAttributes))
}

func body (_ htmlAttributes: [HTMLAttribute] = [], @XMLBuilder _ content: () -> [XMLElement] ) -> XMLElement {
    return XMLElement(name: "body", children: content(), attributes: attributes( htmlAttributes: htmlAttributes))
}

func body (_ htmlAttributes: [HTMLAttribute] = [], @XMLBuilder _ content: () -> (String, [XMLElement]) ) -> XMLElement {
    let (content, elements) = content()
    return XMLElement(name: "body", content: content, children: elements, attributes: attributes( htmlAttributes: htmlAttributes))
}



func div ( _ htmlAttributes: [HTMLAttribute] = [], @XMLBuilder _ content: () -> String) -> XMLElement {
    return XMLElement(name: "div", content: content(), attributes: attributes( htmlAttributes: htmlAttributes))
}

func div (_ htmlAttributes: [HTMLAttribute] = [], @XMLBuilder _ content: () -> [XMLElement] ) -> XMLElement {
    return XMLElement(name: "div", children: content(), attributes: attributes( htmlAttributes: htmlAttributes))
}

func div (_ htmlAttributes: [HTMLAttribute] = [], @XMLBuilder _ content: () -> (String, [XMLElement]) ) -> XMLElement {
    let (content, elements) = content()
    return XMLElement(name: "div", content: content, children: elements, attributes: attributes( htmlAttributes: htmlAttributes))
}



func p ( _ htmlAttributes: [HTMLAttribute] = [], @XMLBuilder _ content: () -> String) -> XMLElement {
    return XMLElement(name: "p", content: content(), attributes: attributes( htmlAttributes: htmlAttributes))
}

func p (_ htmlAttributes: [HTMLAttribute] = [], @XMLBuilder _ content: () -> [XMLElement] ) -> XMLElement {
    return XMLElement(name: "p", children: content(), attributes: attributes( htmlAttributes: htmlAttributes))
}

func p (_ htmlAttributes: [HTMLAttribute] = [], @XMLBuilder _ content: () -> (String, [XMLElement]) ) -> XMLElement {
    let (content, elements) = content()
    return XMLElement(name: "p", content: content, children: elements, attributes: attributes( htmlAttributes: htmlAttributes))
}




func pretty(_ element: XMLElement) {
    let xmldoc = XMLDocument(rootElement: element)
    xmldoc.documentContentKind = .html
    print(xmldoc.xmlString(options: [ .nodePrettyPrint, .documentTidyHTML, .nodePreserveWhitespace]))
}


pretty (
    
    html( lang: .en_GB ) {
        
        body {
            div ([ .class("dismissed") ]) {
                p {"para 1"}
                p {"para 2"}
            }
            p {}
        }
    }
)


pretty (
    
    html( lang: .en_GB ) {
        body  {
            div ([ .id("wella-wella")  ]) {
                p { "tell me more" }
                p { "tell me more" }
                div {
                    p {"did you get very far?"}
                }
            }
            div {
                p ([ .class( "wella" ), .id( "wella" ) ]) {
                    "tell me more tell me more"
                }
                div {
                    p {"like did he have a car?"}
                    div {
                        p {"a wella wella wella"}
                    }
                }
            }
        }
    }

)

Sources of info that were super useful

https://www.andyibanez.com/posts/understanding-function-builders/
https://medium.com/@carson.katri/create-your-first-function-builder-in-5-minutes-b4a717390671
https://vihan.org/blog/swift-function-builders/
https://dev.to/gualtierofr/introduction-to-function-builders-4c1