import type {CssStyle, HtmlDomNode} from "./domTree";
import type {MathDomNode} from "./mathMLTree";


// To ensure that all nodes have compatible signatures for these methods.
export interface VirtualNode {
    toNode(): Node;
    toMarkup(): string;
}

function isMathDomNode(node: VirtualNode): node is MathDomNode {
    return 'toText' in node;
}


/**
 * This node represents a document fragment, which contains elements, but when
 * placed into the DOM doesn't have any representation itself. It only contains
 * children and doesn't have any DOM node properties.
 */
export class DocumentFragment<ChildType extends VirtualNode>
    implements HtmlDomNode, MathDomNode {
    children: ReadonlyArray<ChildType>;
    classes: string[];
    height: number;
    depth: number;
    maxFontSize: number;
    style: CssStyle;          // Never used; needed for satisfying interface.

    constructor(children: ReadonlyArray<ChildType>) {
        this.children = children;
        this.classes = [];
        this.height = 0;
        this.depth = 0;
        this.maxFontSize = 0;
        this.style = {};
    }

    hasClass(className: string): boolean {
        return this.classes.includes(className);
    }

    /** Convert the fragment into a node. */
    toNode(): Node {
        const frag = document.createDocumentFragment();

        for (let i = 0; i < this.children.length; i++) {
            frag.appendChild(this.children[i].toNode());
        }

        return frag;
    }

    /** Convert the fragment into HTML markup. */
    toMarkup(): string {
        let markup = "";

        // Simply concatenate the markup for the children together.
        for (let i = 0; i < this.children.length; i++) {
            markup += this.children[i].toMarkup();
        }

        return markup;
    }

    /**
     * Converts the math node into a string, similar to innerText. Applies to
     * MathDomNode's only.
     */
    toText(): string {
        return this.children.map((child: ChildType): string => {
            if (isMathDomNode(child)) {
                return child.toText();
            }
            throw new Error(
                `Expected MathDomNode with toText, got ${child.constructor.name}`);
        }).join("");
    }
}
