frontend/node_modules/katex/src/functions/operatorname.ts

import defineFunction, {ordargument} from "../defineFunction";
import defineMacro from "../defineMacro";
import {makeSpan} from "../buildCommon";
import {MathNode, newDocumentFragment, SpaceNode, TextNode} from "../mathMLTree";
import {SymbolNode} from "../domTree";
import {assembleSupSub} from "./utils/assembleSupSub";
import {assertNodeType} from "../parseNode";

import * as html from "../buildHTML";
import * as mml from "../buildMathML";

import type {HtmlBuilderSupSub, MathMLBuilder} from "../defineFunction";
import type {AnyParseNode, ParseNode} from "../parseNode";

// NOTE: Unlike most `htmlBuilder`s, this one handles not only
// "operatorname", but also  "supsub" since \operatorname* can
// affect super/subscripting.
export const htmlBuilder: HtmlBuilderSupSub<"operatorname"> = (grp, options) => {
    // Operators are handled in the TeXbook pg. 443-444, rule 13(a).
    let supGroup;
    let subGroup;
    let hasLimits = false;
    let group: ParseNode<"operatorname">;
    if (grp.type === "supsub") {
        // If we have limits, supsub will pass us its group to handle. Pull
        // out the superscript and subscript and set the group to the op in
        // its base.
        supGroup = grp.sup;
        subGroup = grp.sub;
        group = assertNodeType(grp.base, "operatorname");
        hasLimits = true;
    } else {
        group = assertNodeType(grp, "operatorname");
    }

    let base;
    if (group.body.length > 0) {
        const body = group.body.map((child): AnyParseNode => {
            const childText = "text" in child ? child.text : undefined;
            if (typeof childText === "string") {
                return {
                    type: "textord",
                    mode: child.mode,
                    text: childText,
                };
            } else {
                return child;
            }
        });

        // Consolidate function names into symbol characters.
        const expression = html.buildExpression(
            body, options.withFont("mathrm"), true);

        for (let i = 0; i < expression.length; i++) {
            const child = expression[i];
            if (child instanceof SymbolNode) {
                // Per amsopn package,
                // change minus to hyphen and \ast to asterisk
                child.text = child.text.replace(/\u2212/, "-")
                    .replace(/\u2217/, "*");
            }
        }
        base = makeSpan(["mop"], expression, options);
    } else {
        base = makeSpan(["mop"], [], options);
    }

    if (hasLimits) {
        return assembleSupSub(base, supGroup, subGroup, options,
            options.style, 0, 0);

    } else {
        return base;
    }
};

const mathmlBuilder: MathMLBuilder<"operatorname"> = (group, options) => {
    // The steps taken here are similar to the html version.
    let expression: Array<MathNode | TextNode> = mml.buildExpression(
        group.body, options.withFont("mathrm"));

    // Is expression a string or has it something like a fraction?
    let isAllString = true;  // default
    for (let i = 0; i < expression.length; i++) {
        const node = expression[i];
        if (node instanceof SpaceNode) {
            // Do nothing
        } else if (node instanceof MathNode) {
            switch (node.type) {
                case "mi":
                case "mn":
                case "mspace":
                case "mtext":
                    break;  // Do nothing yet.
                case "mo": {
                    const child = node.children[0];
                    if (node.children.length === 1 &&
                        child instanceof TextNode) {
                        child.text =
                            child.text.replace(/\u2212/, "-")
                                .replace(/\u2217/, "*");
                    } else {
                        isAllString = false;
                    }
                    break;
                }
                default:
                    isAllString = false;
            }
        } else {
            isAllString = false;
        }
    }

    if (isAllString) {
        // Write a single TextNode instead of multiple nested tags.
        const word = expression.map(node => node.toText()).join("");
        expression = [new TextNode(word)];
    }

    const identifier = new MathNode("mi", expression);
    identifier.setAttribute("mathvariant", "normal");

    // \u2061 is the same as &ApplyFunction;
    // ref: https://www.w3schools.com/charsets/ref_html_entities_a.asp
    const operator = new MathNode("mo",
        [mml.makeText("\u2061", "text")]);

    if (group.parentIsSupSub) {
        return new MathNode("mrow", [identifier, operator]);
    } else {
        return newDocumentFragment([identifier, operator]);
    }
};

// \operatorname
// amsopn.dtx: \mathop{#1\kern\z@\operator@font#3}\newmcodes@
defineFunction({
    type: "operatorname",
    names: ["\\operatorname@", "\\operatornamewithlimits"],
    props: {
        numArgs: 1,
    },
    handler: ({parser, funcName}, args) => {
        const body = args[0];
        return {
            type: "operatorname",
            mode: parser.mode,
            body: ordargument(body),
            alwaysHandleSupSub: (funcName === "\\operatornamewithlimits"),
            limits: false,
            parentIsSupSub: false,
        };
    },
    htmlBuilder,
    mathmlBuilder,
});

defineMacro("\\operatorname",
  "\\@ifstar\\operatornamewithlimits\\operatorname@");