import { htmlTrie } from "./generated/encode-html.js";
import { xmlReplacer, getCodePoint } from "./escape.js";

const htmlReplacer = /[\t\n\f!-,./:-@[-`{-}\u0080-\uFFFF]/g;

/**
 * Encodes all characters in the input using HTML entities. This includes
 * characters that are valid ASCII characters in HTML documents, such as `#`.
 *
 * To get a more compact output, consider using the `encodeNonAsciiHTML`
 * function, which will only encode characters that are not valid in HTML
 * documents, as well as non-ASCII characters.
 *
 * If a character has no equivalent entity, a numeric hexadecimal reference
 * (eg. `ü`) will be used.
 */
export function encodeHTML(input: string): string {
    return encodeHTMLTrieRe(htmlReplacer, input);
}
/**
 * Encodes all non-ASCII characters, as well as characters not valid in HTML
 * documents using HTML entities. This function will not encode characters that
 * are valid in HTML documents, such as `#`.
 *
 * If a character has no equivalent entity, a numeric hexadecimal reference
 * (eg. `ü`) will be used.
 */
export function encodeNonAsciiHTML(input: string): string {
    return encodeHTMLTrieRe(xmlReplacer, input);
}

function encodeHTMLTrieRe(regExp: RegExp, input: string): string {
    let returnValue = "";
    let lastIndex = 0;
    let match;

    while ((match = regExp.exec(input)) !== null) {
        const { index } = match;
        returnValue += input.substring(lastIndex, index);
        const char = input.charCodeAt(index);
        let next = htmlTrie.get(char);

        if (typeof next === "object") {
            // We are in a branch. Try to match the next char.
            if (index + 1 < input.length) {
                const nextChar = input.charCodeAt(index + 1);
                const value =
                    typeof next.n === "number"
                        ? next.n === nextChar
                            ? next.o
                            : undefined
                        : next.n.get(nextChar);

                if (value !== undefined) {
                    returnValue += value;
                    lastIndex = regExp.lastIndex += 1;
                    continue;
                }
            }

            next = next.v;
        }

        // We might have a tree node without a value; skip and use a numeric entity.
        if (next === undefined) {
            const cp = getCodePoint(input, index);
            returnValue += `&#x${cp.toString(16)};`;
            // Increase by 1 if we have a surrogate pair
            lastIndex = regExp.lastIndex += Number(cp !== char);
        } else {
            returnValue += next;
            lastIndex = index + 1;
        }
    }

    return returnValue + input.substr(lastIndex);
}