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import { Page } from "../core/file.ts";import { assign, merge } from "../core/utils/object.ts";import { log } from "../core/utils/log.ts";
import type Site from "../core/site.ts";import type { Data } from "../core/file.ts";
export interface Options {  /** The list of extensions used for this plugin */  extensions?: string[];
  /** Available languages */  languages: string[];
  /** A prefix-free language */  defaultLanguage?: string;}
// Default optionsexport const defaults: Options = {  extensions: [".html"],  languages: [],};
export default function multilanguage(userOptions: Options) {  const options = merge(defaults, userOptions);
  return (site: Site) => {    // Configure the merged keys    options.languages.forEach((lang) => site.mergeKey(lang, "object"));
    /**     * Preprocessor to setup multilanguage pages     *     * + prevent incorrect data type of "page.data.lang"     * + display guidance (warning log) to some bug-potential cases     * + convert "page.data.lang" array type page (if yes) to string type page     */    site.preprocess(options.extensions, (filteredPages, allPages) => {      for (const page of filteredPages) {        const { data } = page;        const languages = data.lang as string | string[] | undefined;
        // If the "lang" variable is not defined, use the default language        if (languages === undefined) {          data.lang = options.defaultLanguage;          continue;        }
        // If the "lang" variable is a string, check if it's a valid language        if (typeof languages === "string") {          if (!options.languages.includes(languages)) {            log.warn(              `[multilanguage plugin] The language "${languages}" in the page ${page.sourcePath} is not defined in the "languages" option.`,            );          }          continue;        }
        // The "lang" variable of the pages must be an array        if (!Array.isArray(languages)) {          throw new Error(`Invalid "lang" variable in ${page.sourcePath}`);        }
        // Check if these "languages" are all valid language codes        if (languages.some((lang) => !options.languages.includes(lang))) {          log.warn(            `[multilanguage plugin] One or more languages in the page ${page.sourcePath} are not defined in the "languages" option.`,          );          continue;        }
        // Create a new page per language        const newPages: Page[] = [];        const id = data.id ?? page.src.path.slice(1);
        for (const lang of languages) {          const newData: Data = { ...data, lang, id };          const newPage = page.duplicate(undefined, newData);          newPages.push(newPage);        }
        // Replace the current page with the multiple language versions        allPages.splice(allPages.indexOf(page), 1, ...newPages);      }    });
    /**     * Preprocessor to process the multilanguage data     *     * + convert plain url to language url     * + create the alternates     * + sort the alternates     */    site.preprocess(options.extensions, (pages) => {      for (const page of pages) {        const { data } = page;        const { lang } = data;
        // Resolve the language data        for (const key of options.languages) {          if (key in data) {            if (key === lang) {              assign(data, data[key]);            }            delete data[key];          }        }
        const { url } = data;        const isLangUrl = url.startsWith(`/${lang}/`);        const isDefaultLang = lang === options.defaultLanguage;        if (!isLangUrl && !isDefaultLang) {          // Preprocess to prefix all urls with the language code          data.url = `/${lang}${url}`;        } else if (isLangUrl && isDefaultLang) {          // Preprocess to unprefix all urls with the default language code          data.url = url.slice(lang.length + 1);        }
        // Create the alternates object if it doesn't exist        const { id, type } = data;        if (data.alternates || id === undefined) {          data.alternates ??= [data];          continue;        }
        const alternates: Data[] = [];        const ids = new Map<string, Page>();
        pages.filter((page) => page.data.id == id && page.data.type === type)          .forEach((page) => {            const id = `${page.data.lang}-${page.data.id}-${page.data.type}`;            const existing = ids.get(id);            if (existing) {              log.warn(                `[multilanguage plugin] The pages ${existing.sourcePath} and ${page.sourcePath} have the same id, type and language.`,              );            }            ids.set(id, page);            alternates.push(page.data);            page.data.alternates = alternates;          });
        // Sort the alternates by language        alternates.sort((a, b) =>          options.languages.indexOf(a.lang!) -          options.languages.indexOf(b.lang!)        );      }    });
    /**     * Preprocessor to process the Unmatched Language URL     *     * + convert unmatchedLangUrl any value to URL string value     */    site.preprocess(options.extensions, (pages) => {      for (const page of pages) {        page.data.unmatchedLangUrl = getUnmatchedLangPath(          page,          pages,        );      }    });
    // Include automatically the <link rel="alternate"> elements    // with the other languages    site.process(options.extensions, (pages) => {      for (const page of pages) {        const { document } = page;        const alternates = page.data.alternates;        const lang = page.data.lang as string | undefined;
        if (!document || !alternates || !lang) {          continue;        }
        // Include <html lang="${lang}"> attribute element if it's missing        if (!document.documentElement?.getAttribute("lang")) {          document.documentElement?.setAttribute("lang", lang);        }
        // Insert the <link> elements automatically        for (const data of alternates) {          const meta = document.createElement("link");          meta.setAttribute("rel", "alternate");          meta.setAttribute("hreflang", data.lang as string);          meta.setAttribute("href", site.url(data.url, true));          document.head.appendChild(meta);          document.head.appendChild(document.createTextNode("\n"));        }
        if (page.data.unmatchedLangUrl) {          appendHreflang(            "x-default",            site.url(page.data.unmatchedLangUrl, true),            document,          );        }      }    });  };}
function getUnmatchedLangPath(  currentPage: Page<Data>,  filteredPages: Page<Data>[],): string | undefined {  const { sourcePath } = currentPage;  const { unmatchedLangUrl, alternates } = currentPage.data;
  if (!unmatchedLangUrl) return void 0;
  // If unmatchedLang is an external URL string  if (URL.canParse(unmatchedLangUrl)) {    return unmatchedLangUrl;  }
  // If unmatchedLang is an source path string  if (unmatchedLangUrl.startsWith("/")) {    const langSelectorPage = filteredPages.some(      (page) => page.data.url === unmatchedLangUrl,    );
    if (!langSelectorPage) {      log.warn(        `[multilanguage plugin] The URL <cyan>${unmatchedLangUrl}</cyan> of unmatchedLangUrl option is not found in ${sourcePath}.`,      );    }    return langSelectorPage ? unmatchedLangUrl : void 0;  }
  // If unmatchedLang is language code → resolve to URL of that language  const lang = alternates?.find((data) => data.lang === unmatchedLangUrl);  if (!lang) {    log.warn(      `[multilanguage plugin] The URL for lang code "${unmatchedLangUrl}" of unmatchedLangUrl option is not found in ${sourcePath}.`,    );  }  return lang?.url;}
function appendHreflang(lang: string, url: string, document: Document) {  const meta = document.createElement("link");  meta.setAttribute("rel", "alternate");  meta.setAttribute("hreflang", lang);  meta.setAttribute("href", url);  document.head.appendChild(meta);  document.head.appendChild(document.createTextNode("\n"));}