import { previewTemplate } from '../../lib/seo/template-preview';
import type { SeoEditorEnv } from '../env';
import type { EditedPost } from '../hooks/use-seo-meta';

/** What the variables resolve to for this post, term or author right now. */
export interface LiveValues {
  post: EditedPost;
  keyword: string;
  primaryTerm: string;
  firstTerm: string;
}

const textOf = (html: string): string =>
  html
    .replace(/<!--[\s\S]*?-->/g, ' ')
    .replace(/<[^>]+>/g, ' ')
    .replace(/&nbsp;/g, ' ')
    .replace(/\s+/g, ' ')
    .trim();

/** Characters of an automatic excerpt, as the server cuts it. */
const EXCERPT_LENGTH = 145;

/**
 * The excerpt, or the start of the content, cut the way the server cuts
 * it: at a word, with an ellipsis, inside the 920 pixels Google shows.
 */
export const excerptOf = (post: EditedPost): string => {
  // The text without its headings, as the server reads it.
  const body = textOf(
    post.content.replace(/<h[1-6]\b[^>]*>[\s\S]*?<\/h[1-6]>/gi, ' ')
  );
  const source =
    (post.excerpt.trim() ? textOf(post.excerpt) : '') ||
    body ||
    textOf(post.content);
  if (source.length <= EXCERPT_LENGTH) {
    return source;
  }
  let cut = source.slice(0, EXCERPT_LENGTH);
  const space = cut.lastIndexOf(' ');
  if (space > 60) {
    cut = cut.slice(0, space);
  }
  return `${cut.replace(/[\s,;:.\-–—]+$/, '')}…`;
};

/**
 * A title or description template rendered for the object in the editor,
 * with the server's examples standing in for what only the server knows.
 */
export const renderTemplate = (
  template: string,
  env: SeoEditorEnv,
  live: LiveValues
): string => {
  const now = new Date();
  const values: Record<string, string> = {
    '%title%': live.post.title,
    '%excerpt%': env.object === 'user' ? '' : excerptOf(live.post),
    '%focuskw%': live.keyword,
    '%category%': live.firstTerm,
    '%primary_category%': live.primaryTerm || live.firstTerm,
    '%pt_single%': env.object === 'post' ? env.typeLabel : '',
    '%term%': env.object === 'term' ? live.post.title : '',
    '%term_description%':
      env.object === 'term' ? textOf(live.post.excerpt) : '',
    '%page%': '',
    '%currentyear%': String(now.getFullYear()),
    '%currentdate%': now.toLocaleDateString(),
    '%date%': now.toLocaleDateString(),
  };
  if (env.object === 'user') {
    values['%author%'] = live.post.title;
  }
  const variables = env.variables.map(variable => ({
    ...variable,
    example: variable.name in values ? values[variable.name] : variable.example,
  }));

  return previewTemplate(template, variables, env.separator);
};