import type { CrawledPageResult } from "@/server/lib/audit/types";

export type QuickAuditPriority = "Critical Impact" | "High Priority" | "Good Health";

export interface QuickAuditFinding {
  domain: string;
  score: number;
  action: string;
  issue: string;
  priority: QuickAuditPriority;
  current: string;
  suggested: string;
}

const TITLE_MAX_LENGTH = 60;
const DESCRIPTION_MAX_LENGTH = 160;

type Issue = Omit<QuickAuditFinding, "domain" | "score"> & { weight: number };

/**
 * Picks the single most-impactful real issue on a crawled page, plus a
 * composite score from every issue found. Used by the public marketing-site
 * "quick audit" widget, which crawls exactly one real page (via
 * {@link import("@/server/workflows/site-audit-workflow-helpers").crawlPage})
 * — this never fabricates a finding for a page it hasn't actually fetched.
 */
export function selectQuickAuditFinding(
  domain: string,
  page: CrawledPageResult,
): QuickAuditFinding {
  const title = page.title.trim();
  const description = page.metaDescription.trim();
  const issues: Issue[] = [];

  if (!title) {
    issues.push({
      weight: 30,
      action: "Add a title tag",
      issue:
        "This page has no <title> tag — search engines fall back to a generic or URL-based title in results.",
      priority: "Critical Impact",
      current: "<!-- no <title> tag found -->",
      suggested: `<title>${domain} | Describe this page in 50-60 characters</title>`,
    });
  } else if (title.length > TITLE_MAX_LENGTH) {
    issues.push({
      weight: 15,
      action: "Shorten the title tag",
      issue: `Title tag is ${title.length} characters — Google truncates titles past ~${TITLE_MAX_LENGTH} characters in search results.`,
      priority: "High Priority",
      current: `<title>${title}</title>`,
      suggested: `<title>${title.slice(0, TITLE_MAX_LENGTH - 1).trim()}…</title>`,
    });
  }

  if (!description) {
    issues.push({
      weight: 20,
      action: "Add a meta description",
      issue:
        "No meta description found — Google will auto-generate a snippet from page content instead.",
      priority: "High Priority",
      current: '<!-- no <meta name="description"> tag found -->',
      suggested: `<meta name="description" content="Describe what ${domain} offers in one or two sentences, under ${DESCRIPTION_MAX_LENGTH} characters." />`,
    });
  } else if (description.length > DESCRIPTION_MAX_LENGTH) {
    issues.push({
      weight: 8,
      action: "Shorten the meta description",
      issue: `Meta description is ${description.length} characters — Google truncates snippets past ~${DESCRIPTION_MAX_LENGTH} characters.`,
      priority: "High Priority",
      current: `<meta name="description" content="${description}" />`,
      suggested: `<meta name="description" content="${description.slice(0, DESCRIPTION_MAX_LENGTH - 1).trim()}…" />`,
    });
  }

  if (page.h1Count === 0) {
    issues.push({
      weight: 18,
      action: "Add an H1 heading",
      issue:
        "No <h1> tag found on this page — a single clear H1 helps both users and search engines understand the page topic.",
      priority: "High Priority",
      current: "<!-- no <h1> tag found -->",
      suggested: "<h1>State the page's main topic here</h1>",
    });
  } else if (page.h1Count > 1) {
    issues.push({
      weight: 10,
      action: "Use a single H1 per page",
      issue: `${page.h1Count} <h1> tags found — multiple H1s dilute the page's topical signal.`,
      priority: "High Priority",
      current: `${page.h1Count}× <h1>…</h1>`,
      suggested: "Keep exactly one <h1>; demote the rest to <h2>.",
    });
  }

  if (!page.canonicalUrl) {
    issues.push({
      weight: 10,
      action: "Add a canonical tag",
      issue:
        "No canonical URL found — without one, duplicate or parameterized versions of this page can compete with each other in search results.",
      priority: "High Priority",
      current: '<!-- no <link rel="canonical"> tag found -->',
      suggested: `<link rel="canonical" href="${page.url}" />`,
    });
  }

  if (page.imagesMissingAlt > 0) {
    issues.push({
      weight: 6,
      action: "Add alt text to images",
      issue: `${page.imagesMissingAlt} of ${page.imagesTotal} images on this page are missing alt text.`,
      priority: "Good Health",
      current: '<img src="...">',
      suggested: '<img src="..." alt="Describe what the image shows">',
    });
  }

  if (issues.length === 0) {
    return {
      domain,
      score: 96,
      action: "No critical issues found on this quick scan",
      issue:
        "Title, meta description, H1, and canonical tag all look healthy on this page.",
      priority: "Good Health",
      current: `<title>${title}</title>`,
      suggested:
        "Run a full crawl in CrawlerX to check Core Web Vitals, internal linking, and every other page on the site.",
    };
  }

  issues.sort((a, b) => b.weight - a.weight);
  const totalPenalty = issues.reduce((sum, issue) => sum + issue.weight, 0);
  const score = Math.max(35, 100 - totalPenalty);
  const { weight: _weight, ...top } = issues[0];

  return { domain, score, ...top };
}